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Going from a math career to a cs career: how to do it?

- by Joseph

Hey, I'm looking for some advice on how to successfully make the transition from mathematics to CS. My academic background is in mathematics (BS and MSc), and I've taken loads of math courses as well. You name it, and I took it: Measure Theory, Algebra, PDES, Manifolds, Complex Analysis, etc. I progressed quite far along this track, and at one point, I thought I would be a professional mathematician...But around the time I was finishing my MSc, I really got sick of it. Studying very abstract mathematics was fun, but it really lost it's appeal to me. Outside of a couple hundred people, I'm not sure if anybody would understand my research. I did not want to be 60 years old and say that my only contribution to the world consisted of published papers. Anyways, I've been an off and on hobbyist programmer since 2002. I've programmed in C and Java (just small projects), and I really started to be drawn to the area as time passed. There's a real appeal to CS work because, well, it actually means something to other people out there! I enjoy all parts of it: designing webpages (a real artistic appeal). On the other end, I do enjoy toying with compilers and more nitty-gritty stuff as well. Suffice to say, I have broad interests out there. Anyways, I know it's a bit late, but I was wondering if there were other folks out there who made the change, and if so, how I could do so. I know I have some fairly big gaps to fill in terms of data structures, lack of internship experience, etc. But I really would like to make this work. So my question is simply: How can I make the switch from math to CS? To pay the bills, I'll be doing financial analysis for a company, but I'd like to eventually transition into a developer type position. I've been reading "Algorithm Design" by Tardos and doing all the problems. It's not hard to make progress since the problems are far more concrete than the stuff I've been doing the past six years. I feel I can make fairly rapid progress in picking up all the materials from data structures, etc. but none of it can substitute the past several years I've lost. Anyways, I'm eager to learn but would love some advice/concrete direction. Thanks, Joseph

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physics game programming box2d - orientating a turret-like object using torques

- by egarcia

This is a problem I hit when trying to implement a game using the LÖVE engine, which covers box2d with Lua scripting. The objective is simple: A turret-like object (seen from the top, on a 2D environment) needs to orientate itself so it points to a target. The turret is on the x,y coordinates, and the target is on tx, ty. We can consider that x,y are fixed, but tx, ty tend to vary from one instant to the other (i.e. they would be the mouse cursor). The turret has a rotor that can apply a rotational force (torque) on any given moment, clockwise or counter-clockwise. The magnitude of that force has an upper limit called maxTorque. The turret also has certain rotational inertia, which acts for angular movement the same way mass acts for linear movement. There's no friction of any kind, so the turret will keep spinning if it has an angular velocity. The turret has a small AI function that re-evaluates its orientation to verify that it points to the right direction, and activates the rotator. This happens every dt (~60 times per second). It looks like this right now: function Turret:update(dt) local x,y = self:getPositon() local tx,ty = self:getTarget() local maxTorque = self:getMaxTorque() -- max force of the turret rotor local inertia = self:getInertia() -- the rotational inertia local w = self:getAngularVelocity() -- current angular velocity of the turret local angle = self:getAngle() -- the angle the turret is facing currently -- the angle of the like that links the turret center with the target local targetAngle = math.atan2(oy-y,ox-x) local differenceAngle = _normalizeAngle(targetAngle - angle) if(differenceAngle <= math.pi) then -- counter-clockwise is the shortest path self:applyTorque(maxTorque) else -- clockwise is the shortest path self:applyTorque(-maxTorque) end end ... it fails. Let me explain with two illustrative situations: The turret "oscillates" around the targetAngle. If the target is "right behind the turret, just a little clock-wise", the turret will start applying clockwise torques, and keep applying them until the instant in which it surpasses the target angle. At that moment it will start applying torques on the opposite direction. But it will have gained a significant angular velocity, so it will keep going clockwise for some time... until the target will be "just behind, but a bit counter-clockwise". And it will start again. So the turret will oscillate or even go in round circles. I think that my turret should start applying torques in the "opposite direction of the shortest path" before it reaches the target angle (like a car braking before stopping). Intuitively, I think the turret should "start applying torques on the opposite direction of the shortest path when it is about half-way to the target objective". My intuition tells me that it has something to do with the angular velocity. And then there's the fact that the target is mobile - I don't know if I should take that into account somehow or just ignore it. How do I calculate when the turret must "start braking"?

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WinRT ControlTemplate ItemsPanel

- by user1427149

I'm new to WinRT and am trying to create a standard gridview which has a group heading with a number of tiles beneath it. That bit is easy. I'm trying to modify it so that beneath the grid of tiles I can also add a footer using the containers style: <GridView x:Name="itemGridView" AutomationProperties.AutomationId="ItemGridView" AutomationProperties.Name="Grouped Items" Margin="116,0,40,46" ItemsSource="{Binding Source={StaticResource groupedItemsViewSource}}" ItemTemplate="{StaticResource Project200x200ItemTemplate}" SelectionMode="None" IsItemClickEnabled="True" ItemClick="ItemView_ItemClick"> <GridView.ItemsPanel> <ItemsPanelTemplate> <VirtualizingStackPanel Orientation="Horizontal"/> </ItemsPanelTemplate> </GridView.ItemsPanel> <GridView.GroupStyle> <GroupStyle> <GroupStyle.HeaderTemplate> <DataTemplate> <Grid Margin="1,0,0,6"> <Button AutomationProperties.Name="Group Title" Content="{Binding Name}" Click="Header_Click" Style="{StaticResource TextButtonStyle}" FontWeight="{Binding IsSelected, ConverterParameter=FontWeight, Converter={StaticResource BooleanToFontWeightConverter}}" /> </Grid> </DataTemplate> </GroupStyle.HeaderTemplate> <GroupStyle.Panel> <ItemsPanelTemplate> <VariableSizedWrapGrid Background="Red" Orientation="Vertical" Margin="0,0,40,0" /> </ItemsPanelTemplate> </GroupStyle.Panel> <GroupStyle.ContainerStyle> <Style TargetType="GroupItem"> <Setter Property="Template"> <Setter.Value> <ControlTemplate> <StackPanel> <ContentPresenter/> <ItemsPresenter/> <TextBlock Text="*** End of group ***"/> </StackPanel> </ControlTemplate> </Setter.Value> </Setter> </Style> </GroupStyle.ContainerStyle> </GroupStyle> </GridView.GroupStyle> </GridView> This almost works but after adding the container style, the grid of tiles no longer shows... the group header and 'End of group' textblock is showing, but I've lost the tile grid. Can anyone spot what I'm doing wrong...?

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stringstream problem - vector iterator not dereferencable

- by andreas

Hello I've got a problem with the following code snippet. It is related to the stringstream "stringstream css(cv.back())" bit. If it is commented out the program will run ok. It is really weird, as I keep getting it in some of my programs, but if I just create a console project the code will run fine. In some of my Win32 programs it will and in some it won't (then it will return "vector iterator not dereferencable" but it will compile just fine). Any ideas at all would be really appreciated. Thanks! vector<double> cRes(2); vector<double> pRes(2); int readTimeVects2(vector<double> &cRes, vector<double> &pRes){ string segments; vector<string> cv, pv, chv, phv; ifstream cin("cm.txt"); ifstream pin("pw.txt"); ifstream chin("hm.txt"); ifstream phin("hw.txt"); while (getline(cin,segments,'\t')) { cv.push_back(segments); } while (getline(pin,segments,'\t')) { pv.push_back(segments); } while (getline(chin,segments,'\t')) { chv.push_back(segments); } while (getline(phin,segments,'\t')) { phv.push_back(segments); } cin.close(); pin.close(); chin.close(); phin.close(); stringstream phss(phv.front()); phss >> pRes[0]; phss.clear(); stringstream chss(chv.front()); chss >> cRes[0]; chss.clear(); stringstream pss(pv.back()); pss >> pRes[1]; pss.clear(); stringstream css(cv.back()); css >> cRes[1]; css.clear(); return 0; }

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How can I get image data from QTKit without color or gamma correction in Snow Leopard?

- by Nick Haddad

Since Snow Leopard, QTKit is now returning color corrected image data from functions like QTMovies frameImageAtTime:withAttributes:error:. Given an uncompressed AVI file, the same image data is displayed with larger pixel values in Snow Leopard vs. Leopard. Currently I'm using frameImageAtTime to get an NSImage, then ask for the tiffRepresentation of that image. After doing this, pixel values are slightly higher in Snow Leopard. For example, a file with the following pixel value in Leopard: [0 180 0] Now has a pixel value like: [0 192 0] Is there any way to ask a QTMovie for video frames that are not color corrected? Should I be asking for a CGImageRef, CIImage, or CVPixelBufferRef instead? Is there a way to disable color correction altogether prior to reading in the video files? I've attempted to work around this issue by drawing into a NSBitmapImageRep with the NSCalibratedColroSpace, but that only gets my part of the way there: // Create a movie NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys : nsFileName, QTMovieFileNameAttribute, [NSNumber numberWithBool:NO], QTMovieOpenAsyncOKAttribute, [NSNumber numberWithBool:NO], QTMovieLoopsAttribute, [NSNumber numberWithBool:NO], QTMovieLoopsBackAndForthAttribute, (id)nil]; _theMovie = [[QTMovie alloc] initWithAttributes:dict error:&error]; // .... NSMutableDictionary *imageAttributes = [NSMutableDictionary dictionary]; [imageAttributes setObject:QTMovieFrameImageTypeNSImage forKey:QTMovieFrameImageType]; [imageAttributes setObject:[NSArray arrayWithObject:@"NSBitmapImageRep"] forKey: QTMovieFrameImageRepresentationsType]; [imageAttributes setObject:[NSNumber numberWithBool:YES] forKey:QTMovieFrameImageHighQuality]; NSError* err = nil; NSImage* image = (NSImage*)[_theMovie frameImageAtTime:frameTime withAttributes:imageAttributes error:&err]; // copy NSImage into an NSBitmapImageRep (Objective-C) NSBitmapImageRep* bitmap = [[image representations] objectAtIndex:0]; // Draw into a colorspace we know about NSBitmapImageRep *bitmapWhoseFormatIKnow = [[NSBitmapImageRep alloc] initWithBitmapDataPlanes:NULL pixelsWide:getWidth() pixelsHigh:getHeight() bitsPerSample:8 samplesPerPixel:4 hasAlpha:YES isPlanar:NO colorSpaceName:NSCalibratedRGBColorSpace bitmapFormat:0 bytesPerRow:(getWidth() * 4) bitsPerPixel:32]; [NSGraphicsContext saveGraphicsState]; [NSGraphicsContext setCurrentContext:[NSGraphicsContext graphicsContextWithBitmapImageRep:bitmapWhoseFormatIKnow]]; [bitmap draw]; [NSGraphicsContext restoreGraphicsState]; This does convert back to a 'Non color corrected' colorspace, but the color values NOT are exactly the same as what is stored in the Uncompressed AVI files we are testing with. Also this is much less efficient because it is converting from RGB - "Device RGB" - RGB. Also, I am working in a 64-bit application, so dropping down to the Quicktime-C API is not an option. Thanks for your help.

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PulpCore music playback - loop sound and animate volume

- by Peter Perhác

I have been experimenting with PulpCore, trying to create my own tower defence game (not-playable yet), and I am enjoying it very much I ran into a problem that I can't quite figure out. I extended PulpCore with the JOrbis thing to allow OGG files to be played. Works fine. However, pulpCore seems to have a problem with looping the sound WHILE animating the volume level. I tried this with wav file too, to make sure it isn't jOrbis that breaks it. The code is like this: Sound bgMusic = Sound.load("music/music.ogg"); Playback musicPlayback; ... musicVolume = new Fixed(0.75); musicPlayback = bgMusic.loop(musicVolume); //TODO figure out why it's NOT looping when volume is animated // musicVolume.animate(0, musicVolume.get(), FADE_IN_TIME); This code, for as long as the last line is commented out, plays the music.ogg again and again in an endless loop (which I can stop by calling stop on the Playback object returned from loop(). However, I would like the music to fade in smoothly, so following the advice of the PulpCore API docs, I added the last line which will create the fade-in but the music will only play once and then stop. I wonder why is that? Here is a bit of the documentation: Playback pulpcore.sound.Sound.loop(Fixed level) Loops this sound clip with the specified volume level (0.0 to 1.0). The level may have a property animation attached. Parameters: level Returns: a Playback object for this unique sound playback (one Sound can have many simultaneous Playback objects) or null if the sound could not be played. So what could be the problem? I repeat, with the last line, the sound fades in but doesn't loop, without it it loops but starts with the specified 0.75 volume level. Why can't I animate the volume of the looped music playback? What am I doing wrong? Anyone has any experience with pulpCore and has come across this problem? Anyone could please download PulpCore and try to loop music which fades-in (out)? note: I need to keep a reference to the Playback object returned so I can kill music later.

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What to do when you need more verbs in REST

- by Richard Levasseur

There is another similar question to mine, but the discussion veered away from the problem I'm encounting. Say I have a system that deals with expense reports (ER). You can create and edit them, add attachments, and approve/reject them. An expense report might look like this: GET /er/1 => {"title": "Trip to NY", "totalcost": "400 USD", "comments": [ "john: Please add the total cost", "mike: done, can you approve it now?" ], "approvals": [ {"john": "Pending"}, {"finance-group": "Pending"}] } That looks fine, right? Thats what an expense report document looks like. If you want to update it, you can do this: POST /er/1 {"title": "Trip to NY 2010"} If you want to approve it, you can do this: POST /er/1/approval {"approved": true} But, what if you want to update the report and approve it at the same time? How do we do that? If you only wanted to approve, then doing a POST to something like /er/1/approval makes sense. We could put a flag in the URL, POST /er/1?approve=1, and send the data changes as the body, but that flag doesn't seem RESTful. We could put special field to be submitted, too, but that seems a bit hacky, too. If we did that, then why not send up data with attributes like set_title or add_to_cost? We could create a new resource for updating and approving, but (1) I can't think of how to name it without verbs, and (2) it doesn't seem right to name a resource based on what actions can be done to it (what happens if we add more actions?) We could have an X-Approve: True|False header, but headers seem like the wrong tool for the job. It'd also be difficult to get set headers without using javascript in a browser. We could use a custom media-type, application/approve+yes, but that seems no better than creating a new resource. We could create a temporary "batch operations" url, /er/1/batch/A. The client then sends multiple requests, perhaps POST /er/1/batch/A to update, then POST /er/1/batch/A/approval to approve, then POST /er/1/batch/A/status to end the batch. On the backend, the server queues up all the batch requests somewhere, then processes them in the same backend-transaction when it receives the "end batch processing" request. The downside with this is, obviously, that it introduces a lot of complexity. So, what is a good, general way to solve the problem of performing multiple actions in a single request? General because its easy to imagine additional actions that might be done in the same request: Suppress or send notifications (to email, chat, another system, whatever) Override some validation (maximum cost, names of dinner attendees) Trigger backend workflow that doesn't have a representation in the document.

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Stack Overflow Exploit in C

- by Fernando Gonzalez

Hey there guys, the question is actually about stack overflows in C. I have an assigment that I can not get done for the life of me, i've looked at everything in the gdb and I just cant figure it. The question is the following: int i,n; void confused() { printf("who called me"); exit(0); } void shell_call(char *c) { printf(" ***Now calling \"%s\" shell command *** \n",c); system(c); exit(0); } void victim_func() { int a[4]; printf("[8]:%x\n", &a[8]); printf("Enter n: "); scanf("%d",&n); printf("Enter %d HEX Values \n",n); for(i=0;i<n;i++) scanf("%x",&a[i]); printf("Done reading junk numbers\n"); } int main() { printf("ls=736c --- ps = 7370 --- cal = 6c6163\n"); printf("location of confused %x \n", confused); printf("location of shell_call %x \n", shell_call); victim_func(); printf("Done, thank you\n"); } Ok, so I managed to get the first question correctly, which is to arbitrarily call one of the two functions not explicitly called in the main path. By the way, this has to be done while running the program without any modifications. I did this by running the program, setting N to 7, which gets me to the Function Pointer of the victim_func frame, I write a[7] with the memory address of confused or shell_call, and it works. (I have a 64 bit machine, thats why I have to get it to 7, since the EBI pointer is 2 ints wide, instead of 1) My question is the following, how could I control which argument gets passed to the shell_code funcion? ie. how do i write a string to char* c. The whole point is executing unix commands like "ps" etc, by running only the program. I figured writing the EBI pointer with the hex representation of "ps" and setting the arg list of shell_call to that, but that didn't work. I also tried inputing argsv arguments and setting the arg list of shell_call to the arg_list of main, but didnt work either. I think the second version should work, but i believe im not setting the arg list of the new stack frame correctly ( I did it by writing a[8] to 0, since its the first part of the functin pointer, and writing a[9]=736c and a[10]=0000, but its probably not right since those are the parameters of victim_func. So how do i access the parameters of shell_call?

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Oracle sample data problems

- by Jay

So, I have this java based data trasformation / masking tool, which I wanted to test out on Oracle 10g. The good part with Oracle 10g is that you get a load of sample schemas with half a million records in some. The schemas are : SH, OE, HR, IX and etc. So, I installed 10g, found out that the installation scripts are under ORACLE_HOME/demo/scripts. I customized these scripts a bit to run in batch mode. That solves one half of my requirement - to create source data for my testing my data transformation software. The second half of the requirement is that I create the same schemas under different names (TR_HR, TR_OE and so on...) without any data. These schemas would represent my target schemas. So, in short, my software would pick up data from a table in a schema and load it up in to the same table in a different schema. Now, I have two issues in creating my target schema and emptying it. I would like this in a batch job. But the oracle scripts you get, the sample schema names are not configurable. So, I tried creating a script, replacing OE with TR_OE, HR with TR_HR and so on. However, this approach is kind of irritating coz the sample schemas are kind of complicated in the way they are created; Oracle creates synonyms, views, materialized views, data types and lot of weird stuff. I would like the target schemas (TR_HR, TR_OE,...) to be empty. But some of the schemas have circular references, which would not allow me to delete data. The only work around seems to be removing certain foreign keys, deleting data and then adding the constraints back. Is there any easy way to all this, without all this fuss? I would need a complicated data set for my testing (complicated as in tables with triggers, multiple hierarchies.. for instance.. a child table that has children up to 5 levels, a parent table that refers to an IOT table and an IOT table that refers to a non-IOT table etc..). The sample schemas are just about perfect from a data set perspective. The only challenge I see is in automating this whole process of loading up the source schemas, and then creating the target schemas and emptying them. Appreciate your help and suggestions.

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access exception when invoking method of an anonymous class using java reflection

- by Asaf David

Hello I'm trying to use an event dispatcher to allow a model to notify subscribed listeners when it changes. the event dispatcher receives a handler class and a method name to call during dispatch. the presenter subscribes to the model changes and provide a Handler implementation to be called on changes. Here's the code (I'm sorry it's a bit long). EventDispacther: package utils; public class EventDispatcher<T> { List<T> listeners; private String methodName; public EventDispatcher(String methodName) { listeners = new ArrayList<T>(); this.methodName = methodName; } public void add(T listener) { listeners.add(listener); } public void dispatch() { for (T listener : listeners) { try { Method method = listener.getClass().getMethod(methodName); method.invoke(listener); } catch (Exception e) { System.out.println(e.getMessage()); } } } } Model: package model; public class Model { private EventDispatcher<ModelChangedHandler> dispatcher; public Model() { dispatcher = new EventDispatcher<ModelChangedHandler>("modelChanged"); } public void whenModelChange(ModelChangedHandler handler) { dispatcher.add(handler); } public void change() { dispatcher.dispatch(); } } ModelChangedHandler: package model; public interface ModelChangedHandler { void modelChanged(); } Presenter: package presenter; public class Presenter { private final Model model; public Presenter(Model model) { this.model = model; this.model.whenModelChange(new ModelChangedHandler() { @Override public void modelChanged() { System.out.println("model changed"); } }); } } Main: package main; public class Main { public static void main(String[] args) { Model model = new Model(); Presenter presenter = new Presenter(model); model.change(); } } Now, I except to get the "model changed" message. However, I'm getting an java.lang.IllegalAccessException: Class utils.EventDispatcher can not access a member of class presenter.Presenter$1 with modifiers "public". I understand that the class to blame is the anonymous class i created inside the presenter, however I don't know how to make it any more 'public' than it currently is. If i replace it with a named nested class it seem to work. It also works if the Presenter and the EventDispatcher are in the same package, but I can't allow that (several presenters in different packages should use the EventDispatcher) any ideas?

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Team matchups for Dota Bot

- by Dan

I have a ghost++ bot that hosts games of Dota (a warcraft 3 map that is played 5 players versus 5 players) and I'm trying to come up with good formulas to balance the players going into a match based on their records (I have game history for several thousand games). I'm familear with some of the concepts required to match up players, like confidence based on sample size of the number of games they played, and also perameter approximation and degrees of freedom and thus throwing out any variables that don't contribute enough to the r^2. My bot collects quite a few variables for each player from each game: The Important ones: Win/Lose/Game did not finish # of Player Kills # of Player Deaths # of Kills player assisted The not so important ones: # of enemy creep kills # of creep sneak attacks # of neutral creep kills # of Tower kills # of Rax kills # of courier kills Quick explination: The kills/deaths don't determine who wins, but the gold gained and lost from this usually is enough to tilt the game. Tower/Rax kills are what the goal of the game is (once a team looses all their towers/rax their thrown can be attacked if that is destroyed they lose), but I don't really count these as important because it is pretty random who gets the credit for the tower kill, and chances are if you destroy a tower it is only because some other player is doing well and distracting the otherteam elsewhere on the map. I'm getting a bit confused when trying to deal with the fact that 5 players are on a team, so ultimately each individual isn't that responsible for the team winner or losing. Take a player that is really good at killing and has 40 kills and only 10 deaths, but in their 5 games they've only won 1. Should I give him extra credit for such a high kill score despite losing? (When losing it is hard to keep a positive kill/death ratio) Or should I dock him for losing assuming that despite the nice kill/death ratio he probably plays in a really greedy way only looking out for himself and not helping the team? Ultimately I don't think I have to guess at questions like this because I have so much data... but I don't really know how to look at the data to answer questions like this. Can anyone help me come up with formulas to help team balance and predict the outcome? Thanks, Dan

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ObjectDisposedException from core .NET code

- by John

I'm having this issue with a live app. (Unfortunately this is post-mortem debugging - I only have this stack trace. I've never seen this personally, nor am I able to reproduce). I get this Exception: message=Cannot access a disposed object. Object name: 'Button'. exceptionMessage=Cannot access a disposed object. Object name: 'Button'. exceptionDetails=System.ObjectDisposedException: Cannot access a disposed object. Object name: 'Button'. at System.Windows.Forms.Control.CreateHandle() at System.Windows.Forms.Control.get_Handle() at System.Windows.Forms.Control.PointToScreen(Point p) at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent) at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks) at System.Windows.Forms.Control.WndProc(Message& m) at System.Windows.Forms.ButtonBase.WndProc(Message& m) at System.Windows.Forms.Button.WndProc(Message& m) at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m) at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m) at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam) exceptionSource=System.Windows.Forms exceptionTargetSite=Void CreateHandle() It looks like a mouse event is arriving at a form after the form has been disposed. Note there is none of my code in this stack trace. The only weird (?) thing I'm doing, is that I do tend to Dispose() Forms quite aggressively when I use them with ShowModal() (see "Aside" below). But I only do this after ShowModal() has returned (that should be safe right)? I think I read that events might be queued up in the event queue, but I can't believe this would be the problem. I mean surely the framework must be tolerant to old messages? I can well imagine that under stress messages might back-log and surely the window might go away at any time? Any ideas? If you could even suggest ways of reproducing, that might be useful. John Aside: TBH I've never quite understood whether calling Dispose() after Form.ShowDialog() is strictly necessary - the MSDN docs for ShowDialog() are to my mind a bit ambiguous.

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get_or_create generic relations in Django & python debugging in general

- by rabidpebble

I ran the code to create the generically related objects from this demo: http://www.djangoproject.com/documentation/models/generic_relations/ Everything is good intially: >>> bacon.tags.create(tag="fatty") <TaggedItem: fatty> >>> tag, newtag = bacon.tags.get_or_create(tag="fatty") >>> tag <TaggedItem: fatty> >>> newtag False But then the use case that I'm interested in for my app: >>> tag, newtag = bacon.tags.get_or_create(tag="wholesome") Traceback (most recent call last): File "<console>", line 1, in <module> File "/usr/local/lib/python2.6/dist-packages/django/db/models/manager.py", line 123, in get_or_create return self.get_query_set().get_or_create(**kwargs) File "/usr/local/lib/python2.6/dist-packages/django/db/models/query.py", line 343, in get_or_create raise e IntegrityError: app_taggeditem.content_type_id may not be NULL I tried a bunch of random things after looking at other code: >>> tag, newtag = bacon.tags.get_or_create(tag="wholesome", content_type=TaggedItem) ValueError: Cannot assign "<class 'generics.app.models.TaggedItem'>": "TaggedItem.content_type" must be a "ContentType" instance. or: >>> tag, newtag = bacon.tags.get_or_create(tag="wholesome", content_type=TaggedItem.content_type) InterfaceError: Error binding parameter 3 - probably unsupported type. etc. I'm sure somebody can give me the correct syntax, but the real problem here is that I have no idea what is going on. I have developed in strongly typed languages for over ten years (x86 assembly, C++ and C#) but am new to Python. I find it really difficult to follow what is going on in Python when things like this break. In the languages I mentioned previously it's fairly straightforward to figure things like this out -- check the method signature and check your parameters. Looking at the Django documentation for half an hour left me just as lost. Looking at the source for get_or_create(self, **kwargs) didn't help either since there is no method signature and the code appears very generic. A next step would be to debug the method and try to figure out what is happening, but this seems a bit extreme... I seem to be missing some fundamental operating principle here... what is it? How do I resolve issues like this on my own in the future?

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Problem with PHP 'PHP_SELF'

- by shinjuo

I am having a bit of trouble. It does not seem to be a big deal, but I have created a page that the user can edit a MySQL database. Once they click submit it should process the php within the if statement and echo 1 record updated. The problem is that it does not wait to echo the statement. It just seems to ignore the way I wrote my if and display the whole page. Can anyone see where I went wrong. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title></title> </head> <body> <form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post"> <?php require("serverInfo.php"); ?> <?php $res = mysql_query("SELECT * FROM cardLists order by cardID") or die(mysql_error()); echo "<select name = 'Cards'>"; while($row=mysql_fetch_assoc($res)) { echo "<option value=\"$row[cardID]\">$row[cardID]</option>"; } echo "</select>"; ?> Amount to Add: <input type="text" name="Add" /> <input type="submit" /> </form> <?php if(isset($_POST['submit'])); { require("serverInfo.php"); mysql_query("UPDATE `cardLists` SET `AmountLeft` = `AmountLeft` + ".mysql_real_escape_string($_POST['Add'])." WHERE `cardID` = '".mysql_real_escape_string($_POST['Cards'])."'"); mysql_close($link); echo "1 record Updated"; } ?> <br /> <a href="index.php"> <input type="submit" name="main" id="main" value="Return To Main" /></a> </body> </html>

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How to sort my paws?

- by Ivo Flipse

In my previous question I got an excellent answer that helped me detect where a paw hit a pressure plate, but now I'm struggling to link these results to their corresponding paws: I manually annotated the paws (RF=right front, RH= right hind, LF=left front, LH=left hind). As you can see there's clearly a pattern repeating pattern and it comes back in aknist every measurement. Here's a link to a presentation of 6 trials that were manually annotated. My initial thought was to use heuristics to do the sorting, like: There's a ~60-40% ratio in weight bearing between the front and hind paws; The hind paws are generally smaller in surface; The paws are (often) spatially divided in left and right. However, I’m a bit skeptical about my heuristics, as they would fail on me as soon as I encounter a variation I hadn’t thought off. They also won’t be able to cope with measurements from lame dogs, whom probably have rules of their own. Furthermore, the annotation suggested by Joe sometimes get's messed up and doesn't take into account what the paw actually looks like. Based on the answers I received on my question about peak detection within the paw, I’m hoping there are more advanced solutions to sort the paws. Especially because the pressure distribution and the progression thereof are different for each separate paw, almost like a fingerprint. I hope there's a method that can use this to cluster my paws, rather than just sorting them in order of occurrence. So I'm looking for a better way to sort the results with their corresponding paw. For anyone up to the challenge, I have pickled a dictionary with all the sliced arrays that contain the pressure data of each paw (bundled by measurement) and the slice that describes their location (location on the plate and in time). To clarfiy: walk_sliced_data is a dictionary that contains ['ser_3', 'ser_2', 'sel_1', 'sel_2', 'ser_1', 'sel_3'], which are the names of the measurements. Each measurement contains another dictionary, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10] (example from 'sel_1') which represent the impacts that were extracted. Also note that 'false' impacts, such as where the paw is partially measured (in space or time) can be ignored. They are only useful because they can help recognizing a pattern, but won't be analyzed. And for anyone interested, I’m keeping a blog with all the updates regarding the project!

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Changing the itemsSource of a treeview makes it's children invisible, when they were already display

- by Marnix Kraus

I found some strange problem in WPF, using the itemsSource of a treeview. I hope I can make this specific problem clear for you. First; a story. There is a treeview. It has a list with treeviewitems as itemsSource. This list is called _roots. There is another list, called _leafs. For as in a treeview, the _roots contain the _leafs in some hierarchical way. For example: <TreeviewItem Header="Jungle"> <TreeviewItem> <SpecialTreeviewItem Header="Monkey"/> <SpecialTreeviewItem Header="Apple"/> </TreeviewItem> </TreeviewItem> Now I am trying to switch between these two lists as itemsSource. It seemed to work fine, but it doesn't: When the Jungle-item is un-expanded, and I change the itemsSource to _leafs, and change it back again to _roots, everything works fine and all items can be expanded and showed. But when the Jungle-item is expanded (and the special items are already visible) and I change it to the _leafs itemsSource, and then change the itemsSource back to _roots, all special items have disappeared!! Also, when I do the same as case 2, but first un-expand the Jungle-item again, the special items also disappear. I did a lot of debugging, before posting this question here and come to the following conclusion: Printing on the event: visibility changed, the visibility is set to false for all items that were already visible (that is, when _roots become visible, the special items become invisible (because they were already visible)) So, IsVisible is false for the items, but Visibility = Visible. Which is a bit strange. The problem seems to depend on the use of the _roots list, which in a certain way contain the _leafs. When I change the itemsSource to different lists with special items in it, everything works fine. The hierarchical structure of the _roots make this thing broken. I hope that this is a complete overview of my problem. Help would be appreciated.

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No norwegian characters in LaTeX

- by DreamCodeR

Hi, I have translated a document from English to Norwegian in the LaTeX format, and while using norwegian special characters, I get an error using \usepackage[utf8x]{inputenc} to try and display the norwegian (scandinavian) special characters in PostScript/PDF/DVI format, saying Package utf8x Error: MalformedUTF-8sequence. So while that didn't work, I tried out another possible solution: \usepackage{ucs} \usepackage[norsk]babel And when I tried to save that in Emacs I get this message: These default coding systems were tried to encode text in the buffer `lol.tex': (utf-8-unix (905 . 4194277) (916 . 4194245) (945 . 4194278) (950 . 4194277) (954 . 4194296) (990 . 4194277) (1010 . 4194277) (1013 . 4194278) (1051 . 4194277) (1078 . 4194296) (1105 . 4194296)) However, each of them encountered characters it couldn't encode: utf-8-unix cannot encode these: \345 \305 \346 \345 \370 \345 \345 \346 \345 \370 ... Thanks to Emacs I have the possibility to check out the properties of those characters and the first one tells me: character: \345 (4194277, #o17777745, #x3fffe5) preferred charset: eight-bit (Raw bytes 128-255) code point: 0xE5 syntax: w which means: word buffer code: #xE5 file code: not encodable by coding system utf-8-unix display: not encodable for terminal Which doesn't tell me much. When I try to build this with texi2dvi --dvipdf filename.text I get a perfectly fine PDF, all without the special norwegian characters. When I am about to save Emacs also ask me: "Select coding system (default raw-text):" And I type in utf-8 to choose its coding system. I have also tried to choose default raw-text to see if I get some different result. But nothing. At last I tried \lstset{inputencoding=utf8x, extendedchars=\true} ... a code I came over while trying to google the solution to this problem. Which gives me this error: Undefined control sequence. So basically, I have tried every encoding option I have been able to find and nothing works. I am desperately trying to make this work since the norwegian translation must be published before the deadline. As an additional information I may add that I found out later on that I only had the en_US.UTF-8 in my locale, so I added nb_NO.UTF-8 and nb_NO.ISO-8859-15 and ran locale-gen + reboot without any changes. I hope I provided enough information to get some assistance, the characters in question is æ ø å.

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Using respond_to ... format.json and jQuery Form Plugin by malsup

- by Topher Fangio

Hello all, I'm having a tad bit of trouble getting the jQuery Form Plugin to work properly with a file-upload field. When I use the plugin to submit the form without a file-upload field, the format.json portion of the respond_to do |format| block is called properly. However, by adding the file-upload field, it only executes the format.html portion which makes my javascript code think that an error has occurred. Has anyone run into this before or know a way to force the plugin to always use json? Alternatively, can I modify the url that the plugin uses to force Rails to render the json? Thanks very much for any help! Code below: # app/controllers/details_controller.rb def create @detail = Detail.new(params[:detail]) style = params[:detail_style].to_sym || :thumb data = { :id => '5', :url => 'test.rails' } respond_to do |format| if @detail.save flash[:notice] = 'Your image has been saved.' data = { :id => @detail.id, :url => @detail.data.url(style) } format.html { redirect_to :action => 'index' } format.json { render :json => "<textarea>#{data.to_json}</textarea>", :status => :created } else format.html { render :action => 'new' } format.json { render :json => @detail.errors, :status => :unprocessable_entity } end end end /* app/views/sidebar/_details.html.erb (excerpt) */ <% form_for(Detail.new, :html => { :multipart => true } ) do |f| %> <%= hidden_field_tag 'detail_style', 'thumb' %> <%= f.label :image, "Recent Images" %> <%= f.file_field :image%> <p> <%= f.submit "Upload" %> </p> <% end %> <script> $(document).ready(function() { var options = { dataType: 'json', success: function(json, statusText) { console.log("success: " + json); }, error: function(xhr, statusText, errorThrown) { console.log("error: " + xhr.responseText); } }; $('#new_detail').ajaxForm(options); });

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architecture python question

- by tom smith

hi. creating a distributed crawling python app. it consists of a master server, and associated client apps that will run on client servers. the purpose of the client app is to run across a targeted site, to extract specific data. the clients need to go "deep" within the site, behind multiple levels of forms, so each client is specifically geared towards a given site. each client app looks something like main: parse initial url call function level1 (data1) function level1 (data) parse the url, for data1 use the required xpath to get the dom elements call the next function call level2 (data) function level2 (data2) parse the url, for data2 use the required xpath to get the dom elements call the next function call level3 function level3 (dat3) parse the url, for data3 use the required xpath to get the dom elements call the next function call level4 function level4 (data) parse the url, for data4 use the required xpath to get the dom elements at the final function.. --all the data output, and eventually returned to the server --at this point the data has elements from each function... my question: given that the number of calls that is made to the child function by the current function varies, i'm trying to figure out the best approach. each function essentialy fetches a page of content, and then parses the page using a number of different XPath expressions, combined with different regex expressions depending on the site/page. if i run a client on a single box, as a sequential process, it'll take awhile, but the load on the box is rather small. i've thought of attempting to implement the child functions as threads from the current function, but that could be a nightmare, as well as quickly bring the "box" to its knees! i've thought of breaking the app up in a manner that would allow the master to essentially pass packets to the client boxes, in a way to allow each client/function to be run directly from the master. this process requires a bit of rewrite, but it has a number of advantages. a bunch of redundancy, and speed. it would detect if a section of the process was crashing and restart from that point. but not sure if it would be any faster... i'm writing the parsing scripts in python.. so... any thoughts/comments would be appreciated... i can get into a great deal more detail, but didn't want to bore anyone!! thanks! tom

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Problem inserting JavaScript into a CKEditor Instance running inside a jQuery-UI Dialog Box

- by PlasmaFlux

Hello Overflowers! Here's what's going on: I'm building an app (using PHP, jQuery, etc), part of which lets users edit various bits of a web page (Header, Footer, Main Content, Sidebar) using CKEditor. It's set up so that each editable bit has an "Edit Content" button in the upper right that, on click, launches an instance of CKEditor inside a jQuery-UI Dialog box. After the user is done editing, they can click an 'Update Changes' button that passes the edited content back off to the main page and closes the Dialog/CKeditor. It's all working magnificently, save for one thing. If someone inserts any JavaScript code, wrapped in 'script' tags, using either the Insert HTML Plugin for CKEditor or by going to 'Source' in CKEditor and placing the code in the source, everything seems okay until they click the 'Update Changes' button. The JavaScript appears to be inserting properly, but when 'Update Changes' is clicked, instead of the Dialog closing and passing the script back into the div where it belongs, what I get instead is an all-white screen with just the output of the JavaScript. For example, a simple 'Hello World' script results in a white screen with the string 'Hello World' in the upper left corner; for more intricate scripts, like an API call to, say Aweber, that generates a newsletter signup form, I get an all-white screen with the resulting form from the Aweber API call perfectly rendered in the middle of the screen. One of the most confusing parts is that, on these pages, if I click 'View Source', I get absolutely nothing. Blank emptiness. Here's all my code that handles the launching of the CKEditor instance inside the jQuery-UI Dialog, and the passing of the edited data back into its associated div on click of the 'Update Changes' button: $(function() { $('.foobar_edit_button') .button() .click(function() { var beingEdited = $(this).nextAll('.foobar_editable').attr('id'); var content = $(this).nextAll('.foobar_editable').html(); $('#foobar_editor').html(content); $('#foobar_editor').dialog( { open:function() { $(this).ckeditor(function() { CKFinder.SetupCKEditor( this, '<?php echo '/foobar/lib/editor/ckfinder/'; ?>' ); }); }, close:function() { $(this).ckeditorGet().destroy(); }, autoOpen: false, width: 840, modal: true, buttons: { 'Update Changes': function() { // TODO: submit changes to server via ajax once its completed: for ( instance in CKEDITOR.instances ) CKEDITOR.instances[instance].updateElement(); var edited_content = $('#foobar_editor').html(); $('#' + beingEdited).html(edited_content); $(this).dialog('close'); } } }); $('#foobar_editor').dialog('open'); }); }); I'm all sorts of confused. If anyone can point me in the right direction, it will be greatly appreciated. Thanks!

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Add inner-marging to a 4 columns CSS

- by Martín Marconcini

I am not a CSS expert (mainly because I haven’t had the need to use much HTML/CSS stuff lately), so I came up with the following style/divs to create a 4 column layout: <style type="text/css">  </style> note: most of this stuff comes from this google result, I just adapted it to 4 columns. The HTML then looks like this: <div class="columns col4"> <div class="column first”> SOME TEXT </div> <div class="column last”> SOME LAST TEXT </div> Ok, I’ve simplified that a bit (there’s a small image and some < h2 text in there too) but the thing is that I’d like to add some space between the columns. Here’s how it looks now: Do you have any idea what CSS property should I touch? note: If I add margin or padding, one column shifts down because (as I understand it) it doesn’t fit. There might be other CSSs as well, since this came in a template (I have been asked for this change, but I didn’t do any of this, as usual). Thanks for any insight.

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problem with jquery : minipulating val() property of element

- by P4ul

Hi, Please help! I have some form elements in a div on a page: <div id="box"> <div id="template"> <div> <label for="username">Username</label> <input type="text" class="username" name="username[]" value="" / > <label for="hostname">hostname</label> <input type="text" name="hostname[]" value=""> </div> </div> </div> using jquery I would like to take a copy of #template, manipulate the values of the inputs and insert it after #template so the result would look something like: <div id="box"> <div id="template"> <div> <label for="username">Username</label> <input type="text" class="username" name="username[]" value="" / > <label for="hostname">hostname</label> <input type="text" name="hostname[]" value=""> </div> </div> <div> <label for="username">Username</label> <input type="text" class="username" name="username[]" value="paul" / > <label for="hostname">hostname</label> <input type="text" name="hostname[]" value="paul"> </div> </div> I am probably going about this the wrong way but the following test bit of javascript code run in firebug on the page does not seem to change the values of the inputs. var cp = $('#template').clone(); cp.children().children().each( function(i,d){ if( d.localName == 'INPUT' ){ $(d).val('paul'); //.css('background-color', 'red'); } }); $("#box").append(cp.html()); although if I uncomment "//.css('background-color', 'red');" the inputs will turn red.

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If Then Statement Condition Being Ignored With Optimisations On

- by Matma

I think im going mad but can some show me what im missing, it must be some stupidly simple i just cant see the wood for the trees. BOTH side of this if then else statement are being executed? Ive tried commenting out the true side and moving the condition to a seperate variable with the same result. However if i explicitly set the condition to 1=0 or 1=1 then the if then statement is operating as i would expect. i.e. only executing one side of the equation... The only time ive seen this sort of thing is when the compiler has crashed and is no longer compiling (without visible indication that its not) but ive restarted studio with the same results, ive cleaned the solution, built and rebuilt with no change? please show me the stupid mistake im making using vs2005 if it matters. Dim dset As DataSet = New DataSet If (CboCustomers.SelectedValue IsNot Nothing) AndAlso (CboCustomers.SelectedValue <> "") Then Dim Sql As String = "Select sal.SalesOrderNo As SalesOrder,cus.CustomerName,has.SerialNo, convert(varchar,sal.Dateofpurchase,103) as Date from [dbo].[Customer_Table] as cus " & _ " inner join [dbo].[Hasp_table] as has on has.CustomerID=cus.CustomerTag " & _ " inner join [dbo].[salesorder_table] as sal On sal.Hasp_ID =has.Hasp_ID Where cus.CustomerTag = '" & CboCustomers.SelectedValue.ToString & "'" Dim dap As SqlDataAdapter = New SqlDataAdapter(Sql, FormConnection) dap.Fill(dset, "dbo.Customer_Table") DGCustomer.DataSource = dset.Tables("dbo.Customer_Table") Else Dim erm As String = "wtf" End If EDIT: i have found that this is something to do with the release config settings im using, i guesing its the optimisations bit. does anyone know of any utils/addons for vs that show if a line has been optimised out. delphi, my former language showed blue dots in the left margin to show that it was a compiled line, no dot meaning it wasnt compiled in, is there anything like that for vs? alternatively can someone explain how optimisations would affect this simple if statement causeing it to run both sides? EDIT2: using this thread as possible causes/solutions : http://stackoverflow.com/questions/2135509/bug-only-occurring-when-compile-optimization-enabled. It does the same with release = optimisations on, x86, x64 and AnyCPU Goes away with optimisations off. Im using V2005 on a x64 win7 machine, if that matters. Thanks

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chaining array of tasks with continuation

- by Andrei Cristof

I have a Task structure that is a little bit complex(for me at least). The structure is: (where T = Task) T1, T2, T3... Tn. There's an array (a list of files), and the T's represent tasks created for each file. Each T has always two subtasks that it must complete or fail: Tn.1, Tn.2 - download and install. For each download (Tn.1) there are always two subtasks to try, download from two paths(Tn.1.1, Tn.1.2). Execution would be: First, download file: Tn1.1. If Tn.1.1 fails, then Tn.1.2 executes. If either from download tasks returns OK - execute Tn.2. If Tn.2 executed or failed - go to next Tn. I figured the first thing to do, was to write all this structure with jagged arrays: private void CreateTasks() { //main array Task<int>[][][] mainTask = new Task<int>[_queuedApps.Count][][]; for (int i = 0; i < mainTask.Length; i++) { Task<int>[][] arr = GenerateOperationTasks(); mainTask[i] = arr; } } private Task<int>[][] GenerateOperationTasks() { //two download tasks Task<int>[] downloadTasks = new Task<int>[2]; downloadTasks[0] = new Task<int>(() => { return 0; }); downloadTasks[1] = new Task<int>(() => { return 0; }); //one installation task Task<int>[] installTask = new Task<int>[1] { new Task<int>(() => { return 0; }) }; //operations Task is jagged - keeps tasks above Task<int>[][] operationTasks = new Task<int>[2][]; operationTasks[0] = downloadTasks; operationTasks[1] = installTask; return operationTasks; } So now I got my mainTask array of tasks, containing nicely ordered tasks just as described above. However after reading the docs on ContinuationTasks, I realise this does not help me since I must call e.g. Task.ContinueWith(Task2). I'm stumped about doing this on my mainTask array. I can't write mainTask[0].ContinueWith(mainTask[1]) because I dont know the size of the array. If I could somehow reference the next task in the array (but without knowing its index), but cant figure out how. Any ideas? Thank you very much for your help. Regards,

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How do I use IImgCtx to get load an image with an alpha channel?

- by fret

I have some working code that uses IImgCtx to load images, but I can't work out how to get at the alpha channel. For images like .gif's and .png's there are transparent pixels, but using anything other than a 24-bit bitmap as a drawing surface doesn't work. For reference on the interface: http://www.codeproject.com/KB/graphics/JianImgCtxDecoder.aspx My code looks like this: IImgCtx *Ctx = 0; HRESULT hr = CoCreateInstance(CLSID_IImgCtx, NULL, CLSCTX_INPROC_SERVER, IID_IImgCtx, (LPVOID*)&Ctx); if (SUCCEEDED(hr)) { GVariant Fn = Name; hr = Ctx->Load(Fn.WStr(), 0); if (SUCCEEDED(hr)) { SIZE Size = { -1, -1 }; ULONG State = 0; while (true) { hr = Ctx->GetStateInfo(&State, &Size, false); if (SUCCEEDED(hr)) { if ((State & IMGLOAD_COMPLETE) || (State & IMGLOAD_STOPPED) || (State & IMGLOAD_ERROR)) { break; } else { LgiSleep(1); } } else break; } if (Size.cx > 0 && Size.cy > 0 && pDC.Reset(new GMemDC)) { if (pDC->Create(Size.cx, Size.cy, 32)) { HDC hDC = pDC->StartDC(); if (hDC) { RECT rc = { 0, 0, pDC->X(), pDC->Y() }; Ctx->Draw(hDC, &rc); pDC->EndDC(); } } else pDC.Reset(); } } Ctx->Release(); Where "StartDC" basically wraps CreateCompatibleDC(NULL) and "EndDC" wraps DeleteDC, with appropriate SelectObjects for the HBITMAPS etc. And pDC-Create(x, y, bit_depth) calls CreateDIBSection(...DIB_RGB_COLORS...). So it works if I create a 24 bits/pixel bitmap but has no alpha to speak of, and it leaves the 32 bits/pixel bitmap blank. Now this interface apparently is used by Internet Explorer to load images, and obviously THAT supports transparency, so I believe that it's possible to get some level of alpha out of the interface. The question is how? (I also have fall back code that will call libpng/libjpeg/my .gif loader etc)

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