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• Rotate canvas along its center based on user touch - Android

  - by Ganapathy

  I want to rotate the canvas circularly on its center axis based on user touch. i want to rotate based on center but its rotating based on top left corner . so i am able to see only 1/4 for rotation of image. any idea.. Like a old phone dialer . I have tried like as follows onDraw(Canvas canvas){ canvas.save(); // do my rotation canvas.rotate(rotation,0,0); canvas.drawBitmap( ((BitmapDrawable)d).getBitmap(),0,0,p ); canvas.restore(); } @Override public boolean onTouchEvent(MotionEvent e) { float x = e.getX(); float y = e.getY(); updateRotation(x,y); mPreviousX = x; mPreviousY = y; invalidate(); } private void updateRotation(float x, float y) { double r = Math.atan2(x - centerX, centerY - y); rotation = (int) Math.toDegrees(r); }

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• How do I clip an image in OpenGL ES on Android?

  - by Maxim Shoustin

  My game involves "wiping off" an image by touch: After moving a finger over it, it looks like this: At the moment, I'm implementing it with Canvas, like this: 9Paint pTouch; 9int X = 100; 9int Y = 100; 9Bitmap overlay; 9Canvas c2; 9Rect dest; pTouch = new Paint(Paint.ANTI_ALIAS_FLAG); pTouch.setXfermode(new PorterDuffXfermode(Mode.SRC_OUT)); pTouch.setColor(Color.TRANSPARENT); pTouch.setMaskFilter(new BlurMaskFilter(15, Blur.NORMAL)); overlay = BitmapFactory.decodeResource(getResources(),R.drawable.wraith_spell).copy(Config.ARGB_8888, true); c2 = new Canvas(overlay); dest = new Rect(0, 0, getWidth(), getHeight()); Paint paint = new Paint();9 paint.setFilterBitmap(true); ... @Override protected void onDraw(Canvas canvas) { ... c2.drawCircle(X, Y, 80, pTouch); canvas.drawBitmap(overlay, 0, 0, null); ... } @Override 9public boolean onTouchEvent(MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: case MotionEvent.ACTION_MOVE: { X = (int) event.getX(); Y = (int) event.getY();9 invalidate(); c2.drawCircle(X, Y, 80, pTouch);9 break; } } return true; ... What I'm essentially doing is drawing transparency onto the canvas, over the red ball image. Canvas and Bitmap feel old... Surely there is a way to do something similar with OpenGL ES. What is it called? How do I use it? [EDIT] I found that if I draw an image and above new image with alpha 0, it goes to be transparent, maybe that direction? Something like: gl.glColor4f(0.0f, 0.0f, 0.0f, 0.01f);

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• Android Game Development problem whith size and speed

  - by Charlton Santana

  I have been coding speed for an object. I have made it so the object will move from one end of the screen to another at a speed depending on the screen size, at the monemt I have made it so it will take one second to pass the screen. So i have worked out the speed in code but when I go to assign the speed it tells me to force close and i do not understand why. Here is the code: MainGame Code: @Override protected void onDraw(Canvas canvas) { setBlockSpeed(getWidth()); } private int blockSpeed; private void setBlockSpeed(int screenWidth){ Log.d(TAG, "screenWidth " + screenWidth); blockSpeed = screenWidth / 100; // 100 is the FPS.. i want it to take 1 second to pass the screen Math.round(blockSpeed); // to make it a whole number block.speed = blockSpeed; // if i dont put blockSpeed and put eg 8 it still tells me to force close } Block.java Code: public int speed; public void draw(Canvas canvas) { canvas.drawBitmap(bitmap, x - (bitmap.getWidth() / 2), y - (bitmap.getHeight() / 2), null); if(dontmove == 0){ this.x -= speed; } }

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• How do I draw a 2d plane and rotate camara (To be a board) in a 3d XNA game?

  - by Mech0z

  I am trying to create a simple board game, but the 3d part of this is really killing me. From what I can gather I have created a plane, but it never moves even though I turn the camara, but that partially makes sense as I only turn the camara with a 3d model, but in my head that makes 0 sense, in my head if I turn the camara it should affect ALL my models? But with this code the camara only "cares" about the 3d cylinder, the plane is just completely still private void OnDraw(object sender, GameTimerEventArgs e) { SharedGraphicsDeviceManager.Current.GraphicsDevice.Clear(Color.CornflowerBlue); foreach (ModelMesh mesh in cylinderModel.Meshes) { foreach (BasicEffect effect in mesh.Effects) { //effect.World = Matrix.CreateRotationX((float)e.TotalTime.TotalSeconds * 2); effect.View = Matrix.CreateLookAt(cameraPosition, Vector3.Zero, Vector3.Up); effect.Projection = Matrix.CreatePerspectiveFieldOfView(MathHelper.ToRadians(45.0f), aspectRatio, 1.0f, 10000.0f); effect.EnableDefaultLighting(); } mesh.Draw(); } //cameraPosition.Z -= 5.0f; _effect.World = Matrix.CreateRotationZ((MathHelper.ToRadians(((float)e.TotalTime.Milliseconds / 2) % 360))); foreach (EffectPass pass in _effect.CurrentTechnique.Passes) { pass.Apply(); SharedGraphicsDeviceManager.Current.GraphicsDevice.DrawUserPrimitives(PrimitiveType.TriangleStrip, _vertices, 0, 1, VertexPositionColor.VertexDeclaration); } } Is there a way to get the camara to affect all models?

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• How to attach a scroll bar to a canvas in android ?

  - by panzerschreck

  Hello, I am drawing up a grid on a canvas as below, I have not been able to get the scroll bar to appear, I looked around for examples, but none of them give details on drawing scroll bars for custom views. Your help is much appreciated. public class GridActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // i tried to do as in the documentation nothing seems to happen LinearLayout lLayout = new LinearLayout(this); lLayout.addView(new CustomDrawableView(this), new ViewGroup.LayoutParams(800,600)); FrameLayout fLayout = new FrameLayout(this); fLayout.addView(lLayout, new ViewGroup.LayoutParams(800,600)); setContentView(fLayout); } private class GridView extends ScrollView { private ShapeDrawable[] mDrawable; public GridView (Context context) { // some initialization } protected void onDraw(Canvas canvas) { for each i mDrawable[i].draw(canvas) } } }

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• Syntax error on token "QUOTE", VariableDeclaratorId expected after this token

  - by user356812

  I've posted a bigger chunk of the code below. You can see that initially QUOTE was procedural- coded in place. I'm trying to learn how to use declarative design so I want to do the same thing but by using resources. It seems like I need to access the string.xml thru the @R.id tag and identify QUOTE with that string value. But I don't know enough to negotiate this. Any tips? Thanks! public class circle extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(new GraphicsView(this)); } static public class GraphicsView extends View { //private static final String QUOTE = "Happy Birthday to David."; private final String QUOTE = getString(R.string.quote); ..... @Override protected void onDraw(Canvas canvas) { // Drawing commands go here canvas.drawPath(circle, cPaint); canvas.drawTextOnPath(QUOTE, circle, 0, 20, tPaint);

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• Transparent View with Android

  - by victorusmo

  Hi everybody, I try to have a bitmap moving over my android application. I m be able to have my bitmap behind my text view, but not over them. public void onCreate(Bundle savedInstanceState) ... // ll is a FrameLayout ll.addView(text1); ll.addView(text2); ll.addView(new Panel(this),200,400); my Panel class is defined like this : class Panel extends SurfaceView ...... @Override public void onDraw(Canvas canvas) { canvas.drawColor(0, PorterDuff.Mode.CLEAR); Bitmap bitmap; GraphicObject.Coordinates coords; for (GraphicObject graphic : _graphics) { bitmap = graphic.getGraphic(); coords = graphic.getCoordinates(); canvas.drawBitmap(bitmap, coords.getX(), coords.getY(), null); } } Can you help me ? How Can i Draw a transparent bitmap over my views of my application Thanks a lot, Cheers, Victor

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• Android programming - How to acces [to draw on] XML view in main.xml layout, using code

  - by user556248

  Ok I'm a newbie at Android programming, have a hard time with the graphics part. Understand the beauty of creating layout in XML file, but lost how to access various elements, especially a View element to draw on it. See example of my layout main.xml here; <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/root" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent"> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="wrap_content"> <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/Title" android:text="App title" android:layout_width="fill_parent" android:layout_height="wrap_content" android:textColor="#000000" android:background="#A0A0FF"/> </LinearLayout> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/PaperLayout" android:layout_width="fill_parent" android:layout_height="0dp" android:layout_weight="1" android:orientation="horizontal" android:focusable="true"> <View android:id="@+id/Paper" android:layout_width="fill_parent" android:layout_height="fill_parent" /> </LinearLayout> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="wrap_content"> <Button android:id="@+id/File" android:layout_width="fill_parent" android:layout_weight="1" android:layout_height="34dp" android:layout_alignParentTop="true" android:layout_centerInParent="true" android:clickable="true" android:textSize="10sp" android:text="File" /> <Button android:id="@+id/Edit" android:layout_width="fill_parent" android:layout_weight="1" android:layout_height="34dp" android:clickable="true" android:textSize="10sp" android:text="Edit" /> </LinearLayout> </LinearLayout> As you can see I have a custom app title bar, then a View filling middle, and finally two buttons in bottom. Catching button events and responding to, for example changing title bar text and changing View background color works fine, but how the heck do I access and more importantly draw on the view defined in main.xml UPDATE: That for your suggestion, however besides that I need a View, not ImageView and you are missing a parameter on canvas.drawText and an ending bracket, it does not work. Now this is most likely because you missed the fact that I am a newbie and assuming I can fill in any blanks. Now first of all I do NOT understand why in my main.xml layout file I can create a View or even a SurfaceView element, which is what I need, but according to your solution I don't even specify the View like Anyways I edited my main.xml according to your solution, and slimmed it down a bit for simplicity; <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/root" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent"> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="wrap_content"> <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/Title" android:text="App title" android:layout_width="fill_parent" android:layout_height="wrap_content" android:textColor="#000000" android:background="#A0A0FF"/> </LinearLayout> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/PaperLayout" android:layout_width="fill_parent" android:layout_height="0dp" android:layout_weight="1" android:orientation="horizontal" android:focusable="true"> <com.example.MyApp.CustomView android:id="@+id/Paper" android:layout_width="fill_parent" android:layout_height="fill_parent" /> <com.example.colorbook.CustomView/> </LinearLayout> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="wrap_content"> <Button android:id="@+id/File" android:layout_width="fill_parent" android:layout_weight="1" android:layout_height="34dp" android:layout_alignParentTop="true" android:layout_centerInParent="true" android:clickable="true" android:textSize="10sp" android:text="File" /> </LinearLayout> </LinearLayout> In my main java file, MyApp.java, I added this after OnCreate; public class CustomView extends ImageView { @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); canvas.drawText("Your Text", 1, 1, null); } } But I get error on the "CustomView" part; "Implicit super constructor ImageView() is undefined for default constructor.Must define an explicit constructor" Eclipse suggests 3 quick fixes about adding constructor, but none helps, well it removes error but gives error on app when running. I hope somebody can break this down for me and provide a solution, and perhaps explain why I can't just create a View element in my main.xml layotu file and draw on it in code.

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• Android Canvas.drawText

  - by Gaz

  Hi All, I have a view, I'm drawing with the Canvas object in the onDraw(Canvas canvas) method. My code is: Paint paint = new Paint(); paint.setColor(Color.WHITE); paint.setStyle(Style.FILL); canvas.drawPaint(paint); paint.setColor(android.R.color.black); paint.setTextSize(20); canvas.drawText("Some Text", 10, 25, paint); The problem is the text doesn't show through the background, what am I doing wrong? If I remove the canvas.drawPaint(paint) and paint.setColor(android.R.color.black) you can see the text on the screen.....

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• Custom view in ListView disappears while scrolling in Android

  - by troorl

  Hi. I wrote a simple custom view for rows in ListView. It works fine, but when I try to scroll the list, I see only white rows without content. And when scrolling is over, rows continue to show again. This is how I draw a custom view: @Override protected void onDraw(Canvas canvas) { if(poster != null) { canvas.drawBitmap(poster, padding, padding, paint); } canvas.drawText(title, 55 + padding, 16 + padding, paint); } Maybe I missed something? P.S. This is short screencast (400kb) http://dl.dropbox.com/u/190203/test.mpeg

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• Custom View embed in Gallery crashes while key press

  - by tao

  Hi there, I'd like to find some stuff to replace the Tab component, so I'd make a custom View named StringView, which has the ability to display text, and to embed it into a Gallery. But it always crashes with error "NullPointerException at InputMethodManager". I have no idea about this, any help&tip&suggest are appreciate. Detail of my issue: First I'd created a class StringView extends View: public class StringView extends View { protected final Paint mPaint = new Paint(Paint.ANTI_ALIAS_FLAG); protected String mString; protected int mAscent; // Constructor public StringView(Context context, String string) { super(context); mPaint.setARGB(255, 255, 60, 10); mPaint.setTextSize(30); //mPaint.setFakeBoldText(true); mString = string; setPadding(20,15,20,15); } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); int w = this.getPaddingLeft(); int h = this.getPaddingTop() - mAscent; canvas.drawText(mString, w, h, mPaint); } public void setString(String str) { mString = str; this.requestLayout(); this.invalidate(); } public String getString() { return mString; } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { setMeasuredDimension(measureWidth(widthMeasureSpec), measureHeight(heightMeasureSpec)); } /** * Determines the width of this view * @param measureSpec A measureSpec packed into an int * @return The width of the view, honoring constraints from measureSpec */ private int measureWidth(int measureSpec) { int result = 0; int specMode = MeasureSpec.getMode(measureSpec); int specSize = MeasureSpec.getSize(measureSpec); if (specMode == MeasureSpec.EXACTLY) { // We were told how big to be result = specSize; } else { // Measure the text result = (int) mPaint.measureText(mString) + getPaddingLeft() + getPaddingRight(); if (specMode == MeasureSpec.AT_MOST) { // Respect AT_MOST value if that was what is called for by measureSpec result = Math.min(result, specSize); } } return result; } /** * Determines the height of this view * @param measureSpec A measureSpec packed into an int * @return The height of the view, honoring constraints from measureSpec */ private int measureHeight(int measureSpec) { int result = 0; int specMode = MeasureSpec.getMode(measureSpec); int specSize = MeasureSpec.getSize(measureSpec); mAscent = (int) mPaint.ascent(); if (specMode == MeasureSpec.EXACTLY) { // We were told how big to be result = specSize; } else { // Measure the text (beware: ascent is a negative number) result = (int) (-mAscent + mPaint.descent()) + getPaddingTop() + getPaddingBottom(); if (specMode == MeasureSpec.AT_MOST) { // Respect AT_MOST value if that was what is called for by measureSpec result = Math.min(result, specSize); } } return result; } } Second I put it in to Gallery through Adapter Gallery gallery = (Gallery) findViewById(R.id.gallery); gallery.setAdapter(new ImageAdapter(this)); ImageAdapter: public class ImageAdapter extends BaseAdapter { int mGalleryItemBackground; private Context mContext; private View[] mImages = genSerielImageViews(); public ImageAdapter(Context c) { mContext = c; TypedArray a = obtainStyledAttributes(R.styleable.Gallery); mGalleryItemBackground = a.getResourceId( R.styleable.Gallery_android_galleryItemBackground, 0); a.recycle(); } private View[] genSerielImageViews() { if (true) { int N = 6; StringView[] views = new StringView[N]; for (int i=0; i<N; i++) { views[i] = new StringView(mContext, "ITEM #" + Integer.toString(i) ); } return views; } else { int N = 6; TextView[] views = new TextView[N]; for (int i=0; i<N; i++) { views[i] = new TextView( mContext ); views[i].setText("CCTV #" + Integer.toString(i) ); } return views; } } public int getCount() { return mImages.length; } public Object getItem(int position) { return position; } public long getItemId(int position) { return position; } public View getView(int position, View convertView, ViewGroup parent) { return mImages[position]; } } Then Compile&Run, press keypad RIGHT and I got a crash, It's turns out a weird InputMethodManager error: 03-18 07:22:33.568: ERROR/AndroidRuntime(958): Uncaught handler: thread main exiting due to uncaught exception 03-18 07:22:33.648: ERROR/AndroidRuntime(958): java.lang.NullPointerException 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at android.view.inputmethod.InputMethodManager.startInputInner(InputMethodManager.java:940) 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at android.view.inputmethod.InputMethodManager.checkFocus(InputMethodManager.java:1114) 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at android.view.ViewRoot.handleMessage(ViewRoot.java:1869) 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at android.os.Handler.dispatchMessage(Handler.java:99) 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at android.os.Looper.loop(Looper.java:123) 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at android.app.ActivityThread.main(ActivityThread.java:4310) 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at java.lang.reflect.Method.invokeNative(Native Method) 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at java.lang.reflect.Method.invoke(Method.java:521) 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860) 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at dalvik.system.NativeStart.main(Native Method) Thanks.

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• How do I antialias the clip boundary on Android's canvas?

  - by Jesse Wilson

  I'm using Android's android.graphics.Canvas class to draw a ring. My onDraw method clips the canvas to make a hole for the inner circle, and then draws the full outer circle over the hole: clip = new Path(); clip.addRect(outerCircle, Path.Direction.CW); clip.addOval(innerCircle, Path.Direction.CCW); canvas.save(); canvas.clipPath(clip); canvas.drawOval(outerCircle, lightGrey); canvas.restore(); The result is a ring with a pretty, anti-aliased outer edge and a jagged, ugly inner edge: What can I do to antialias the inner edge? I don't want to cheat by drawing a grey circle in the middle because the dialog is slightly transparent. (This transparency isn't as subtle on on other backgrounds.)

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• Drawing a bitmap in a canvas after calling setBitmap doesn't work

  - by kodbar_k

  I'm drawing a bitmap in a canvas and i want to have the result in a new bitmap, but i still have a black screen as result. This is my code, part of the onDraw(Canvas canvas) method : if (bitmapTemplate == null) { canvasBis = new Canvas(); bitmapTemplate = Bitmap.createBitmap(canvas.getWidth()+30,canvas.getHeight(),Bitmap.Config.ARGB_8888); drawZones(canvasBis,bitmapTemplate); } bitmapRes = Bitmap.createBitmap(canvas.getWidth()+30,canvas.getHeight(),Bitmap.Config.ARGB_8888); canvas.setBitmap(bitmapRes); canvas.drawBitmap(bitmapTemplate, matrix, null); My goal is to have a new bitmap (bitmapRes) by applying a matrix on an existing bitmap (bitmapTemplate). With this code i alway have a black screen, but when i remove the line canvas.setBitmap(bitmapRes) i have a result but not in a new bitmap. any ideas please ? Maybe transparency ? Thanks in advance. drawZones draws some zones in bitmapTemplate.

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• Drawing text at an angle (e.g. upside down) in Android

  - by Damian

  I'm trying to build a custom clock view in Android. See image http://twitpic.com/1devk7 So far to draw the time and hour markers I have been using the Canvas.rotate method to get the desired effect. However, notice that it is difficult to interpret the numbers in the lower half of the clock (e.g. 6 or 9?) because of the angle in which they are drawn. When using drawText, is it possible to draw the text at 45/90/180 degrees so that all text appears upright when my onDraw method has finished?

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• Android: make a scrollable custom view

  - by Martyn

  Hey, I've rolled my own custom view and can draw to the screen alright, but what I'd really like to do is set the measuredHeigh of the screen to, say, 1000px and let the user scroll on the Y axis, but I'm having problems doing this. Can anyone help? Here's some code: public class TestScreen extends Activity { CustomDrawableView mCustomDrawableView; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); mCustomDrawableView = new CustomDrawableView(this); setContentView(mCustomDrawableView); } } and public class CustomDrawableView extends View { public CustomDrawableView(Context context) { super(context); setVerticalScrollBarEnabled(true); setMinimumHeight(1000); } @Override protected void onDraw(Canvas canvas) { canvas.drawLine(...); // more drawing } } I've tried to override scrollTo, scrollBy, awakenScrollBars etc with a call to super but to no avail. Am I missing something silly, or am I making some fundamental mistake? Thank you in advance, Martyn

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• Drawing random circles

  - by ViktorC

  I am trying to draw a cupola circles at random positions in an Android application. I draw them on a bitmap and then draw that bitmap on the canvas. This is the function where a draw the circles: private void drawRandomCircles(int numOfCircles) { Canvas c = new Canvas(b); Paint cPaint = new Paint; cPaitn.setColor(Color.RED); for(int i = 0; i < numOfCircles; i++) { int x = Math.Random % 100; int y = Math.Random % 100; c.drawCircle(x, y, 20, cPaint) } } The Bitmap b is global. And after calling this function I just draw the bitmap in the onDraw method. Now the problem is that I only get one circle drawn on the screen, no matter the size of numOfCircles. Any clue what is happening here?

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• When can I find out the width/height of my view

  - by michael

  When is the earliest I can find out the actual (after layout) width/height of my view? I tried to do that @Override protected void onFinishInflate() { super.onFinishInflate(); w = getWidth(); h = getHeight(); } But it gives me 0. I have cases in which the view is invisible in the beginning and that programmically become visible. I think I can do that in onDraw(), but i dont' want to do that in everything I draw() something.

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• 2 or more Controls only 1 is considered Active

  - by Don

  I have 2 controls (MyCtrl) next to each other called ctrlLeft and ctrlRight. Whenever one receives interaction it is considered active (by default the left one). I override OnDraw and customize the look of the active one a bit. Currently I have a property Active and an event that I subscribe to from all MyCtrl in there I store a reference to the active one like this: if (sender is MyCtrl) { ctrlActive = (sender as MyCtrl); ctrlLeft.Active = !(ctrlRight.Active = (ctrlActive == ctrlRight)); } Either way I need to have ctrlActive as I use it for other things but what I am wondering is if this is the best way make them aware of each other? Another option I thought of was to store references to every possible MyCtrl and then loop through em all and activate / deactivate the one that match sender just in case I in the future add a ctrlMiddle. Are my thoughts wrong, is there better options to do this. For example, how does radiobuttons accomplish their similar functionality?

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• how to draw a Bitmap to a Canvas with a variable alpha

  - by steelbytes

  Hi, I'm trying to draw a Bitmap to a Canvas with a variable amount of alpha. But I only get nothing (when alpha<255) or the 'full' bitmap (when alpha==255). Have also tried loading as a Drawable, and using drawable.setAlpha, but that gave the same result. my init BitmapFactory.Options opts = new BitmapFactory.Options(); opts.inScaled = false; opts.inSampleSize = 1; Bitmap img = BitmapFactory.decodeResource(getResources(),R.drawable.sample,opts); my onDraw() Paint p = new Paint(Paint.ANTI_ALIAS_FLAG|Paint.FILTER_BITMAP_FLAG); p.setColor((alpha<<24)+0xffffff); // alpha in range 0..255 canvas.drawBitmap(img, null, imgRect, p);

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• Movement in game programming

  - by hanesjw

  This question may have been asked before, but I'm starting to get into game programming on the Android. I'm having a hard time figuring out the best way to move an object. To put it simply, lets say I have a bitmap located on 0,0 and i want to move it across the screen. The obvious way to do it would be to simply increment the X position by one every time the Surface View onDraw method gets called. But what if I wanted to make it move faster? I could increment it by two or three instead of one, but then the movement starts to get really choppy and stupid looking. What is the best way to go about doing this?

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• glTranslate, how exactly does it work?

  - by mykk

  I have some trouble understanding how does glTranslate work. At first I thought it would just simply add values to axis to do the transformation. However then I have created two objects that would load bitmaps, one has matrix set to GL_TEXTURE: public class Background { float[] vertices = new float[] { 0f, -1f, 0.0f, 4f, -1f, 0.0f, 0f, 1f, 0.0f, 4f, 1f, 0.0f }; .... private float backgroundScrolled = 0; public void scrollBackground(GL10 gl) { gl.glLoadIdentity(); gl.glMatrixMode(GL10.GL_MODELVIEW); gl.glTranslatef(0f, 0f, 0f); gl.glPushMatrix(); gl.glLoadIdentity(); gl.glMatrixMode(GL10.GL_TEXTURE); gl.glTranslatef(backgroundScrolled, 0.0f, 0.0f); gl.glPushMatrix(); this.draw(gl); gl.glPopMatrix(); backgroundScrolled += 0.01f; gl.glLoadIdentity(); } } and another to GL_MODELVIEW: public class Box { float[] vertices = new float[] { 0.5f, 0f, 0.0f, 1f, 0f, 0.0f, 0.5f, 0.5f, 0.0f, 1f, 0.5f, 0.0f }; .... private float boxScrolled = 0; public void scrollBackground(GL10 gl) { gl.glMatrixMode(GL10.GL_MODELVIEW); gl.glLoadIdentity(); gl.glTranslatef(0f, 0f, 0f); gl.glPushMatrix(); gl.glMatrixMode(GL10.GL_MODELVIEW); gl.glLoadIdentity(); gl.glTranslatef(boxScrolled, 0.0f, 0.0f); gl.glPushMatrix(); this.draw(gl); gl.glPopMatrix(); boxScrolled+= 0.01f; gl.glLoadIdentity(); } } Now they are both drawn in Renderer.OnDraw. However background moves exactly 5 times faster. If I multiply boxScrolled by 5 they will be in sinc and will move together. If I modify backgrounds vertices to be float[] vertices = new float[] { 1f, -1f, 0.0f, 0f, -1f, 0.0f, 1f, 1f, 0.0f, 0f, 1f, 0.0f }; It will also be in sinc with the box. So, what is going under glTranslate?

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• Collision between sprites in game programming?

  - by Lyn Maxino

  I've since just started coding for an android game using eclipse. I've read Beginning Android Game Programming and various other e-books. Recently, I've encountered a problem with collision between sprites. I've used this code template for my program. package com.project.CAI_test; import java.util.Random; import android.graphics.Bitmap; import android.graphics.Canvas; import android.graphics.Rect; public class Sprite { // direction = 0 up, 1 left, 2 down, 3 right, // animation = 3 back, 1 left, 0 front, 2 right int[] DIRECTION_TO_ANIMATION_MAP = { 3, 1, 0, 2 }; private static final int BMP_ROWS = 4; private static final int BMP_COLUMNS = 3; private static final int MAX_SPEED = 5; private GameView gameView; private Bitmap bmp; private int x = 0; private int y = 0; private int xSpeed; private int ySpeed; private int currentFrame = 0; private int width; private int height; public Sprite(GameView gameView, Bitmap bmp) { this.width = bmp.getWidth() / BMP_COLUMNS; this.height = bmp.getHeight() / BMP_ROWS; this.gameView = gameView; this.bmp = bmp; Random rnd = new Random(); x = rnd.nextInt(gameView.getWidth() - width); y = rnd.nextInt(gameView.getHeight() - height); xSpeed = rnd.nextInt(MAX_SPEED * 2) - MAX_SPEED; ySpeed = rnd.nextInt(MAX_SPEED * 2) - MAX_SPEED; } private void update() { if (x >= gameView.getWidth() - width - xSpeed || x + xSpeed <= 0) { xSpeed = -xSpeed; } x = x + xSpeed; if (y >= gameView.getHeight() - height - ySpeed || y + ySpeed <= 0) { ySpeed = -ySpeed; } y = y + ySpeed; currentFrame = ++currentFrame % BMP_COLUMNS; } public void onDraw(Canvas canvas) { update(); int srcX = currentFrame * width; int srcY = getAnimationRow() * height; Rect src = new Rect(srcX, srcY, srcX + width, srcY + height); Rect dst = new Rect(x, y, x + width, y + height); canvas.drawBitmap(bmp, src, dst, null); } private int getAnimationRow() { double dirDouble = (Math.atan2(xSpeed, ySpeed) / (Math.PI / 2) + 2); int direction = (int) Math.round(dirDouble) % BMP_ROWS; return DIRECTION_TO_ANIMATION_MAP[direction]; } public boolean isCollition(float x2, float y2) { return x2 > x && x2 < x + width && y2 > y && y2 < y + height; } } The above code only detects collision between the generated sprites and the surface border. What I want to achieve is a collision detection that is controlled by the update function without having to change much of the coding. Probably several lines placed in the update() function. Tnx for any comment/suggestion.

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• Help: Android paint/canvas issue; drawing smooth curves

  - by Wrapper

  How do I get smooth curves instead of dots or circles, when I draw with my finger on the touch screen, in Android? I am using the following code- public class DrawView extends View implements OnTouchListener { private static final String TAG = "DrawView"; List<Point> points = new ArrayList<Point>(); Paint paint = new Paint(); public DrawView(Context context) { super(context); setFocusable(true); setFocusableInTouchMode(true); this.setOnTouchListener(this); paint.setColor(Color.WHITE); paint.setAntiAlias(true); } @Override public void onDraw(Canvas canvas) { for (Point point : points) { canvas.drawCircle(point.x, point.y, 5, paint); // Log.d(TAG, "Painting: "+point); } } public boolean onTouch(View view, MotionEvent event) { // if(event.getAction() != MotionEvent.ACTION_DOWN) // return super.onTouchEvent(event); Point point = new Point(); point.x = event.getX(); point.y = event.getY(); points.add(point); invalidate(); Log.d(TAG, "point: " + point); return true; } } class Point { float x, y; @Override public String toString() { return x + ", " + y; } }

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• Scrolling a Canvas smoothly in Android

  - by prepbgg

  I'm new to Android. I am drawing bitmaps, lines and shapes onto a Canvas inside the OnDraw(Canvas canvas) method of my view. I am looking for help on how to implement smooth scrolling in response to a drag by the user. I have searched but not found any tutorials to help me with this. The reference for Canvas seems to say that if a Canvas is constructed from a Bitmap (called bmpBuffer, say) then anything drawn on the Canvas is also drawn on bmpBuffer. Would it be possible to use bmpBuffer to implement a scroll ... perhaps copy it back to the Canvas shifted by a few pixels at a time? But if I use Canvas.drawBitmap to draw bmpBuffer back to Canvas shifted by a few pixels, won't bmpBuffer be corrupted? Perhaps, therefore, I should copy bmpBuffer to bmpBuffer2 then draw bmpBuffer2 back to the Canvas. A more straightforward approach would be to draw the lines, shapes, etc. straight into a buffer Bitmap then draw that buffer (with a shift) onto the Canvas but so far as I can see the various methods: drawLine(), drawShape() and so on are not available for drawing to a Bitmap ... only to a Canvas. Could I have 2 Canvases? One of which would be constructed from the buffer bitmap and used simply for plotting the lines, shapes, etc. and then the buffer bitmap would be drawn onto the other Canvas for display in the View? I should welcome any advice! Answers to similar questions here (and on other websites) refer to "blitting". I understand the concept but can't find anything about "blit" or "bitblt" in the Android documentation. Are Canvas.drawBitmap and Bitmap.Copy Android's equivalents?

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• Android: How to get a custom view to redraw partially?

  - by Peterdk

  I have a custom view that fills my entire screen. (A piano keyboard) When a user touches the key, it would cause a invalidate() to be called and the whole keyboard gets redrawn to show the new state with a touched key. Currently the view is very simple, but I plan to add a bit more nice graphics. Since the whole keyboard is dynamically rendered this would make redrawing the entire keyboard more expensive. So I thought, let's look into partial redrawing. Now I call invalidate(Rect dirty) with the correct dirty region. I set my onDraw(Canvas canvas) method to only draw the keys in the dirty region if I do indeed want a partial redraw. This results in those keys being drawn, but the rest of the keyboard is totally black/not drawn at all. Am I wrong in expecting that calling invalidate(Rect dirty) would "cache" the current canvas, and only "allows" drawing in the dirty region? Is there any way I can achieve what I want? (A way to "cache" the canvas and only redraw the dirty area?"

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