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  • determining the starting speed for an accelerated animation (in flash/actionscript but it's a math question)

    - by vulkanino
    This question burns my brain. I have an object on a plane, but for the sake of simplicity let's work just on a single dimension, thus the object has a starting position xs. I know the ending position xe. The object has to move from starting to ending position with an accelerated (acceleration=a) movement. I know the velocity the object has to have at the ending position (=ve). In my special case the ending speed is zero, but of course I need a general formula. The only unknown is the starting velocity vs. The objects starts with vs in xs and ends with ve in xe, moving along a space x with an acceleration a in a time t. Since I'm working with flash, space is expressed in pixels, time is expressed in frames (but you can reason in terms of seconds, it's easy to convert knowing the frames-per-second). In the animation loop (think onEnterFrame) I compute the new velocity and the new position with (a=0.4 for example): vx *= a (same for vy) x += vx (same for y) I want the entire animation to last, say, 2 seconds, which at 30 fps is 60 frames. Now you know that in 60 frames my object has to move from xs to xe with a constant deceleration so that the ending speed is 0. How do I compute the starting speed vs? Maybe there's a simpler way to do this in Flash, but I am now interested in the math/physics behind this.

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  • Messing with the Team

    - by Robert May
    Good Product Owners will help the team be the best that they can be.  Bad product owners will mess with the team and won’t care about the team.  If you’re a product owner, seek to do good and avoid bad behavior at all costs.  Remember, this is for YOUR benefit and you have much power given to you.  Use that power wisely. Scope Creep The product owner has several tools at his disposal to inject scope into an iteration.  First, the product owner can use defects to inject scope.  To do this, they’ll tell the team what functionality that they want to see in a feature.  Then, after the feature is developed, the Product Owner will decide that they don’t really like how the functionality behaves.  To change it, rather than creating a new story, they’ll add a defect.  The functionality is correct, as designed, but the Product Owner doesn’t like it.  By creating the defect, the Product Owner destroys the trust that the team has of the product owner.  They may not be able to count the story, because the Product Owner changed the story in the iteration, and the team then ends up looking like they have low velocity for something over which they have no control.  This is bad.  One way to deal with this is to add “Product Owner Time” to the iteration.  This will slow the velocity, but then the ScrumMaster can tell stake holders that this time is strictly in place to deal with bad behavior of the Product Owner. Another mechanism often used to inject Scope is the concept of directed development.  Outside of planning, stand-ups, or any other meeting, the Product Owner will take a developer aside and ask them to complete a task for them.  This is bad!  The team should be allocating all of their time to development.  If the Product Owner asks for a favor, then time that would normally be used for development will be used for a pet project of the Product Owner and the team will not get credit for this work.  Selfish product owners do this, and I typically see people who were “managers” do this behavior.  Authoritarian command and control development environments also see this happen.  The best thing that can happen is for the team member to report the issue to the ScrumMaster and the ScrumMaster to get very aggressive with management and the Product Owner to try and stop the behavior.  This may result in the ScrumMaster being fired, but if the behavior continues, Scrum is doomed.  This problem is especially bad in cases where the team member’s direct supervisor is the Product Owner.  I don’t recommend that the Product Owner or ScrumMaster have a direct report relationship with team members, since team members need the ability to say no.  To work around this issue, team members need to say no.  If that fails, team members need to add extra time to the iteration to deal with the scope creep injection and accept the lower velocity. As discussed above, another mechanism for injecting scope is by changing acceptance tests after the work is complete.  This is similar to adding defects to change scope and is bad.  To get around, add time for Product Owner uncertainty to the iteration and make sure that stakeholders are aware of the need to add this time because of the Product Owner. Refusing to Prioritize Refusing to prioritize causes chaos for the team.  From the team’s perspective, things that are not important will be worked on while things that the team knows are vital will be ignored.  A poor Product Owner will often pick the stories for the iteration on a whim.  This leads to the team working on many different aspects of the product and results in a lower velocity, since each iteration the team must switch context to the new area of development. The team will also experience confusion about priorities.  In one iteration, Feature X was the highest priority and had to be done.  Then, the following iteration, even though parts of Feature X still need to be completed, no stories to address them will be in the iteration.  However, three iterations later, Feature X will again become high priority. This will cause the team to not trust the Product Owner, and eventually, they’ll stop caring about the features they implement.  They won’t know what is important, so to insulate themselves from the ever changing chaos, they’ll become apathetic to all features.  Team members are some of the most creative people in a company.  By losing their engagement, the company is going to have a substandard product because the passion for the product won’t be in the team. Other signs that the Product Owner refuses to prioritize is that no one outside of the product owner will be consulted on priorities.  Additionally, the product, release, and iteration backlogs will be weak or non-existent. Dealing with this issue is not easy.  This really isn’t something the team can fix, short of taking over the role of Product Owner themselves.  An appeal to the stake holders might work, but only if the Product Owner isn’t a “manager” themselves.  The ScrumMaster needs to protect the team and do what they can to either get the Product Owner to prioritize or have the Product Owner replaced. Managing the Team A Product Owner that is also the “boss” of team members is a Scrum team that is waiting to fail.  If your boss tells you to do something, failing to do that something can cause you to be fired.  The team needs the ability to tell the Product Owner NO.  If the product owner introduces scope creep, the team has a responsibility to tell the Product Owner no.  If the Product Owner tries to get the team to commit to more than they can accomplish in an iteration, the team needs the ability to tell the Product Owner no. If the Product Owner is your boss and determines your pay increases, you’re probably not going to ever tell them no, and Scrum will likely fail.  The team can’t do much in this situation. Another aspect of “managing the team” that often happens is the Product Owner tries to tell the team how to develop the stories that are in the iteration.  This is one reason why I recommend that Product Owners are NOT technical people.  That way, the team can come up with the tasks that are needed to accomplish the stories and the Product Owner won’t know better.  If the Product Owner is technical, the ScrumMaster will need to take great care to protect the team from the ScrumMaster changing how the team thinks they need to implement the stories. Product Owners can also try to manage the team by their body language.  If the team says a task is going to take 6 hours to complete, and the Product Owner disagrees, they will use some kind of sour body language to indicate this disagreement.  In weak teams, this may cause the team to revise their estimate down, which will result in them taking longer than estimated and may result in them missing the iteration.  The ScrumMaster will need to make sure that the Product Owner doesn’t send such messages and that the team ignores them and estimates what they REALLY think it will take to complete the tasks.  Forcing the team to deal with such items in the retrospective can be helpful. Absenteeism The team is completely dependent upon the Product Owner to develop features for the customer.  The Product Owner IS the voice of the customer and without them, the team will lack direction.  Being the Product Owner is a full time job!  If the Product Owner cannot dedicate daily time with the team, a different product owner should be found. The Product Owner needs to attend every stand-up, planning meeting, showcase, and retrospective that the team has.  The team also must be able to have instant communication with the product owner.  They must not be required to schedule meetings to speak with their product owner.  The team must be the highest priority task that the Product Owner has. The best way to work around an absent Product Owner is to appoint a new Product Owner in the team.  This person will be responsible for making the decisions that the Product Owner should be making and to act as the liaison to the absent Product Owner.  If the delegate Product Owner doesn’t have authority to make decisions for the team, Scrum will fail.  If the Product Owner is absent, the ScrumMaster should seek to have that Product Owner replaced by someone who has the time and ability to be a real Product Owner. Making it Personal Too often Product Owners will become convinced that their ideas are the ones that matter and that anyone who disagrees is making a personal attack on them.  Remember that Product Owners will inherently be at odds with many people, simply because they have the need to prioritize.  Others will frequently question prioritization because they only see part of the picture that Product Owners face. Product Owners must have a thick skin and think egos.  If they don’t, they tend to make things personal, which causes them to become emotional and causes them to take actions that can destroy the trust that team members have in the Product Owner. If a Product Owner is making things person, the best thing that team members can do is reassure them that its not personal, but be firm about doing what is best for the Company and for the users.  The ScrumMaster should also spend significant time coaching the Product Owner on how to not react emotionally and how to accept criticism without becoming defensive. Conclusion I’m sure there are other ways that a Product Owner can mess with the team, but these are the most common that I’ve seen.  I would encourage all Product Owners to seek to be a good Product Owner.  If you find yourself behaving in any of the bad product owner ways, change your behavior today!  Your team will thank you. Remember, being Product Owner is very difficult!  Product Owner is one of the most difficult roles in Scrum.  However, it can also be one of the most rewarding roles in Scrum, since Product Owners literally see their ideas brought to life on the computer screen.  Product Owners need to be very patient, even in the face of criticism and need to be willing to make tough decisions on priority, but then not become offended when others disagree with those decisions.  Companies should spend the time needed to find the right product owners for their teams.  Doing so will only help the company to write better software. Technorati Tags: Scrum,Product Owner

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  • How to implement friction in a physics engine based on "Advanced Character Physics"

    - by paldepind
    I have implemented a physics engine based on the concepts in the classic text Advanced Character Physics by Thomas Jakobsen. Friction is only discussed very briefly in the article and Jakobsen himself notes how "other and better friction models than this could and should be implemented." Generally how could one implement a believable friction model on top of the concepts from the mentioned article? And how could the found friction be translated into rotation on a circle? I do not want this question to be about my specific implementation but about how to combine Jakobsens ideas with a great friction system more generally. But here is a live demo showing the current state of my engine which does not handle friction in any way: http://jsfiddle.net/Z7ECB/embedded/result/ Below is a picture showing and example on how collision detection could work in an engine based in the paper. In the Verlet integration the current and previous position is always stored. Based on these a new position is calculated. In every frame I calculate the distance between the circles and the lines. If this distance is less than a circles radius a collision has occurred and the circle is projected perpendicular out of the offending line according to the size of the overlap (offset on the picture). Velocity is implicit due to Verlet integration so changing position also changes the velocity. What I need to do know is to somehow determine the amount of friction on the circle and move it backwards parallel to the line in order to reduce its speed.

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  • Follow point of interest by applying torque

    - by azymm
    Given a body with an orientation angle and a point of interest or targetAngle, is there an elegant solution for keeping the body oriented towards the point of interest by applying torque or impulses? I have a naive solution working below, but the effect is pretty 'wobbly', it'll overshoot each time, slowly getting closer to the target angle - undesirable effect in my case. I'd like to find a solution that is more intelligent - that can accelerate to near the target angle then decelerate and stop right at the target angle (or within a small range). If it helps, I'm using box2d and the body is a rectangle. def gameloop(dt): targetAngle = get_target_angle() bodyAngle = get_body_angle() deltaAngle = targetAngle - bodyAngle if deltaAngle > PI: deltaAngle = targetAngle - (bodyAngle + 2.0 * PI) if deltaAngle < -PI: deltaAngle = targetAngle - (bodyAngle - 2.0 * PI) # multiply by 2, for stronger reaction deltaAngle = deltaAngle * 2.0; body.apply_torque(deltaAngle); One other thing, when body has no linear velocity, the above solution works ok. But when the body has some linear velocity, the solution above causes really wonky movement. Not sure why, but would appreciate any hints as to why that might be.

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  • What is the definition of "Big Data"?

    - by Ben
    Is there one? All the definitions I can find describe the size, complexity / variety or velocity of the data. Wikipedia's definition is the only one I've found with an actual number Big data sizes are a constantly moving target, as of 2012 ranging from a few dozen terabytes to many petabytes of data in a single data set. However, this seemingly contradicts the MIKE2.0 definition, referenced in the next paragraph, which indicates that "big" data can be small and that 100,000 sensors on an aircraft creating only 3GB of data could be considered big. IBM despite saying that: Big data is more simply than a matter of size. have emphasised size in their definition. O'Reilly has stressed "volume, velocity and variety" as well. Though explained well, and in more depth, the definition seems to be a re-hash of the others - or vice-versa of course. I think that a Computer Weekly article title sums up a number of articles fairly well "What is big data and how can it be used to gain competitive advantage". But ZDNet wins with the following from 2012: “Big Data” is a catch phrase that has been bubbling up from the high performance computing niche of the IT market... If one sits through the presentations from ten suppliers of technology, fifteen or so different definitions are likely to come forward. Each definition, of course, tends to support the need for that supplier’s products and services. Imagine that. Basically "big data" is "big" in some way shape or form. What is "big"? Is it quantifiable at the current time? If "big" is unquantifiable is there a definition that does not rely solely on generalities?

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  • Game physics presentation by Richard Lord, some questions

    - by Steve
    I been implementing (in XNA) the examples in this physics presentation by Richard Lord where he discusses various integration techniques. Bearing in mind that I am a newcomer to game physics (and physics in general) I have some questions. 15 slides in he shows ActionScript code for a gravity example and an animation showing a bouncing ball. The ball bounces higher and higher until it is out of control. I implemented the same in C# XNA but my ball appeared to be bouncing at a constant height. The same applies to the next example where the ball bounces lower and lower. After some experimentation I found that if I switched to a fixed timestep and then on the first iteration of Update() I set the time variable to be equal to elapsed milliseconds (16.6667) I would see the same behaviour. Doing this essentially set the framerate, velocity and acceleration to zero for the first update and introduced errors(?) into the algorithm causing the ball's velocity to increase (or decrease) over time. I think! My question is, does this make the integration method used poor? Or is it demonstrating that it is poor when used with variable timestep because you can't pass in a valid value for the first lot of calculations? (because you cannot know the framerate in advance). I will continue my research into physics but can anyone suggest a good method to get my feet wet? I would like to experiment with variable timestep, acceleration that changes over time and probably friction. Would the Time Corrected Verlet be OK for this?

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  • Sprite and Physics components or sub-components?

    - by ashes999
    I'm taking my first dive into creating a very simple entity framework. The key concepts (classes) are: Entity (has 0+ components, can return components by type) SpriteEntity (everything you need to draw on screen, including lighting info) PhysicsEntity (velocity, acceleration, collision detection) I started out with physics notions in my sprite component, and then later removed them to a sub-component. The separation of concerns makes sense; a sprite is enough information to draw anything (X, Y, width, height, lighting, etc.) and physics piggybacks (uses the parent sprite to get X/Y/W/H) while adding physics notions of velocity and collisions. The problem is that I would like collisions to be on an entity level -- meaning "no matter what your representation is (be it sprites, text, or something else), collide against this entity." So I refactored and redirected collision handling from entities to sprite.physics, while mapping and returning the right entity on physics collisions. The problem is that writing code like this.GetComponent<SpriteComponent>().physics is a violation of abstraction. Which made me think (this is the TLDR): should I keep physics as a separate component from sprites, or a sub-component, or something else? How should I share data and separate concerns?

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  • Box2D: How to get the Exact Collision Point and ignore the collision (from 2 "ghost bodies")

    - by Moritz
    I have a very basic problem with Box2D. For a arenatype game where you can throw scriptable "missiles" at other players I decided to use Box2D for the collision detection between the players and the missiles. Players and missiles have their own circular shape with a specific size (varying). But I don´t want to use dynamic bodies because the missiles need to move themselve in any way they want to (defined in the script) and shouldnt be resolved unless the script wants it. The behavior I look for is as following (for each time step): velocity of missiles is set by the specific missile script each missile is moved according to that velocity if a collision accurs now, I want to get the exact position of impact, and now I need a mechanism to decide if the missile should just ignore the collision (for example collision between two fireballs which shouldnt interact) or take it (so they are resolved and dont overlap anymore) So is there a way in Box2D to create Ghost bodies and listen to collisions from them, then deciding if they should ignore the collision or should take them and resolve their position? I hope I was clear enough and would be happy about any help!

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  • jerky walljump in unity rigidbody2d

    - by Lilz Votca Love
    hey there i know people have encountered issues with it before i looked upon the different solutions provided but i couldnt get any fix at all.im making a 2d game and am stuck with the walljump.i detect the wall wonderfully i also detect the jump and it works the player jumps off the wall when facing right with the use of rigidbody.addforce(new vector2(-1,2)*jumpforce) now when jumping on the oposite wall using the same vector with the sign in x axis changed to 1,the player jumps too but it goes more in the y axis than it should.Here is an image to show you the curves it(the player) follows. check the following url to see the behaviour https://scontent-b-mad.xx.fbcdn.net/hphotos-xpf1/t1.0-9/1470386_10152415957141154_156025539179003805_n.jpg voila the green one is happennig when player faces right and the other one happens when he is not here is the section of code if (wall) { if (wallJump) { if (facingRight) { rigidbody2D.velocity = Vector2.zero; flip (); rigidbody2D.AddForce (new Vector2 (-1f, 2f) * Jumpforce / 1.5f); Debug.Log ("saut mural gauche" + new Vector2 (-1f, 2f) * Jumpforce / 1.5f); } else { rigidbody2D.velocity = Vector2.zero; flip (); rigidbody2D.AddForce (new Vector2 (1f, 2f) * Jumpforce / 1.5f); Debug.Log ("saut mural droit--" + new Vector2 (Mathf.Sign (1f), 2f) * Jumpforce / 1.5f + "jump" + jump); } } } else { wallJump = false; } here the code is not optimized yet but i assure you it works so guys any help would be so awesome!! thanks

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  • 2D Rectangle Collision Response with Multiple Rectangles

    - by Justin Skiles
    Similar to: Collision rectangle response I have a level made up of tiles where the edges of the level are made up of collidable rectangles. The player's collision box is represented by a rectangle as well. The player can move in 8 directions. The player's velocity is equal in X and Y directions and constant. Each update, I am checking the player's collision against all tiles that are a certain distance away. When the player collides with a rectangle, I am finding the intersection depth and resolving along the most shallow axis followed by the other axis. This resolution happens for both axes simultaneously. See below for two examples of situations where I am having trouble. Moving up-left against the left wall In the scenario below, the player is colliding with two tiles. The tile intersection depth is equal on both axes for the top tile and more shallow in the X axis for the middle tile. Because the player is moving up the wall, the player should slide in an upward direction along the wall. This works properly as long as the rectangle with the more shallow depth is evaluated first. If the equal intersection depth rectangle is evaluated first, there is a chance the player becomes stuck. Moving up-left against the top wall Here is an identical scenario with the exception that the collision is with the top wall. The same problem occurs at the corners when intersection depth is equal for both axes. I guess my overall question is: How can I ensure that collision response occurs on tiles that have non-equal intersection depth before tiles that have equal intersection depth in order to get around the weirdness that occurs at these corners. Sean's answer in the linked question was good, but his solution required having different velocity components in a certain direction. My situation has equal velocities, so there's no good way to tell which direction to resolve at corners. I hope I have made my explanation clear.

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  • Good 2D Platformer Physics

    - by Joe Wreschnig
    I have a basic character controller set up for a 2D platformer with Box2D, and I'm starting to tweak it to try to make it feel good. Physics engines have a lot of knobs to tweak, and it's not clear to me, writing with a physics engine for the first time, which ones I should use. Should jumping apply a force for several ticks? An impulse? Directly set velocity? How do I stop the avatar from sticking to walls without taking away all its friction (or do I take away all the friction, but only in the air)? Should I model the character as a capsule? A box with rounded corners? A box with two wheels? Just one big wheel? I feel like someone must have done this before! There seem to be very few resources available on the web that are not "baby's first physics", which all cut off where I'm hoping someone has already solved the issues. Most examples of physics engines for platformers have floaty-feeling controls, or in-air jumps, or easily exploitable behavior when temporary penetration is too high, etc. Some examples of what I mean: A short tap of jump jumps a short distance; a long tap jumps higher. Short skidding when stopping or reversing directions at high velocity. Standing stably on inclines (but maybe sliding down them when ducking). Analog speed when using an analog controller. All the other things that separate good platformers from bad platformers. Dare I suggest, stable moving platforms? I'm not really looking for "hey, do this." Obviously, the right thing to do is dependent on what I want in the game. But I'm hoping someone somewhere has gone through the possibilities and said "well technique A does feature X well, technique B does Y well, but that doesn't work with C", or has some worked examples beyond "if (key == space) character.impulse(0, 1)"

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  • How to represent an agile project to people focused on waterfall [closed]

    - by ahsteele
    Our team has been asked to represent our development efforts in a project plan. No one is unhappy with our work or questioning our ability to deliver, we are just participating in an IT cattle call for project plans. Trouble is we are an agile team and haven't thought about our work in terms of a formal project plan. While we have a general idea of what we are working on next we aren't 100% sure until we plan an iteration. Until now our team has largely operated in a vacuum and has not been required to present our methodology or metrics to outside parties. We follow most of the practices espoused in Extreme Programming. We hold quarterly planning meetings to have a general idea of the stories we are going to work on for a quarter. That said, our stories are documented on 3x5 cards and are only estimated at the beginning of the iteration in which they are going to be worked. After estimation we document the story in Team Foundation Sever. During an iteration, we attach code to stories and mark stories as completed once finished. From this data we are able to generate burn down and velocity charts. Most importantly we know our average velocity for an iteration keeping us from biting off more than we can chew. I am not looking to modify the way we do development but want to present our development activities in a report that someone only familiar with waterfall will understand. In What Does an Agile Project Plan Look Like, Kent McDonald does a good job laying out the differences between agile and waterfall project plans. He specifies the differences in consumable bullets: An agile project plan is feature based An Agile Project Plan is organized into iterations An Agile Project Plan has different levels of detail depending on the time frame An Agile Project Plan is owned by the Team Being able to explain the differences is great, but how best to present the data?

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  • Collision within a poly

    - by G1i1ch
    For an html5 engine I'm making, for speed I'm using a path poly. I'm having trouble trying to find ways to get collision with the walls of the poly. To make it simple I just have a vector for the object and an array of vectors for the poly. I'm using Cartesian vectors and they're 2d. Say poly = [[550,0],[169,523],[-444,323],[-444,-323],[169,-523]], it's just a pentagon I generated. The object that will collide is object, object.pos is it's position and object.vel is it's velocity. They're both 2d vectors too. I've had some success to get it to find a collision, but it's just black box code I ripped from a c++ example. It's very obscure inside and all it does though is return true/false and doesn't return what vertices are collided or collision point, I'd really like to be able to understand this and make my own so I can have more meaningful collision. I'll tackle that later though. Again the question is just how does one find a collision to walls of a poly given you know the poly vertices and the object's position + velocity? If more info is needed please let me know. And if all anyone can do is point me to the right direction that's great.

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  • #altnetseattle - Kanban

    - by GeekAgilistMercenary
    The two main concepts of Kanban is to keep the queues minimum and to maintain visibility. Management/leadership needs to make sure the Kanban Queue doesn’t get starved.  This is key and also very challenging, being the queue needs to be minimal but also can’t get too small during the course of work.  This is to maintain maximum velocity. Phases of the Kanban need to be kept flowing too, bottlenecks need removed ASAP when brought up. Victory Wall – I dig that idea.  Somewhere to look to see the success of the team. The POs work in Rally or other tools for some client management, but it causes issues with the lack of "visibility" – a key fundamental ideal & part of Kanban. One of the big issues is fitting things into a sprint, when Kanban is used with Scrum, but longer sprints are wasteful. Kanban work sizes are of a set size. At this point I got a bit side tracked by the actual conversation and missed out on note taking.  Overall, people doing Kanban and Lean Style Software Development I would say are some of the happiest coders around.  The clean focus, good velocity, sizing, and other approaches that are inferred by Kanban help developers be the rock stars and succeed. This is definitely a topic I will be commenting on a lot more in the near future.

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  • Player sprite moving slower on iPhone 4

    - by nvillec
    I just finished getting movement/jump animation for a player sprite in Xcode using Cocos2D. The basic movement algorithm is a timer that updates every 0.01 sec, changing the sprite position to (sprite.position.x + xVel, sprite.position.y + yVel). Each time a movement button is tapped, the appropriate velocity (initialized to 0) is changed to whatever speed I choose, then a stop movement button returns the velocity to 0. It's not an ideal solution but I'm very new at this and stoked to at least have that working with little help from the internet. So I may not have explained that perfectly, but it is in fact working to my satisfaction in Xcode's iPhone Simulator, however when I build it for my device and run it on my phone, the sprite's movement speed is noticeably slower than in Xcode. At first I thought it must have to do with the resolution of the iPhone 4, making the sprite's movement path twice as long, but I found that if I pull up the multitask bar, then return to the app the speed will sometimes jump back to normal. My second theory was that the code is just inefficient and is bogging the processes down, but I would see this reflected in the frame rate wouldn't I? It stays at 59-60 the whole time, and the spritesheet animation runs at the correct speed. Has anyone experienced this? Is this a really obvious issue that I'm completely missing? Any help (or tips for optimizing my approach to movement) would be much appreciated!

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  • How to get the Exact Collision Point and ignore the collision (from 2 "ghost bodies")

    - by Moritz
    I have a very basic problem with Box2D. For a arenatype game where you can throw scriptable "missiles" at other players I decided to use Box2D for the collision detection between the players and the missiles. Players and missiles have their own circular shape with a specific size (varying). But I don´t want to use dynamic bodies because the missiles need to move themselve in any way they want to (defined in the script) and shouldnt be resolved unless the script wants it. The behavior I look for is as following (for each time step): velocity of missiles is set by the specific missile script each missile is moved according to that velocity if a collision accurs now, I want to get the exact position of impact, and now I need a mechanism to decide if the missile should just ignore the collision (for example collision between two fireballs which shouldnt interact) or take it (so they are resolved and dont overlap anymore) So is there a way in Box2D to create Ghost bodies and listen to collisions from them, then deciding if they should ignore the collision or should take them and resolve their position? I hope I was clear enough and would be happy about any help!

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  • Confusion with floats converted into ints during collision detection

    - by TheBroodian
    So in designing a 2D platformer, I decided that I should be using a Vector2 to track the world location of my world objects to retain some sub-pixel precision for slow-moving objects and other such subtle nuances, yet representing their bodies with Rectangles, because as far as collision detection and resolution is concerned, I don't need sub-pixel precision. I thought that the following line of thought would work smoothly... Vector2 wrldLocation; Point WorldLocation; Rectangle collisionRectangle; public void Update(GameTime gameTime) { Vector2 moveAmount = velocity * (float)gameTime.ElapsedGameTime.TotalSeconds wrldLocation += moveAmount; WorldLocation = new Point((int)wrldLocation.X, (int)wrldLocation.Y); collisionRectangle = new Rectangle(WorldLocation.X, WorldLocation.Y, genericWidth, genericHeight); } and I guess in theory it sort of works, until I try to use it in conjunction with my collision detection, which works by using Rectangle.Offset() to project where collisionRectangle would supposedly end up after applying moveAmount to it, and if a collision is found, finding the intersection and subtracting the difference between the two intersecting sides to the given moveAmount, which would theoretically give a corrected moveAmount to apply to the object's world location that would prevent it from passing through walls and such. The issue here is that Rectangle.Offset() only accepts ints, and so I'm not really receiving an accurate adjustment to moveAmount for a Vector2. If I leave out wrldLocation from my previous example, and just use WorldLocation to keep track of my object's location, everything works smoothly, but then obviously if my object is being given velocities less than 1 pixel per update, then the velocity value may as well be 0, which I feel further down the line I may regret. Does anybody have any suggestions about how I might go about resolving this?

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  • What to do when TDD tests reveal new functionality that is needed that also needs tests?

    - by Joshua Harris
    What do you do when you are writing a test and you get to the point where you need to make the test pass and you realize that you need an additional piece of functionality that should be separated into its own function? That new function needs to be tested as well, but the TDD cycle says to Make a test fail, make it pass then refactor. If I am on the step where I am trying to make my test pass I'm not supposed to go off and start another failing test to test the new functionality that I need to implement. For example, I am writing a point class that has a function WillCollideWith(LineSegment): public class Point { // Point data and constructor ... public bool CollidesWithLine(LineSegment lineSegment) { Vector PointEndOfMovement = new Vector(Position.X + Velocity.X, Position.Y + Velocity.Y); LineSegment pointPath = new LineSegment(Position, PointEndOfMovement); if (lineSegment.Intersects(pointPath)) return true; return false; } } I was writing a test for CollidesWithLine when I realized that I would need a LineSegment.Intersects(LineSegment) function. But, should I just stop what I am doing on my test cycle to go create this new functionality? That seems to break the "Red, Green, Refactor" principle. Should I just write the code that detects that lineSegments Intersect inside of the CollidesWithLine function and refactor it after it is working? That would work in this case since I can access the data from LineSegment, but what about in cases where that kind of data is private?

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  • Adjusting the rate of movement of different objects on the same timer

    - by theUg
    I have a series of objects moving along the straight lines. I want to implement slight changes of velocity of each of the object. Constraint is existing model of animation. I am new to this, and not sure if it is the best way to accommodate varying speeds, but what do I know? It is a Java application that repaints the panel every time the timer expires. Timer is set via swing.Timer object that is set by timer delay constant. Every time the game is stepped objects’ coordinates advanced by an increment constant. Most of the objects are of the same class. Is there fairly easy way to refactor existing system to allow changing velocity for an individual object? Is there some obvious common solution I am not aware about? Idea I am having right now is to set timer delay fairly small, and only move objects every so many cycles of animation so that the apparent speed can be adjusted by varying how often they get moved. But that seems fairly involved, and I do not think it is the most elegant solution in terms of performance what with repainting the whole frame every 3-5 milliseconds. Can it be done by advancing the objects so many (varying) times during the certain interval (let’s say 35ms for something like 28fps), and use repaint() method to redraw just individual object? Do I need to mess with pausing animation for smoothness at higher redraw rates? Is it common practise to check for collision at larger step interval, but draw animation a lot more frequently?

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  • Estimate angle to launch missile, maths question

    - by Jonathan
    I've been working on this for an hour or two now and my maths really isn't my strong suit which is definitely not a good thing for a game programmer but that shouldn't stop me enjoying a hobby surely? After a few failed attempts I was hoping someone else out there could help so here's the situation. I'm trying to implement a bit of faked intelligence when the A.I fires it's missiles at a target in a 2D game world. By predicting the likely position the target will be in given it's current velocity and the time it will take the missile to reach it's target. I created an image to demonstrate my thinking: http://i.imgur.com/SFmU3.png which also contains the logic I use for accelerating the missile after launch. The ship that fires the missile can fire within a total of 40 degree angle, 20 either side of itself, but this could likely become variable. My current attempt was to break the space between the two lines into segments which match the targets width. Then calculate the time it would take the missile to get to that location using the formula. So for each iteration of this we total up the values and that tells us the distance travelled, ad it would then just need compared to distance to the segment. startVelocity * ((startVelocity * acceleration)^(currentframe-1) So for example. If we start at a velocity of 1f/frame with an acceleration of 0.1f the formula, at frame 4, would be 1 * (1.1^3) = 1.331 But I quickly realized I was getting lost when trying to put this into practice. Does this seem like a correct starting point or am I going completely the wrong way about it? Any pointers would help me greatly. Maths really isn't my strong suit so I get easily lost in these matters and don't even really know a good phrase to search for with this. So I guess in summary my question is more about the correct way to approach this problem and any additional code samples on top of that would be great but I'm not averse to working out the complete code from helpful pointers.

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  • Trouble with speed and vectors

    - by Eegabooga
    I'm working on adding bullets to my game. Right now I can shoot bullets in the direction that I would like from a ship by getting the ship's angle: int speed = 5; int dx = -(cos(degreesToRadians(ship.angle)) * speed); // rate of change in the x direction int dy = -(sin(degreesToRadians(ship.angle)) * speed); // rate of change in the y direction bulletPosition.addX(dx); // addX(dx) is simply bulletPosition.x += dx bulletPosition.addY(dy); The ship is pretty much the exact same thing, except I use the += operator: int dx += -(cos(degreesToRadians(angle)) * 0.15) int dy += -(sin(degreesToRadians(angle)) * 0.15); shipPosition.addX(dx); shipPosition.addY(dy); I would like to be able to add the ship's velocity to the bullet's velocity, but I'm a little confused as to how should get the speed from the ship's vector. I thought that adding the ship's dx to the bullet's dx like int dx = -(cos(degreesToRadians(ship.angle)) * speed * dx) would work because I'm adding the rate of change of the ship to the rate of change of the bullet, but that doesn't work. So here's the final question: How can I get the speed of my ship and apply it to my bullet's speed? Thanks in advance for all help :)

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  • Dynamic Jump spot

    - by Pasquale Sada
    I have an initial velocity V(Vx,Vy,VZ) and a spot where he stands still at S(Sx,Sy,Sz). What I'm trying to achieve is a jump on a spot E(Ex,Ey,Ez) where you have clicked on(only lower or higher spot, because I've in place a simple steering behavior for even terrains). There are no obstacle around. I've implemented a formula that can make him jump in a precise way on a spot but you need to declare an angle: the problem arise when the selected spot is straight above your head. It' pretty lame that the char hang there and can reach a thing that is 1cm above is head. I'll share the code I'm using: Vector3 dir = target - transform.position; // get target direction float h = dir.y; // get height difference dir.y = 0; // retain only the horizontal direction float dist = dir.magnitude ; // get horizontal distance float a = angle * Mathf.Deg2Rad; // convert angle to radians dir.y = dist * Mathf.Tan(a); // set dir to the elevation angle dist += h / Mathf.Tan(a); // correct for small height differences // calculate the velocity magnitude float vel = Mathf.Sqrt(dist * Physics.gravity.magnitude / Mathf.Sin(2 *a)); return vel * dir.normalized;

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  • When I shoot from a gun while walking, the bullet is off the center, but when stand still it's fine

    - by Vlad1k
    I am making a small project in Unity, and whenever I walk with the gun and shoot at the same time, the bullets seem to curve and shoot off 2-3 CMs from the center. When I stand still this doesn't happen. This is my main Javascript code: @script RequireComponent(AudioSource) var projectile : Rigidbody; var speed = 500; var ammo = 30; var fireRate = 0.1; private var nextFire = 0.0; function Update() { if(Input.GetButton ("Fire1") && Time.time > nextFire) { if(ammo != 0) { nextFire = Time.time + fireRate; var clone = Instantiate(projectile, transform.position, transform.root.rotation); clone.velocity = transform.TransformDirection(Vector3 (0, 0, speed)); ammo = ammo - 1; audio.Play(); } else { } } } I assume that these two lines need to be tweaked: var clone = Instantiate(projectile, transform.position, transform.root.rotation); clone.velocity = transform.TransformDirection(Vector3 (0, 0, speed)); Thanks in advanced, and please remember that I just started Unity, and I might have a difficult time understanding some things. Thanks!

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  • XNA - 2D Rotation of an object to a selected direction

    - by lobsterhat
    I'm trying to figure out the best way of rotating an object towards the directional input of the user. I'm attempting to mimic making turns on ice skates. For instance, if the player is moving right and the input is down and left, the player should start rotating to the right a set amount each tick. I'll calculate a new vector based on current velocity and rotation and apply that to the current velocity. That should give me nice arcing turns, correct? At the moment I've got eight if/else statements for each key combination which in turn check the current rotation: // Rotate to 225 if (keyboardState.IsKeyDown(Keys.Up) && keyboardState.IsKeyDown(Keys.Left)) { // Rotate right if (rotation >= 45 || rotation < 225) { rotation += ROTATION_PER_TICK; } // Rotate left else if (rotation < 45 || rotation > 225) { rotation -= ROTATION_PER_TICK; } } This seems like a sloppy way to do this and eventually, I'll need to do this check about 10 times a tick. Any help toward a more efficient solution is appreciated.

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  • What sort of data should be sent for mouse-based movement in a multiplayer game?

    - by Daniel
    I'm new to the Multiplayer Rodeo here so please bear with me... I am just getting started and I'm trying to figure out how to deal with movement. I've looked at the question Best way to implement mouse-based movement in MMOG which gives me a pretty good idea, but I'm still struggling with what kind of data should be sent to the server. If a player is on position [x:0, y:0] and I click with the mouse on [x:40, y:40] to start movement, what information should I send to the server? Should I calculate the position based on velocity on client side and just send the expected location? Or should I send current location and velocity and direction? When the server is updating the clients on the players' whereabouts, should the position be sent only, and the clients expected to interpolate/predict movement, or can the direction sent from the client (instead of just coordinates) be used. My concern(or confusion) is regarding the ping/lag frequency of data update and use of a predictive algorithm, as I'd like the movement to be smooth even with a high latency, and prevent ability to cheat(though that's not the top priority).

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