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• how to keep display tick rate steady when using continuous collision detection?

  - by nas Ns

  (I've just found about this forum). I hope it is ok to repost my question again here. I posted this question at stackoverflow, but it looks like I might get better help here. Here is the question: I've implemented basic particles motion simulation with continuous collision detection. But there is small issue in display. Assume simple case of circles moving inside square. All elastic collisions. no firction. All motion is constant speed. No forces are involved, no gravity. So when a particle is moving, it is always moving at constant speed (in between collisions) What I do now is this: Let the simulation time step be 1 second (for example). This is the time step simulation is advanced before displaying the new state (unless there is a collision sooner than this). At start of each time step, time for the next collision between any particles or a particle with a wall is determined. Call this the TOC time; let’s say TOC was .5 seconds in this case. Since TOC is smaller than the standard time step, then the system is moved by TOC and the new system is displayed so that the new display shows any collisions as just taking place (say 2 circles just touched each other’s, or a circle just touched a wall) Next, the collision(s) are resolved (i.e. speeds updated, changed directions etc..). A new step is started. The same thing happens. Now assume there is no collision detected within the next 1 second (those 2 circles above will not be in collision any more, even though they are still touching, due to their speeds showing they are moving apart now), Hence, simulation time is advanced now by the full one second, the standard time step, and particles are moved on the screen using 1 second simulation time and new display is shown. You see what has just happened: One frame ran for .5 seconds, but the next frame runs for 1 second, may be the 3rd frame is displayed after 2 seconds, may be the 4th frame is displayed after 2.8 seconds (because TOC was .8 seconds then) and so on. What happens is that the motion of a particle on the screen appears to speed up or slow down, even though it is moving at constant speed and was not even involved in a collision. i.e. Looking at one particle on its own, I see it suddenly speeding up or slowing down, becuase another particle had hit a wall. This is because the display tick is not uniform. i.e. the frame rate update is changing, giving the false illusion that a particle is moving at non-constant speed while in fact it is moving at constant speed. The motion on the screen is not smooth, since the screen is not updating at constant rate. I am not able to figure how to fix this. If I want to show 2 particles at the moment of the collision, I must draw the screen at different times. Drawing the screen always at the same tick interval, results in seeing 2 particles before the collision, and then after the collision, and not just when they colliding, which looked bad when I tried it. So, how do real games handle this issue? How to display things in order to show collisions when it happen, yet keep the display tick constant? These 2 requirements seem to contradict each other’s.

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• Rotation matrix for a 3D vector

  - by Shashwat

  I have a direction vector on which I have to apply some rotation to align it to positive z-axis. To use Matrix.CreateRotationX(angle) of XNA, I need the angle for which I'd have to compute cos or tan inverse. I think this is a complex task to do. Also, eventually those are also converted to sin(angle) and cos(angle) in the matrix. Is there any inbuilt way to create rotation matrix from a 3D vector? However, I can write the function but still asking if there is one already there.

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• How can be data oriented programming applied for GUI system?

  - by Miro

  I've just learned basics of Data oriented programming design, but I'm not very familiar with that yet. I've also read Pitfalls of Object Oriented Programming GCAP 09. It seems that data oriented programming is much better idea for games, than OOP. I'm just creating my own GUI system and it's completely OOP. I'm thinking if is data oriented programming design applicable for structured things like GUI. The main problem I see is that every type widget has different data, so I can hardly group them into arrays. Also every type of widget renders differently so I still need to call virtual functions.

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• DirectX 9.0c and C++ GUI

  - by SullY

  Well, I'm trying to code a gui for my engine, but I've got some problems. I know how to make a UI overlay but buttons are still black magic for me. Anything I tried was to compilcated ( if it goes big ). To Example I tried to look if the mouse position is the same as the Pixel that is showing the button. But If I use some bigger areas it's getting to complicated. Now I'm searching for a Tutorial how to implement your own gui. I'm really confused about it. Well I hope you have/ know some good tutorials. By the way, I took a look at the DXUTSample, but it's to big to get overview.

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• Changing coordinate system from Z-up to Y-up

  - by Jari Komppa

  Blender's coordinate system is different from what I'm used to, in that Z points upwards instead of Y. What would be the simplest way of converting all the world data (so that all animations, texture coordinates, etc still work) so that Y points upwards? Clarification: Object positions are defined as matrices, so just switching translation/rotation/scale information in matrices is not a trivial task.

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• How do I keep a 3D model on the screen in OpenGL?

  - by NoobScratcher

  I'm trying to keep a 3D model on the screen by placing my glDrawElement functions inside the draw function with the declarations at the top of .cpp. When I render the model, the model attaches it self to the current vertex buffer object. This is because my whole graphical user interface is in 2D quads except the window frame. Is there a way to avoid this from happening? or any common causes of this? Creating the file object: int index = IndexAssigner(1, 1); //make a fileobject and store list and the index of that list in a c string ifstream file (list[index].c_str() ); //Make another string //string line; points.push_back(Point()); Point p; int face[4]; Model rendering code: int numfloats = 4; float* point=reinterpret_cast<float*>(&points[0]); int num_bytes=numfloats*sizeof(float); cout << "Size Of Point" << sizeof(Point) << endl; GLuint vertexbuffer; glGenVertexArrays(1, &vao[3]); glGenBuffers(1, &vertexbuffer); glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer); glBufferData(GL_ARRAY_BUFFER, points.size()*sizeof(points), points.data(), GL_STATIC_DRAW); glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, num_bytes, &points[0]); glEnableClientState(GL_VERTEX_ARRAY); glVertexPointer(3, GL_FLOAT, points.size(), &points[0]); glEnableClientState(GL_INDEX_ARRAY); glIndexPointer(GL_FLOAT, faces.size(), faces.data()); glEnableVertexAttribArray(0); glDrawElements(GL_QUADS, points.size(), GL_UNSIGNED_INT, points.data()); glDrawElements(GL_QUADS, faces.size(), GL_UNSIGNED_INT, faces.data());

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• How do I optimize searching for the nearest point?

  - by Rootosaurus

  For a little project of mine I'm trying to implement a space colonization algorithm in order to grow trees. The current implementation of this algorithm works fine. But I have to optimize the whole thing in order to make it generate faster. I work with 1 to 300K of random attraction points to generate one tree, and it takes a lot of time to compute and compare distances between attraction points and tree node in order to keep only the closest treenode for an attraction point. So I was wondering if some solutions exist (I know they must exist) in order to avoid the time loss looping on each tree node for each attraction point to find the closest... and so on until the tree is finished.

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• How do I pass vertex and color positions to OpenGL shaders?

  - by smoth190

  I've been trying to get this to work for the past two days, telling myself I wouldn't ask for help. I think you can see where that got me... I thought I'd try my hand at a little OpenGL, because DirectX is complex and depressing. I picked OpenGL 3.x, because even with my OpenGL 4 graphics card, all my friends don't have that, and I like to let them use my programs. There aren't really any great tutorials for OpenGL 3, most are just "type this and this will happen--the end". I'm trying to just draw a simple triangle, and so far, all I have is a blank screen with my clear color (when I set the draw type to GL_POINTS I just get a black dot). I have no idea what the problem is, so I'll just slap down the code: Here is the function that creates the triangle: void CEntityRenderable::CreateBuffers() { m_vertices = new Vertex3D[3]; m_vertexCount = 3; m_vertices[0].x = -1.0f; m_vertices[0].y = -1.0f; m_vertices[0].z = -5.0f; m_vertices[0].r = 1.0f; m_vertices[0].g = 0.0f; m_vertices[0].b = 0.0f; m_vertices[0].a = 1.0f; m_vertices[1].x = 1.0f; m_vertices[1].y = -1.0f; m_vertices[1].z = -5.0f; m_vertices[1].r = 1.0f; m_vertices[1].g = 0.0f; m_vertices[1].b = 0.0f; m_vertices[1].a = 1.0f; m_vertices[2].x = 0.0f; m_vertices[2].y = 1.0f; m_vertices[2].z = -5.0f; m_vertices[2].r = 1.0f; m_vertices[2].g = 0.0f; m_vertices[2].b = 0.0f; m_vertices[2].a = 1.0f; //Create the VAO glGenVertexArrays(1, &m_vaoID); //Bind the VAO glBindVertexArray(m_vaoID); //Create a vertex buffer glGenBuffers(1, &m_vboID); //Bind the buffer glBindBuffer(GL_ARRAY_BUFFER, m_vboID); //Set the buffers data glBufferData(GL_ARRAY_BUFFER, sizeof(m_vertices), m_vertices, GL_STATIC_DRAW); //Set its usage glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex3D), 0); glVertexAttribPointer(1, 4, GL_FLOAT, GL_TRUE, sizeof(Vertex3D), (void*)(3*sizeof(float))); //Enable glEnableVertexAttribArray(0); glEnableVertexAttribArray(1); //Check for errors if(glGetError() != GL_NO_ERROR) { Error("Failed to create VBO: %s", gluErrorString(glGetError())); } //Unbind... glBindVertexArray(0); } The Vertex3D struct is as such... struct Vertex3D { Vertex3D() : x(0), y(0), z(0), r(0), g(0), b(0), a(1) {} float x, y, z; float r, g, b, a; }; And finally the render function: void CEntityRenderable::RenderEntity() { //Render... glBindVertexArray(m_vaoID); //Use our attribs glDrawArrays(GL_POINTS, 0, m_vertexCount); glBindVertexArray(0); //unbind OnRender(); } (And yes, I am binding and unbinding the shader. That is just in a different place) I think my problem is that I haven't fully wrapped my mind around this whole VertexAttribArray thing (the only thing I like better in DirectX was input layouts D:). This is my vertex shader: #version 330 //Matrices uniform mat4 projectionMatrix; uniform mat4 viewMatrix; uniform mat4 modelMatrix; //In values layout(location = 0) in vec3 position; layout(location = 1) in vec3 color; //Out values out vec3 frag_color; //Main shader void main(void) { //Position in world gl_Position = vec4(position, 1.0); //gl_Position = projectionMatrix * viewMatrix * modelMatrix * vec4(in_Position, 1.0); //No color changes frag_color = color; } As you can see, I've disable the matrices, because that just makes debugging this thing so much harder. I tried to debug using glslDevil, but my program just crashes right before the shaders are created... so I gave up with that. This is my first shot at OpenGL since the good old days of LWJGL, but that was when I didn't even know what a shader was. Thanks for your help :)

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• How do I get the point coords of a rotated SFML shaperect?

  - by user15498

  I am trying to get collisions of bullets working, and am using SFML. I am using code to get the position of the points of the rectangle for collisions, however I think there's a way to do this without having to get points but by simply getting the points from SFML, since the shape is a rectangle and the points are stored in that way. Is there a way to do that? Through a combination of getPoint() and getGlobalBounds() maybe? While on this topic, is it better to use shapeRects or sprites? I used to only use sprites, however with the addition of textures and more low level stuff I think it would be best to switch to using rectangles and setting their size.

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• Amazon GameCircle Integration

  - by user1095509

  I'm trying to integrate Amazon GameCircle and I have been able to successfully initialize GameCircle in my app, but the problem is when I click on the button that displays achievements, the GameCircle achievement list comes up but it says "You have unlocked 0 of 0 achievements". Same happens with leaderboards i.e there are no leaderboards for this app. I have created a Leaderboard and a few achievements on the online developer portal for Amazon but they don't show for some reason. Can someone help me with this. Any links/resources that help with integrating GameCircle will be appreciated. Thanks.

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• Calculate vector direction

  - by Starkers

  Is the direction angle always measured from the plus x axis? Does a vector in the +,+ quadrant always have a direction between 0 and 90, and in -,+ between 90 and 180 and in -,- between 180 and 270 and in -,+ between 270 and 360 ? Also, how should we calculate the direction using tan? Would that mean nested if statements to find out what quadrant we're in, and then applying the appropriate "work arounds"? E.g. If we were in the -,+ (like in the diagram) would we find the angle from the + axis would be 90 + tan^-1(y/x), the 90 + only used because we're in the -,+ quadrant. Also, that's just a quick solution, may be off, I just want to know if we use nested if statements to get the angle from the + x axis. Finally, should we find the distance in degrees or radians?

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• Colored Collision Detection

  - by tugrul büyükisik

  Several years ago, i made a fast collision detection for 2D, it was just checking a bullets front-pixel's color to check if it were to hit something. Lets say the target rgb color is (124,200,255) then it just checks for that color. After the collision detection, it paints the target with appropriate picture. So, collision detection is made in background without drawing but then painted and drawed. How can i do this in 3D? Because, a vertex is not just exist like a 2D picture's pixel. I looked at some java3D and other programs and understood that 3D world is made of objects. Not just pictures. Is there a program that truly fills the world with vertices ? But it could be needing terabytes of ram even more. Do you know an easy way to interpolate the color of a vertex in java3D or similar program? Note: for a rgb color-identifier, i can make 255*255*255 different 2D objects in background.

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• Simple 2D Flight Physics with Box2D

  - by MarkPowell

  I'm trying to build a simple side scroller with an airplane being the player. As such, I want to build simple flight controls with simple but realistic-feeling physics. I'm making use of cocos2D and Box2D. I have a basic system working, but just can't get the physics feeling correct. I am applying force to the plane (which is a b2CircleShape) based on the user's input. So, basically, if the user pushes up, body_->ApplyForce(b2Vec2(10,30), body_->GetPosition()) is called. Similarly, for down -30 is used. This works and the plane flys along with up/down causing it to dive or climb. But it just doesn't feel right. There is no slowdown on climbs, nor speed up during dives. My simple solution is far to simple. How can I get a better feel for a plane climbing/diving? Thanks!

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• Transform 3d viewport vector to 2d vector

  - by learning_sam

  I am playing around with 3d transformations and came along an issue. I have a 3d vector already within the viewport and need to transform it to a 2d vector. (let's say my screen is 10x10) Does that just straight works like regualar transformation or is something different here? i.e.: I have the vector a = (2, 1, 0) within the viewport and want the 2d vector. Does that works like this and if yes how do I handle the "0" within the 3rd component?

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• HLSL: An array of textures and sampler states

  - by nate142

  The shader must switch between multiple textures depending on the Alpha value of the original texture for each pixel. Now this would word fine if I didn't have to worry about SamplerStates. I have created my array of textures and can select a texture based on the Alpha value of the pixel. But how do I create an Array of SamplerStates and link it to my array of textures? I attempted to treat the SamplerState as a function by adding the (int i) but that didn't work. Also I can't use Texture.Sample since this is shader model 2.0. //shader model 2.0 (DX9) texture subTextures[255]; SamplerState MeshTextureSampler(int i) { Texture = (subTextures[i]); }; float4 SampleCompoundTexture(float2 texCoord, float4 diffuse) { float4 SelectedColor = SAMPLE_TEXTURE(Texture, texCoord); int i = SelectedColor.a; texture SelectedTx = subTextures[i]; return tex2D(MeshTextureSampler(i), texCoord) * diffuse; }

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• Keypress Left is called twice in Update when key is pressed only once

  - by Simran kaur

  I have a piece of code that is changing the position of player when left key is pressed. It is inside of Update() function. I know, Update is called multiple times, but since I have an ifstatement to check if left arrow is pressed, it should update only once. I have tested using print statement that once pressed, it gets called twice. Problem: Position updated twice when key is pressed only once. Below given is the structure of my code: void Update() { if (Input.GetKeyDown (KeyCode.LeftArrow)) { print ("PRESSEEEEEEEEEEEEEEEEEEDDDDDDDDDDDDDD"); } } I looked up on web and what was suggested id this: if (Event.current.type == EventType.KeyDown && Event.current.keyCode == KeyCode.LeftArrow) { print("pressed"); } But, It gives me an error that says: Object reference not set to instance of an object How can I fix this?

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• Coordinate and positioning problem on iOS with cocos2d-x

  - by Vexille

  I'm using cocos2d-x alongside with Marmalade and running some tests and tutorials before starting an actual project with them. So far things are working reasonably well on the windows simulator, Android and even on Blackberry's Playbook, but on iOS devices (iPhone and iPad) the positioning seems to be off. To make things clearer, I put together a scene that just draws an image in the middle of the screen. It worked as expected on everything else, but this is the result I got on an iPhone: To get the coordinates for the center of the screen I'm using the VisibleRect class from the TestCpp sample. It just uses sharedOpenGLView to get the visible size and visible origin, and calculate the center from that. CCSprite* test = CCSprite::create("Ball.png", CCRectMake(0, 0, 80, 80) ); test->setPosition( ccp(VisibleRect::center().x, VisibleRect::center().y) ); this->addChild(test); Also I have a noBorder policy set on AppDelegate: CCEGLView::sharedOpenGLView()->setDesignResolutionSize(designSize.width, designSize.height, kResolutionNoBorder); One funny thing is that I tried to deploy the TestCpp sample project to some iOS devices and it worked reasonably well on the iPhone, but on the iPad the application was only being drawn on a small portion of the screen - just like what happened on the iPhone when I tried using the ShowAll policy.

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• 2D mouse coordinates from 3d object projection

  - by user17753

  Not entirely certain of the nomenclature here -- basically, after placing a model in world coordinates and setting up a 3D camera to look at it the model has been projected onto the screen in a 2D fashion. What I'd like to do is determine if the mouse is inside the projected view of the model. Is there a way to "unproject" in the XNA framework? Or what is this process called as, so that I can better search for it?

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• Find angle for projectile to meet target in parabolic arc

  - by TheBroodian

  I'm making a thing that launches projectiles in 2D. Its projectiles are fired with a set initial velocity, and are only affected by gravity. Assuming that its target is within range, and that there aren't any obstacles, how would my thing find the appropriate angle at which to launch its projectile (in radians)? The equation for this is found here: Wikipedia: Angle Required to Hit Coordinate Sadly, I'm not a physicist (a.k.a. can't read smart people math) and am having a hard time reading its breakdown. If not only for the sake of anybody else that might read this other than myself, would anybody be kind enough to break the equation down into baby words please?

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• UDK : UTWeap_RocketLauncher gift CreateInventory: Any idea why this does not work properly?

  - by John Sloan

  I am giving the player an instanced class of UTWeap_RocketLauncher in an instance of UTGame. PlayerPawn.CreateInventory(class'FobikRocketLauncher',false); // Does not work PlayerPawn.CreateInventory(class'FobikLinkGun',false); // Works Even if I give the original class (eg. UTWeap_RocketLauncher) it does not actually show up. However if I do a "GiveWeapons" cheat, I get it just fine. It also works if I had code it into the map. - But UTWeap_LinkGun works fine either way. Any ideas? It shows the default ammo amount, and the icon on the HUD.

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• problems texture mapping in modern OpenGL 3.3 using GLSL #version 150

  - by RubyKing

  Hi all I'm trying to do texture mapping using Modern OpenGL and GLSL 150. The problem is the texture shows but has this weird flicker I can show a video here http://www.youtube.com/watch?v=xbzw_LMxlHw and I have everything setup best I can have my texcords in my vertex array sent up to opengl I have my fragment color set to the texture values and texel values I have my vertex sending the textures cords to texture cordinates to be used in the fragment shader I have my ins and outs setup and I still don't know what I'm missing that could be causing that flicker. here is my code FRAGMENT SHADER #version 150 uniform sampler2D texture; in vec2 texture_coord; varying vec3 texture_coordinate; void main(void){ gl_FragColor = texture(texture, texture_coord); } VERTEX SHADER #version 150 in vec4 position; out vec2 texture_coordinate; out vec2 texture_coord; uniform vec3 translations; void main() { texture_coord = (texture_coordinate); gl_Position = vec4(position.xyz + translations.xyz, 1.0); } Last bit here is my vertex array with texture cordinates GLfloat vVerts[] = { 0.5f, 0.5f, 0.0f, 0.0f, 1.0f , 0.0f, 0.5f, 0.0f, 1.0f, 1.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.5f, 0.0f, 0.0f, 1.0f, 0.0f}; //tex x and y HERE IS THE ACTUAL FULL SOURCE CODE if you need to see all the code in its fullest glory here is a link to every file http://ideone.com/7kQN3 thank you for your help

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• Selection of a mesh with arbitrary region

  - by Tigran

  Considering example: I have a mesh(es) on the OpenGL screen and would like to select a part of it (say for delete purpose). There is a clear way to do the selction via Ray Tracing, or via Selection provided by OpenGL itself. But, for my users, considering that meshes can get wired surfaces, I need to implement a selection via a Arbitrary closed region, so all triangles that appears present inside that region has to be selected. To be more clear, here is screen shot: I want all triangles inside black polygon to be selected, identified, whatever in some way. How can I achieve that ?

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• 2d ball collision code problem XNA, over accelerated balls and stick together sometimes. help please? [closed]

  - by Sivan

  public static void Collision(Ball ball1, Ball ball2) { Vector3 x = new Vector3((ball1.BallPosition.X - ball2.BallPosition.X), (ball1.BallPosition.Y - ball2.BallPosition.Y), 0); x.Normalize(); Vector3 v1 = new Vector3(ball1.Speed, 0); float x1 = Vector3.Dot(x, v1); Vector3 v1x = x * x1; Vector3 v1y = v1 - v1x; x = -x; Vector3 v2 = new Vector3(ball2.Speed, 0); float x2 = Vector3.Dot(x, v2); Vector3 v2x = x * x2; Vector3 v2y = v2 - v2x; float m1 = 12, m2 = 4; float combinedMass = m1 + m2; Vector3 newVelA = (v1x * ((m1 - m2) / combinedMass)) + (v2x * ((2f * m2) / combinedMass)) + v1y; Vector3 newVelB = (v1x * ((2f * m1) / combinedMass)) + (v2x * ((m2 - m1) / combinedMass)) + v2y; ball1.Speed = new Vector2(newVelA.X, newVelA.Y); ball2.Speed = new Vector2(newVelB.X,newVelB.Y ); }

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• Marching squares: Finding multiple contours within one source field?

  - by TravisG

  Principally, this is a follow-up-question to a problem from a few weeks ago, even though this is about the algorithm in general without application to my actual problem. The algorithm basically searches through all lines in the picture, starting from the top left of it, until it finds a pixel that is a border. In pseudo-C++: int start = 0; for(int i=0; i<amount_of_pixels; ++i) { if(pixels[i] == border) { start = i; break; } } When it finds one, it starts the marching squares algorithm and finds the contour to whatever object the pixel belongs to. Let's say I have something like this: Where everything except the color white is a border. And have found the contour points of the first blob: For the general algorithm it's over. It found a contour and has done its job. How can I move on to the other two blobs to find their contours as well?

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• Bouncing ball isssue

  - by user

  I am currently working on the 2D Bouncing ball physics that bounces the ball up and down. The physics behaviour works fine but at the end the velocity keep +3 then 0 non-stop even the ball has stopped bouncing. How should I modify the code to fix this issue? ballPos = D3DXVECTOR2( 50, 100 ); velocity = 0; accelaration = 3.0f; isBallUp = false; void GameClass::Update() { velocity += accelaration; ballPos.y += velocity; if ( ballPos.y >= 590 ) isBallUp = true; else isBallUp = false; if ( isBallUp ) { ballPos.y = 590; velocity *= -1; } // Graphics Rendering m_Graphics.BeginFrame(); ComposeFrame(); m_Graphics.EndFrame(); }

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