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• How can I keep straight alpha during rendering particles?

  - by April

  Rencently,I was trying to save textures of 3D particles so that I can reuse the in 2D rendering.Now I had some problem with alpha channel.Some artist told me I that my textures should have unpremultiplied alpha channel.When I try to get the rgb value back,I got strange result.Some area went lighter and even totally white.I mainly focus on additive and blend mode,that is: ADDITIVE: srcAlpha VS 1 BLEND: srcAlpha VS 1-srcAlpha I tried a technique called premultiplied alpha.This technique just got you the right rgb value,its all you need on screen.As for alpha value,it worked well with BLEND mode,but not ADDITIVE mode.As you can see in parameters,BLEND mode always controlled its value within 1.While ADDITIVE mode cannot guarantee. I want proper alpha,but it just got too big or too small consider to rgb.Now what can I do?Any help will be great thankful. PS:If you don't understand what I am trying to do,there is a commercial software called "Particle Illusion".You can create various particles and then save the scene to texture,where you can choose to remove background of particles. Now,I changed the title.For some software like maya or AE,what I want is called [straight alpha].

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• processing gamestate with a window of commands across time?

  - by rook2pawn

  I have clients sending client updates at a 100ms intervals. i pool the command inputs and create a client command frame. the commands come into the server in these windows and i tag them across time as they come in. when i do a server tick i intend to process this list of commands i.e. [ {command:'duck',timestamp:350,player:'a'}, {command:'shoot',timestamp:395,player:'b'}, {command:'move', timestamp:410,player:'c'} {command:'cover',timestamp:420,player:'a'} ] how would i efficiently update the gamestate based on this list? the two solutions i see are 1) simulate time via direct equation to figure out how far everyone would move or change as if the real gameupdate was ticking on the worldtick..but then unforseen events that would normally trigger during real update would not get triggered such as powerups or collissions 2) prepare to run the worldupdate multiple times and figure out which commands get sent to which worldupdate. this seems better but a little more costly is there a canonical way to do this?

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• Adding gesture recognizer (or dragging) to CCSprite

  - by user339946

  I'm trying to allow a CCSprite to be dragged across the screen. I've succeeded so far by doing it on a Layer level (from this tutorial). However, this only allows ONE sprite to be dragged at a time as the method implementation can only identify a single sprite to move at a time. I'd like to be able to perhaps add a gesture recognizer or somehow implement ccTouchesBegan/Moved in my own little CCSprite subclass. However, from what I understand, you can't just add gesture recognizers to CCSprites. ccTouchMoved are also not available on CCSprites?? Really confused as to how to implement touches on Cocos2D. What is the easiest way to add some position translation code to a CCSprite so it can be dragged around? Thanks!

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• Looking for algorithms regarding scaling and moving

  - by user1806687

  I've been bashing my head for the past couple of weeks trying to find algorithms that would help me accomplish, on first look very easy task. So, I got this one object currently made out of 5 cuboids (2 sides, 1 top, 1 bottom, 1 back), this is just for an example, later on there will be whole range of different set ups. I have included three pictures of this object(as said this is just for an example). Now, the thing is when the user scales the whole object this is what should happen: X scale: top and bottom cuboids should get scaled by a scale factor, sides should get moved so they are positioned just like they were before(in this case at both ends of top and bottom cuboids), back should get scaled so it fits like before(if I simply scale it by a scale factor it will leave gaps on each side). Y scale: sides should get scaled by a scale factor, top and bottom cuboid should get moved, and back should also get scaled. Z scale: sides, top and bottom cuboids should get scaled, back should get moved. Here is an image of the example object (a thick walled box, with one face missing, where each wall is made by a cuboid): Front of the object: Hope you can help,

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• How to detect and collide two elastic line segments?

  - by Tautrimas

  There are 4 moving physical nodes in 3D space. They are paired with two elastic line segments / strings (1 <- 2; 3 <- 4). Part I: How to detect the collision of two segments? Part II: On the moment of collision, fifth node is created at the intersection point and here you have the force-based graph. 5-th node (bend point) can slide among the strings as in a real world. Given the new coordinates of 4 nodes, how to calculate the position of the 5-th node on the next frame? I assume string force on the nodes to be F = -k * x where x is the string length. All I came up to is that the force between 5 and 1 equals 5 and 2 (the same with 3 and 4). What are the other properties?.

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• gradient coloring of an object

  - by perrakdar

  I have an object(FBX format) in my project, it's a line drawn in 3D max. I want to color the line in XNA so that the color starts from a specific RGB color in both the start and end points of the line and finish in a specific RGB color.(e.x., from (255,255,255) to (128,128,128). Something like gradient coloring of an object. I need to do that programmatically, since later in my code I have to change these two specific colors a lot.

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• Looking for feedback on design pattern for simple 2D environment

  - by Le Mot Juiced

  I'm working in iOS. I am trying to make a very simple 2D environment where there are some basic shapes you can drag around with your finger. These shapes should interact in various ways when dropped on each other, or when single-tapped versus double-tapped, etc. I don't know the name for the design pattern I'm thinking of. Basically, you have a bunch of arrays named after attributes, such as "double-tappable" or "draggable" or "stackable". You assign these attributes to the shapes by putting the shapes in the arrays. So, if there's a double-tap event, the code gets the location of it, then iterates through the "double-tappable" array to see if any of its members are in that location. And so on: every interactive event causes a scan through the appropriate array or arrays. It seems like that should work, but I'm wondering if there's a better pattern for the purpose.

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• Drawing Transparency in XNA 4.0

  - by dpaz

  Using C# (VS2010) with XNA 4.0, I have a terrain layer (RenderTarget2D) in a 2D side-scroller. My visual system tracks updates to redraw individual tiles, but I am having trouble finding a way to clear out the rectangle where the tile will be drawn, which I must do because A) there may no longer be a tile or B) the tile may itself contain transparency. How can I draw a rectangle of transparency onto an existing RenderTarget2D? I essentially want to clear just that rectangular portion of it. My Google searches have not yielded anything relevant.

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• Knockback enemy based off of direction sprite is facing

  - by pengume

  Hey Everyone, Today I am trying to make it so if I hit the enemy then the enemy well be knocked backwards in the direction the sprite is facing. I am rotating the sprite around 360 degrees using a joystick on the screen and wanted to know the best practice or ways to accomplish this. I have come up with a few ideas but none of them make use of the sprites angle he is facing just a check to see if I hit the bottom then move him upward and so forth. I am just stumped on how to apply the sprites angle to the enemies x and y coordinate and move him accordingly. Has anyone tried this and have suggestions or things to look for? Thanks in advance.

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• SDL Bullet Movement

  - by Code Assasssin

  I'm currently working on my first space shooter, and I'm in the process of making my ship shoot some bullets/lasers. Unfortunately, I'm having a hard time getting the bullets to fly vertically. I'm a total noob when it comes to this so you might have a hard time understanding my code :/ // Position Bullet Function projectilex = x + 17; projectiley = y + -20; if(keystates[SDLK_SPACE]) { alive = true; } And here's my show function if(alive) { if(frame == 2) { frame = 0; } apply_surface(projectilex,projectiley,ShootStuff,screen,&lazers[frame]); frame++; projectiley + 1; } I'm trying to get the bullet to fly vertically... and I have no clue how to do that. I've tried messing with the y coordinate but that makes things worse. The laser/bullet just follows the ship :( How would I get it to fire at the starting position and keep going in a vertical line without it following the ship? int main( int argc, char* args[] ) { Player p; Timer fps; bool quit = false; if( init() == false ) { return 1; } //Load the files if( load_files() == false ) { return 1; } clip[ 0 ].x = 0; clip[ 0 ].y = 0; clip[ 0 ].w = 30; clip[ 0 ].h = 36; clip[ 1 ].x = 31; clip[ 1 ].y = 0; clip[ 1 ].w = 39; clip[ 1 ].h = 36; clip[ 2 ].x = 71; clip[ 2 ].y = 0; clip[ 2 ].w = 29; clip[ 2 ].h = 36; lazers [ 0 ].x = 0; lazers [ 0 ].y = 0; lazers [ 0 ].w = 3; lazers [ 0 ].h = 9; lazers [ 1 ].x = 5; lazers [ 1 ].y = 0; lazers [ 1 ].w = 3; lazers [ 1 ].h = 7; while( quit == false ) { fps.start(); //While there's an event to handle while( SDL_PollEvent( &event ) ) { p.handle_input(); //If a key was pressed //If the user has Xed out the window if( event.type == SDL_QUIT ) { //Quit the program quit = true; } } //Scroll background bgX -= 8; //If the background has gone too far if( bgX <= -GameBackground->w ) { //Reset the offset bgX = 0; } p.move(); apply_surface( bgX, bgY,GameBackground, screen ); apply_surface( bgX + GameBackground->w, bgY, GameBackground, screen ); apply_surface(0,0, FullHealthBar,screen); p.shoot(); p.show(); //Apply the message //Update the screen if( SDL_Flip( screen ) == -1 ) { return 1; } SDL_Flip(GameBackground); if( fps.get_ticks() < 1000 / FRAMES_PER_SECOND ) { SDL_Delay( ( 1000 / FRAMES_PER_SECOND ) - fps.get_ticks() ); } } //Clean up clean_up(); return 0; }

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• How do I retain previously drawn graphics?

  - by Cromanium

  I've created a simple program that draws lines from a fixed point to a random point each frame. I wanted to keep each line on the screen. However, it always seems to be cleared each time it draws on the spriteBatch even without GraphicsDevice.Clear(color) being called. What seems to be the problem? protected override void Draw(GameTime gameTime) { spriteBatch.Begin(); DrawLine(spriteBatch); spriteBatch.End(); base.Draw(gameTime); } private void DrawLine(SpriteBatch spriteBatch) { Random r = new Random(); Vector2 a = new Vector2(50, 100); Vector2 b = new Vector2(r.Next(0, 640), r.Next(0,480)); Texture2D filler= new Texture2D(GraphicsDevice, 1, 1, false, SurfaceFormat.Color); filler.SetData(new[] { Color.Black }); float length = Vector2.Distance(a, b); float angle = (float)Math.Atan2(b.Y - a.Y, b.X - a.X); spriteBatch.Draw(filler, a, null, Color.Black, angle, Vector2.Zero, new Vector2(length,10.0f), SpriteEffects.None, 0f); } What am I doing wrong?

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• Dropping multiple objects using an array in Actionscript?

  - by Eratosthenes

  I'm trying to get these fireBalls to drop more often, I'm not sure if I'm using Math.random correctly. Also, for some reason I'm getting a null reference because I think the fireBalls array waits for one to leave the stage before dropping another one? This is the relevant code: var sun:Sun=new Sun var fireBalls:Array=new Array() var left:Boolean; function onEnterFrame(event:Event){ if (left) { sun.x = sun.x - 15; }else{ sun.x = sun.x + 15; } if (fireBalls.length>0&&fireBalls[0].y>stage.stageHeight){ // Fireballs exit stage removeChild(fireBalls[0]); fireBalls.shift(); } for (var j:int=0; j<fireBalls.length; j++){ fireBalls[j].y=fireBalls[j].y+15; if (fireBalls[j].y>stage.stageHeight-fireBall.width/2){ } } if (Math.random()<.2){ // Fireballs shooting from Sun var fireBall:FireBall=new FireBall; fireBall.x=sun.x; addChild(fireBall); fireBalls.push(fireBall); } }

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• Lwjgl camera causing movement to be mirrored

  - by pangaea

  I'm having a problem in that everything is rendered and the movement is fine. However, everything seems to be mirrored. In the sense that the TriangleMob should move towards me, but it doesn't instead it mirrors my action. I move forward the TriangleMob moves backwards. I move left, it moves right. I move backwards, it moves forward. The code works if I do this glPushMatrix(); glTranslatef(-position.x, -position.y, -position.z); glCallList(objectDisplayList); glPopMatrix(); However, I'm scared this will cause a problem later on. I suppose the code works. However, shouldn't the call be glPushMatrix(); glTranslatef(position.x, position.y, position.z); glCallList(objectDisplayList); glPopMatrix(); I think the problem could be caused by how I'm doing the camera, which is this glLoadIdentity(); glRotatef(player.getRotation().x, 1.0f, 0.0f, 0.0f); glRotatef(player.getRotation().y, 0.0f, 1.0f, 0.0f); glRotatef(player.getRotation().z, 0.0f, 0.0f, 1.0f); glTranslatef(player.getPosition().x, player.getPosition().y, player.getPosition().z);

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• Retrieve the coordinates of the *occluding* (closest/drawn) pixels during 3D overlap, using OpenGL?

  - by Big Rich

  Hi, Sorry if the question is not worded well, I'm a new to both 3D and OpenGL. How could I go about obtaining the 3D coordinates of the occluding object, at the point where occlusion is happening (i.e. the 'intersection' of the object in front/closest to the screen)? Just to offer a [very] rudimentary, visual, example, if you were to form an index-finger cross, with your right hand closest to your face, I'd like to know the coordinates of the part of your right finger which obscures the other finger (obviously back within the OpenGL context - no jokers ;-) ). If there is a way to find out both about the occluder (hider) and the occluded (hidden) objects in OpenGL, then that would be of great use, also. Cheers Rich

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• Particle system lifetimes in OpenGL ES 2

  - by user16547

  I don't know how to work with my particle's lifetimes. My design is simple: each particle has a position, a speed and a lifetime. At each frame, each particle should update its position like this: position.y = position.y + INCREMENT * speed.y However, I'm having difficulties in choosing my INCREMENT. If I set it to some sort of FRAME_COUNT, it looks fine until FRAME_COUNT has to be set back to 0. The effect will be that all particles start over at the same time, which I don't want to happen. I want my particles sort of live "independent" of each other. That's the reason I need a lifetime, but I don't know how to make use of it. I added a lifetime for each particle in the particle buffer, but I also need an individual increment that's updated on each frame, so that when PARTICLE_INCREMENT = PARTICLE_LIFETIME, each increment goes back to 0. How can I achieve something like that?

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• Keep Getting Syntax Error C2199?

  - by DARK3ZOOZ

  Here's my problem I'm trying to define something, but keep getting a syntax error Code: #define R_RegisterShader 0x50C8A0 int (*trap_R_RegisterShader)( const char *name, int Arg_1 ) = (int (_cdecl *)(const char *, int ))R_RegisterShader; ^^^^^^^ This last part is where I keep getting the error if you need more lines of codes, just let me know. thanks http://gyazo.com/1a47ebc12cfbd6ea72feb72c686ae84d screenshot of error

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• Settings object with singleton pattern

  - by axis

  I need to build an object that will have only one instance because this Object is dedicated to the storage of vital settings for my application and I would like to avoid a misuse of this type or a conflict at run-time. The most popular solution for this, according to the internet, is the Singleton pattern. But I would like to know about other ideas or solutions for this; also I would like to know if other solutions can be much more easy to grasp for an user of this hypothetical library. Thanks.

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• What is the best way to manage large 3d worlds (i.e minecraft style)?

  - by SomeXnaChump

  After playing minecraft I was marvelling a bit at their large worlds but at the same time finding it extremely slow to navigate, even with a quad core and meaty graphics card. Now I assume its fairly slow because: A) Its written in Java, and as most of the actual spatial partitioning and other memory management activities happen in there it would be slower than a native C++ version. B) They are not partitioning their world very well I could be wrong on both assumptions, however it got me thinking about the best way to manage large worlds. As it is more of a true 3d world, where a block can exist in any part of the world, it is basically a big 3d array [x][y][z], where each block in the world has a type (i.e BlockType.Empty = 0, BlockType.Dirt = 1 etc). Now I am assuming to make this sort of world performant you would need to: a) Use a tree of some variety (oct/kd/bsp) to split all the cubes out, it seems like an oct/kd would be the better option as you can just partition on a per cube level not a per triangle level. b) Use some algorithm to work out if the blocks within the scene can currently be seen, as blocks closer to the user could obfuscate the blocks behind, making it pointless to render them. c) Keep the block object themselves lightweight, so it is quick to add and remove them from the trees I guess there is no right answer to this, but I would be interested to see peoples opinions on the subject.

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• SDL: How would I add tile layers with my area class as a singleton?

  - by Tony

  I´m trying to wrap my head around how to get this done, if at all possible. So basically I have a Area class, Map class and Tile class. My Area class is a singleton, and this is causing some confusion. I´m trying to draw like this: Background / Tiles / Entities / Overlay Tiles / UI. void C_Application::OnRender() { // Fill the screen black SDL_FillRect( Surf_Screen, &Surf_Screen->clip_rect, SDL_MapRGB( Surf_Screen->format, 0x00, 0x00, 0x00 ) ); // Draw background // Draw tiles C_Area::AreaControl.OnRender(Surf_Screen, -C_Camera::CameraControl.GetX(), -C_Camera::CameraControl.GetY()); // Draw entities for(unsigned int i = 0;i < C_Entity::EntityList.size();i++) { if( !C_Entity::EntityList[i] ) { continue; } C_Entity::EntityList[i]->OnRender( Surf_Screen ); } // Draw overlay tiles // Draw UI // Update the Surf_Screen surface SDL_Flip( Surf_Screen); } Would be nice if someone could give a little input. Thanks.

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• what's wrong with my lookAt and move forward code?

  - by alaslipknot

  so am still in the process of getting familiar with libGdx and one of the fun things i love to do is to make basics method for reusability on future projects, and for now am stacked on getting a Sprite rotate toward target (vector2) and then move forward based on that rotation the code am using is this : // set angle public void lookAt(Vector2 target) { float angle = (float) Math.atan2(target.y - this.position.y, target.x - this.position.x); angle = (float) (angle * (180 / Math.PI)); setAngle(angle); } // move forward public void moveForward() { this.position.x += Math.cos(getAngle())*this.speed; this.position.y += Math.sin(getAngle())*this.speed; } and this is my render method : @Override public void render(float delta) { // TODO Auto-generated method stub Gdx.gl.glClearColor(0, 0, 0.0f, 1); Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT); // groupUpdate(); Vector3 mousePos = new Vector3(Gdx.input.getX(), Gdx.input.getY(), 0); camera.unproject(mousePos); ball.lookAt(new Vector2(mousePos.x, mousePos.y)); // if (Gdx.input.isTouched()) { ball.moveForward(); } batch.begin(); batch.draw(ball.getSprite(), ball.getPos().x, ball.getPos().y, ball .getSprite().getOriginX(), ball.getSprite().getOriginY(), ball .getSprite().getWidth(), ball.getSprite().getHeight(), .5f, .5f, ball.getAngle()); batch.end(); } the goal is to make the ball always look at the mouse cursor, and then move forward when i click, am also using this camera : // create the camera and the SpriteBatch camera = new OrthographicCamera(); camera.setToOrtho(false, 800, 480); aaaand the result was so creepy lol Thank you

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• How to render a texture partly transparent?

  - by megamoustache

  Good Morning StackOverflow, I'm having a bit of a problem right now as I can't seem to find a way to render part of a texture transparently with openGL. Here is my setting : I have a quad, representing a wall, covered with this texture (converted to PNG for uploading purposes). Obviously, I want the wall to be opaque, except for the panes of glass. There is another plane behind the wall which is supposed to show a landscape. I want to see the landscape from behind the window. Each texture is a TGA with alpha channel. The "landscape" is rendered first, then the wall. I thought it would be sufficient to achieve this effect but apparently it's not the case. The part of the window supposed to be transparent is black and the landscape only appears when I move past the wall. I tried to fiddle with GLBlendFunc() after having enabled it but it doesn't seem to do the trick. Am i forgetting an important step ? Thank you :)

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• 3D Box Collision Data Import

  - by cboe

  I'm trying to implement a collision system using oriented bounding boxes, using a center for the box, it's extents as a 3D Vector and a rotation matrix, which is all stuff I picked up online and seem to be somewhat the standard. Detecting the center is no problem so I'm gonna leave these out here. My problem however is importing the data from a 3D file. Say I've placed a box with 2 units length on each side aligned to the world axis. The logic results here are extents of 1,1,1 and I use an identity matrix for rotation - easy. However I'm stuck when I rotate the box in the 3D program, say 30 degrees each axis. How would I parse the box? I only have these 8 vertices as information, and I guess what I would need to do is to find out the rotation of said box, apply it to the vertices so they are aligned to world axes and then calculate the extents out of that. How do I get the rotation of the box when I only have the vertex information of the box available?

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• Triangles in a C++ STL Vector as an Objective-C member sometimes draws incorrectly in OpenGL ES

  - by Rahil627

  The polygons draw correctly 80% of the time. When it fails, a vertex is dislocated. The polygon is consistently drawn with the wrong vertex. I checked that the vector is correct during initialization, even when it's wrongly drawn. I'm using Cocos2d. The class member: @interface Polygon : CCSprite { std::vector<float> triangleVertices; } The draw function called in [Polygon draw]: + (void)drawTrianglesWithVertices:(const std::vector<float> &)v { //glEnableClientState(GL_VERTEX_ARRAY); glDisable(GL_TEXTURE_2D); glDisableClientState(GL_TEXTURE_COORD_ARRAY); glDisableClientState(GL_COLOR_ARRAY); glVertexPointer(2, GL_FLOAT, 0, &v[0]); glDrawArrays(GL_TRIANGLES, 0, v.size()); //glDisableClientState(GL_VERTEX_ARRAY); glEnableClientState(GL_COLOR_ARRAY); glEnableClientState(GL_TEXTURE_COORD_ARRAY); glEnable(GL_TEXTURE_2D); } Any ideas?

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• Size of an image imported with FreeImage

  - by KaiserJohaan

  I'm having abit of a brainfart and I can't quite grasp what I'm doing wrong. It's quite simple, I am importing an image with FreeImage (http://freeimage.sourceforge.net/) which has a method FreeImage_GetBits that returns a pointer to the first byte of the image data. I then try to load all the data into memory using (bitsperpixel / 8) * pixelsWidth ' pixelHeight, like this: uint32_t bitsPerPixel = FreeImage_GetBPP(bitmap); // resolves to 24 uint32_t widthInPixels = FreeImage_GetWidth(bitmap); // resolves to 1024 uint32_t heightInPixels = FreeImage_GetHeight(bitmap); // resolves to 1024 // container is a std::vector<uint8_t> pkgMaterial.mTextureData.insert(pkgMaterial.mTextureData.begin(), FreeImage_GetBits(bitmap), FreeImage_GetBits(bitmap) + ((bitsPerPixel/8) * widthInPixels * heightInPixels)); I have a jpg which is 31 kilobytes in size on disc. Yet when I load it using the above formula, I see the vector is then filled with 3145728 bytes, which is approx 3145 kilobytes. What am I doing wrong?

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• is this the correct way to use glTexCoordPointer?

  - by RubyKing

  Hey all Just trying to work out how to use this function glTexCoordPointer. Here is the man pages http://www.opengl.org/sdk/docs/man/xhtml/glTexCoordPointer.xml which states that I must set a pointer to the first element of the array that uses the texture cordinate. Here is my array static const GLfloat GUIVertices[] = { //FIRST QUAD 1.0f, 1.0f, 0.0f, 1.0f, 1.0f, 0.0f, -1.0f, 1.0f, 0.0f, 1.0f, 0.0f, 0.0f, -1.0f, 0.94f, 0.0f, 1.0f, 0.0f, 1.0f, 1.0f, 0.94f, 0.0f, 1.0f, 1.0f, 1.0f, //2ND QUAD // x y z w X Y 1.0f, -1.0f, 0.0f, 1.0f, 1.0f, 0.0f, -1.0f,-1.0f, 0.0f, 1.0f, 0.0f, 0.0f, -1.0f,-0.94f, 0.0f,1.0f, 0.0f, 1.0f, 1.0f, -0.94f, 0.0f,1.0f, 1.0f, 1.0, }; But how do I set the pointer correctly? like this glTexCoordPointer(1, GL_FLOAT, 6, reinterpret_cast(29 * sizeof(float)) ); for the fifth element on the 2nd quad first row. any help is thankful

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