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• What are the semantics of glRotate and glTranslate's parameters?

  - by Zarkopafilis

  I have been trying to play with OpenGL after watching some tutorials and I don't understand how the glTranslatef and glRotatef functions work. I believe a simple picture would help me. I understand that glTranslatef changes the position of the "camera" (but does it change the position in wich the shapes are getting drawn)? However, I don't understand the rotation concept at all. If I do glRotatef(1,0,0,1) it makes my quad spin around. If I just do glRotatef(1,0,0,0) it makes the quad smaller (further away) but if I try to rotate around the X or Y axis, I get a black screen. I don't understand the angle either. Help would be appreciated.

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• What is involved with writing a lobby server?

  - by Kira

  So I'm writing a Chess matchmaking system based on a Lobby view with gaming rooms, general chat etc. So far I have a working prototype but I have big doubts regarding some things I did with the server. Writing a gaming lobby server is a new programming experience to me and so I don't have a clear nor precise programming model for it. I also couldn't find a paper that describes how it should work. I ordered "Java Network Programming 3rd edition" from Amazon and still waiting for shipment, hopefully I'll find some useful examples/information in this book. Meanwhile, I'd like to gather your opinions and see how you would handle some things so I can learn how to write a server correctly. Here are a few questions off the top of my head: (may be more will come) First, let's define what a server does. It's primary functionality is to hold TCP connections with clients, listen to the events they generate and dispatch them to the other players. But is there more to it than that? Should I use one thread per client? If so, 300 clients = 300 threads. Isn't that too much? What hardware is needed to support that? And how much bandwidth does a lobby consume then approx? What kind of data structure should be used to hold the clients' sockets? How do you protect it from concurrent modification (eg. a player enters or exists the lobby) when iterating through it to dispatch an event without hurting throughput? Is ConcurrentHashMap the correct answer here, or are there some techniques I should know? When a user enters the lobby, what mechanism would you use to transfer the state of the lobby to him? And while this is happening, where do the other events bubble up? Screenshot : http://imageshack.us/photo/my-images/695/sansrewyh.png/

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• How are vertex shader outs sent as inputs to the fragment shader?

  - by Jeffrey

  I'm learning some OpenGL 3.2 way of doing things and I think it's quite great, I'm actually understanding more of shaders and non-fixed pipeline in 1 week rather than those 2 years I tried to learn OpenGL fixed pipeline functions. But here's my question: From what I think I've understood the vertex shader is run for each vertexes in the VBO. But the fragments shader is run per each pixel (is that right?) which is a huge number compared to let's say 3 vertexes of a triangle. Now it seems that in the vertex shader the out variables (like colors and stuff) are passed 1 to 1 to the fragment shader. But let's say that I pass to the fragment shader the position of the vertex in the vertex shader. How is all executed? What vertex (A, B or C of the hipothetical triangle) is passed per each fragment and why?

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• Need the co-ordinates of innerPolygon

  - by user960567

  Let say I have this diagram, Given that i have all the co-ordinates of outer polygon and the distance between inner and outer polygon is d is also given. How to calculate the inner polygon co-ordinates? Edit: I was able to solved the issue by getting the mid-points of all lines. From these mid-points I can move d distance, So I can get three points. No I have 3 points and 3 slopes. From this, I can get three new equations. Simultaneously, solving the equation get the 3 points.

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• Cocos2d Box2d contact listener call different method in collided object

  - by roma86

  I have the building object, wen it hit with other, i want to call some method inside it. Building.mm -(void)printTest { NSLog(@"printTest method work correctly"); } in my ContactListener i trying to call it so: ContactListener.mm #import "ContactListener.h" #import "Building.h" void ContactListener::BeginContact(b2Contact* contact) { b2Body* bodyA = contact->GetFixtureA()->GetBody(); b2Body* bodyB = contact->GetFixtureB()->GetBody(); Building *buildA = (Building *)bodyA->GetUserData(); Building *buildB = (Building *)bodyB->GetUserData(); if (buildB.tag == 1) { NSLog(@"tag == 1"); } if (buildA.tag == 2) { NSLog(@"tag == 2"); [buildA printTest]; } } NSLog(@"tag == 2"); work correctly, but [buildA printTest]; get error Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[CCSprite printTest]: unrecognized selector sent to instance 0x18595f0' Obviously I'm referring to the wrong object. How i can get different method and property in contacted objects from contactlistener class? Thanks.

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• Why isnt my data persisting with nskeyedarchiver?

  - by aking63

  Im just working on what should be the "finishing touches" of my first iPhone game. For some reason, when I save with NSKeyedArchiver/Unarchiver, the data seems to load once and then gets lost or something. Here's what I've been able to deduce: When I save in this viewController, pop to the previous one, and then push back into this one, the data is saved and prints as I want it to. But when I save in this viewController, then push a new one and pop back into this one, the data is lost. Any idea why this might be happening? Do I have this set up all wrong? I copied it from a book months ago. Here's the methods I use to save and load. - (void) saveGameData { NSLog(@"LS:saveGameData"); // SAVE DATA IMMEDIATELY NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); NSString *documentsDirectory = [paths objectAtIndex:0]; NSString *gameStatePath = [documentsDirectory stringByAppendingPathComponent:@"gameState.dat"]; NSMutableData *gameSave= [NSMutableData data]; NSKeyedArchiver *encoder = [[NSKeyedArchiver alloc] initForWritingWithMutableData:gameSave]; [encoder encodeObject:categoryLockStateArray forKey:kCategoryLockStateArray]; [encoder encodeObject:self.levelsPlist forKey:@"levelsPlist"]; [encoder finishEncoding]; [gameSave writeToFile:gameStatePath atomically:YES]; NSLog(@"encoded catLockState:%@",categoryLockStateArray); } - (void) loadGameData { NSLog(@"loadGameData"); // If there is a saved file, perform the load NSMutableData *gameData = [NSData dataWithContentsOfFile:[[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0] stringByAppendingPathComponent:@"gameState.dat"]]; // LOAD GAME DATA if (gameData) { NSLog(@"-Loaded Game Data-"); NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:gameData]; self.levelsPlist = [unarchiver decodeObjectForKey:@"levelsPlist"]; categoryLockStateArray = [unarchiver decodeObjectForKey:kCategoryLockStateArray]; NSLog(@"decoded catLockState:%@",categoryLockStateArray); } // CREATE GAME DATA else { NSLog(@"-Created Game Data-"); self.levelsPlist = [[NSMutableDictionary alloc] initWithContentsOfFile:[[NSBundle mainBundle] pathForResource:kLevelsPlist ofType:@"plist"]]; } if (!categoryLockStateArray) { NSLog(@"-Created categoryLockStateArray-"); categoryLockStateArray = [[NSMutableArray alloc] initWithCapacity:[[self.levelsPlist allKeys] count]]; for (int i=0; i<[[self.levelsPlist allKeys] count]; i++) { [categoryLockStateArray insertObject:[NSNumber numberWithBool:FALSE] atIndex:i]; } } // set the properties of the categories self.categoryNames = [self.levelsPlist allKeys]; NUM_CATEGORIES = [self.categoryNames count]; thisCatCopy = [[NSMutableDictionary alloc] initWithDictionary:[[levelsPlist objectForKey:[self.categoryNames objectAtIndex:pageControl.currentPage]] mutableCopy]]; NUM_FINISHED = [[thisCatCopy objectForKey:kNumLevelsBeatenInCategory] intValue]; }

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• Spherical harmonics lighting interpolation

  - by TravisG

  I want to use hardware filtering to smooth out colors in texels of a texture when I'm accessing texels at coordinates that are not directly at the center of the texel, the catch being that the texels store 2 bands of spherical harmonics coefficients (=4 coefficients), not RGBA intensity values. Can I just use hardware filtering like that (GL_LINEAR with and without mip mapping) without any considerations? In other terms: If I were to first convert the coefficients back to intensity representations, than manually interpolate between two intensities, would the resulting intensity be the same as if I interpolated between the coefficient vectors directly and then converted the interpolated result to intensities?

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• In 3D camera math, calculate what Z depth is pixel unity for a given FOV

  - by badweasel

  I am working in iOS and OpenGL ES 2.0. Through trial and error I've figured out a frustum to where at a specific z depth pixels drawn are 1 to 1 with my source textures. So 1 pixel in my texture is 1 pixel on the screen. For 2d games this is good. Of course it means that I also factor in things like the size of the quad and the size of the texture. For example if my sprite is a quad 32x32 pixels. The quad size is 3.2 units wide and tall. And the texcoords are 32 / the size of the texture wide and tall. Then the frustum is: matrixFrustum(-(float)backingWidth/frustumScale,(float)backingWidth/frustumScale, -(float)backingHeight/frustumScale, (float)backingHeight/frustumScale, 40, 1000, mProjection); Where frustumScale is 800 for a retina screen. Then at a distance of 800 from camera the sprite is pixel for pixel the same as photoshop. For 3d games sometimes I still want to be able to do this. But depending on the scene I sometimes need the FOV to be different things. I'm looking for a way to figure out what Z depth will achieve this same pixel unity for a given FOV. For this my mProjection is set using: matrixPerspective(cameraFOV, near, far, (float)backingWidth / (float)backingHeight, mProjection); With testing I found that at an FOV of 45.0 a Z of 38.5 is very close to pixel unity. And at an FOV of 30.0 a Z of 59.5 is about right. But how can I calculate a value that is spot on? Here's my matrixPerspecitve code: void matrixPerspective(float angle, float near, float far, float aspect, mat4 m) { //float size = near * tanf(angle / 360.0 * M_PI); float size = near * tanf(degreesToRadians(angle) / 2.0); float left = -size, right = size, bottom = -size / aspect, top = size / aspect; // Unused values in perspective formula. m[1] = m[2] = m[3] = m[4] = 0; m[6] = m[7] = m[12] = m[13] = m[15] = 0; // Perspective formula. m[0] = 2 * near / (right - left); m[5] = 2 * near / (top - bottom); m[8] = (right + left) / (right - left); m[9] = (top + bottom) / (top - bottom); m[10] = -(far + near) / (far - near); m[11] = -1; m[14] = -(2 * far * near) / (far - near); } And my mView is set using: lookAtMatrix(cameraPos, camLookAt, camUpVector, mView); * UPDATE * I'm going to leave this here in case anyone has a different solution, can explain how they do it, or why this works. This is what I figured out. In my system I use a 10th scale unit to pixels on non-retina displays and a 20th scale on retina displays. The iPhone is 640 pixels wide on retina and 320 pixels wide on non-retina (obsolete). So if I want something to be the full screen width I divide by 20 to get the OpenGL unit width. Then divide that by 2 to get the left and right unit position. Something 32 units wide centered on the screen goes from -16 to +16. Believe it or not I have an excel spreadsheet do all this math for me and output all the vertex data for my sprite sheet. It's an arbitrary thing I made up to do .1 units = 1 non-retina pixel or 2 retina pixels. I could have made it .01 units = 2 pixels and someday I might switch to that. But for now it's the other. So the width of the screen in units is 32.0, and that means the left most pixel is at -16.0 and the right most is at 16.0. After messing a bit I figured out that if I take the [0] value of an identity modelViewProjection matrix and multiply it by 16 I get the depth required to get 1:1 pixels. I don't know why. I don't know if the 16 is related to the screen size or just a lucky guess. But I did a test where I placed a sprite at that calculated depth and varied the FOV through all the valid values and the object stays steady on screen with 1:1 pixels. So now I'm just calculating the unityDepth that way. If someone gives me a better answer I'll checkmark it.

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• How exactly does app ranking work?

  - by qweasdzxc1

  So I've been in the app industry for around half a year and I still don't know how exactly ranking higher for your app will help increase downloads. That sounds like a question with an obvious answer but this is what's going through my mind so hear me out: Unless your app is ranked within the top 100, no one can see it in the featured categories. So even if my app jumped from 400th to 300th place, would there really even be a difference in downloads? And I'm saying 400th to 300th in ranking in my specific category. Indie developers like me don't even come close to ranking for the overall category. So far, the only usefulness of trying to get a higher rank is to get featured or something like that, but big companies have tons of money to throw on marketing...so the chances of any indie developer getting featured is rare. The only thing that I can see ranking being good for is to rank for your keywords so that when someone searches for that word, your app will hopefully appear in the top 10-25 results. Can anyone confirm my thoughts or add anything else that I might have missed out on? How exactly do users find your app if you're not in the top 100 app in your category?

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• Accounting for waves when doing planar reflections

  - by CloseReflector

  I've been studying Nvidia's examples from the SDK, in particular the Island11 project and I've found something curious about a piece of HLSL code which corrects the reflections up and down depending on the state of the wave's height. Naturally, after examining the brief paragraph of code: // calculating correction that shifts reflection up/down according to water wave Y position float4 projected_waveheight = mul(float4(input.positionWS.x,input.positionWS.y,input.positionWS.z,1),g_ModelViewProjectionMatrix); float waveheight_correction=-0.5*projected_waveheight.y/projected_waveheight.w; projected_waveheight = mul(float4(input.positionWS.x,-0.8,input.positionWS.z,1),g_ModelViewProjectionMatrix); waveheight_correction+=0.5*projected_waveheight.y/projected_waveheight.w; reflection_disturbance.y=max(-0.15,waveheight_correction+reflection_disturbance.y); My first guess was that it compensates for the planar reflection when it is subjected to vertical perturbation (the waves), shifting the reflected geometry to a point where is nothing and the water is just rendered as if there is nothing there or just the sky: Now, that's the sky reflecting where we should see the terrain's green/grey/yellowish reflection lerped with the water's baseline. My problem is now that I cannot really pinpoint what is the logic behind it. Projecting the actual world space position of a point of the wave/water geometry and then multiplying by -.5f, only to take another projection of the same point, this time with its y coordinate changed to -0.8 (why -0.8?). Clues in the code seem to indicate it was derived with trial and error because there is redundancy. For example, the author takes the negative half of the projected y coordinate (after the w divide): float waveheight_correction=-0.5*projected_waveheight.y/projected_waveheight.w; And then does the same for the second point (only positive, to get a difference of some sort, I presume) and combines them: waveheight_correction+=0.5*projected_waveheight.y/projected_waveheight.w; By removing the divide by 2, I see no difference in quality improvement (if someone cares to correct me, please do). The crux of it seems to be the difference in the projected y, why is that? This redundancy and the seemingly arbitrary selection of -.8f and -0.15f lead me to conclude that this might be a combination of heuristics/guess work. Is there a logical underpinning to this or is it just a desperate hack? Here is an exaggeration of the initial problem which the code fragment fixes, observe on the lowest tessellation level. Hopefully, it might spark an idea I'm missing. The -.8f might be a reference height from which to deduce how much to disturb the texture coordinate sampling the planarly reflected geometry render and -.15f might be the lower bound, a security measure.

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• My Sprite comes out the screen

  - by IlNero

  If i an action moves the sprite,how can i keep the CCSprite on the screen???? this is my code: [enemy runAction:[CCSequence actions:[CCMoveBy actionWithDuration:2.0 position:ccp(-winSize.width*0.4, 0)], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(winSize.width*0.2, -winSize.width*0.2), randomValueBetween(winSize.height*0.2, -winSize.height*0.2))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(winSize.width*0.2, -winSize.width*0.2), randomValueBetween(winSize.height*0.2, -winSize.height*0.2))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(winSize.width*0.2, -winSize.width*0.2), randomValueBetween(winSize.height*0.2, -winSize.height*0.2))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(winSize.width*0.2, -winSize.width*0.2), randomValueBetween(winSize.height*0.2, -winSize.height*0.2))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(winSize.width*0.2, -winSize.width*0.2), randomValueBetween(winSize.height*0.2, -winSize.height*0.2))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(-winSize.width*0.3,winSize.width*0.3), randomValueBetween(winSize.height*0.3, -winSize.height*0.3))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(-winSize.width*0.2,winSize.width*0.2), randomValueBetween(winSize.height*0.2, -winSize.height*0.2))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(-winSize.width*0.3,winSize.width*0.3), randomValueBetween(winSize.height*0.3, -winSize.height*0.3))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(-winSize.width*0.2,winSize.width*0.2), randomValueBetween(winSize.height*0.2, -winSize.height*0.2))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(-winSize.width*0.3,winSize.width*0.3), randomValueBetween(winSize.height*0.3, -winSize.height*0.3))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(-winSize.width*0.2,winSize.width*0.2), randomValueBetween(winSize.height*0.2, -winSize.height*0.2))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:2.0 position:ccp(-winSize.width*1.5, 0)], [CCCallFuncN actionWithTarget:self selector:@selector(invisNode:)], nil]]; but whit this code the sprite sometimes comes out the screen, i need the sprite moves randomly in the screen without comes out..

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• Rendering multiple squares fast?

  - by Sam

  so I'm doing my first steps with openGL development on android and I'm kinda stuck at some serious performance issues... What I'm trying to do is render a whole grid of single colored squares on to the screen and I'm getting framerates of ~7FPS. The squares are 9px in size right now with one pixel border in between, so I get a few thousand of them. I have a class "Square" and the Renderer iterates over all Squares every frame and calls the draw() method of each (just the iteration is fast enough, with no openGL code the whole thing runs smootlhy at 60FPS). Right now the draw() method looks like this: // Prepare the square coordinate data GLES20.glVertexAttribPointer(mPositionHandle, COORDS_PER_VERTEX, GLES20.GL_FLOAT, false, vertexStride, vertexBuffer); // Set color for drawing the square GLES20.glUniform4fv(mColorHandle, 1, color, 0); // Draw the square GLES20.glDrawElements(GLES20.GL_TRIANGLES, drawOrder.length, GLES20.GL_UNSIGNED_SHORT, drawListBuffer); So its actually only 3 openGL calls. Everything else (loading shaders, filling buffers, getting appropriate handles, etc.) is done in the Constructor and things like the Program and the handles are also static attributes. What am I missing here, why is it rendering so slow? I've also tried loading the buffer data into VBOs, but this is actually slower... Maybe I did something wrong though. Any help greatly appreciated! :)

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• Drawing flaming letters in 3D with OpenGL ES 2.0

  - by Chiquis

  I am a bit confused about how to achieve this. What I want is to "draw with flames". I have achieved this with textures successfully, but now my concern is about doing this with particles to achieve the flaming effect. Am I supposed to create a path along which I should add many particle emitters that will be emitting flame particles? I understand the concept for 2D, but for 3D are the particles always supposed to be facing the user? Something else I'm worried about is the performance hit that will occur by having that many particle emitters, because there can be many letters and drawings at the same time, and each of these elements will have many particle emitters. More detailed explanation: I have a path of points, which is my model. Imagine a dotted letter "S" for example. I want make the "S" be on fire. The "S" is just an example it can be a circle, triangle, a line, pretty much any path described by my set of points. For achieving this fire effect I thought about using particles. So I am using a program called "Particle Designer" to create a fire style particle emitter. This emitter looks perfect on 2D on the iphone screen dimensions. So then I thought that I could probably draw an S or any other figure if i place many particle emitters next to each other following the path described. To move from the 2D version to the 3D version I thought about, scaling the emitter (with a scale matrix multiplication in its model matrix) and then moving it to a point in my 3D world. I did this and it works. So now I have 1 particle emitter in the 3D world. My question is, is this how you would achieve a flaming letter? Is this too inefficient if i expect to have many flaming paths on my world? Am i supposed to rotate the particle's quad so that its always looking at the user? (the last one is because i noticed that if u look at it from the side the particles start to flatten out)

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• World to Pixel Transformation

  - by D00d

  My objects have a location in world coordinates (basically 1.0f is a meter). If I simply draw my objects using their world coordinates, each meter will correspond to a pixel. Obviously that's not what I want. Now, I don't want to have to apply a transformation to each and every object's position when I draw them. As I happen to be using XNA, and spritebatch allows a Matrix to be passed in as an argument in it's begin method, I was wondering if there is a way to pass the World to Pixel transformation in there. Any suggestions? So far Matrix.CreateScale(new Vector3(zoom, zoom, 1)) puts the objects in their proper spot, but it also scales up the sprites. Is there a way to transform the position without enlarging the sprite? Thanks

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• how does HDR work?

  - by dotminic

  I'm trying to understand what HDR is and how it works. I understand the basic concepts and have an slight idea of how it is implemented with D3D/hlsl. However it's still pretty foggy. Say I'm rendering a sphere with a texture of the earth and a small point list of vertices to act as stars, how would I render this in HDR ? Here are a few things I'm confused about: I'm guessing, I can't use just any basic image format for the texture as the values would be limited to [0, 255] and clamped to [0, 1] in a shader. Same goes for the back buffer, I take it the format needs to be a float point format ? What are the other steps involved ? Surely there has to be more than just using floating point formats to render to a render target and then apply some bloom as a post process ? (considering the output will be 8bpp anyway) Basically, what are the steps for HDR ? How does it work ? I can't seem to find any good papers / articles that describe the process, other than this one, but it seems to skim over the basics a little, so it's confusing.

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• Are there any reasons to use Legacy (2.X) OpenGL?

  - by user27886

  The benefits are well documented of the Modern OpenGL 3.X & 4.X API's, but I'm wondering if there are ANY benefits to keeping with the old OpenGL, Or if learning OpenGL 2.X is a complete waste of time now no matter what? Particularly I've wondered if using the OpenGL 2.X API is appropriate if the target platform had graphics hardware capable of only up to OpenGL 2.X. Would a driver update on said target platform allow programs compiled using the Modern OpenGL API's to be released on this old platform? If they both work, which would be faster? Thanks

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• What is the most serious limitation of Unity?

  - by ashes999

  Having read this heated question about Unity vs. UDK vs. ID something, I'm curious to know: what the repeatedly-hit, most crippling limitation(s) of Unity? In order to keep this question non-subjective, again, I'm talking about the top repeated offender(s) of Unity are. This is something that, as a Unity user, you really wish someone had told you about before you started using it. I have heard from someone that Unity does not deal well with version control, since it generates a lot of binary files (which are un-diffable). This, to me, is not really crippling as I work alone. Thoughts?

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• Are these non-standard applications of rendering practical in games?

  - by maul

  I've recently got into 3D and I came up with a few different "tricky" rendering techniques. Unfortunately I don't have the time to work on this myself, but I'd like to know if these are known methods and if they can be used in practice. Hybrid rendering Now I know that ray-tracing is still not fast enough for real-time rendering, at least on home computers. I also know that hybrid rendering (a combination of rasterization and ray-tracing) is a well known theory. However I had the following idea: one could separate a scene into "important" and "not important" objects. First you render the "not important" objects using traditional rasterization. In this pass you also render the "important" objects using a special shader that simply marks these parts on the image using a special color, or some stencil/depth buffer trickery. Then in the second pass you read back the results of the first pass and start ray tracing, but only from the pixels that were marked by the "important" object's shader. This would allow you to only ray-trace exactly what you need to. Could this be fast enough for real-time effects? Rendered physics I'm specifically talking about bullet physics - intersection of a very small object (point/bullet) that travels across a straight line with other, relatively slow-moving, fairly constant objects. More specifically: hit detection. My idea is that you could render the scene from the point of view of the gun (or the bullet). Every object in the scene would draw a different color. You only need to render a 1x1 pixel window - the center of the screen (again, from the gun's point of view). Then you simply check that central pixel and the color tells you what you hit. This is pixel-perfect hit detection based on the graphical representation of objects, which is not common in games. Afaik traditional OpenGL "picking" is a similar method. This could be extended in a few ways: For larger (non-bullet) objects you render a larger portion of the screen. If you put a special-colored plane in the middle of the scene (exactly where the bullet will be after the current frame) you get a method that works as the traditional slow-moving iterative physics test as well. You could simulate objects that the bullet can pass through (with decreased velocity) using alpha blending or some similar trick. So are these techniques in use anywhere, and/or are they practical at all?

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• How do I create a big multiplayer world in UDK?

  - by Dorpe

  I want to create a big multiplayer world in UDK and I'm having a few difficulties. I created the biggest terrain possible but then any terrain related action I do takes forever. However, I've seen videos of people make same size terrain and working without a problem. My pc is strong enough, so maybe someone can tell me what I'm doing wrong. I want to make it even bigger then the biggest terrain size, so I was thinking of doing level streaming but then I read that streaming is working server side which means if I have a player on every terrain all terrains will still be loaded and I want to save as much memory possible so it will work well online. Thanks for any help you can give.

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• What is the recommended way to output values to FBO targets? (OpenGL 3.3 + GLSL 330)

  - by datSilencer

  I'll begin by apologizing for any dumb assumptions you might find in the code below since I'm still pretty much green when it comes to OpenGL programming. I'm currently trying to implement deferred shading by using FBO's and their associated targets (textures in my case). I have a simple (I think :P) geometry+fragment shader program and I'd like to write its Fragment Shader stage output to three different render targets (previously bound by a call to glDrawBuffers()), like so: #version 330 in vec3 WorldPos0; in vec2 TexCoord0; in vec3 Normal0; in vec3 Tangent0; layout(location = 0) out vec3 WorldPos; layout(location = 1) out vec3 Diffuse; layout(location = 2) out vec3 Normal; uniform sampler2D gColorMap; uniform sampler2D gNormalMap; vec3 CalcBumpedNormal() { vec3 Normal = normalize(Normal0); vec3 Tangent = normalize(Tangent0); Tangent = normalize(Tangent - dot(Tangent, Normal) * Normal); vec3 Bitangent = cross(Tangent, Normal); vec3 BumpMapNormal = texture(gNormalMap, TexCoord0).xyz; BumpMapNormal = 2 * BumpMapNormal - vec3(1.0, 1.0, -1.0); vec3 NewNormal; mat3 TBN = mat3(Tangent, Bitangent, Normal); NewNormal = TBN * BumpMapNormal; NewNormal = normalize(NewNormal); return NewNormal; } void main() { WorldPos = WorldPos0; Diffuse = texture(gColorMap, TexCoord0).xyz; Normal = CalcBumpedNormal(); } If my render target textures are configured as: RT1:(GL_RGB32F, GL_RGB, GL_FLOAT, GL_TEXTURE0, GL_COLOR_ATTACHMENT0) RT2:(GL_RGB32F, GL_RGB, GL_FLOAT, GL_TEXTURE1, GL_COLOR_ATTACHMENT1) RT3:(GL_RGB32F, GL_RGB, GL_FLOAT, GL_TEXTURE2, GL_COLOR_ATTACHMENT2) And assuming that each texture has an internal format capable of contaning the incoming data, will the fragment shader write the corresponding values to the expected texture targets? On a related note, do the textures need to be bound to the OpenGL context when they are Multiple Render Targets? From some Googling, I think there are two other ways to output to MRTs: 1: Output each component to gl_FragData[n]. Some forum posts say this method is deprecated. However, looking at the latest OpenGL 3.3 and 4.0 specifications at opengl.org, the core profiles still mention this approach. 2: Use a typed output array variable for the expected type. In this case, I think it would be something like this: out vec3 [3] output; void main() { output[0] = WorldPos0; output[1] = texture(gColorMap, TexCoord0).xyz; output[2] = CalcBumpedNormal(); } So which is then the recommended approach? Is there a recommended approach at all if I plan to code on top of OpenGL 3.3? Thanks for your time and help!

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• What Java class should I use to represent a Vector?

  - by user8363

  Does Java have a built-in Vector class suitable for handling collision detection / response? It should have methods like subtract(Vector v), normalize(), dotProduct(Vector v), ... It seems logical to use java.awt.Rectangle and java.awt.Polygon to calculate collisions. Would I be right to use these classes for this purpose? I understand collision detection; I'm only wondering what approach to it is idiomatic in Java. I'm new to the language and to application development in general.

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• Client Side Prediction for a Look Vector

  - by Mike Sawayda

  So I am making a first person networked shooter. I am working on client-side prediction where I am predicting player position and look vectors client-side based on input messages received from the server. Right now I am only worried about the look vectors though. I am receiving the correct look vector from the server about 20 times per second and I am checking that against the look vector that I have client side. I want to interpolate the clients look vector towards the correct one that is server side over a period of time. Therefore no matter how far you are away from the servers look vector you will interpolate to it over the same amount of time. Ex. if you were 10 degrees off it would take the same amount of time as if you were 2 degrees off to be correctly lined up with the server copy. My code looks something like this but the problem is that the amount that you are changing the clients copy gets infinitesimally small so you will actually never reach the servers copy. This is because I am always calculating the difference and only moving by a percentage of that every frame. Does anyone have any suggestions on how to interpolate towards the servers copy correctly? if(rotationDiffY > ClientSideAttributes::minRotation) { if(serverRotY > clientRotY) { playerObjects[i]->collisionObject->rotation.y += (rotationDiffY * deltaTime); } else { playerObjects[i]->collisionObject->rotation.y -= (rotationDiffY deltaTime); } }

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• StringBuffer behavior in LWJGL

  - by Michael Oberlin

  Okay, I've been programming in Java for about ten years, but am entirely new to LWJGL. I have a specific problem whilst attempting to create a text console. I have built a class meant to abstract input polling to it, which (in theory) captures key presses from the Keyboard object and appends them to a StringBuilder/StringBuffer, then retrieves the completed string after receiving the ENTER key. The problem is, after I trigger the String return (currently with ESCAPE), and attempt to print it to System.out, I consistently get a blank line. I can get an appropriate string length, and I can even sample a single character out of it and get complete accuracy, but it never prints the actual string. I could swear that LWJGL slipped some kind of thread-safety trick in while I wasn't looking. Here's my code: static volatile StringBuffer command = new StringBuffer(); @Override public void chain(InputPoller poller) { this.chain = poller; } @Override public synchronized void poll() { //basic testing for modifier keys, to be used later on boolean shift = false, alt = false, control = false, superkey = false; if(Keyboard.isKeyDown(Keyboard.KEY_LSHIFT) || Keyboard.isKeyDown(Keyboard.KEY_RSHIFT)) shift = true; if(Keyboard.isKeyDown(Keyboard.KEY_LMENU) || Keyboard.isKeyDown(Keyboard.KEY_RMENU)) alt = true; if(Keyboard.isKeyDown(Keyboard.KEY_LCONTROL) || Keyboard.isKeyDown(Keyboard.KEY_RCONTROL)) control = true; if(Keyboard.isKeyDown(Keyboard.KEY_LMETA) || Keyboard.isKeyDown(Keyboard.KEY_RMETA)) superkey = true; while(Keyboard.next()) if(Keyboard.getEventKeyState()) { command.append(Keyboard.getEventCharacter()); } if (Framework.isConsoleEnabled() && Keyboard.isKeyDown(Keyboard.KEY_ESCAPE)) { System.out.println("Escape down"); System.out.println(command.length() + " characters polled"); //works System.out.println(command.toString().length()); //works System.out.println(command.toString().charAt(4)); //works System.out.println(command.toString().toCharArray()); //blank line! System.out.println(command.toString()); //blank line! Framework.disableConsole(); } //TODO: Add command construction and console management after that } } Maybe the answer's obvious and I'm just feeling tired, but I need to walk away from this for a while. If anyone sees the issue, please let me know. This machine is running the latest release of Java 7 on Ubuntu 12.04, Mate desktop environment. Many thanks.

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• ScissorStack LIBGDX example?

  - by user36531

  I cant find a good resource/tutorial on how to do this. I would appreciate it if someone could provide a scissorstack example from an entity class. ie. using scissorstack on PlayerClass such that the map renders around the Player sprite, say 5 tiles. which would then allow me to create a Pawn class and apply same methodology to give a pawn sprite a lower number, like only rendering 1 tile around the location of the pawn.

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• Java 2D World question

  - by Munkybunky

  I have a 2D world background made up of a Grid of graphics, which I display on screen with a viewport (800x600) and it all works. My question is I have the following code to convert the mouse co-ordinates to world co-ordinates then World co-ordinates to grid co-ordinates then grid co-ordinates to screen co-ordinates. //Add camerax to mouse screen co-ords to convert to world co-ords. int cursorx_world=(int)camerax+(int)GameInput.mousex; int cursorx_grid=(int)cursorx_world/blocksize; // World Co-ords / gridsize give grid co-ords int cursorx_screen=-(int)camerax+(cursorx_grid*blocksize); So is there anyway I can convert straight from mouse screen co-ords to screen co-ordinates?

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