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Search found 10 results on 1 pages for 'dreta'.

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• Shader inputs in a general purpose engine

  - by dreta

  I'm not familiar with SDKs like Unity or UDK that much, so i can't check this offhand. Do general purpose engines allow users to create custom uniform variables? The way i see it, and the way i have implemented it in an engine i'm writing to learn 3D, is that there is a "set" of uniforms provided by the engine and if you want to write a custom shader then you utilize uniforms you need to create a wanted effect. Now, the thing is, first of all i'm not an artist, second of all, i didn't have a chance to create complex scenes yet. So my question is, is it common practice to define variables that the engine provides and only allow the user to work with what they're given? Allowing users to add custom programs and use them where they want is not hard, but i have issues imagining how you'd go about doing the same for uniforms.

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• Decal implementation

  - by dreta

  I had issues finding information about decals, so maybe this question will help others. The implementation is for a forward renderer. Could somebody confirm if i got decal implementation right? You define a cube of any dimension that'll define the projection volume in common space. You check for triangle intersection with the defined cube to recieve triangles that the projection will affect. You clip these triangles and save them. You then use matrix tricks to calculate UV coordinates for the saved triangles that'll reference the texture you're projecting. To do this you take the vectors representing height, width and depth of the cube in common space, so that f.e. the bottom left corner is the origin. You put that in a matrix as the i, j, k unit vectors, set the translation for the cube, then you inverse this matrix. You multiply the vertices of the saved triangles by this matrix, that way you get their coordinates inside of a 0 to 1 size cube that you use as the UV coordinates. This way you have the original triangles you're projecting onto and you have UV coordinates for them (the UV coordinates are referencing the texture you're projecting). Then you rerender the saved triangles onto the scene and they overwrite the area of projection with the projected image. Now the questions that i couldn't find answers for. Is the last point right? I've never done software clipping, but it seems error prone enough, due to limited precision, that the'll be some z fighting occuring for the projected texture. Also is the way of getting UV coordinates correct?

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• Why did the old 3D games have "jittery" graphics?

  - by dreta

  I've been playing MediEvil lately and it got me wondering, what causes some of the old 3D games have "flowing" graphics when moving? It's present in games like Final Fantasy VII, MediEvil, i remember Dungeon Keeper 2 having the same thing in zoom mode, however f.e. Quake 2 didn't have this "issue" and it's just as old. The resolution doesn't seem to be the problem, everything is rendered perfectly fine when you stand still. So is the game refreshing slowly or it's something to do with buffering?

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• Collision detection in 3D space

  - by dreta

  I've got to write, what can be summed up as, a compelte 3D game from scratch this semester. Up untill now i have only programmed 2D games in my spare time, the transition doesn't seem tough, the game's simple. The only issue i have is collision detection. The only thing i could find was AABB, bounding spheres or recommendations of various physics engines. I have to program a submarine that's going to be moving freely inside of a cave system, AFAIK i can't use physics libraries, so none of the above solves my problem. Up untill now i was using SAT for my collision detection. Are there any similar, great algorithms, but crafted for 3D collision? I'm not talking about octrees, or other optimalizations, i'm talking about direct collision detection of one set of 3D polygons with annother set of 3D polygons. I thought about using SAT twice, project the mesh from the top and the side, but then it seems so hard to even divide 3D space into convex shapes. Also that seems like far too much computation even with octrees. How do proffessionals do it? Could somebody shed some light.

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• Game programming basics under Windows

  - by dreta

  I've been trying to learn some Windows programming using the Win32 API. Now, i'm used to working with the OS layer being abstracted away, mostly thanks to libraries like SFML or Allegro. Could you guys help me out and tell me if i'm thinking right here. The place for my gameloop is where i'm reading the messages? while (TRUE) { if (PeekMessage (&msg, NULL, 0, 0, PM_REMOVE)) { if (msg.message == WM_QUIT) break ; TranslateMessage (&msg) ; DispatchMessage (&msg) ; } else { //my game loop goes here } } Now the slightly bigger issue, that is, drawing. Do i run my drawing where i normaly do it, inside the game loop after the game logic? Or do i do it when WM_PAIN is being called and just call InvalidateRect (hwnd, NULL, TRUE); when i want to draw? This does feel weird, the WM_PAINT is a queued message, so i don't know for sure when it'll be called. So if i wanted to avoid this, do i just get the device handle inside the game loop and only ValidateRect (hwnd, NULL); in the WM_PAINT case (beside the ValidateRect (hwnd, NULL); called after drawing in the game loop)? Actually, now that i think about it, do i even need WM_PAINT in this situation or can i skip it and let DefWindowProc handle it (does it validate the screen if WM_PAINT isn't processed)? If this is any important, i'm setting up my code for OpenGL.

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• Sorting objects before rendering

  - by dreta

  I'm trying to implement a scene graph and in all the articles i've come across there is talk about object sorting. So you'd sort your objects by "material" for example. Now untill i sat down and started implementing it, i kind of took this for granted, because it made sense. But now i'm wondering what does sorting actually change? In my engine, i have a manager for UBOs, i use those to store data that'll be shared between programs, at the moment that only involves time, camera and projection matrices and lights (i'm not worrying about managing which lights affect which objects ATM). Now for each model i have to change the model to world matrix uniform, no sorting is going to change that. So is the jump from changing this matrix to also setting a material for each object that bad? I vaguely remember reading somewhere that each time you change something in the pipeline, it has to get flushed and that can cause performance issues. But for each drawing call i'm setting up a model to world matrix anyway, so what sense does it make to ever be concerned about this? BTW is there any information about whether changing a uniform and calling glBufferSubData is more (or less) expensive.

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• Shader inputs in a general purpouse engine

  - by dreta

  I'm not familiar with SDKs like Unity or UDK that much, so i can't check this off hand. Do general purpouse engines allow users to create custom uniform variables? The way i see it, and the way i have implemented it in an engine i'm writing to learn 3D, is that there is a "set" of uniforms provided by the engine and if you want to write a custom shader then you utilize uniforms you need to create a wanted effect. Now, the thing is, first of all i'm not an artist, second of all, i didn't have a chance to create complex scenes yet. So my question is, is it common practice to define variables that the engine provides and only allow the user to work with what they're given? Allowing users to add custom programs and use them where they want is not hard, but i have issues imagining how you'd go about doing the same for uniforms.

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• Shader compile log depending on hardware

  - by dreta

  I'm done with the core of my graphics engine and I'm testing it on every platform I can get my hands on. Now, what I noticed is that different drivers return different shader and program compile log content. For example, on my friend's laptop if you successfuly compile a shader then the log is simply empty. However on my PC I get some useful information along with it. So if I compile a vertex shader, I'll get: Vertex shader was successfully compiled to run on hardware. Which isn't that impressive, but is what happens when I compile a program. On my friend's computer the log is empty, since the program compiles. However on my own computer I get: Vertex shader(s) linked, fragment shader(s) linked. Which is awesome, because I'm attaching a geometry shader with 0 (I have a geometry shader file with trash, so it doesn't compile and the pointer is set to 0), and the compiler just tells me which shaders linked. Now it got me thinking, if I was going to buy a graphics card, is there a way for me to get the information about whether or not I'll get this "extended" compile information? Maybe it's vendor specific? Now I don't expect an answer TBH, this seems a bit obscure, but maybe somebody has any experience with this and could post it.

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• Determining whether two fast moving objects should be submitted for a collision check

  - by dreta

  I have a basic 2D physics engine running. It's pretty much a particle engine, just uses basic shapes like AABBs and circles, so no rotation is possible. I have CCD implemented that can give accurate TOI for two fast moving objects and everything is working smoothly. My issue now is that i can't figure out how to determine whether two fast moving objects should even be checked against each other in the first place. I'm using a quad tree for spacial partitioning and for each fast moving object, i check it against objects in each cell that it passes. This works fine for determining collision with static geometry, but it means that any other fast moving object that could collide with it, but isn't in any of the cells that are checked, is never considered. The only solution to this i can think of is to either have the cells large enough and cross fingers that this is enough, or to implement some sort of a brute force algorithm. Is there a proper way of dealing with this, maybe somebody solved this issue in an efficient manner. Or maybe there's a better way of partitioning space that accounts for this?

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• Starting out with OpenGL when most tutorials are out of date

  - by AUTO

  I'm sure there are already a bunch of questions like this asked, but the constant updating of the OpenGL library throws them all away, and in a month or two, the answers here will be worthless again. I am ready to start programming in OpenGL using C++. I've got a working compiler (DevCpp; do NOT ask me to switch to VC++, and don't ask me why). Now I'm just looking for a solid tutorial on how to program with OpenGL. My assistant found the tutorial provided by NeHe Productions, but as I've come to find out, it's WAY OUT OF DATE! (although I did pull together a basic window to support an OpenGL canvas) Then I went online, and found the OpenGL SuperBible, which apparently uses freeglut? But what I'd like to know is whether or not SuperBible 5th edition is up to date any longer. The suggestion to freeglut I found said the latest version was 2.6.0 but now it's 2.8.0! Is the OpenGL SuperBible still a good, and fairly up-to-date place to start? Is there a better place to go to learn OpenGL? Am I allowed to simply store freeglut in the DevCpp include directory (maybe in GL), or is there some important procedure? Are there any comments or suggestions that I didn't think to ask since I'm only just beginning? @dreta cleared some things up for me, so now I have a better idea of what to ask: I think I'd like to start out with OpenGL using a wrapper library instead of directly accessing OpenGL.I just think that, for a beginner, it would be easier for me to program and get good results, while I don't yet have to understand all the grimy details (as @stephelton mentioned). The problem is, I can't find any library that doesn't have undefined references to no longer supported functions. Freeglut sounds operational, but it still uses GLU.Does anyone know what I can do?Also, I tried compiling the first SuperBible's source, but I got errors since GLAPI is not being defined as a type, the error originating in the GLU library. I'd like to use the SuperBible, but I don't know how to fix this.

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