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

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• How can I write only to the stencil buffer in OpenGL ES 2.0?

  - by stephelton

  I'd like to write to the stencil buffer without incurring the cost of my expensive shaders. As I understand it, I write to the stencil buffer as a 'side effect' of rendering something. In this first pass where I write to the stencil buffer, I don't want to write anything to the color or depth buffer, and I definitely don't want to run through my lighting equations in my shaders. Do I need to create no-op shaders for this (and can I just discard fragments), or is there a better way to do this? As the title says, I'm using OpenGL ES 2.0. I haven't used the stencil buffer before, so if I seem to be misunderstanding something, feel free to be verbose.

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• File format for animated scene

  - by stephelton

  I've got a custom OpenGL based rendering engine and I'd like to add support for cinema-type scene animation. The artist that is helping me uses primarily 3DSMax. I'd like a file format for exporting and importing this data. I'm also in need of a file format for skeletal animation data, which may have an impact here. I've been looking at MAXScript to manually export this stuff, which would buy me the most flexibility, but I have virtually no experience with 3DSMax itself, so I get a little lost when it comes to terminology. So I'd like to know what file formats exist for animated scene data, and whether they are appropriate for my use (my fear is that they will be way too broad for my fairly simple needs.) The way I view animated scene data is basically a bunch of references to [animated] models with keyframe-based matrices describing their orientation over time. And probably some special camera stuff to handle perspective. I might also want some event type stuff for adding/removing objects. Is this a sane concept?

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• How can I unit test rendering output?

  - by stephelton

  I've been embracing Test-Driven Development (TDD) recently and it's had wonderful impacts on my development output and the resiliency of my codebase. I would like to extend this approach to some of the rendering work that I do in OpenGL, but I've been unable to find any good approaches to this. I'll start with a concrete example so we know what kinds of things I want to test; lets say I want to create a unit cube that rotates about some axis, and that I want to ensure that, for some number of frames, each frame is rendered correctly. How can I create an automated test case for this? Preferably, I'd even be able to write a test case before writing any code to render the cube (per usual TDD practices.) Among many other things, I'd want to make sure that the cube's size, location, and orientation are correct in each rendered frame. I may even want to make sure that the lighting equations in my shaders are correct in each frame. The only remotely useful approach to this that I've come across involves comparing rendered output to a reference output, which generally precludes TDD practice, and is very cumbersome. I could go on about other desired requirements, but I'm afraid the ones I've listed already are out of reach.

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• How can I convert an image from raw data in Android without any munging?

  - by stephelton

  I have raw image data (may be png, jpg, ...) and I want it converted in Android without changing its pixel depth (bpp). In particular, when I load a grayscale (8 bpp) image that I want to use as alpha (glTexImage() with GL_ALPHA), it converts it to 16 bpp (presumably 5_6_5). While I do have a plan b (actually, I'm probably on plan 'e' by now, this is really becoming annoying) I would really like to discover an easy way to do this using what is readily available in the api. So far, I'm using BitmapFactory.decodeByteArray(). While I'm at it. I'm doing this from a native environment via jni (passing the buffer in from C, and a new buffer back to C from Java). Any portable solution in C/C++ would be preferable, but I don't want to introduce anything that might break in future versions of Android, etc.

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• Questions before I revamp my rendering engine to use shaders (GLSL)

  - by stephelton

  I've written a fairly robust rendering engine using OpenGL ES 1.1 (fixed-function.) I've been looking into revamping the engine to use OpenGL ES 2.0, which necessitates that I use shaders. I've been absorbing information all day long and still have some questions. Firstly, lighting. The fixed-function pipeline is guaranteed to have at least 8 lights available. My current engine finds lights that are "close" to the primitives being drawn and enables them; I don't know how many lights are going to be enabled until I draw a given model. Nothing is dynamically allocated in GLSL, so I have to define in a shader some number of lights to be used, right? So if I want to stick with 8, should I write my general purpose shader to have 8 lights and then use uniforms to tell it how many / which lights to use? Which brings me to another question: should I be concerned with the amount of data I'm allocating in a shader? Recent video cards have hundreds of "stream processors." If I've got a fragment shader being used on some number of fragments in a given triangle, I assume they must each have their own stack to work on. Are read-only variables copied here, or read when needed? My initial goal is to rework my code so that it is virtually identical to the current implementation. What I have in mind is to create my own matrix stack so that I can implement something along the lines of push/popMatrix and apply all my translations, rotations, and scales to this matrix, then provide the matrix to the vertex shader so that it can make very quick vertex translations. Is this approach sound? Edit: My original intention was to ask if there was a tutorial that would explain the bare minimum necessary to jump from fixed-function to using shaders. Thanks!

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• How does opengl-es 2 assemble primitives?

  - by stephelton

  Two things I'm quite confused about. 1) OpenGL ES 2.0 creates primitives before the vertex shader is invoked. Why, then, does it not automatically provide the vertex shader the position of the vertex? 2) OpenGL ES 2.0 supports glDrawElements(), but it does not support glEnableClientState() or GL_VERTEX_ARRAY, so how can this call possibly be used to construct primitives? NOTE: this is OpenGL ES 2.0, NOT normal OpenGL! Thanks!

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• How can I convert an image from raw data in Android without any munging?

  - by stephelton

  I have raw image data (may be .png, .jpg, ...) and I want it converted in Android without changing its pixel depth (bpp). In particular, when I load a grayscale (8 bpp) image that I want to use as alpha (glTexImage() with GL_ALPHA), it converts it to 16 bpp (presumably 5_6_5). While I do have a plan B (actually, I'm probably on plan 'E' by now, this is really becoming annoying) I would really like to discover an easy way to do this using what is readily available in the API. So far, I'm using BitmapFactory.decodeByteArray(). While I'm at it. I'm doing this from a native environment via JNI (passing the buffer in from C, and a new buffer back to C from Java). Any portable solution in C/C++ would be preferable, but I don't want to introduce anything that might break in future versions of Android, etc.

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• How many achievements should I include, and of what challenge?

  - by stephelton

  I know this question is fairy broad and subjective, but I'm wondering if there's been any published research into what an optimal number of achievements is and what kind of challenge they should present. The game this question directly relates to is a shoot-em-up, but an ideal answer is fairly theoretical. If there are there are too few achievements, or they are not challenging, I would expect they would fail in their goal to keep people playing. If there are too many, or they are unreasonably difficult, I would expect people to quickly give up. I personally witnessed the latter happening in Starcraft 2; a section of the achievements would have you win hundreds of games against their AI opponents (boring!)

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• Phone complains that identical GLSL struct definition differs in vert/frag programs

  - by stephelton

  When I provide the following struct definition in linked frag and vert shaders, my phone (Samsung Vibrant / Android 2.2) complains that the definition differs. struct Light { mediump vec3 _position; lowp vec4 _ambient; lowp vec4 _diffuse; lowp vec4 _specular; bool _isDirectional; mediump vec3 _attenuation; // constant, linear, and quadratic components }; uniform Light u_light; I know the struct is identical because its included from another file. These shaders work on a linux implementation and on my Android 3.0 tablet. Both shaders declare "precision mediump float;" The exact error is: Uniform variable u_light type/precision does not match in vertex and fragment shader Am I doing anything wrong here, or is my phone's implementation broken? Any advice (other than file a bug report?)

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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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