I am working with the following architecture:
- OpenGL ES 2 on iOS
- Two EAGL contexts with the same ShareGroup
- Two threads (server, client = main thread); the server renders stuff to textures, the client displays the textures using simple textured quads.
Additional detail to the server thread (working code)
An fbo is created during initialization:
void init(void) {
glGenFramebuffer(1, &fbo);
}
The render loop of the server looks roughly like this:
GLuint loop(void) {
glBindFrameBuffer(GL_FRAMEBUFFER, fbo);
glViewport(0,0,width,height);
GLuint tex;
glGenTextures(1, &tex);
glBindTexture(GL_TEXTURE_2D, tex);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, tex, 0);
// Framebuffer completeness check omitted
glClear(GL_COLOR_BUFFER_BIT);
// actual drawing code omitted
// the drawing code bound other textures, so..
glBindTexture(GL_TEXTURE_2D, tex);
glGenerateMipmap(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, GL_NONE);
glFlush();
return tex;
}
All this works fine so far.
New (buggy) code
Now i want to add Multisampling to the server thread, using the GL_APPLE_framebuffer_multisample extension and modified the the initialization code like this:
void init(void) {
glGenFramebuffer(1, &resolve_fbo);
glGenFramebuffers(1, &sample_fbo);
glBindFramebuffer(GL_FRAMEBUFFER, sample_fbo);
glGenRenderbuffers(1, &sample_colorRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, sample_colorRenderbuffer);
glRenderbufferStorageMultisampleAPPLE(GL_RENDERBUFFER, 4, GL_RGBA8_OES, width, height);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, sample_colorRenderbuffer);
// Framebuffer completeness check (sample_fbo) omitted
glBindRenderbuffer(GL_RENDERBUFFER, GL_NONE);
glBindFramebuffer(GL_FRAMEBUFFER, GL_NONE);
}
The main loop has been changed to:
GLuint loop(void) {
glBindFrameBuffer(GL_FRAMEBUFFER, sample_fbo);
glViewport(0,0,width,height);
GLuint tex;
glGenTextures(1, &tex);
glBindTexture(GL_TEXTURE_2D, tex);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);
glClear(GL_COLOR_BUFFER_BIT);
// actual drawing code omitted
glBindFramebuffer(GL_FRAMEBUFFER, resolve_fbo);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, tex, 0);
// Framebuffer completeness check (resolve_fbo) omitted
// resolve multisampling
glBindFramebuffer(GL_DRAW_FRAMEBUFFER_APPLE, resolve_fbo);
glBindFramebuffer(GL_READ_FRAMEBUFFER_APPLE, sample_fbo);
glResolveMultisampleFramebufferAPPLE();
// the drawing code bound other textures, so..
glBindTexture(GL_TEXTURE_2D, tex);
glGenerateMipmap(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, GL_NONE);
glFlush();
return tex;
}
What i see now is that a texture contains data from multiple loop() calls, blended together. I guess I'm either missing an 'unbind' of some sort, or probably a glFinish()
call (I previously had such a problem at a different point, I set texture data with glTexImage2D()
and used it right afterwards - that required a glFinish()
call to force the texture to be updated).
However inserting a glFinish()
after the drawing code didn't change anything here..
Oh nevermind, such a stupid mistake. I omitted the detail that the loop() method actually contains a for loop and renders multiple textures, the mistake was that i bound the sample fbo only before this loop, so after the first run the resolve fbo was bound..
Moving the fbo binding inside the loop fixed the problem.
Anyway, thanks @ all the readers and sorry for wasting your time :)