rendering framebuffer texture not working
Post: #1
I have read numerous articles/tutorials online regarding drawing a texture to a framebuffer in opengl, but I am having no luck getting it to work. I am creating a framebuffer, drawing a texture to the fbo, and then drawing the fbo texture to the screen but nothing displays (just a black screen). I am at a loss. If i comment out the fbo code and draw the embedded texture directly to the screen, that works. Is there some iphone specific logic that i am missing (independent of opengl)? Here is my code:
Code:
// INITIALIZATION
glEnable(GL_TEXTURE_2D);
glEnable(GL_BLEND);
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
// Load Test Texture
glGenTextures(1, &textureTest);
glBindTexture(GL_TEXTURE_2D, textureTest); // Bind Our Texture
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); // Linear Filtered
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); // Linear Filtered
[self loadTexture: @"texture"]; // calls glTexImage2D with image data from png
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glViewport(0,0, 320.0f,480.0f);
glOrthof(0,320.0f, 480.0f,0, -1.0f, 1.0f); // left, right, bottom, top
glMatrixMode(GL_MODELVIEW);
//FBO Setup
glGenTextures(1, &textureFBO); // texture handle
glBindTexture(GL_TEXTURE_2D, textureFBO); //bind it.
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 512, 512, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); // Linear Filtered
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); // Linear Filtered
glGenFramebuffersOES(1, &FBO); // frame buffer
glBindFramebufferOES(GL_FRAMEBUFFER_OES, FBO); //bind the frame buffer
// attach texture to framebuffer color buffer
glFramebufferTexture2DOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_TEXTURE_2D, textureFBO, 0);
if(glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES) != GL_FRAMEBUFFER_COMPLETE_OES) printf("CANNOT CREATE FRAMEBUFFER\n");
// MAIN DRAWING LOOP
static const Vertex3D vertices[] = {
{ 0.0, 100.0, 0.0},
{ 100.0, 100.0, 0.0},
{ 0.0, 200.0, 0.0},
{ 100.0, 200.0, 0.0}
};
static const GLfloat texCoords[] = {
0.0, 1.0,
1.0, 1.0,
0.0, 0.0,
1.0, 0.0
};
glClear(GL_COLOR_BUFFER_BIT);
glLoadIdentity();
// Render to texture
glBindFramebufferOES(GL_FRAMEBUFFER_OES, FBO);
// Draw test texture
glBindTexture(GL_TEXTURE_2D, textureTest);
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glVertexPointer(3, GL_FLOAT, 0, vertices);
glTexCoordPointer(2, GL_FLOAT, 0, texCoords);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glBindTexture(GL_TEXTURE_2D, 0); //disable any bound textures.
// End draw test texture
// Render to screen
glBindFramebufferOES(GL_FRAMEBUFFER_OES, 0);
// Draw FBO texture
glBindTexture(GL_TEXTURE_2D, textureFBO);
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glVertexPointer(3, GL_FLOAT, 0, vertices);
glTexCoordPointer(2, GL_FLOAT, 0, texCoords);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glBindTexture(GL_TEXTURE_2D, 0); //disable any bound textures.
// End draw FBO texture
Post: #3
This is your problem:
On the iPhone, there is no "window". The EAGLLayer is also using an FBO, and that FBO's id is not zero. So you need to bind back to whatever that id is to see the results on-screen.
If you look at the iPhone ImageProcessing sample, you'll see that:
1) The EAGLView's -initWithCoder: gens the "system framebuffer". The other view-related functions like -reshapeFramebuffer only reallocate the storage for renderbuffers; the FBO id is only created once, so it is constant for the life of the view.
2) initGL() in the underlying Imaging.c remembers the "display framebuffer" by querying it with GL_FRAMEBUFFER_BINDING_OES. This id is rebound when results need to be rendered on-screen.
You can communicate the "system framebuffer" id any way you like-- this sample is split into ObjC and vanilla C portions, so querying it from GL is simplest.
Code:
glBindFramebufferOES(GL_FRAMEBUFFER_OES, 0);On the iPhone, there is no "window". The EAGLLayer is also using an FBO, and that FBO's id is not zero. So you need to bind back to whatever that id is to see the results on-screen.
If you look at the iPhone ImageProcessing sample, you'll see that:
1) The EAGLView's -initWithCoder: gens the "system framebuffer". The other view-related functions like -reshapeFramebuffer only reallocate the storage for renderbuffers; the FBO id is only created once, so it is constant for the life of the view.
2) initGL() in the underlying Imaging.c remembers the "display framebuffer" by querying it with GL_FRAMEBUFFER_BINDING_OES. This id is rebound when results need to be rendered on-screen.
You can communicate the "system framebuffer" id any way you like-- this sample is split into ObjC and vanilla C portions, so querying it from GL is simplest.
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