OpenGL ES 2.0 rendering to multiple textures

Question

I am building an iPad app using OpenGL ES 2.0. What I need to do is render to multiple textures and then render all the textures to view. I draw using GL_POINTS based on the user touch location. My code that I have now is:

Generate frame buffer, textures, and render buffer:

glGenFramebuffers(1, &viewFramebuffer);
glGenRenderbuffers(1, &viewRenderbuffer);
glBindFramebuffer(GL_FRAMEBUFFER, viewFramebuffer);
glBindRenderbuffer(GL_RENDERBUFFER, viewRenderbuffer);

glGenTextures(1, layers);
glBindTexture(GL_TEXTURE_2D, layers[0]);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA,  self.bounds.size.width, self.bounds.size.height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, layers[0], 0);

Draw:

glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
....
glDrawArrays(GL_POINTS, 0, (int)vertexCount);
glBindRenderbuffer(GL_RENDERBUFFER, viewRenderbuffer);
[context presentRenderbuffer:GL_RENDERBUFFER];

The above works OK, however when I want to render to a new texture my application stops drawing any new content. I bind a new texture like this:

glGenTextures(1, &layers[1]);
glBindTexture(GL_TEXTURE_2D, layers[1]);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA,  self.bounds.size.width, self.bounds.size.height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, layers[1], 0);

And then call the drawing method again. My code works when rendering to the first texture but when I try to generate a new texture to render to, the app stops drawing. Can anyone help out?

Most likely has nothing to do with your problem, but is there any reason why you're partly using the extension (OES) version of FBO entry points and definitions? — Reto Koradi
@RetoKoradi Not sure why that was there. I am following tutorial from Apple's GLPaint and that is how it was done. I changed GL_FRAMEBUFFER_OES to GL_FRAMEBUFFER but the problem persists. Any suggestions? — Amendale
Do you check the frame buffer state after you do this new attachment? Also the correct frame buffer must be bound not just the texture before you execute this line (but that most likely already is). Anyway I am not sure you can even do this but if what you did is ok I would expect that both of the textures are attached to the frame buffer so it should draw to both. Anyway Why do you even try to do this, you can simply generate a new frame buffer and attach the texture. As for the render buffer if I remember correctly you do not need it if you have the texture attached.. — Matic Oblak
@MaticOblak What I am trying to achieve is a layered drawing, in which I have control of individual layers. I am following a suggestion offered here. My draw cycle consists of 1) bind textureFrameBuffer 2) attach a texture to textureFrameBuffer 3) draw to texture 4)repeat for different textures 5) bind viewFrameBuffer 6) draw textures to viewFrameBuffer 7) render view from viewFrameBuffer. Do you think this is the wrong approach? — Amendale

Amendale Amendale · Accepted Answer · 2014-09-08T00:52:25

I got my code to work. I had several problems with my frameBuffers not generating correctly and my textures not binding accurately. Lesson learned - always check state of frameBuffer after generation! Here it is:

Setup frameBuffers:

// Generate textureFrameBuffer for handling drawing to textures
glGenFramebuffers(1, &textureFrameBuffer);
glBindFramebuffer(GL_FRAMEBUFFER, textureFrameBuffer);

// Generate renderBufferer for drawing to screen
glGenRenderbuffers(1, &viewRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, viewRenderbuffer);
[context renderbufferStorage:GL_RENDERBUFFER fromDrawable:(id<EAGLDrawable>)self.layer];
glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &backingWidth);
glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_HEIGHT, &backingHeight);

//Generate first texture and bind to textureFrameBuffer
glGenTextures(1, &layers[0]);
glBindTexture(GL_TEXTURE_2D, layers[0]);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA,  backingWidth, backingHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, layers[0], 0);

//check if frameBuffer is OK
if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE){
    NSLog(@"failed to make complete framebuffer objects %x", glCheckFramebufferStatus(GL_FRAMEBUFFER));
    return NO;
}

//Generate viewFrameBuffer for drawing to view
glGenFramebuffers(1, &viewFramebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, viewFramebuffer);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, viewRenderbuffer);

if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
{
    NSLog(@"failed to make complete framebuffer object %x", glCheckFramebufferStatus(GL_FRAMEBUFFER));
}

To draw to first texture:

glBindFramebuffer(GL_FRAMEBUFFER, textureFrameBuffer);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, layers[0], 0);
....
glDrawArrays(GL_POINTS, 0, (int)vertexCount);

To generate and bind second texture:

glGenTextures(1, &layers[1]);
glBindFramebuffer(GL_FRAMEBUFFER, textureFrameBuffer);
glBindTexture(GL_TEXTURE_2D, layers[1]);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA,  backingWidth, backingHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, layers[1], 0);

Draw to second texture:

glBindFramebuffer(GL_FRAMEBUFFER, textureFrameBuffer);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, layers[1], 0);
....
glDrawArrays(GL_POINTS, 0, (int)vertexCount);

To draw all textures to screen:

// Bind view buffer
glBindFramebuffer(GL_FRAMEBUFFER, viewFramebuffer);
//clear screen every frame
glClear(GL_COLOR_BUFFER_BIT);
//bind layer texture
for (int i=0; i<= layerCount; i++) {
    glBindTexture(GL_TEXTURE_2D, layers [i]);
    ....
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
}

[context presentRenderbuffer:viewFramebuffer];

OpenGL ES 2.0 rendering to multiple textures

1 Answers