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OpenGL: Trouble with Render to Texture & Framebuffer Object

Asked 2010-11-24T08:32:01.243
15

I'd like to render a scene to an initially empty texture. To do so, I use a Framebuffer Object to which I attach an empty 2d texture and a depth buffer. After the set up, as for testing, I draw a simple quad into the scene. Every vertex has a different color, so I eventually expect a color-interpolated quad in the texture. I then use that texture containing the quad and map it on another quad. So evetually, I have a quad in my default Framebuffer which has a texture containing a colored quad. I hope this is not too confusing...

Anyway, I must be missing something here, since what I get is nothing but a grey texture. I basically followed this instructions which are pretty straight forward. However, I cannot quite figure out what I am missing here. I would be grateful if somebody could give me a clue.

Thanks Walter

This is the code I have so far: // create frame buffer object glGenFramebuffers(1, &frameBufferObject);

// create depth buffer
glGenRenderbuffers(1, &depthAttachment);

// create empty texture
int width = 512;
int height = 512;
int numberOfChannels = 3;
GLuint internalFormat = GL_RGB;
GLuint format = GL_RGB;

unsigned char* texels = new unsigned char[width * height * numberOfChannels];

glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

glTexImage2D(GL_TEXTURE_2D, 0, internalFormat, width, height, 0, format, GL_UNSIGNED_BYTE, texels);

glGenerateMipmap(GL_TEXTURE_2D);

delete[] texels;
texels = NULL;

// activate & bind empty texture
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, texture);

// attach empty texture to
opengl rendering render texture-mapping framebuffer
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1 Answer

5

I resolved this issue.

So here is what I do. Maybe there is some better / smarter way to do it, but it works perfectly fine now. Feel free to suggest adaptions...

I don't list the error handling beneath. You can find that further up in this question.

// create frame buffer object
glGenFramebuffers(1, frameBufferObject);

// create empty texture
int width = 512;
int height = 512;
int numberOfChannels = 3;
GLuint internalFormat = GL_RGB8;
GLuint format = GL_RGB;

unsigned char* texels = new unsigned char[width * height * numberOfChannels];

glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

glTexImage2D(GL_TEXTURE_2D, 0, internalFormat, width, height, 0, format, GL_UNSIGNED_BYTE, texels);

delete[] texels;
texels = NULL;

// draw the colored quad into the initially empty texture
glDisable(GL_CULL_FACE);
glDisable(GL_DEPTH_TEST);

// store attibutes
glPushAttrib(GL_VIEWPORT_BIT | GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

// reset viewport
glViewport(0, 0, width, height);

// setup modelview matrix
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glLoadIdentity();

// setup projection matrix
glMatrixMode(GL_PROJECTION);
glPushMatrix();
glLoadIdentity();

// setup orthogonal projection
glOrtho(-width / 2, width / 2, -height / 2, height / 2, 0, 1000);

// bind framebuffer object
glBindFramebuffer(GL_FRAMEBUFFER, frameBufferObject);

// attach empty texture to framebuffer object
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture, 0);

// check framebuffer status (see above)

// bind framebuffer object (IMPORTANT! bind before adding color attachments!)
glBindFramebuffer(GL_FRAMEBUFFER, frameBufferObject);

// define render targets
answered 2010-12-03T05:25:47.063

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