CODEWITHSUNDEEP
openglframebuffer
Dan
Dan

Reputation: 13210

Clearing FBO doesn't clear everything

I have code which is the equivalent of the following:

init code:

glCullFace(GL_FRONT_AND_BACK);
glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LESS);
//clear to pink
glClearColor(1.0f, 0.0f, 1.0f, 0.0f);

GLuint textureObject;
glGenTextures(1, &textureObject);
glBindTexture(GL_TEXTURE_2D, textureObject);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_BASE_LEVEL, 0);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 0);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 512, 512, 0, GL_RGBA,
    GL_UNSIGNED_BTYE, NULL);

GLuint fbo;
glGenFramebuffers(1, &fbo);
glBindFramebuffer(GL_FRAMEBUFFER, fbo);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D,
    textureObject, 0);
glReadBuffer(GL_COLOR_ATTACHMENT0);
glDrawBuffer(GL_COLOR_ATTACHMENT0);
assert(glCheckFramebufferStatus(GL_DRAW_FRAMEBUFFER)
    == GL_FRAMEBUFFER_COMPLETE);

Object obj = CreateAFullscreenQuad(textureObject);

draw code:

glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fbo);
glViewport(0, 0, 512, 512);
//clear to cyan
GLfloat clear[] = {0, 1, 1, 1};
glClearBufferfv(GL_COLOR, 0, clear);
SetUpPerspectiveAndCameraMatrix();
DrawSomeStuff();

glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
glViewport(0, 0, window.width, window.height);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
SetUpPerspectiveAndCameraMatrix();
obj.Draw();
SwapBuffers();

glxinfo excerpt:

OpenGL vendor string: VMware, Inc.
OpenGL renderer string: Gallium 0.4 on llvmpipe (LLVM 3.4, 128 bits)
OpenGL version string: 2.1 Mesa 10.1.3

The problem is that the call to glClearBufferfv doesn't seem to clear the whole buffer. As you can see, it clears the triangular shape, but it doesn't touch the other areas. They are also not the glClearColor color (pink). If I use the regular glClear call, it does the same thing, but pink instead of cyan.

Clear problem

Upvotes: 1

Views: 1204

Answers (1)

Dan
Dan

Reputation: 13210

Turns out I created a feedback loop by drawing the fullscreen quad while the FBO was bound, drawing the contents of the buffer to itself. Apparently the effects of this end up being interspersed with the effects of glClear.

Upvotes: 2

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