I am learning to use Frame Buffer Objects. For this purpose, I chose to render a triangle to a texture and then map that to a quad.
When I render the triangle, I clear the color to something blue. So, when I render the texture on the quad from fbo, it only renders everything blue, but doesn't show up the triangle. I can't seem to figure out why this is happening. Can someone please help me out with this ?
I'll post the rendering code here, since glCheckFramebufferStatus doesn't complain when I setup the FBO. I've pasted the setup code at the end. Here is my rendering code:
void FrameBufferObject::Render(unsigned int elapsedGameTime)
{
glBindFramebuffer(GL_FRAMEBUFFER, m_FBO);
glClearColor(0.0, 0.6, 0.5, 1);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// adjust viewport and projection matrices to texture dimensions
glPushAttrib(GL_VIEWPORT_BIT);
glViewport(0,0, m_FBOWidth, m_FBOHeight);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, m_FBOWidth, 0, m_FBOHeight, 1.0, 100.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
DrawTriangle();
glPopAttrib();
// setting FrameBuffer back to window-specified Framebuffer
glBindFramebuffer(GL_FRAMEBUFFER, 0); //unbind
// back to normal viewport and projection matrix
//glViewport(0, 0, 1280, 768);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0, 1.33, 1.0, 1000.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glClearColor(0, 0, 0, 0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
render(elapsedGameTime);
}
void FrameBufferObject::DrawTriangle()
{
glPushMatrix();
glBegin(GL_TRIANGLES);
glColor3f(1, 0, 0);
glVertex2d(0, 0);
glVertex2d(m_FBOWidth, 0);
glVertex2d(m_FBOWidth, m_FBOHeight);
glEnd();
glPopMatrix();
}
void FrameBufferObject::render(unsigned int elapsedTime)
{
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, m_TextureID);
glPushMatrix();
glTranslated(0, 0, -20);
glBegin(GL_QUADS);
glColor4f(1, 1, 1, 1);
glTexCoord2f(1, 1); glVertex3f(1,1,1);
glTexCoord2f(0, 1); glVertex3f(-1,1,1);
glTexCoord2f(0, 0); glVertex3f(-1,-1,1);
glTexCoord2f(1, 0); glVertex3f(1,-1,1);
glEnd();
glPopMatrix();
glBindTexture(GL_TEXTURE_2D, 0);
glDisable(GL_TEXTURE_2D);
}
void FrameBufferObject::Initialize()
{
// Generate FBO
glGenFramebuffers(1, &m_FBO);
glBindFramebuffer(GL_FRAMEBUFFER, m_FBO);
// Add depth buffer as a renderbuffer to fbo
// create depth buffer id
glGenRenderbuffers(1, &m_DepthBuffer);
glBindRenderbuffer(GL_RENDERBUFFER, m_DepthBuffer);
// allocate space to render buffer for depth buffer
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, m_FBOWidth, m_FBOHeight);
// attaching renderBuffer to FBO
// attach depth buffer to FBO at depth_attachment
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, m_DepthBuffer);
// Adding a texture to fbo
// Create a texture
glGenTextures(1, &m_TextureID);
glBindTexture(GL_TEXTURE_2D, m_TextureID);
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_RGBA8, m_FBOWidth, m_FBOHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0); // onlly allocating space
glBindTexture(GL_TEXTURE_2D, 0);
// attach texture to FBO
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, m_TextureID, 0);
// Check FBO Status
if( glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
std::cout << "\n Error:: FrameBufferObject::Initialize() :: FBO loading not complete \n";
// switch back to window system Framebuffer
glBindFramebuffer(GL_FRAMEBUFFER, 0);
}
Thanks!
