Using glTexImage2D to render to texture, blank result. (Dreamcast GLdc) - opengl

Question

I am trying to create a quick render to texture example using GLdc, a OpenGL implementation for the Sega Dreamcast. I have verified that both my Texture and Framebuffer Object are complete, yet the texture resulting from the framebuffer only has 1 white dot in it.
First, I generate an empty texture and prepare it to be written to.
func genTextures(){
glGenTextures(1, &renderedTexture[0]);
glBindTexture(GL_TEXTURE_2D, renderedTexture[0]);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR); // scale linearly when image smaller than texture
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 128, 128, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);
}
Next, I generate an FBO and bind the new texture we just created to it.
func genFBO() {
glGenFramebuffersEXT(1, &fbo);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo);
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT,
GL_TEXTURE_2D, renderedTexture[0], 0);
}
At this point the FBO and the Texture should both be considered complete. The main loop is structured something like this:
int main(int argc, char **argv)
{
glKosInit();
InitGL(640, 480);
ReSizeGLScene(640, 480);
genTextures();
genFBO();
while(1) {
if(check_start())
break;
// I checked here for FBO and Texture completeness, both return True.
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo); // bind to the FBO
DrawGLScene(); // Draw our cube to the FBO
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0); // back to default
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
ReSizeGLScene(640,480);
DrawGLUI(); //Draw the quad with the framebuffers texture
}
return 0;
}
Here are the two functions that draw geometry:
void DrawGLScene()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);// Clear The Screen And The Depth Buffer
glLoadIdentity(); // Reset The View
glTranslatef(0.0f,0.0f,-5.0f); // move 5 units into the screen.
glRotatef(xrot,1.0f,0.0f,0.0f); // Rotate On The X Axis
glRotatef(yrot,0.0f,1.0f,0.0f); // Rotate On The Y Axis
glRotatef(zrot,0.0f,0.0f,1.0f); // Rotate On The Z Axis
glBindTexture(GL_TEXTURE_2D, texture[0]); // choose the texture to use.
glBegin(GL_QUADS); // begin drawing a cube
// Draw my textured cube, works fine.
glEnd(); // done with the polygon.
xrot+=1.5f; // X Axis Rotation
yrot+=1.5f; // Y Axis Rotation
zrot+=1.5f; // Z Axis Rotation
glKosSwapBuffers();
}
void DrawGLUI(){
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glClearColor(0.0f, 0.0f, 0.0f, 0.0f); // This Will Clear The Background Color To Black
glClearDepth(1.0); // Enables Clearing Of The Depth Buffer
glLoadIdentity();
glMatrixMode(GL_PROJECTION);
glDisable(GL_DEPTH_TEST);
glEnable(GL_TEXTURE_2D);
glLoadIdentity();
glBindTexture(GL_TEXTURE_2D, renderedTexture[0]);
glBegin(GL_QUADS);
//glColor3f(1.0f, 0.0f, 0.0);
glTexCoord2f(0.0, 0.0); glVertex2f(0.0, 0.0);
glTexCoord2f(1.0, 0.0); glVertex2f(1.0, 0.0);
glTexCoord2f(1.0, 1.0); glVertex2f(1.0, 1.0);
glTexCoord2f(0.0, 1.0); glVertex2f(0.0, 1.0);
glEnd();
glEnable(GL_DEPTH_TEST);
ReSizeGLScene(640,480);
glFlush();
}
The result is
Where I would like to have the cube rendered to a texture then that texture applied to the quad in the upper right corner...

Answer 1

The size of the viewport must be adjusted to the size of the framebuffer with glViewport when the framebuffer is switched:
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo);
glViewport(0, 0, 128, 128);
// [...]
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
glViewport(0, 0, 640, 480);
// [...]