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carmellose

OpenGL render to texture and glClearColor problem

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hi guys, i managed to do a simple render to texture of a series of cubes. I believed it worked, but when i tryed to change the background color of the texture i saw it does not. Actually, i try to set the bg color to green in the texture, but it has absolutly no effect. here's my code (the relevant parts) :
void DrawObject(void) {

	int i;
	float z=3;
	/*
	 * The texture defined in a FBO carries its own
	 * viewport. So here we define the viewport and
	 * initilizations that needs to come with it.
	 */
	glPushAttrib(GL_VIEWPORT_BIT);
	

	glDisable(GL_TEXTURE_2D);
	glEnable(GL_DEPTH_TEST);

        // ===> HEre i tryed to set the background to green .... no effect at all ?!?!??
 	glClearColor(0,1,0,1);
	/*
	 * draw objects here
	 */ 
	glMatrixMode(GL_PROJECTION);
	glPushMatrix();
	glLoadIdentity();

	gluPerspective(60,SX/(float)SY,z-.1f,100);

	glMatrixMode(GL_MODELVIEW); 

	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	glPushMatrix();

	glLoadIdentity();

	glTranslatef(3,0,-3);
	glRotatef(30,0,1,0);

#define NOBJECTS (6)
	for (i=0;i<NOBJECTS;++i) {

		glTranslatef(0,0,-z);

		glBegin(GL_QUADS);				
		glColor3f(0.0f,1.0f,0.0f);			
		glVertex3f( 1.0f, 1.0f,-1.0f);			
		glVertex3f(-1.0f, 1.0f,-1.0f);		
		glVertex3f(-1.0f, 1.0f, 1.0f);	
		glVertex3f( 1.0f, 1.0f, 1.0f);

		//etc for the rest of the faces ...
                // ...
                // ...

		glEnd();	
	}
#undef NOBJECTS
	
	//revert to previous modelview matrix
	glPopMatrix();
	//revert to previous projection matrix
	glMatrixMode(GL_PROJECTION); 
	glPopMatrix();
	//switch back to the modelview 
	glMatrixMode(GL_MODELVIEW);
	//
	glPopAttrib();

}


void RenderToTexture (void) {


        //FBO initialization ...
        // ...
        // ...

	/***************************************
	 * 	Render To Texture 
	 ***************************************/
	// (draw something here, rendering to texture)
	glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, myFBO);
	glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, myDBO);
	DrawObject();  
		
	//Bind 0, which means render to back buffer
	glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
	glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, 0);

}

/*
 * main routine to display openGL scene
 * */
void DrawGLScene(void) {

	RenderToTexture(); 

	/* Draw the scene as a texture */

	glEnable(GL_TEXTURE_2D);
	glBindTexture(GL_TEXTURE_2D, TEX_SCENE_SOURCE_IMAGE);

	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
	
	glBegin(GL_QUADS);
	glTexCoord3f (0, 0, -1);
	glVertex3f	 (-1,1 , -1);
	glTexCoord3f (1, 0, -1);
	glVertex3f	 (1, 1, -1);
	glTexCoord3f (1, 1, -1);
	glVertex3f	 (1, -1, -1);
	glTexCoord3f (0, 1, -1);
	glVertex3f	 (-1, -1, -1);
	glEnd();

	glutSwapBuffers();
	return;	
}

/*
 * Init the GL runtime
 * */
bool GLInit(void) {	

	glViewport(0,0,SX,SY);

	glPixelStorei(GL_UNPACK_ALIGNMENT, 1); /* Tightly packed texture data. */
	glEnable(GL_DEPTH_TEST);
	glDepthFunc(GL_LEQUAL);

	glClearColor(0, 1, 0, 0);  
	glClearDepth(1.0f);	
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

	return true;
}




what did i do wrong ? i don't get it! thanks in advance if anyone has ideas cheers

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The problem you're facing is quite simple. You don't render anything when clear the buffer. If you want a green background, disable depth testing, then render a single quad that will fill the entire screen, and that will render the green background you're looking for.

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Quote:
Original post by Gorax
The problem you're facing is quite simple. You don't render anything when clear the buffer. If you want a green background, disable depth testing, then render a single quad that will fill the entire screen, and that will render the green background you're looking for.


hello,
does that mean i can't use glClearColor/glClear when rendering to a texture ??!?

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