Sign in to follow this  

OpenGL glCopyTexImage2D strange result

Recommended Posts

Hi I am using glCopyTexImage2D to render current game screen to texture and then use it as still background for menu. Everything works fine except that texture is somehow not filled fully, some black parts are shown instead. Here is image to show it better: Image Hosted by Here is the code i use to render it:

//save viewport and set up new one
int viewport[4];

//first let's draw the mainscene to the texture
//and then use that texture 


//clear any rendering made
glMatrixMode( GL_MODELVIEW );

//draw the scene

//and render to texture

	//draws current scene to the texture and use it after
	void RenderToTextureStart()

	void RenderToTextureEnd()

		//save data to texture using glCopyTexImage2D
            //backimage.texID - is the texture we save to
		glBindTexture(GL_TEXTURE_2D,backimage.TextId(0 ));
		glCopyTexImage2D(GL_TEXTURE_2D, 0, GL_RGB,
			0,0, 512, 512, 0);
		//restore viewport
		glViewport( viewport[0],viewport[1],viewport[2],viewport[3]);

	//draws background scene
	void DrawBack()



			  glBindTexture( GL_TEXTURE_2D , backimage.TextId(0 ) );
		      glBegin(GL_QUADS);// Drawing Using Triangles
		          glTexCoord2f(0.0f, 0.0f);          // Top
		          glVertex3f(-0.77f,  -0.578f , 0);      		
	              glTexCoord2f(1.0f, 0.0f);
		          glVertex3f( 0.77f , -0.578f, 0);              // Bottom Left
		          glTexCoord2f(1.0f, 1.0f);
		          glVertex3f( 0.77f,   0.578f, 0);              // Bottom Right

		          glTexCoord2f(0.0f, 1.0f);
		          glVertex3f(-0.77f , 0.578f, 0);              // Bottom Right

Overall I am using SDL , OpenGL and DevIL One more thing is that this only occurs at 640x480 resolution. Higher resolutions work correctly ( 800x600 1024x768 ...) Here is what I get at 320x240. Strange :) Image Hosted by I hope some one can help me out. [Edited by - DMINATOR on May 26, 2005 6:10:25 PM]

Share this post

Link to post
Share on other sites
The buffer you render to is only as large as your window, so when you try to copy to a texture that is larger than this, only part of the texture will be filled.
(In other words, the top part of the texture is black because the window has height 480 and the texture is 512 pixels high.)

You have several options:
* Use a smaller texture
* Use only part of a texture (glCopyTexSubImage2D)
* Use pbuffers
* Render a small part of the texture every time and copy into the same texture (again glCopyTexSubImage2D.)
* and probably a bunch more...

I'd say the simplest would be to either use a texture that is small enough (512x256 for 640x480 window) or use only part of a larger texture (512x512 for 640x480, and render with texture coordinates 0 to 480/512 in y-direction.)

Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this