I have copied the back buffer with glCopyTexSubImage2D, but whenever I
display a shape with the texture, the intensity of the colours depend upon
the value that has been used for clearing the buffer, so if I clear with

    glClearColor (1.0, 1.0, 0.0, 0.0);

and then draw a triangle using

    glColor3f (1.0, 0.0, 1.0);

The copy the buffer, clear it to black and draw a shape with colour (1.0,
1.0, 1.0); using the texture coordinates, I will get a shape with the
corrext background colour, but the Triangle in the texture will be Red, the
blue value has been lost.  Why does this happen?

Thanks,

Darren

"Darren Guscott" <darren.guscott@nospam.baesystems.com> schrieb im 
Newsbeitrag news:41654e03$1_1@baen1673807.greenlnk.net...
>I have copied the back buffer with glCopyTexSubImage2D, but whenever 
>I
> display a shape with the texture, the intensity of the colours 
> depend upon
> the value that has been used for clearing the buffer, so if I clear 
> with
>
>    glClearColor (1.0, 1.0, 0.0, 0.0);
>
> and then draw a triangle using
>
>    glColor3f (1.0, 0.0, 1.0);
>
> The copy the buffer, clear it to black and draw a shape with colour 
> (1.0,
> 1.0, 1.0); using the texture coordinates, I will get a shape with 
> the
> corrext background colour, but the Triangle in the texture will be 
> Red, the
> blue value has been lost.  Why does this happen?

Send a code snippet starting with glClear anding with glEnd of drawing 
the image you just copied with glCopyTexSubImage2D. It's really hard 
to tell (for me) this way.
I guess you have not really allocated memory correctly or you have set 
the wrong pixel format description when copying sub image... 

Here's the code, it is all in classes but I have just pulled them together
for this snippet.

 wglMakeCurrent(m_hDC, m_hRC);

 // Clear the buffers.
 glClearColor (0.0, 0.0, 1.0, 0.0);    // Clear to BLUE buffer
 glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    // perform OpenGL viewport and generic Initialisaion
    glEnable(GL_TEXTURE_2D);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(-25,25,-20,20,-1,1);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
 glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);


 // Draw a GREEN triangle
 glColor3f (0.0f, 1.0f, 0.0f);
 glBegin (GL_TRIANGLES);
  glVertex2f (10.0f, 10.0f);
  glVertex2f (10.0f, 0.0f);
  glVertex2f (-20.0f, 10.0f);
 glEnd();


 glReadBuffer        (GL_BACK);
 glBindTexture       (GL_TEXTURE_2D, m_Texture);

 if (asd == 0)
 {
  glCopyTexImage2D    (GL_TEXTURE_2D, 0, GL_RGB, 0, 0, 256, 256, 0);
 }
 else
 {
  glCopyTexSubImage2D (GL_TEXTURE_2D, 0, 0, 0, 0, 0, 256, 256);
 }

 if ((x = glGetError()) != GL_NO_ERROR)
 {
  m_strLastError = "OpenGL error copying the back buffer to texture.";
  return false;
 }

    // Clear the buffer.
 glClearColor (1.0, 1.0, 1.0, 0.0);
 glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

 //Texture wrap to quad.
 glColor3f (1.0f, 1.0f, 1.0f);

 glBegin(GL_QUADS);
  glTexCoord2f (0.0f, 0.0f);
  glVertex2f   (0.0f, 0.0f);

  glTexCoord2f (1.0f, 0.0f);
  glVertex2f   (10.0f, 0.0f);

  glTexCoord2f (1.0f, 1.0f);
  glVertex2f   (10.0f, 10.0f);

  glTexCoord2f (0.0f, 1.0f);
  glVertex2f   (0.0f, 10.0f);

 glEnd();

   glFlush();

I now have it down to one function, If I only copy the backbuffer once, I
get the correct result, if I try to capture on every frame, then I get the
problems, this is when I am continually overwriting the same texture.
"Darren Guscott" <darren.guscott@nospam.baesystems.com> wrote in message
news:41654e03$1_1@baen1673807.greenlnk.net...
> I have copied the back buffer with glCopyTexSubImage2D, but whenever I
> display a shape with the texture, the intensity of the colours depend upon
> the value that has been used for clearing the buffer, so if I clear with
>
>     glClearColor (1.0, 1.0, 0.0, 0.0);
>
> and then draw a triangle using
>
>     glColor3f (1.0, 0.0, 1.0);
>
> The copy the buffer, clear it to black and draw a shape with colour (1.0,
> 1.0, 1.0); using the texture coordinates, I will get a shape with the
> corrext background colour, but the Triangle in the texture will be Red,
the
> blue value has been lost.  Why does this happen?
>
> Thanks,
>
> Darren
>
>