How to udpate the depth buffer without using glCopyPixels()

[Judie]

I am able to create a texture from the framebuffer and draw a quad as
my background with this texture instead of redrawing my background
each time.

I am able to save the depth buffer information and copy it back to the
depth buffer using glDrawPixels() and then I can render on top of the
background and if part of an object should be overlapped by the
background, it is not drawn as expected.

But what i really want is to be able to use the saved depth buffer as
a texture and apply it to my background quad and have it write to the
depth buffer so that I don't need to use the glDrawPixels(). It
doesn't seem like

glEnable2D();
glReadPixels(0, 0, Width, Height, GL_DEPTH_COMPONENT,
GL_UNSIGNED_INT, m_DepthBuffer);
glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, Width, Height, 0,
GL_DEPTH_COMPONENT, GL_UNSIGNED_INT, m_DepthBuffer);
glGenTextures(1, &m_DepthBufferTexture);
glBindTexture(GL_TEXTURE_2D, m_DepthBufferTexture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, Width, Height, 0,
GL_DEPTH_COMPONENT, GL_UNSIGNED_INT, m_DepthBuffer);
glDisable2D();

was meant to do this because my rendering algorithm:

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnable2D();
glEnable(GL_TEXTURE_2D);
glColor3f( 1.0f, 1.0f, 1.0f );
glDepthFunc(GL_ALWAYS);

//render the background quad with the color texture

glDepthMask(GL_FALSE);
glBindTexture(GL_TEXTURE_2D, m_BackBufferTexture);
DrawBackgroundQuad();
glDepthMask(GL_TRUE);

//render the background quad with the color texture
glColorMask(0,0,0,0);
glBindTexture(GL_TEXTURE_2D, m_DepthBufferTexture);

DrawBackgroundQuad();
glColorMask(1,1,1,1);
glDepthFunc(GL_LEQUAL);

glDisable(GL_TEXTURE_2D);
glDisable2D();

DrawOtherObjects();

SwapBuffers(mhDC);

Doesn't seem to be putting the correct information into the depth
buffer. I am using OpenGL version 2.0. Has anybody used a texture for
the depth buffer in this way?

Judie

[fungus]

On Jan 16, 5:21 pm, Judie <judie.m.stan...@gmail.com> wrote:
> Has anybody used a texture for the depth buffer in this way?
>

To answer the question: glDrawPixels() is the only way.

But...the general advice is "don't do it".

It's a nice theory but it's almost never faster than just
redrawing the whole scene. Modern graphics cards
store the depth buffer in compressed format so trying
to store/restore it is very inefficient. The background
has to be incredibly complex to make this worth while.

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