[Mesa-dev] Depthbuffer gl_FragDepth / glReadPixels on VMWare

[José Fonseca]

D3D9 API limits the blits to/from depth-stencil buffers as well. The API
is pretty much designed to ensure that depth-stencil buffers stay in
VRAM (probably in a hardware specific layout) and never get out of
there.

Several vendors allow binding the depth buffer as a texture, but they
implicitly do shadow mapping. It might be possible to read the depth
values with certain non-standard depth formats supported by major
vendors. Reading the stencil buffer is pretty much impossible AFAICT.

Jose 

On Tue, 2011-01-25 at 06:04 -0800, stefanb at starnberg-mail.de wrote:
> Hi Jose,
> 
> thanks for the quick reply: I'm using Win7 for both, guest (32bit)
> and host (64bit).
> 
> I do the depth buffer reads only for debugging / regression testing.
> Would a copy depth-to-texture and shader blit to the color channels
> work ? Reading the color back buffer via glReadPixels is ok.
> 
> Regards,
> 
> Stefan
> 
> 
> Zitat von José Fonseca <jfonseca at vmware.com>:
> 
> > On Tue, 2011-01-25 at 01:13 -0800, stefanb at starnberg-mail.de wrote:
> >> Hi,
> >>
> >> i'm trying to get one of our testsuites running in VMWare
> >> (VMware, Inc. Gallium 0.3 on SVGA3D; build: RELEASE; OGL 2.1 Mesa
> >> 7.7.1-DEVEL).
> >> With the GDI backend everything works fine (tested in 7.7,7.8,7.10).
> >>
> >> I have a glsl shader that writes depth like
> >>
> >> void main()
> >> {
> >>    vec4 v = texure2D(tex,gl_TexCoord[0].st);
> >>
> >>    gl_FragColor = vec4(0,0,0,0);
> >>    gl_FragDepth = v.x;
> >> }
> >>
> >> which doesn't work when running in VMWare's Mesa.
> >>
> >> Even a simple clear and readback of the depth buffer doesn't work, like:
> >>   glClearDepth(0.6f);
> >>   glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
> >>   glReadPixels(0,0,m_Dim[0], m_Dim[1], GL_DEPTH_STENCIL_EXT,
> >> GL_UNSIGNED_INT_24_8_EXT, tmpBufferInt);
> >>    or
> >>   glReadPixels(0,0,m_Dim[0], m_Dim[1], GL_DEPTH_COMPONENT, GL_FLOAT,
> >> tmpBuffer);
> >>
> >> Both reads return all zeros.
> >>
> >> I don't know if VMWare's Mesa is a different branch and if this is the right
> >> place to report those bugs (if it is a bug)
> >>
> >> Stefan
> >
> > Stefan,
> >
> > What guest OS and host OS are you using?
> >
> > We can only comment here on the open sourced Linux OpenGL guest drivers.
> >
> > The typical procedure is to file a SR through
> > http://www.vmware.com/support/contacts/ , which ensures the issue will
> > be included in our internal bug database, and then triage and addressed
> > in an eventual release.
> >
> > That said, I can advance that reading the depth-stencil buffer currently
> > doesn't work on Windows hosts due to limitations that D3D9 API imposes
> > on locking depth-stencil buffers. But it should work on Linux/MacOSX
> > hosts.
> >
> > Jose
> >
> >
> >
> 
>