[Mesa-dev] Depthbuffer gl_FragDepth / glReadPixels on VMWare

[José Fonseca]

Depth-writing shaders should work. Although it is very hard to know
whether they work or not given the depth-buffer can't be read. But it
should be possible to verify by checking the values with depth-testing.
If it doesn't work then sounds like bug.

Jose

On Wed, 2011-01-26 at 02:25 -0800, stefanb at starnberg-mail.de wrote:
> Hi Jose,
> 
> thanks for the info, i got it working now:
> 
> - Instead of reading depth I just render 256 greylevel quads and
>    readback the color buffer (performance is not an issue here,
>    I just need an image that tells me that the depth buffer is ok)
> 
> - The GLSL depth-write shader doesn't work when the texture format
>    is DEPTH_COMPONENT. I've changed it to LUMINANCE16 when running
>    on Mesa/VMWare.
> 
> Again, thanks for the help.
> 
> Stefan
> 
> 
> Zitat von José Fonseca <jfonseca at vmware.com>:
> 
> > 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
> >> >
> >> >
> >> >
> >>
> >>
> >
> >
> >
> >
> 
>