[Mesa-users] Mesa 18.3 swrast

[Brian Paul]

On 01/29/2019 04:20 PM, Michael Saunders wrote:
> We have successfully used Mesa in our visualization product for many 
> years as a great workaround for customers who experience hardware 
> rendering problems as well as for offscreen rendering. We are upgrading 
> to Mesa 18 and ran into rendering issues that I haven't been able to 
> track down online.
> 
> I built Mesa libGL.so.1 on a CentOS 6 platform (we are required to build 
> on the oldest platform that we support) but when used on a number of 
> CentOS 7 platforms we experience rending problems. Some of these target 
> machines have native NVidia drivers installed and others have the 
> default Linux drivers backed by Mesa. Running glxgears using the 
> Mesa libGL.so.1 that I built consistently renders areas colored using 
> glClear or areas rendered using alpha blending allow live window 
> contents from behind the drawing area to bleed through. When I move the 
> GL drawing area around or if the underlying window contents change it 
> changes my OpenGL drawing area that is in the Window above them. Is this 
> a known issue and is there a configuration setting that I need to set to 
> avoid it?
> 
> Options used to build Mesa libGL.so.1:
> ./configure \
>      --with-gallium-drivers=swrast \
>      --with-platforms=x11 \
>      --enable-llvm \
>      --disable-dri \
>      --disable-egl \
>      --disable-gbm \
>      --disable-gles1 \
>      --disable-gles2
> 
> Any insight that you might have would be appreciated.
> 
> Thanks,
> Michael
> 
> Note bleed through from underlying window with a simple OpenGL 
> application like glxgears using Mesa libGL.so.1
> Screenshot1.png
> 
> The same problem is demonstrated in our OpenGL product using Mesa libGL.so.1
> Screenshot2.png

IIRC, this is something that the window manager is doing.

I bet both the demo and your app are clearing the window background with 
glClearColor(0,0,0,0) - that is, with alpha=0.  If you set alpha=1, does 
that clear it up?

Which window manager are you using?  Maybe you need to change some 
compositing setting.

-Brian