Bug 10967 - wrong addresses (?) for 3D drawing : clipping or what ?
wrong addresses (?) for 3D drawing : clipping or what ?
Status: NEW
Product: Mesa
Classification: Unclassified
Component: Drivers/DRI/Unichrome
x86 (IA32) Linux (All)
: medium normal
Assigned To: Default DRI bug account
Depends on:
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Reported: 2007-05-16 05:57 UTC by Pierre Nerzic
Modified: 2008-01-03 16:16 UTC (History)
1 user (show)

See Also:
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Description Pierre Nerzic 2007-05-16 05:57:37 UTC
I own a VIA EPIA800ML, with unichrome graphic adapter. I am using Ubuntu 7.04 with mesa 6.5.2. Dri is installed and works.

The problem appears when using blender or winehq with 3D OpenGL software :
there seems to be an address (offset ???) wrong calculation or clipping when positionning the 3D window on the screen.
Let me explain with ascii graphics :

The big rectangle is the screen, the small one inside is a 3D window. The application tries to draw something inside the window, I can only see the part marked with V. The right and bottom part stays blank.
|xxxxxxxxxx                   |
|xxxx+--------+               |
|xxxx|VVVVV   |               |
|xxxx|VVVVV   |               |
|    |        |               |
|    +--------+               |
|                             |

The 3D scene should be fully visible inside the window BUT seems to be clipped by the area marked xxx, which has the same size than the window. So I can only see the part marked VVV - but its origins is correctly in the upper left corner of the window : it is not drawn in the screen coordinates.

When I move the window, the clipping area stays in (0,0), masking a larger amount if I move to the right or bottom.
The only way to see the full 3D view is to move the window at screen(0,0).

There is also a same problem with the menus, for instance in blender. Every menu or widget appears corrupt or blank. I suspect the same problem : the menu would be cleanly displayed only if at screen(0,0) (?).

Is this a problem with the stencil buffer, the clipping area, the hardware driver ?

I was thinking of the hardware because :
1) there is generally a lot of noisy pixels around the 3D area : the border of the window is very dirty, with random lines and pixel patterns (there is no segmentation failure).
2) the mouse cursor (image) is draw very badly : I can see a white square around the previous position in the menus

Very surprisingly, there is no problem with glxgears : I can move its window without any problem (560 fps). Does it use stencils or scissors ?

I would be very interested to help in finding this bug, but I can find no explanations on the internals of mesa and dri/drm.

Many thanks for all,
pierre.nerzic domain free.fr  (replace domain by at)
Comment 1 Alex Deucher 2007-05-16 06:02:53 UTC
You might try a newer mesa or mesa from git.  IIRC, there were some via fixes for similar sounding problems.