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https://bugs.freedesktop.org/show_bug.cgi?id=9539
Summary: Rendering Error
Product: Mesa
Version: 6.5
Platform: Other
OS/Version: Linux
Status: NEW
Severity: normal
Priority: P2
Component: Other
AssignedTo: [email protected]
ReportedBy: [EMAIL PROTECTED]
Some triangles disappear at some viewing angles. This problem shows up with
perspective projection only, never orthogonal.
Although it looks like some triangles disappear what might really be happening
is that those triangles are covered by others that should have been behind them,
i.e., the Z buffer test is wrong. For example, triangles only seem to disappear
when the viewing angle is right AND another part of the surface is behind the
part that seems to have disappeared.
In addition I've found that the problem depends on the angle of view. For
example, the test case below is a roughly rectangular patch that has a slight
arc. The problem only shows up when the patch is viewed from near the edge and
from one particular size of the rectangle.
The application, paraview 2.4.4, when used in client/server mode, can easily
switch between real OpenGL (on my workstation) or Mesa (on the server). The
server does not have a graphics card. The image is always correct using real
OpenGL.
The problem is seen with both Mesa 6.5.2 and 6.4.2. "Make" was run twice for
each, with configuratons "linux" and "osmesa".
The system has 16 dual-core Itanium2 processors. The application, however, is
serial and uses only 1 processor. The OS is Suse SLES8.
Example files related to this bug can be downloaded via anonymous ftp from
ftp.psc.edu under pub/outgoing/eschenbe/Mesa. Here's a summary:
mesaBug.mpg - a short video showing the triangles coming and going as the
surface is rotated
mesaBug.vtk - The smallest subset of the surface that I could make that exhibits
the problem; in legacy VTK binary format. All other images use this data.
mesaBugAxes.png, mesaBugWire.png - The small surface with axes turned on to show
the size of the surface. Real OpenGL rendering was used because Mesa wouldn't
draw the axes (may be a ParaView problem). Also shown in wireframe mode to
better see the triangles.
mesaBugTop.png - A view from the top just to help you get oriented. No problems
from this view angle.
mesaBugEdge.png - Some triangles have disappeared.
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