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https://bugs.freedesktop.org/show_bug.cgi?id=4996
Summary: Restoring texture attribute group breaks texgen eye
plane
Product: Mesa
Version: 6.4
Platform: PC
URL: http://memfrob.de/~memfrob/texgen_test.c
OS/Version: All
Status: NEW
Severity: normal
Priority: P2
Component: Mesa core
AssignedTo: [email protected]
ReportedBy: [EMAIL PROTECTED]
CC: [EMAIL PROTECTED]
Mesa does not correctly restore the plane equations for eye linear texture
coordinate generation, when saving/restoring the texture attribute group.
Looking through the mesa-6.4 source, i noticed the following code in
pop_texture_group (src/mesa/main/attrib.c), which seems to be the
culprit:
_mesa_TexGenfv(GL_S, GL_EYE_PLANE, unit->EyePlaneS);
_mesa_TexGenfv(GL_T, GL_EYE_PLANE, unit->EyePlaneT);
_mesa_TexGenfv(GL_R, GL_EYE_PLANE, unit->EyePlaneR);
_mesa_TexGenfv(GL_Q, GL_EYE_PLANE, unit->EyePlaneQ);
As the eye plane is stored in eye space, this restoration pattern
again transforms the to-be-restored equation with the modelview matrix
active while glPopAttrib is called, and thereby corrupting the
equation.
A simple glut application, that demonstrates the mentioned behaviour
can be downloaded at
http://memfrob.de/~memfrob/texgen_test.c
A sample screenshot is also available
http://memfrob.de/~memfrob/texgen_test_result.png
The application simply draws three textured cubes, with active eye
linear texture coordinate generation. Before the second cube is
drawn, the texture attribute group is saved, and then restored before
the third cube is drawn.
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