[Mesa3d-dev] Calling glGetError during glBegin/End

[Allen B. <ba...@lo...>]

Hi,

While trying to diagnose a rendering problem with my code, I added a
call to glGetError after each glVertex call between glBegin and glEnd.
With Mesa compiled with debugging turned on, _mesa_error was reporting
INVALID OPERATION to stdout even though glGetError itself returned 0.
According to the man page, this is the correct result but it also
mentions that there should be no other side effects. However, when
calling glGetError, the FLUSH_VERTICES macro is invoked by the
ASSERT_OUTSIDE_BEGIN_END_WITH_RETVAL macro at the beginning of
_mesa_GetError. This seems to have a (negative) effect on the display
list which is being constructed.

I activated the _tnl_print_cassette function in _tnl_compile_cassette.
WITHOUT calling glGetError between glBegin/End, after all three vertices
have been defined, _tnl_print_cassette produces:

Cassette id 0, 3 rows.
Contains at least one: (0x880001) eye/glbegin, obj, obj-3,
Contains a full complement of: (0x80001) obj, obj-3,
Final begin/end state out/out, errors y/n
3: Obj 0.000000 0.000000 0.000000 1.000000 BEGIN(GL_POLYGON)
(BEGIN,END,)
4: Obj 10.000000 0.000000 0.000000 1.000000
5: Obj 0.000000 10.000000 0.000000 1.000000
6:  END

which seems reasonable. If I call glGetError after each glVertex, then I
get three separate invocations of _tnl_compile_cassette after each
vertex is defined:

Cassette id 0, 1 rows.
Contains at least one: (0x880001) eye/glbegin, obj, obj-3,
Contains a full complement of: (0x880001) eye/glbegin, obj, obj-3,
Final begin/end state in/in, errors y/n
3: Obj 0.000000 0.000000 0.000000 1.000000 BEGIN(GL_POLYGON)
(LAST,BEGIN,)
4:
............ some output deleted ..........
Cassette id 0, 1 rows.
Contains at least one: (0x80001) obj, obj-3,
Contains a full complement of: (0x80001) obj, obj-3,
Final begin/end state in/in, errors n/n
8: Obj 10.000000 0.000000 0.000000 1.000000
9:
............ some output deleted ...........
Cassette id 0, 1 rows.
Contains at least one: (0x80001) obj, obj-3,
Contains a full complement of: (0x80001) obj, obj-3,
Final begin/end state in/in, errors n/n
13: Obj 0.000000 10.000000 0.000000 1.000000
14:
............ some output deleted ...........
Cassette id 0, 0 rows.
Contains at least one: (0x0)
18:  END

When I draw this display list later, I get a torrent of INVALID
OPERATION errors.

This looks like a bug, but perhaps I shouldn't be calling glGetError
between glBegin/End anyway.

As always, thanks for the tremendous effort you guys put into this
library.

Allen