Fix the vertex ordering of merged triangle strips

Culling and gl_FrontFacing depend on the vertex order matching the
value set through glFrontFace. To match the default counter-clockwise
order we need to preserve the parity of triangles relatively to the
start of the indices argument of glDrawElements, but we break this
parity because of the degenerate triangles between merged strips.

Fix the issue by skipping the first degenerate triangle, the parity
of following strips will be preserved since they are then separated
by two triangles.

This fixes a regression of
tests/manual/scenegraph_lancelot/data/shaders/culling/culling_1.qml
triggered by 38cab579a0c5398b7621221fd8609bc43cf1f3c5.

Change-Id: Iefa7eaab68112d31be9d8646bd288eb000528cd5
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>

0 files changed, 0 insertions, 0 deletions