Clear* commands for side-by-side framebuffers require special handling
because only the scissor rectangle of the first viewport is used in the
scissor test as defined in the OpenGL 4.1+ specs.
To enable clearing of each view of a side-by-side framebuffer all views
are iterated over, the corresponding scissor rectangle is set as first,
and a Clear* call is made to the driver. Afterwards the scissor state is
restored.
BUG=angleproject:2062
TEST=angle_end2end_tests
Change-Id: I138663ea61b4f0c9302872108e7dfbadf451b3ec
Reviewed-on: https://chromium-review.googlesource.com/590233
Commit-Queue: Martin Radev <mradev@nvidia.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
