Add the feature of generating linear gradient picture
by using shader. This logic will replace the original
linear gradient picture generating manner in glamor
which firstly use pixman and then upload it to GPU.
Compare it to the result generated by pixman, the
difference of each color component of each pixel is
normally 0, sometimes 1/255, and 2/255 at most. The
pixman use fixed-point but shader use float-point, so may have
difference. The feature of transform matrix and 4 types
of repeat modes have been supported. The array usage in
shader seems slow, so use 8 uniform variables to avoid
using array when stops number is not very big. This
make code look verbose but the performance improved a
lot.
We still have slightly performance regression compare to
original pixman version. There are one further optimization
opportunity which is to merge the gradient pixmap generation
and the latter compositing into one shader, then we don't need
to generate the extra texture, we can use the gradient value
directly at the compositing shader. Hope that can beat pixman
version. Will do that latter.
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Zhigang Gong <zhigang.gong@linux.intel.com>
Signed-off-by: Zhigang Gong <zhigang.gong@linux.intel.com>
1026327cdc