Bug 1721795 - Pack cs_border_solid's vMixColors in to vector to work around driver bug. r=gfx-reviewers,lsalzman

We have in the past encountered a driver bug on Adreno 3xx devices
where using a flat scalar varying causes the fragment shader output to
be incorrect. See bugs 1630356 and 1705433.

We have now encountered this in cs_border_solid too, due to
vMixColors. As before, packing the varying in to a vector works around
the bug.

Differential Revision: https://phabricator.services.mozilla.com/D121211

gfx/wr/webrender/res/cs_border_solid.glsl

@@ -17,8 +17,15 @@ flat varying vec4 vColor1;
 // transition occurs. Used for corners only.
 flat varying vec4 vColorLine;
 
+#if defined(PLATFORM_ANDROID) && !defined(SWGL)
+// Work around Adreno 3xx driver bug. See the v_perspective comment in
+// brush_image or bug 1630356 for details.
+flat varying ivec2 vMixColorsVec;
+#define vMixColors vMixColorsVec.x
+#else
 // A boolean indicating that we should be mixing between edge colors.
 flat varying int vMixColors;
+#endif
 
 // xy = Local space position of the clip center.
 // zw = Scale the rect origin by this to get the outer