Bug 1883336 - Pack the clip planes into 3 varying slots. r=gw

Moving vLocalPos from ps_quad_textured to ps_quad pushed the number of varying slots in ps_quad_mask over the limit (16). vLocalPos is going to be used by some patterns in addition to the texture code so ifdef'ing it out is inconvenient. It is simpler to win back a varying slot by packing the clip planes.

Differential Revision: https://phabricator.services.mozilla.com/D204229

gfx/wr/webrender/res/ps_quad_mask.glsl

@@ -15,10 +15,10 @@ flat varying highp vec4 vClipCenter_Radius_TL;
 flat varying highp vec4 vClipCenter_Radius_TR;
 flat varying highp vec4 vClipCenter_Radius_BR;
 flat varying highp vec4 vClipCenter_Radius_BL;
-flat varying highp vec3 vClipPlane_TL;
+// We pack 4 vec3 clip planes into 3 vec4 to save a varying slot.
-flat varying highp vec3 vClipPlane_TR;
+flat varying highp vec4 vClipPlane_A;
-flat varying highp vec3 vClipPlane_BL;
+flat varying highp vec4 vClipPlane_B;
-flat varying highp vec3 vClipPlane_BR;
+flat varying highp vec4 vClipPlane_C;
 #endif
 flat varying highp vec2 vClipMode;
 
@@ -120,14 +120,18 @@ void pattern_vertex(PrimitiveInfo prim_info) {
     vec2 n_tr = vec2(r_tr.y, -r_tr.x);
     vec2 n_br = r_br.yx;
     vec2 n_bl = vec2(-r_bl.y, r_bl.x);
-    vClipPlane_TL = vec3(n_tl,
+    vec3 tl = vec3(n_tl,
-                         dot(n_tl, vec2(clip.rect.p0.x, clip.rect.p0.y + r_tl.y)));
+                   dot(n_tl, vec2(clip.rect.p0.x, clip.rect.p0.y + r_tl.y)));
-    vClipPlane_TR = vec3(n_tr,
+    vec3 tr = vec3(n_tr,
-                         dot(n_tr, vec2(clip.rect.p1.x - r_tr.x, clip.rect.p0.y)));
+                   dot(n_tr, vec2(clip.rect.p1.x - r_tr.x, clip.rect.p0.y)));
-    vClipPlane_BR = vec3(n_br,
+    vec3 br = vec3(n_br,
-                         dot(n_br, vec2(clip.rect.p1.x, clip.rect.p1.y - r_br.y)));
+                   dot(n_br, vec2(clip.rect.p1.x, clip.rect.p1.y - r_br.y)));
-    vClipPlane_BL = vec3(n_bl,
+    vec3 bl = vec3(n_bl,
-                         dot(n_bl, vec2(clip.rect.p0.x + r_bl.x, clip.rect.p1.y)));
+                   dot(n_bl, vec2(clip.rect.p0.x + r_bl.x, clip.rect.p1.y)));
+
+    vClipPlane_A = vec4(tl.x, tl.y, tl.z, tr.x);
+    vClipPlane_B = vec4(tr.y, tr.z, br.x, br.y);
+    vClipPlane_C = vec4(br.z, bl.x, bl.y, bl.z);
 #endif
 
 }
@@ -154,15 +158,20 @@ vec4 pattern_fragment(vec4 _base_color) {
 #ifdef WR_FEATURE_FAST_PATH
     float dist = sd_rounded_box(clip_local_pos, v_clip_params.xy, v_clip_params.z);
 #else
+    vec3 plane_tl = vec3(vClipPlane_A.x, vClipPlane_A.y, vClipPlane_A.z);
+    vec3 plane_tr = vec3(vClipPlane_A.w, vClipPlane_B.x, vClipPlane_B.y);
+    vec3 plane_br = vec3(vClipPlane_B.z, vClipPlane_B.w, vClipPlane_C.x);
+    vec3 plane_bl = vec3(vClipPlane_C.y, vClipPlane_C.z, vClipPlane_C.w);
+
     float dist = distance_to_rounded_rect(
         clip_local_pos,
-        vClipPlane_TL,
+        plane_tl,
         vClipCenter_Radius_TL,
-        vClipPlane_TR,
+        plane_tr,
         vClipCenter_Radius_TR,
-        vClipPlane_BR,
+        plane_br,
         vClipCenter_Radius_BR,
-        vClipPlane_BL,
+        plane_bl,
         vClipCenter_Radius_BL,
         vTransformBounds
     );