commit 138c21fbec12bead3c7ca1f181c3fd35542ccb00
author Chris Craik <ccraik@google.com> Thu Apr 28 16:59:42 2016 -0700
committer Chris Craik <ccraik@google.com> Tue May 03 14:36:29 2016 -0700
tree 44e5b182b83c2532dd02f1ccb6d9c9186a48c4cf
parent 08ca2e3a7593ced4967c56709a1fe675408d42dc

Use LUT for computing final shadow alpha

bug:27415250

Significantly reduces shadow fragment shader computation.

Change-Id: Ie9b3c712700754b3734d0ae9cda8751c298fc59e

libs/hwui/SpotShadow.cpp

diff --git a/libs/hwui/SpotShadow.cpp b/libs/hwui/SpotShadow.cpp
index 759e39b..760d814 100644
--- a/libs/hwui/SpotShadow.cpp
+++ b/libs/hwui/SpotShadow.cpp
@@ -42,9 +42,8 @@
 // For each RADIANS_DIVISOR, we would allocate one more vertex b/t the normals.
 #define SPOT_CORNER_RADIANS_DIVISOR (M_PI / SPOT_EXTRA_CORNER_VERTEX_PER_PI)
 
-// For performance, we use (1 - alpha) value for the shader input.
-#define TRANSFORMED_PENUMBRA_ALPHA 1.0f
-#define TRANSFORMED_UMBRA_ALPHA 0.0f
+#define PENUMBRA_ALPHA 0.0f
+#define UMBRA_ALPHA 1.0f
 
 #include "SpotShadow.h"
 
@@ -941,11 +940,11 @@
     // Fill the IB and VB for the penumbra area.
     for (int i = 0; i < newPenumbraLength; i++) {
         AlphaVertex::set(&shadowVertices[vertexBufferIndex++], newPenumbra[i].x,
-                newPenumbra[i].y, TRANSFORMED_PENUMBRA_ALPHA);
+                newPenumbra[i].y, PENUMBRA_ALPHA);
     }
     for (int i = 0; i < umbraLength; i++) {
         AlphaVertex::set(&shadowVertices[vertexBufferIndex++], umbra[i].x, umbra[i].y,
-                TRANSFORMED_UMBRA_ALPHA);
+                UMBRA_ALPHA);
     }
 
     for (int i = 0; i < verticesPairIndex; i++) {
@@ -985,14 +984,14 @@
             indexBuffer[indexBufferIndex++] = newPenumbraLength + i;
             indexBuffer[indexBufferIndex++] = vertexBufferIndex;
             AlphaVertex::set(&shadowVertices[vertexBufferIndex++],
-                    closerVertex.x, closerVertex.y, TRANSFORMED_UMBRA_ALPHA);
+                    closerVertex.x, closerVertex.y, UMBRA_ALPHA);
         }
     } else {
         // If there is no occluded umbra at all, then draw the triangle fan
         // starting from the centroid to all umbra vertices.
         int lastCentroidIndex = vertexBufferIndex;
         AlphaVertex::set(&shadowVertices[vertexBufferIndex++], centroid.x,
-                centroid.y, TRANSFORMED_UMBRA_ALPHA);
+                centroid.y, UMBRA_ALPHA);
         for (int i = 0; i < umbraLength; i++) {
             indexBuffer[indexBufferIndex++] = newPenumbraLength + i;
             indexBuffer[indexBufferIndex++] = lastCentroidIndex;