Update the shadow fall off function from cosine to gaussian.
Also tune the parameters to match a better look designed by UX team.
For ambient part, the acos transformed alpha is not needed any more.
b/19370798
Change-Id: I20d2615d1be502eb900942ed756aecd1660dee48
diff --git a/libs/hwui/AmbientShadow.cpp b/libs/hwui/AmbientShadow.cpp
index 0a210d6..a4100a2 100644
--- a/libs/hwui/AmbientShadow.cpp
+++ b/libs/hwui/AmbientShadow.cpp
@@ -45,8 +45,9 @@
/**
* Other constants:
*/
-// For the edge of the penumbra, the opacity is 0.
-#define OUTER_OPACITY (0.0f)
+// For the edge of the penumbra, the opacity is 0. After transform (1 - alpha),
+// it is 1.
+#define TRANSFORMED_OUTER_OPACITY (1.0f)
// Once the alpha difference is greater than this threshold, we will allocate extra
// edge vertices.
@@ -83,11 +84,13 @@
return 1.0 / (1 + MathUtils::max(factoredZ, 0.0f));
}
+// The shader is using gaussian function e^-(1-x)*(1-x)*4, therefore, we transform
+// the alpha value to (1 - alpha)
inline float getTransformedAlphaFromAlpha(float alpha) {
- return acosf(1.0f - 2.0f * alpha);
+ return 1.0f - alpha;
}
-// The output is ranged from 0 to M_PI.
+// The output is ranged from 0 to 1.
inline float getTransformedAlphaFromFactoredZ(float factoredZ) {
return getTransformedAlphaFromAlpha(getAlphaFromFactoredZ(factoredZ));
}
@@ -249,7 +252,7 @@
indexBuffer[indexBufferIndex++] = vertexBufferIndex;
indexBuffer[indexBufferIndex++] = currentInnerVertexIndex;
AlphaVertex::set(&shadowVertices[vertexBufferIndex++], outerVertex.x,
- outerVertex.y, OUTER_OPACITY);
+ outerVertex.y, TRANSFORMED_OUTER_OPACITY);
if (j == 0) {
outerStart = outerVertex;
@@ -285,7 +288,7 @@
(outerLast * startWeight + outerNext * k) / extraVerticesNumber;
indexBuffer[indexBufferIndex++] = vertexBufferIndex;
AlphaVertex::set(&shadowVertices[vertexBufferIndex++], currentOuter.x,
- currentOuter.y, OUTER_OPACITY);
+ currentOuter.y, TRANSFORMED_OUTER_OPACITY);
if (!isCasterOpaque) {
umbraVertices[umbraIndex++] = vertexBufferIndex;