made raster shadows variance shadows

src/core/SkShadowShader.cpp

Index: src/core/SkShadowShader.cpp
diff --git a/src/core/SkShadowShader.cpp b/src/core/SkShadowShader.cpp
index 6ca82fb65d8431509e635324af81aa1e5167055f..f4c566b80bf52fc8d6c5f08635cded74fbff8cab 100644
--- a/src/core/SkShadowShader.cpp
+++ b/src/core/SkShadowShader.cpp
@@ -729,6 +729,7 @@ void SkShadowShaderImpl::ShadowShaderContext::shadeSpan(int x, int y,
                     int shY = SkClampMax(y + yOffset, light.getShadowMap()->height() - 1);
 
                     int shDepth = 0;
+                    int shDepthsq = 0;
 
                     // pixmaps that point to things have nonzero heights
                     if (fShadowMapPixels[l].height() > 0) {
@@ -736,17 +737,32 @@ void SkShadowShaderImpl::ShadowShaderContext::shadeSpan(int x, int y,
                         SkColor shColor(pix);
 
                         shDepth = SkColorGetB(shColor);
+                        shDepthsq = SkColorGetG(shColor) * 256;
                     } else {
                         // Make lights w/o a shadow map receive the full light contribution
                         shDepth = pvDepth;

[robertphillips, 2016/08/30 16:48:37]

It seems like you don't have to compute the square b.c. it will never be used.

[vjiaoblack, 2016/08/30 17:01:26]

Ah right. I guess it'll fail the next if case

+                        shDepthsq = shDepth * shDepth;
                     }
 

[robertphillips, 2016/08/30 16:48:37]

I expect a "if (blurAlgorithm == SkShadowParams::kVariance_ShadowType) {" test
somewhere in here

[vjiaoblack, 2016/08/30 17:01:26]

That doesn't need to be here.

If the shadow map isn't blurred, the shadows will be correctly sharp.

[robertphillips, 2016/08/30 17:04:39]

The variance path is far more expensive than the non-variance path. If one
wanted to profile the performance cost of the variance math vs. plain, they
would have no way to do so.

-                    if (pvDepth >= shDepth) {
-                        // assume object normals are pointing straight up
-                        totalLight.fX += light.dir().fZ * light.color().fX;
-                        totalLight.fY += light.dir().fZ * light.color().fY;
-                        totalLight.fZ += light.dir().fZ * light.color().fZ;
+                    SkScalar lightProb = 1.0f;
+                    if (pvDepth < shDepth) {
+                        int variance = SkTMax(shDepthsq - shDepth * shDepth,
+                                              lightShader.fShadowParams.fMinVariance);
+                        int d = pvDepth - shDepth;
+
+                        lightProb = (SkScalar) variance / ((SkScalar) (variance + d * d));
+

[robertphillips, 2016/08/30 16:48:37]

This formula is a bit hard to parse with the given formatting.

[vjiaoblack, 2016/08/30 17:01:26]

Done.

+                        lightProb = SkMaxScalar((lightProb -
+                                                 lightShader.fShadowParams.fBiasingConstant) /
+                                                (1.0f -
+                                                 lightShader.fShadowParams.fBiasingConstant),
+                                                0.0f);
                     }
+
+                    // assume object normals are pointing straight up
+                    totalLight.fX += light.dir().fZ * light.color().fX * lightProb;
+                    totalLight.fY += light.dir().fZ * light.color().fY * lightProb;
+                    totalLight.fZ += light.dir().fZ * light.color().fZ * lightProb;
                 } else {
                     totalLight += light.color();
                 }