commit 4c8c1e83022e5c7cd55bb70020c49c578d0d16e7
author Jim Van Verth <jvanverth@google.com> Mon Apr 23 17:14:48 2018 -0400
committer Skia Commit-Bot <skia-commit-bot@chromium.org> Tue Apr 24 21:53:06 2018 +0000
tree 28142ce77a4cef4056df0f16d07c165875929ea8
parent 058f2e6ed2921399879d987e3276f96e8c0cd70b

Minor shadow fixes.

Fix inset value for analytic shadows to get full inset (and hence
proper falloff).
Fix compute_radial_values in tessellator to return only positive values
and produce cleaner arcs.
Adjust shadow params in Android sample to match Android.
Fix corner calculation for analytic shadow.

Bug: skia:7486
Change-Id: Ib393b5d577f5a5eb89d3388aa4726ea4dae37055
Reviewed-on: https://skia-review.googlesource.com/123220
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>

samplecode/SampleAndroidShadows.cpp

diff --git a/samplecode/SampleAndroidShadows.cpp b/samplecode/SampleAndroidShadows.cpp
index 5d4cd26..a5fb6fc 100644
--- a/samplecode/SampleAndroidShadows.cpp
+++ b/samplecode/SampleAndroidShadows.cpp
@@ -206,8 +206,8 @@
     void onDrawContent(SkCanvas* canvas) override {
         this->drawBG(canvas);
         const SkScalar kLightWidth = 800;
-        const SkScalar kAmbientAlpha = 0.1f;
-        const SkScalar kSpotAlpha = 0.25f;
+        const SkScalar kAmbientAlpha = 0.039f;
+        const SkScalar kSpotAlpha = 0.19f;
 
         SkPaint paint;
         paint.setAntiAlias(true);

src/gpu/GrRenderTargetContext.cpp

diff --git a/src/gpu/GrRenderTargetContext.cpp b/src/gpu/GrRenderTargetContext.cpp
index e26ec90..bb54122 100644
--- a/src/gpu/GrRenderTargetContext.cpp
+++ b/src/gpu/GrRenderTargetContext.cpp
@@ -1110,7 +1110,7 @@
                 maxOffset = SkScalarSqrt(SkTMax(SkPointPriv::LengthSqd(upperLeftOffset),
                                                 SkPointPriv::LengthSqd(lowerRightOffset))) + dr;
             }
-            insetWidth += maxOffset;
+            insetWidth += SkTMax(blurOutset, maxOffset);
         }
 
         // Outset the shadow rrect to the border of the penumbra

src/gpu/ops/GrShadowRRectOp.cpp

diff --git a/src/gpu/ops/GrShadowRRectOp.cpp b/src/gpu/ops/GrShadowRRectOp.cpp
index ba96941..8d60946 100644
--- a/src/gpu/ops/GrShadowRRectOp.cpp
+++ b/src/gpu/ops/GrShadowRRectOp.cpp
@@ -460,11 +460,19 @@
         // we also skew the vectors we send to the shader that help define the circle.
         // By doing so, we end up with a quarter circle in the corner rather than the
         // elliptical curve.
-        SkVector outerVec = SkVector::Make(0.5f*(outerRadius - umbraInset), -umbraInset);
+
+        // This is a bit magical, but it gives us the correct results at extrema:
+        //   a) umbraInset == outerRadius produces an orthogonal vector
+        //   b) outerRadius == 0 produces a diagonal vector
+        // And visually the corner looks correct.
+        SkVector outerVec = SkVector::Make(outerRadius - umbraInset, -outerRadius - umbraInset);
         outerVec.normalize();
-        SkVector diagVec = SkVector::Make(outerVec.fX + outerVec.fY,
-                                          outerVec.fX + outerVec.fY);
-        diagVec *= umbraInset / (2 * umbraInset - outerRadius);
+        // We want the circle edge to fall fractionally along the diagonal at
+        //      (sqrt(2)*(umbraInset - outerRadius) + outerRadius)/sqrt(2)*umbraInset
+        //
+        // Setting the components of the diagonal offset to the following value will give us that.
+        SkScalar diagVal = umbraInset / (SK_ScalarSqrt2*(outerRadius - umbraInset) - outerRadius);
+        SkVector diagVec = SkVector::Make(diagVal, diagVal);
         SkScalar distanceCorrection = umbraInset / blurRadius;
         SkScalar clampValue = args.fClampValue;
 

src/utils/SkShadowTessellator.cpp

diff --git a/src/utils/SkShadowTessellator.cpp b/src/utils/SkShadowTessellator.cpp
index 98c47a6..0bf1ada 100755
--- a/src/utils/SkShadowTessellator.cpp
+++ b/src/utils/SkShadowTessellator.cpp
@@ -121,7 +121,7 @@
     SkScalar rSin = v1.cross(v2);
     SkScalar theta = SkScalarATan2(rSin, rCos);
 
-    int steps = SkScalarFloorToInt(r*theta*kRecipPixelsPerArcSegment);
+    int steps = SkScalarRoundToInt(SkScalarAbs(r*theta*kRecipPixelsPerArcSegment));
 
     SkScalar dTheta = theta / steps;
     *rotSin = SkScalarSinCos(dTheta, rotCos);