Combine the ambient and spot alphas into the base color

for geometric shadows. 

This matches the analytic shadow approach better, and
is color space invariant.
Also includes cleanup in SampleAndroidShadows.

Bug: skia:6546
Change-Id: I7a7cd060420dae741f967334c8b19542a14f0bcf
Reviewed-on: https://skia-review.googlesource.com/15228
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>

7 files changed, 106 insertions, 438 deletions

diff --git a/include/private/SkShadowFlags.h b/include/private/SkShadowFlags.h
index 23b0f54095..8caf632988 100644
--- a/include/private/SkShadowFlags.h
+++ b/include/private/SkShadowFlags.h
@@ -14,8 +14,10 @@ enum SkShadowFlags {
     /** The occluding object is not opaque. Knowing that the occluder is opaque allows
     * us to cull shadow geometry behind it and improve performance. */
     kTransparentOccluder_ShadowFlag = 0x01,
+    /** Don't try to use analytic shadows. */
+    kGeometricOnly_ShadowFlag = 0x02,
     /** mask for all shadow flags */
-    kAll_ShadowFlag = 0x01
+    kAll_ShadowFlag = 0x03
 };
 
 #endif
diff --git a/samplecode/SampleAndroidShadows.cpp b/samplecode/SampleAndroidShadows.cpp
index 02b494ff20..99e5ff4556 100644
--- a/samplecode/SampleAndroidShadows.cpp
+++ b/samplecode/SampleAndroidShadows.cpp
@@ -21,8 +21,6 @@
 #include "SkView.h"
 #include "sk_tool_utils.h"
 
-#define USE_SHADOW_UTILS
-
 ////////////////////////////////////////////////////////////////////////////
 
 class ShadowsView : public SampleView {
@@ -129,327 +127,27 @@ protected:
         canvas->drawColor(0xFFDDDDDD);
     }
 
-    static void GetOcclRect(const SkPath& path, SkRect* occlRect) {
-        SkRect pathRect;
-        SkRRect pathRRect;
-        if (path.isOval(&pathRect)) {
-            *occlRect = sk_tool_utils::compute_central_occluder(SkRRect::MakeOval(pathRect));
-        } else if (path.isRRect(&pathRRect)) {
-            *occlRect = sk_tool_utils::compute_central_occluder(pathRRect);
-        } else if (path.isRect(occlRect)) {
-            // the inverse transform for the spot shadow occluder doesn't always get us
-            // back to exactly the same position, so deducting a little slop
-            occlRect->inset(1, 1);
-        } else {
-            *occlRect = SkRect::MakeEmpty();
-        }
-    }
-
-    void drawAmbientShadow(SkCanvas* canvas, const SkPath& path, SkScalar zValue, 
-                           SkScalar ambientAlpha) {
-
-        if (ambientAlpha <= 0) {
-            return;
-        }
-
-        const SkScalar kHeightFactor = 1.f / 128.f;
-        const SkScalar kGeomFactor = 64;
-
-        SkScalar umbraAlpha = 1 / (1 + SkMaxScalar(zValue*kHeightFactor, 0));
-        SkScalar radius = zValue*kHeightFactor*kGeomFactor;
-
-        // occlude blur
-        SkRect occlRect;
-        GetOcclRect(path, &occlRect);
-        sk_sp<SkMaskFilter> mf = SkBlurMaskFilter::Make(kNormal_SkBlurStyle,
-                                                        SkBlurMask::ConvertRadiusToSigma(radius),
-                                                        occlRect,
-                                                        SkBlurMaskFilter::kNone_BlurFlag);
-
-        SkPaint paint;
-        paint.setAntiAlias(true);
-        paint.setMaskFilter(std::move(mf));
-        paint.setColor(SkColorSetARGB(fIgnoreShadowAlpha
-                                    ? 255
-                                    : (unsigned char)(ambientAlpha*umbraAlpha*255.999f), 0, 0, 0));
-        canvas->drawPath(path, paint);
-
-        // draw occlusion rect
-#if DRAW_OCCL_RECT
-        SkPaint stroke;
-        stroke.setStyle(SkPaint::kStroke_Style);
-        stroke.setColor(SK_ColorBLUE);
-        canvas->drawRect(occlRect, stroke);
-#endif
-    }
-
-    void drawAmbientShadowAlt(SkCanvas* canvas, const SkPath& path, SkScalar zValue,
-                              SkScalar ambientAlpha) {
-
-        if (ambientAlpha <= 0) {
-            return;
-        }
-
-        const SkScalar kHeightFactor = 1.f / 128.f;
-        const SkScalar kGeomFactor = 64;
-
-        SkScalar umbraAlpha = 1 / (1 + SkMaxScalar(zValue*kHeightFactor, 0));
-        SkScalar radius = zValue*kHeightFactor*kGeomFactor;
-        // distance to outer of edge of geometry from original shape edge
-        SkScalar offset = radius*umbraAlpha;
-
-        SkRect pathRect;
-        SkRRect pathRRect;
-        SkScalar scaleFactors[2];
-        if (!canvas->getTotalMatrix().getMinMaxScales(scaleFactors)) {
-            return;
-        }
-        if (scaleFactors[0] != scaleFactors[1] || radius*scaleFactors[0] >= 64 ||
-            !((path.isOval(&pathRect) && pathRect.width() == pathRect.height()) ||
-              (path.isRRect(&pathRRect) && pathRRect.allCornersCircular()) ||
-              path.isRect(&pathRect))) {
-            this->drawAmbientShadow(canvas, path, zValue, ambientAlpha);
-            return;
-        }
-
-        // For all of these, we inset the offset rect by half the radius to get our stroke shape.
-        SkScalar strokeOutset = offset - SK_ScalarHalf*radius;
-        // Make sure we'll have a radius of at least 0.5 after xform
-        if (strokeOutset*scaleFactors[0] < 0.5f) {
-            strokeOutset = 0.5f / scaleFactors[0];
-        }
-        if (path.isOval(nullptr)) {
-            pathRect.outset(strokeOutset, strokeOutset);
-            pathRRect = SkRRect::MakeOval(pathRect);
-        } else if (path.isRect(nullptr)) {
-            pathRect.outset(strokeOutset, strokeOutset);
-            pathRRect = SkRRect::MakeRectXY(pathRect, strokeOutset, strokeOutset);
-        } else {
-            pathRRect.outset(strokeOutset, strokeOutset);
-        }
-
-        SkPaint paint;
-        paint.setAntiAlias(true);
-        paint.setStyle(SkPaint::kStroke_Style);
-        // we outset the stroke a little to cover up AA on the interior edge
-        SkScalar pad = 0.5f;
-        paint.setStrokeWidth(radius + 2*pad);
-        // handle scale of radius and pad due to CTM
-        radius *= scaleFactors[0];
-        pad *= scaleFactors[0];
-        SkASSERT(radius < 16384);
-        SkASSERT(pad < 64);
-        // Convert radius to 14.2 fixed point and place in the R & G components.
-        // Convert pad to 6.2 fixed point and place in the B component.
-        uint16_t iRadius = (uint16_t)(radius*4.0f);
-        unsigned char alpha = (unsigned char)(ambientAlpha*255.999f);
-        paint.setColor(SkColorSetARGB(fIgnoreShadowAlpha ? 255 : alpha,
-                                      iRadius >> 8, iRadius & 0xff,
-                                      (unsigned char)(4.0f*pad)));
-
-        paint.setColorFilter(SkColorFilter::MakeModeFilter(SK_ColorBLACK, SkBlendMode::kModulate));
-        paint.setShader(SkGaussianEdgeShader::Make());
-        canvas->drawRRect(pathRRect, paint);
-    }
-
-    void drawSpotShadow(SkCanvas* canvas, const SkPath& path, SkScalar zValue,
-                        SkPoint3 lightPos, SkScalar lightWidth, SkScalar spotAlpha) {
-        if (spotAlpha <= 0) {
-            return;
-        }
-
-        SkScalar zRatio = zValue / (lightPos.fZ - zValue);
-        if (zRatio < 0.0f) {
-            zRatio = 0.0f;
-        } else if (zRatio > 0.95f) {
-            zRatio = 0.95f;
-        }
-        SkScalar blurRadius = lightWidth*zRatio;
-
-        // compute the transformation params
-        SkPoint center = SkPoint::Make(path.getBounds().centerX(), path.getBounds().centerY());
-        SkMatrix ctmInverse;
-        if (!canvas->getTotalMatrix().invert(&ctmInverse)) {
-            return;
-        }
-        SkPoint lightPos2D = SkPoint::Make(lightPos.fX, lightPos.fY);
-        ctmInverse.mapPoints(&lightPos2D, 1);
-        SkPoint offset = SkPoint::Make(zRatio*(center.fX - lightPos2D.fX),
-                                       zRatio*(center.fY - lightPos2D.fY));
-        SkScalar scale = lightPos.fZ / (lightPos.fZ - zValue);
-
-        SkAutoCanvasRestore acr(canvas, true);
-
-        sk_sp<SkMaskFilter> mf = SkBlurMaskFilter::Make(kNormal_SkBlurStyle,
-                                                        SkBlurMask::ConvertRadiusToSigma(blurRadius),
-                                                        SkBlurMaskFilter::kNone_BlurFlag);
-
-        SkPaint paint;
-        paint.setAntiAlias(true);
-        paint.setMaskFilter(std::move(mf));
-        paint.setColor(SkColorSetARGB(fIgnoreShadowAlpha
-                                                ? 255 
-                                                : (unsigned char)(spotAlpha*255.999f), 0, 0, 0));
-
-        // apply transformation to shadow
-        canvas->scale(scale, scale);
-        canvas->translate(offset.fX, offset.fY);
-        canvas->drawPath(path, paint);
-    }
-
-    void drawSpotShadowAlt(SkCanvas* canvas, const SkPath& path, SkScalar zValue,
-                        SkPoint3 lightPos, SkScalar lightWidth, SkScalar spotAlpha) {
-        if (spotAlpha <= 0) {
-            return;
-        }
-
-        SkScalar zRatio = zValue / (lightPos.fZ - zValue);
-        if (zRatio < 0.0f) {
-            zRatio = 0.0f;
-        } else if (zRatio > 0.95f) {
-            zRatio = 0.95f;
-        }
-        SkScalar radius = 2.0f*lightWidth*zRatio;
-
-        SkRect pathRect;
-        SkRRect pathRRect;
-        SkScalar scaleFactors[2];
-        if (!canvas->getTotalMatrix().getMinMaxScales(scaleFactors)) {
-            return;
-        }
-        if (scaleFactors[0] != scaleFactors[1] || radius*scaleFactors[0] >= 16384 ||
-            !((path.isOval(&pathRect) && pathRect.width() == pathRect.height()) ||
-              (path.isRRect(&pathRRect) && pathRRect.allCornersCircular()) ||
-              path.isRect(&pathRect))) {
-            this->drawSpotShadow(canvas, path, zValue, lightPos, lightWidth, spotAlpha);
-            return;
-        }
-
-        // For all of these, we need to ensure we have a rrect with radius >= 0.5f in device space
-        const SkScalar minRadius = SK_ScalarHalf/scaleFactors[0];
-        if (path.isOval(nullptr)) {
-            pathRRect = SkRRect::MakeOval(pathRect);
-        } else if (path.isRect(nullptr)) {
-            pathRRect = SkRRect::MakeRectXY(pathRect, minRadius, minRadius);
-        } else {
-            if (pathRRect.getSimpleRadii().fX < minRadius) {
-                pathRRect.setRectXY(pathRRect.rect(), minRadius, minRadius);
-            }
-        }
-
-        // compute the scale and translation for the shadow
-        SkScalar scale = lightPos.fZ / (lightPos.fZ - zValue);
-        SkRRect shadowRRect;
-        pathRRect.transform(SkMatrix::MakeScale(scale, scale), &shadowRRect);
-        SkPoint center = SkPoint::Make(shadowRRect.rect().centerX(), shadowRRect.rect().centerY());
-        SkMatrix ctmInverse;
-        if (!canvas->getTotalMatrix().invert(&ctmInverse)) {
-            return;
-        }
-        SkPoint lightPos2D = SkPoint::Make(lightPos.fX, lightPos.fY);
-        ctmInverse.mapPoints(&lightPos2D, 1);
-        SkPoint offset = SkPoint::Make(zRatio*(center.fX - lightPos2D.fX),
-                                       zRatio*(center.fY - lightPos2D.fY));
-        SkAutoCanvasRestore acr(canvas, true);
-
-        SkPaint paint;
-        paint.setAntiAlias(true);
-        // We want to extend the stroked area in so that it meets up with the caster
-        // geometry. The stroked geometry will, by definition already be inset half the
-        // stroke width but we also have to account for the scaling.
-        // We also add 1/2 to cover up AA on the interior edge.
-        SkScalar scaleOffset = (scale - 1.0f) * SkTMax(SkTMax(SkTAbs(pathRect.fLeft),
-                                                              SkTAbs(pathRect.fRight)),
-                                                       SkTMax(SkTAbs(pathRect.fTop),
-                                                              SkTAbs(pathRect.fBottom)));
-        SkScalar insetAmount = offset.length() - (0.5f * radius) + scaleOffset + 0.5f;
-
-        // compute area
-        SkScalar strokeWidth = radius + insetAmount;
-        SkScalar strokedArea = 2.0f*strokeWidth*(shadowRRect.width() + shadowRRect.height());
-        SkScalar filledArea = (shadowRRect.height() + radius)*(shadowRRect.width() + radius);
-        // If the area of the stroked geometry is larger than the fill geometry, or
-        // if our pad is too big to convert to 6.2 fixed point, just fill it.
-        if (strokedArea > filledArea) {
-            paint.setStyle(SkPaint::kStrokeAndFill_Style);
-            paint.setStrokeWidth(radius);
-        } else {
-            // Since we can't have unequal strokes, inset the shadow rect so the inner
-            // and outer edges of the stroke will land where we want.
-            SkRect insetRect = shadowRRect.rect().makeInset(insetAmount/2.0f, insetAmount/2.0f);
-            SkScalar insetRad = SkTMax(shadowRRect.getSimpleRadii().fX - insetAmount/2.0f,
-                                       minRadius);
-
-            shadowRRect = SkRRect::MakeRectXY(insetRect, insetRad, insetRad);
-            paint.setStyle(SkPaint::kStroke_Style);
-            paint.setStrokeWidth(strokeWidth);
-        }
-        paint.setColorFilter(SkColorFilter::MakeModeFilter(SK_ColorBLACK, SkBlendMode::kModulate));
-        paint.setShader(SkGaussianEdgeShader::Make());
-        // handle scale of radius due to CTM
-        radius *= scaleFactors[0];
-        // don't need to scale pad as it was computed from the transformed offset
-        SkASSERT(radius < 16384);
-        SkScalar pad = 0;
-        SkASSERT(pad < 64);
-        // Convert radius to 14.2 fixed point and place in the R & G components.
-        // Convert pad to 6.2 fixed point and place in the B component.
-        uint16_t iRadius = (uint16_t)(radius*4.0f);
-        unsigned char alpha = (unsigned char)(spotAlpha*255.999f);
-        paint.setColor(SkColorSetARGB(fIgnoreShadowAlpha ? 255 : alpha,
-                                      iRadius >> 8, iRadius & 0xff,
-                                      (unsigned char)(4.0f*pad)));
-
-        // apply transformation to shadow
-        canvas->translate(offset.fX, offset.fY);
-        canvas->drawRRect(shadowRRect, paint);
-    }
-
     void drawShadowedPath(SkCanvas* canvas, const SkPath& path,
                           std::function<SkScalar(SkScalar, SkScalar)> zFunc,
                           const SkPaint& paint, SkScalar ambientAlpha,
                           const SkPoint3& lightPos, SkScalar lightWidth, SkScalar spotAlpha) {
-#ifdef USE_SHADOW_UTILS
-        SkScalar zValue = zFunc(0, 0);
-        if (fUseAlt) {
-            if (fShowAmbient) {
-                this->drawAmbientShadowAlt(canvas, path, zValue, ambientAlpha);
-            }
-            if (fShowSpot) {
-                this->drawSpotShadowAlt(canvas, path, zValue, lightPos, lightWidth, spotAlpha);
-            }
-        } else {
-            if (!fShowAmbient) {
-                ambientAlpha = 0;
-            }
-            if (!fShowSpot) {
-                spotAlpha = 0;
-            }
-
-            //SkShadowUtils::DrawShadow(canvas, path,
-            //                          zValue,
-            //                          lightPos, lightWidth,
-            //                          ambientAlpha, spotAlpha, SK_ColorBLACK);
-            SkShadowUtils::DrawUncachedShadow(canvas, path, zFunc,
-                                              lightPos, lightWidth,
-                                              ambientAlpha, spotAlpha, SK_ColorBLACK);
+        if (!fShowAmbient) {
+            ambientAlpha = 0;
         }
-#else
-        if (fShowAmbient) {
-            if (fUseAlt) {
-                this->drawAmbientShadowAlt(canvas, path, zValue, ambientAlpha);
-            } else {
-                this->drawAmbientShadow(canvas, path, zValue, ambientAlpha);
-            }
+        if (!fShowSpot) {
+            spotAlpha = 0;
         }
-        if (fShowSpot) {
-            if (fUseAlt) {
-                this->drawSpotShadowAlt(canvas, path, zValue, lightPos, lightWidth, spotAlpha);
-            } else {
-                this->drawSpotShadow(canvas, path, zValue, lightPos, lightWidth, spotAlpha);
-            }
+        uint32_t flags = 0;
+        if (fUseAlt) {
+            flags |= SkShadowFlags::kGeometricOnly_ShadowFlag;
         }
-#endif
+        //SkShadowUtils::DrawShadow(canvas, path,
+        //                          zValue,
+        //                          lightPos, lightWidth,
+        //                          ambientAlpha, spotAlpha, SK_ColorBLACK, flags);
+        SkShadowUtils::DrawUncachedShadow(canvas, path, zFunc,
+                                          lightPos, lightWidth,
+                                          ambientAlpha, spotAlpha, SK_ColorBLACK, flags);
 
         if (fShowObject) {
             canvas->drawPath(path, paint);
@@ -577,27 +275,6 @@ protected:
         return true;
     }
 
-protected:
-    SkView::Click* onFindClickHandler(SkScalar x, SkScalar y, unsigned modi) override {
-        return new SkView::Click(this);
-    }
-
-    bool onClick(Click *click) override {
-        SkScalar x = click->fCurr.fX;
-        SkScalar y = click->fCurr.fY;
-
-        SkScalar dx = x - click->fPrev.fX;
-        SkScalar dy = y - click->fPrev.fY;
-
-        if (dx != 0 || dy != 0) {
-            fLightPos.fX += dx;
-            fLightPos.fY += dy;
-            this->inval(nullptr);
-        }
-
-        return true;
-    }
-
 private:
     typedef SampleView INHERITED;
 };
diff --git a/src/gpu/effects/GrBlurredEdgeFragmentProcessor.cpp b/src/gpu/effects/GrBlurredEdgeFragmentProcessor.cpp
index 95b08d2f0d..a37c173c0b 100644
--- a/src/gpu/effects/GrBlurredEdgeFragmentProcessor.cpp
+++ b/src/gpu/effects/GrBlurredEdgeFragmentProcessor.cpp
@@ -23,7 +23,7 @@ public:
         fragBuilder->codeAppendf("vec4 color = %s;", args.fInputColor);
         if (!args.fGpImplementsDistanceVector) {
             fragBuilder->codeAppendf("// assuming interpolant is set in vertex colors\n");
-            fragBuilder->codeAppendf("float factor = 1.0 - color.b;");
+            fragBuilder->codeAppendf("float factor = 1.0 - color.a;");
         } else {
             fragBuilder->codeAppendf("// using distance to edge to compute interpolant\n");
             fragBuilder->codeAppend("float radius = color.r*256.0*64.0 + color.g*64.0;");
@@ -37,14 +37,10 @@ public:
                 fragBuilder->codeAppend("factor = exp(-factor * factor * 4.0) - 0.018;");
                 break;
             case GrBlurredEdgeFP::kSmoothstep_Mode:
-                fragBuilder->codeAppend("factor = smoothstep(factor, 0.0, 1.0);");
+                fragBuilder->codeAppend("factor = smoothstep(1.0, 0.0, factor);");
                 break;
         }
-        if (!args.fGpImplementsDistanceVector) {
-            fragBuilder->codeAppendf("%s = vec4(factor*color.g);", args.fOutputColor);
-        } else {
-            fragBuilder->codeAppendf("%s = vec4(factor*color.a);", args.fOutputColor);
-        }
+        fragBuilder->codeAppendf("%s = vec4(factor);", args.fOutputColor);
     }
 
 protected:
diff --git a/src/utils/SkShadowTessellator.cpp b/src/utils/SkShadowTessellator.cpp
index 36df514534..32a114253a 100755
--- a/src/utils/SkShadowTessellator.cpp
+++ b/src/utils/SkShadowTessellator.cpp
@@ -327,8 +327,7 @@ bool SkBaseShadowTessellator::setTransformedHeightFunc(const SkMatrix& ctm) {
 class SkAmbientShadowTessellator : public SkBaseShadowTessellator {
 public:
     SkAmbientShadowTessellator(const SkPath& path, const SkMatrix& ctm,
-                               SkShadowTessellator::HeightFunc heightFunc,
-                               SkScalar ambientAlpha, bool transparent);
+                               SkShadowTessellator::HeightFunc heightFunc, bool transparent);
 
 private:
     void handleLine(const SkPoint& p) override;
@@ -343,10 +342,9 @@ private:
     }
     SkColor umbraColor(SkScalar z) {
         SkScalar umbraAlpha = SkScalarInvert((1.0f + SkTMax(z*kHeightFactor, 0.0f)));
-        return SkColorSetARGB(255, 0, fAmbientAlpha * 255.9999f, umbraAlpha * 255.9999f);
+        return SkColorSetARGB(umbraAlpha * 255.9999f, 0, 0, 0);
     }
 
-    SkScalar            fAmbientAlpha;
     int                 fCentroidCount;
 
     typedef SkBaseShadowTessellator INHERITED;
@@ -355,10 +353,8 @@ private:
 SkAmbientShadowTessellator::SkAmbientShadowTessellator(const SkPath& path,
                                                        const SkMatrix& ctm,
                                                        SkShadowTessellator::HeightFunc heightFunc,
-                                                       SkScalar ambientAlpha,
                                                        bool transparent)
-        : INHERITED(heightFunc, transparent)
-        , fAmbientAlpha(ambientAlpha) {
+        : INHERITED(heightFunc, transparent) {
     // Set base colors
     SkScalar occluderHeight = heightFunc(0, 0);
     SkScalar umbraAlpha = SkScalarInvert((1.0f + SkTMax(occluderHeight*kHeightFactor, 0.0f)));
@@ -366,8 +362,8 @@ SkAmbientShadowTessellator::SkAmbientShadowTessellator(const SkPath& path,
     // umbraAlpha is the factor that is linearly interpolated from outside to inside, and
     // then "blurred" by the GrBlurredEdgeFP. It is then multiplied by fAmbientAlpha to get
     // the final alpha.
-    fUmbraColor = SkColorSetARGB(255, 0, ambientAlpha * 255.9999f, umbraAlpha * 255.9999f);
-    fPenumbraColor = SkColorSetARGB(255, 0, ambientAlpha * 255.9999f, 0);
+    fUmbraColor = SkColorSetARGB(umbraAlpha * 255.9999f, 0, 0, 0);
+    fPenumbraColor = SkColorSetARGB(0, 0, 0, 0);
 
     // make sure we're not below the canvas plane
     this->setZOffset(path.getBounds(), ctm.hasPerspective());
@@ -654,9 +650,8 @@ void SkAmbientShadowTessellator::addEdge(const SkPoint& nextPoint, const SkVecto
 class SkSpotShadowTessellator : public SkBaseShadowTessellator {
 public:
     SkSpotShadowTessellator(const SkPath& path, const SkMatrix& ctm,
-                            SkShadowTessellator::HeightFunc heightFunc,
-                            const SkPoint3& lightPos, SkScalar lightRadius,
-                            SkScalar spotAlpha, bool transparent);
+                            SkShadowTessellator::HeightFunc heightFunc, const SkPoint3& lightPos,
+                            SkScalar lightRadius, bool transparent);
 
 private:
     void computeClipAndPathPolygons(const SkPath& path, const SkMatrix& ctm,
@@ -700,7 +695,7 @@ private:
 SkSpotShadowTessellator::SkSpotShadowTessellator(const SkPath& path, const SkMatrix& ctm,
                                                  SkShadowTessellator::HeightFunc heightFunc,
                                                  const SkPoint3& lightPos, SkScalar lightRadius,
-                                                 SkScalar spotAlpha, bool transparent)
+                                                 bool transparent)
     : INHERITED(heightFunc, transparent)
     , fLightZ(lightPos.fZ)
     , fLightRadius(lightRadius)
@@ -723,8 +718,8 @@ SkSpotShadowTessellator::SkSpotShadowTessellator(const SkPath& path, const SkMat
     float zRatio = SkTPin(occluderHeight / (fLightZ - occluderHeight), 0.0f, 0.95f);
     SkScalar radius = lightRadius * zRatio;
     fRadius = radius;
-    fUmbraColor = SkColorSetARGB(255, 0, spotAlpha * 255.9999f, 255);
-    fPenumbraColor = SkColorSetARGB(255, 0, spotAlpha * 255.9999f, 0);
+    fUmbraColor = SkColorSetARGB(255, 0, 0, 0);
+    fPenumbraColor = SkColorSetARGB(0, 0, 0, 0);
 
     // Compute the scale and translation for the spot shadow.
     SkMatrix shadowTransform;
@@ -1292,17 +1287,14 @@ void SkSpotShadowTessellator::addEdge(const SkPoint& nextPoint, const SkVector&
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 
 sk_sp<SkVertices> SkShadowTessellator::MakeAmbient(const SkPath& path, const SkMatrix& ctm,
-                                                   HeightFunc heightFunc, SkScalar ambientAlpha,
-                                                   bool transparent) {
-    SkAmbientShadowTessellator ambientTess(path, ctm, heightFunc, ambientAlpha, transparent);
+                                                   HeightFunc heightFunc, bool transparent) {
+    SkAmbientShadowTessellator ambientTess(path, ctm, heightFunc, transparent);
     return ambientTess.releaseVertices();
 }
 
 sk_sp<SkVertices> SkShadowTessellator::MakeSpot(const SkPath& path, const SkMatrix& ctm,
-                                                HeightFunc heightFunc,
-                                                const SkPoint3& lightPos, SkScalar lightRadius,
-                                                SkScalar spotAlpha, bool transparent) {
-    SkSpotShadowTessellator spotTess(path, ctm, heightFunc, lightPos, lightRadius,
-                                     spotAlpha, transparent);
+                                                HeightFunc heightFunc, const SkPoint3& lightPos,
+                                                SkScalar lightRadius,  bool transparent) {
+    SkSpotShadowTessellator spotTess(path, ctm, heightFunc, lightPos, lightRadius, transparent);
     return spotTess.releaseVertices();
 }
diff --git a/src/utils/SkShadowTessellator.h b/src/utils/SkShadowTessellator.h
index f9f4a144c9..d6e784ee45 100644
--- a/src/utils/SkShadowTessellator.h
+++ b/src/utils/SkShadowTessellator.h
@@ -26,7 +26,7 @@ typedef std::function<SkScalar(SkScalar, SkScalar)> HeightFunc;
  * If transparent is true, then the center of the ambient shadow will be filled in.
  */
 sk_sp<SkVertices> MakeAmbient(const SkPath& path, const SkMatrix& ctm,
-                              HeightFunc heightFunc, SkScalar ambientAlpha, bool transparent);
+                              HeightFunc heightFunc, bool transparent);
 
 /**
  * This function generates a spot shadow mesh for a path by walking the transformed path,
@@ -34,8 +34,7 @@ sk_sp<SkVertices> MakeAmbient(const SkPath& path, const SkMatrix& ctm,
  * The center will be clipped against the original path unless transparent is true.
  */
 sk_sp<SkVertices> MakeSpot(const SkPath& path, const SkMatrix& ctm, HeightFunc heightFunc,
-                           const SkPoint3& lightPos, SkScalar lightRadius,
-                           SkScalar spotAlpha, bool transparent);
+                           const SkPoint3& lightPos, SkScalar lightRadius, bool transparent);
 }
 
 #endif
diff --git a/src/utils/SkShadowUtils.cpp b/src/utils/SkShadowUtils.cpp
index 279ca7338c..430ea2c3b1 100644
--- a/src/utils/SkShadowUtils.cpp
+++ b/src/utils/SkShadowUtils.cpp
@@ -54,52 +54,52 @@ private:
 };
 
 static void build_table() {
-    SkDebugf("const uint16_t gByteExpU16Table[256] = {");
+    SkDebugf("const uint8_t gByteExpU8Table[256] = {");
     for (int i = 0; i <= 255; ++i) {
         if (!(i % 8)) {
             SkDebugf("\n");
         }
         SkScalar factor = SK_Scalar1 - i / 255.f;
         factor = SkScalarExp(-factor * factor * 4) - 0.018f;
-        int v = (int)(factor * 65536);
-        SkDebugf(" 0x%04X,", v);
+        int v = (int)(factor * 255.9f);
+        SkDebugf(" 0x%02X,", v);
     }
     SkDebugf("\n};\n");
 }
 
-const uint16_t gByteExpU16Table[256] = {
-    0x0014, 0x003A, 0x0062, 0x008A, 0x00B3, 0x00DE, 0x010A, 0x0136,
-    0x0165, 0x0194, 0x01C4, 0x01F6, 0x0229, 0x025E, 0x0294, 0x02CB,
-    0x0304, 0x033E, 0x0379, 0x03B7, 0x03F5, 0x0435, 0x0477, 0x04BB,
-    0x0500, 0x0546, 0x058F, 0x05D9, 0x0625, 0x0673, 0x06C3, 0x0714,
-    0x0768, 0x07BD, 0x0814, 0x086E, 0x08C9, 0x0926, 0x0986, 0x09E8,
-    0x0A4B, 0x0AB1, 0x0B1A, 0x0B84, 0x0BF1, 0x0C60, 0x0CD2, 0x0D46,
-    0x0DBC, 0x0E35, 0x0EB0, 0x0F2E, 0x0FAF, 0x1032, 0x10B7, 0x1140,
-    0x11CB, 0x1258, 0x12E9, 0x137C, 0x1412, 0x14AB, 0x1547, 0x15E6,
-    0x1688, 0x172D, 0x17D5, 0x187F, 0x192D, 0x19DE, 0x1A92, 0x1B4A,
-    0x1C04, 0x1CC2, 0x1D83, 0x1E47, 0x1F0E, 0x1FD9, 0x20A7, 0x2178,
-    0x224D, 0x2325, 0x2401, 0x24E0, 0x25C2, 0x26A8, 0x2792, 0x287F,
-    0x296F, 0x2A63, 0x2B5A, 0x2C56, 0x2D54, 0x2E56, 0x2F5C, 0x3065,
-    0x3172, 0x3283, 0x3397, 0x34AE, 0x35CA, 0x36E9, 0x380B, 0x3931,
-    0x3A5B, 0x3B88, 0x3CB9, 0x3DED, 0x3F25, 0x4061, 0x41A0, 0x42E2,
-    0x4428, 0x4572, 0x46BF, 0x480F, 0x4963, 0x4ABA, 0x4C14, 0x4D72,
-    0x4ED3, 0x5038, 0x519F, 0x530A, 0x5478, 0x55E9, 0x575D, 0x58D4,
-    0x5A4F, 0x5BCC, 0x5D4C, 0x5ECF, 0x6054, 0x61DD, 0x6368, 0x64F6,
-    0x6686, 0x6819, 0x69AE, 0x6B45, 0x6CDF, 0x6E7B, 0x701A, 0x71BA,
-    0x735D, 0x7501, 0x76A7, 0x784F, 0x79F9, 0x7BA4, 0x7D51, 0x7F00,
-    0x80AF, 0x8260, 0x8413, 0x85C6, 0x877A, 0x8930, 0x8AE6, 0x8C9C,
-    0x8E54, 0x900C, 0x91C4, 0x937D, 0x9535, 0x96EE, 0x98A7, 0x9A60,
-    0x9C18, 0x9DD1, 0x9F88, 0xA13F, 0xA2F6, 0xA4AB, 0xA660, 0xA814,
-    0xA9C6, 0xAB78, 0xAD27, 0xAED6, 0xB082, 0xB22D, 0xB3D6, 0xB57D,
-    0xB722, 0xB8C5, 0xBA65, 0xBC03, 0xBD9E, 0xBF37, 0xC0CD, 0xC25F,
-    0xC3EF, 0xC57B, 0xC704, 0xC889, 0xCA0B, 0xCB89, 0xCD04, 0xCE7A,
-    0xCFEC, 0xD15A, 0xD2C4, 0xD429, 0xD58A, 0xD6E6, 0xD83D, 0xD990,
-    0xDADD, 0xDC25, 0xDD68, 0xDEA6, 0xDFDE, 0xE111, 0xE23E, 0xE365,
-    0xE486, 0xE5A2, 0xE6B7, 0xE7C6, 0xE8CF, 0xE9D1, 0xEACD, 0xEBC3,
-    0xECB2, 0xED9A, 0xEE7C, 0xEF56, 0xF02A, 0xF0F6, 0xF1BC, 0xF27A,
-    0xF332, 0xF3E1, 0xF48A, 0xF52B, 0xF5C5, 0xF657, 0xF6E1, 0xF764,
-    0xF7DF, 0xF852, 0xF8BE, 0xF922, 0xF97E, 0xF9D2, 0xFA1E, 0xFA62,
-    0xFA9F, 0xFAD3, 0xFAFF, 0xFB23, 0xFB40, 0xFB54, 0xFB60, 0xFB64,
+const uint8_t gByteExpU8Table[256] = {
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01,
+    0x01, 0x01, 0x01, 0x01, 0x02, 0x02, 0x02, 0x02,
+    0x03, 0x03, 0x03, 0x03, 0x03, 0x04, 0x04, 0x04,
+    0x04, 0x05, 0x05, 0x05, 0x06, 0x06, 0x06, 0x07,
+    0x07, 0x07, 0x08, 0x08, 0x08, 0x09, 0x09, 0x09,
+    0x0A, 0x0A, 0x0B, 0x0B, 0x0B, 0x0C, 0x0C, 0x0D,
+    0x0D, 0x0E, 0x0E, 0x0F, 0x0F, 0x10, 0x10, 0x11,
+    0x11, 0x12, 0x12, 0x13, 0x14, 0x14, 0x15, 0x15,
+    0x16, 0x17, 0x17, 0x18, 0x19, 0x19, 0x1A, 0x1B,
+    0x1C, 0x1C, 0x1D, 0x1E, 0x1F, 0x1F, 0x20, 0x21,
+    0x22, 0x23, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28,
+    0x29, 0x2A, 0x2B, 0x2C, 0x2D, 0x2E, 0x2F, 0x30,
+    0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x38, 0x39,
+    0x3A, 0x3B, 0x3C, 0x3D, 0x3F, 0x40, 0x41, 0x42,
+    0x44, 0x45, 0x46, 0x48, 0x49, 0x4A, 0x4C, 0x4D,
+    0x4E, 0x50, 0x51, 0x53, 0x54, 0x55, 0x57, 0x58,
+    0x5A, 0x5B, 0x5D, 0x5E, 0x60, 0x61, 0x63, 0x64,
+    0x66, 0x68, 0x69, 0x6B, 0x6C, 0x6E, 0x70, 0x71,
+    0x73, 0x74, 0x76, 0x78, 0x79, 0x7B, 0x7D, 0x7E,
+    0x80, 0x82, 0x84, 0x85, 0x87, 0x89, 0x8A, 0x8C,
+    0x8E, 0x8F, 0x91, 0x93, 0x95, 0x96, 0x98, 0x9A,
+    0x9C, 0x9D, 0x9F, 0xA1, 0xA2, 0xA4, 0xA6, 0xA8,
+    0xA9, 0xAB, 0xAD, 0xAE, 0xB0, 0xB2, 0xB3, 0xB5,
+    0xB7, 0xB8, 0xBA, 0xBB, 0xBD, 0xBF, 0xC0, 0xC2,
+    0xC3, 0xC5, 0xC6, 0xC8, 0xC9, 0xCB, 0xCC, 0xCE,
+    0xCF, 0xD1, 0xD2, 0xD4, 0xD5, 0xD6, 0xD8, 0xD9,
+    0xDA, 0xDC, 0xDD, 0xDE, 0xDF, 0xE0, 0xE2, 0xE3,
+    0xE4, 0xE5, 0xE6, 0xE7, 0xE8, 0xE9, 0xEA, 0xEB,
+    0xEC, 0xED, 0xEE, 0xEF, 0xF0, 0xF0, 0xF1, 0xF2,
+    0xF3, 0xF3, 0xF4, 0xF5, 0xF5, 0xF6, 0xF6, 0xF7,
+    0xF7, 0xF8, 0xF8, 0xF9, 0xF9, 0xF9, 0xFA, 0xFA,
+    0xFA, 0xFA, 0xFA, 0xFB, 0xFB, 0xFB, 0xFB, 0xFB,
 };
 
 void SkGaussianColorFilter::filterSpan(const SkPMColor src[], int count, SkPMColor dst[]) const {
@@ -109,7 +109,7 @@ void SkGaussianColorFilter::filterSpan(const SkPMColor src[], int count, SkPMCol
     }
     for (int i = 0; i < count; ++i) {
         SkPMColor c = src[i];
-        uint8_t a = gByteExpU16Table[SkGetPackedB32(c)] * SkGetPackedG32(c) >> 16;
+        uint8_t a = gByteExpU8Table[SkGetPackedA32(c)];
         dst[i] = SkPackARGB32(a, a, a, a);
     }
 }
@@ -143,12 +143,10 @@ uint64_t resource_cache_shared_id() {
 /** Factory for an ambient shadow mesh with particular shadow properties. */
 struct AmbientVerticesFactory {
     SkScalar fOccluderHeight = SK_ScalarNaN;  // NaN so that isCompatible will fail until init'ed.
-    SkScalar fAmbientAlpha;
     bool fTransparent;
 
     bool isCompatible(const AmbientVerticesFactory& that, SkVector* translate) const {
-        if (fOccluderHeight != that.fOccluderHeight || fAmbientAlpha != that.fAmbientAlpha ||
-            fTransparent != that.fTransparent) {
+        if (fOccluderHeight != that.fOccluderHeight || fTransparent != that.fTransparent) {
             return false;
         }
         translate->set(0, 0);
@@ -159,7 +157,7 @@ struct AmbientVerticesFactory {
         SkScalar z = fOccluderHeight;
         return SkShadowTessellator::MakeAmbient(path, ctm,
                                                 [z](SkScalar, SkScalar) { return z; },
-                                                fAmbientAlpha, fTransparent);
+                                                fTransparent);
     }
 };
 
@@ -178,13 +176,11 @@ struct SpotVerticesFactory {
     SkScalar fOccluderHeight = SK_ScalarNaN; // NaN so that isCompatible will fail until init'ed.
     SkPoint3 fDevLightPos;
     SkScalar fLightRadius;
-    SkScalar fSpotAlpha;
     OccluderType fOccluderType;
 
     bool isCompatible(const SpotVerticesFactory& that, SkVector* translate) const {
         if (fOccluderHeight != that.fOccluderHeight || fDevLightPos.fZ != that.fDevLightPos.fZ ||
-            fLightRadius != that.fLightRadius || fSpotAlpha != that.fSpotAlpha ||
-            fOccluderType != that.fOccluderType) {
+            fLightRadius != that.fLightRadius || fOccluderType != that.fOccluderType) {
             return false;
         }
         switch (fOccluderType) {
@@ -212,8 +208,7 @@ struct SpotVerticesFactory {
         SkScalar z = fOccluderHeight;
         return SkShadowTessellator::MakeSpot(path, ctm,
                                              [z](SkScalar, SkScalar) -> SkScalar { return z; },
-                                             fDevLightPos, fLightRadius,
-                                             fSpotAlpha, transparent);
+                                             fDevLightPos, fLightRadius, transparent);
     }
 };
 
@@ -569,14 +564,21 @@ static bool draw_analytic_shadows(SkCanvas* canvas, const SkPath& path, SkScalar
     return false;
 }
 
+static SkColor compute_render_color(SkColor color, float alpha) {
+    return SkColorSetARGB(alpha*SkColorGetA(color), SkColorGetR(color),
+                          SkColorGetG(color), SkColorGetB(color));
+}
+
 // Draw an offset spot shadow and outlining ambient shadow for the given path.
 void SkShadowUtils::DrawShadow(SkCanvas* canvas, const SkPath& path, SkScalar occluderHeight,
                                const SkPoint3& devLightPos, SkScalar lightRadius,
                                SkScalar ambientAlpha, SkScalar spotAlpha, SkColor color,
                                uint32_t flags, SkResourceCache* cache) {
     // try fast paths
-    if (draw_analytic_shadows(canvas, path, occluderHeight, devLightPos, lightRadius,
-                              ambientAlpha, spotAlpha, color, flags)) {
+    bool skipAnalytic = SkToBool(flags & SkShadowFlags::kGeometricOnly_ShadowFlag);
+    if (!skipAnalytic && draw_analytic_shadows(canvas, path, occluderHeight, devLightPos,
+                                               lightRadius, ambientAlpha, spotAlpha, color,
+                                               flags)) {
         return;
     }
 
@@ -592,10 +594,10 @@ void SkShadowUtils::DrawShadow(SkCanvas* canvas, const SkPath& path, SkScalar oc
         ambientAlpha = SkTMin(ambientAlpha, 1.f);
         AmbientVerticesFactory factory;
         factory.fOccluderHeight = occluderHeight;
-        factory.fAmbientAlpha = ambientAlpha;
         factory.fTransparent = transparent;
 
-        draw_shadow(factory, canvas, shadowedPath, color, cache);
+        SkColor renderColor = compute_render_color(color, ambientAlpha);
+        draw_shadow(factory, canvas, shadowedPath, renderColor, cache);
     }
 
     if (spotAlpha > 0) {
@@ -614,7 +616,6 @@ void SkShadowUtils::DrawShadow(SkCanvas* canvas, const SkPath& path, SkScalar oc
         factory.fOccluderHeight = occluderHeight;
         factory.fDevLightPos = devLightPos;
         factory.fLightRadius = lightRadius;
-        factory.fSpotAlpha = spotAlpha;
 
         SkRRect rrect;
         if (transparent) {
@@ -653,7 +654,9 @@ void SkShadowUtils::DrawShadow(SkCanvas* canvas, const SkPath& path, SkScalar oc
         if (factory.fOccluderType == SpotVerticesFactory::OccluderType::kOpaque) {
             factory.fOccluderType = SpotVerticesFactory::OccluderType::kTransparent;
         }
-        draw_shadow(factory, canvas, shadowedPath, color, cache);
+
+        SkColor renderColor = compute_render_color(color, spotAlpha);
+        draw_shadow(factory, canvas, shadowedPath, renderColor, cache);
     }
 }
 
@@ -665,8 +668,10 @@ void SkShadowUtils::DrawUncachedShadow(SkCanvas* canvas, const SkPath& path,
                                        SkScalar ambientAlpha, SkScalar spotAlpha, SkColor color,
                                        uint32_t flags) {
     // try fast paths
-    if (draw_analytic_shadows(canvas, path, heightFunc(0, 0), lightPos, lightRadius,
-                              ambientAlpha, spotAlpha, color, flags)) {
+    bool skipAnalytic = SkToBool(flags & SkShadowFlags::kGeometricOnly_ShadowFlag);
+    if (!skipAnalytic && draw_analytic_shadows(canvas, path, heightFunc(0, 0), lightPos,
+                                               lightRadius, ambientAlpha, spotAlpha, color,
+                                               flags)) {
         return;
     }
 
@@ -679,13 +684,13 @@ void SkShadowUtils::DrawUncachedShadow(SkCanvas* canvas, const SkPath& path,
     if (ambientAlpha > 0) {
         ambientAlpha = SkTMin(ambientAlpha, 1.f);
         sk_sp<SkVertices> vertices = SkShadowTessellator::MakeAmbient(path, viewMatrix,
-                                                                      heightFunc, ambientAlpha,
-                                                                      transparent);
+                                                                      heightFunc, transparent);
+        SkColor renderColor = compute_render_color(color, ambientAlpha);
         SkPaint paint;
         // Run the vertex color through a GaussianColorFilter and then modulate the grayscale
         // result of that against our 'color' param.
         paint.setColorFilter(SkColorFilter::MakeComposeFilter(
-            SkColorFilter::MakeModeFilter(color, SkBlendMode::kModulate),
+            SkColorFilter::MakeModeFilter(renderColor, SkBlendMode::kModulate),
             SkGaussianColorFilter::Make()));
         canvas->drawVertices(vertices, SkBlendMode::kModulate, paint);
     }
@@ -694,12 +699,13 @@ void SkShadowUtils::DrawUncachedShadow(SkCanvas* canvas, const SkPath& path,
         spotAlpha = SkTMin(spotAlpha, 1.f);
         sk_sp<SkVertices> vertices = SkShadowTessellator::MakeSpot(path, viewMatrix, heightFunc,
                                                                    lightPos, lightRadius,
-                                                                   spotAlpha, transparent);
+                                                                   transparent);
+        SkColor renderColor = compute_render_color(color, spotAlpha);
         SkPaint paint;
         // Run the vertex color through a GaussianColorFilter and then modulate the grayscale
         // result of that against our 'color' param.
         paint.setColorFilter(SkColorFilter::MakeComposeFilter(
-            SkColorFilter::MakeModeFilter(color, SkBlendMode::kModulate),
+            SkColorFilter::MakeModeFilter(renderColor, SkBlendMode::kModulate),
             SkGaussianColorFilter::Make()));
         canvas->drawVertices(vertices, SkBlendMode::kModulate, paint);
     }
diff --git a/tests/ShadowUtilsTest.cpp b/tests/ShadowUtilsTest.cpp
index 56990146f0..f83e44a1fc 100644
--- a/tests/ShadowUtilsTest.cpp
+++ b/tests/ShadowUtilsTest.cpp
@@ -14,29 +14,25 @@
 
 void tessellate_shadow(skiatest::Reporter* reporter, const SkPath& path, const SkMatrix& ctm,
                        bool expectSuccess) {
-    static constexpr SkScalar kAmbientAlpha = 0.25f;
-    static constexpr SkScalar kSpotAlpha = 0.25f;
 
     auto heightFunc = [] (SkScalar, SkScalar) { return 4; };
 
-    auto verts = SkShadowTessellator::MakeAmbient(path, ctm, heightFunc, kAmbientAlpha, true);
+    auto verts = SkShadowTessellator::MakeAmbient(path, ctm, heightFunc, true);
     if (expectSuccess != SkToBool(verts)) {
         ERRORF(reporter, "Expected shadow tessellation to %s but it did not.",
                expectSuccess ? "succeed" : "fail");
     }
-    verts = SkShadowTessellator::MakeAmbient(path, ctm, heightFunc, kAmbientAlpha, false);
+    verts = SkShadowTessellator::MakeAmbient(path, ctm, heightFunc, false);
     if (expectSuccess != SkToBool(verts)) {
         ERRORF(reporter, "Expected shadow tessellation to %s but it did not.",
                expectSuccess ? "succeed" : "fail");
     }
-    verts = SkShadowTessellator::MakeSpot(path, ctm, heightFunc, {0, 0, 128}, 128.f,
-                                          kSpotAlpha, false);
+    verts = SkShadowTessellator::MakeSpot(path, ctm, heightFunc, {0, 0, 128}, 128.f, false);
     if (expectSuccess != SkToBool(verts)) {
         ERRORF(reporter, "Expected shadow tessellation to %s but it did not.",
                expectSuccess ? "succeed" : "fail");
     }
-    verts = SkShadowTessellator::MakeSpot(path, ctm, heightFunc, {0, 0, 128}, 128.f,
-                                          kSpotAlpha, false);
+    verts = SkShadowTessellator::MakeSpot(path, ctm, heightFunc, {0, 0, 128}, 128.f, false);
     if (expectSuccess != SkToBool(verts)) {
         ERRORF(reporter, "Expected shadow tessellation to %s but it did not.",
                expectSuccess ? "succeed" : "fail");