Reland of Add fast normalize for SkLightingImageFilter. (patchset #1 id:1 of https://codereview.chromium.org/1244523002/)

Reason for revert:
Florin will rebaseline the images.

Original issue's description:
> Revert of Add fast normalize for SkLightingImageFilter. (patchset #2 id:20001 of https://codereview.chromium.org/1240023002/)
>
> Reason for revert:
> Speculative revert -- DEPS roll block on linux_blink_rel
>
> https://storage.googleapis.com/chromium-layout-test-archives/linux_blink_rel/71483/layout-test-results/results.html
>
> Original issue's description:
> > Add fast normalize for SkLightingImageFilter.
> >
> > The normalize routine in SkPoint3 is very robust. However, for simple
> > lighting cases we prefer speed over robustness. This fixes a perf
> > regression in smoothness.tough_filters_cases.
> >
> > BUG=chromium:510562
> >
> > Committed: https://skia.googlesource.com/skia/+/dfa0ecf169db87f7afddd93bc1c500de481a62c7
>
> TBR=reed@google.com,senorblanco@google.com,senorblanco@chromium.org,jvanverth@google.com
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=chromium:510562
>
> Committed: https://skia.googlesource.com/skia/+/ac66a8122b27c388cc74b3913d9a9be351a44e54

TBR=reed@google.com,senorblanco@google.com,senorblanco@chromium.org,reed@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:510562

Review URL: https://codereview.chromium.org/1241583007

1 files changed, 15 insertions, 6 deletions

diff --git a/src/effects/SkLightingImageFilter.cpp b/src/effects/SkLightingImageFilter.cpp
index ae49462b5e..b82f6ad916 100644
--- a/src/effects/SkLightingImageFilter.cpp
+++ b/src/effects/SkLightingImageFilter.cpp
@@ -60,6 +60,15 @@ inline void shiftMatrixLeft(int m[9]) {
     m[7] = m[8];
 }
 
+static inline void fast_normalize(SkPoint3* vector) {
+    // add a tiny bit so we don't have to worry about divide-by-zero
+    SkScalar magSq = vector->dot(*vector) + SK_ScalarNearlyZero;
+    SkScalar scale = sk_float_rsqrt(magSq);
+    vector->fX *= scale;
+    vector->fY *= scale;
+    vector->fZ *= scale;
+}
+
 class DiffuseLightingType {
 public:
     DiffuseLightingType(SkScalar kd)
@@ -90,7 +99,7 @@ public:
                     const SkPoint3& lightColor) const {
         SkPoint3 halfDir(surfaceTolight);
         halfDir.fZ += SK_Scalar1;        // eye position is always (0, 0, 1)
-        halfDir.normalize();
+        fast_normalize(&halfDir);
         SkScalar colorScale = SkScalarMul(fKS,
             SkScalarPow(normal.dot(halfDir), fShininess));
         colorScale = SkScalarClampMax(colorScale, SK_Scalar1);
@@ -113,7 +122,7 @@ inline SkPoint3 pointToNormal(SkScalar x, SkScalar y, SkScalar surfaceScale) {
     SkPoint3 vector = SkPoint3::Make(SkScalarMul(-x, surfaceScale),
                                      SkScalarMul(-y, surfaceScale),
                                      SK_Scalar1);
-    vector.normalize();
+    fast_normalize(&vector);
     return vector;
 }
 
@@ -800,7 +809,7 @@ public:
                                             fLocation.fY - SkIntToScalar(y),
                                             fLocation.fZ - SkScalarMul(SkIntToScalar(z),
                                                                        surfaceScale));
-        direction.normalize();
+        fast_normalize(&direction);
         return direction;
     };
     const SkPoint3& lightColor(const SkPoint3&) const { return this->color(); }
@@ -866,7 +875,7 @@ public:
        fSpecularExponent(SkScalarPin(specularExponent, kSpecularExponentMin, kSpecularExponentMax))
     {
        fS = target - location;
-       fS.normalize();
+       fast_normalize(&fS);
        fCosOuterConeAngle = SkScalarCos(SkDegreesToRadians(cutoffAngle));
        const SkScalar antiAliasThreshold = 0.016f;
        fCosInnerConeAngle = fCosOuterConeAngle + antiAliasThreshold;
@@ -888,7 +897,7 @@ public:
         SkPoint3 target = SkPoint3::Make(target2.fX, target2.fY,
                                          SkScalarAve(targetZ.fX, targetZ.fY));
         SkPoint3 s = target - location;
-        s.normalize();
+        fast_normalize(&s);
         return new SkSpotLight(location,
                                target,
                                fSpecularExponent,
@@ -904,7 +913,7 @@ public:
                                             fLocation.fY - SkIntToScalar(y),
                                             fLocation.fZ - SkScalarMul(SkIntToScalar(z),
                                                                        surfaceScale));
-        direction.normalize();
+        fast_normalize(&direction);
         return direction;
     };
     SkPoint3 lightColor(const SkPoint3& surfaceToLight) const {