Add ability to rotate light direction in drawLitAtlas Sample slide

src/core/SkLightingShader.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmapProcState.h"
 #include "SkColor.h"
 #include "SkEmptyShader.h"
@@ skipping 492 matching lines @@
 
         for (int i = 0; i < n; ++i) {
             SkASSERT(0xFF == SkColorGetA(tmpNormal2[i]));  // opaque -> unpremul
             norm.set(SkIntToScalar(SkGetPackedR32(tmpNormal2[i]))-127.0f,
                      SkIntToScalar(SkGetPackedG32(tmpNormal2[i]))-127.0f,
                      SkIntToScalar(SkGetPackedB32(tmpNormal2[i]))-127.0f);
             norm.normalize();
 
             xformedNorm.fX = lightShader.fInvNormRotation.fX * norm.fX +
                              lightShader.fInvNormRotation.fY * norm.fY;
-            xformedNorm.fY = lightShader.fInvNormRotation.fX * norm.fX -
-                             lightShader.fInvNormRotation.fY * norm.fY;
+            xformedNorm.fY = -lightShader.fInvNormRotation.fY * norm.fX +
+                             lightShader.fInvNormRotation.fX * norm.fY;
             xformedNorm.fZ = norm.fZ;
 
             SkColor diffColor = SkUnPreMultiply::PMColorToColor(tmpColor2[i]);
 
             SkColor3f accum = SkColor3f::Make(0.0f, 0.0f, 0.0f);
             // This is all done in linear unpremul color space (each component 0..255.0f though)
             for (int l = 0; l < lightShader.fLights->numLights(); ++l) {
                 const SkLights::Light& light = lightShader.fLights->light(l);
 
                 if (SkLights::Light::kAmbient_LightType == light.type()) {
@@ skipping 197 matching lines @@
                                             invNormRotation, diffLocalM, normLocalM);
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_START(SkLightingShader)
     SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkLightingShaderImpl)
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_END
 
 ///////////////////////////////////////////////////////////////////////////////