Harden linear gradients

src/effects/gradients/SkLinearGradient.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Sk4fLinearGradient.h"
 #include "SkLinearGradient.h"
 
@@ skipping 81 matching lines @@
 //
 static uint32_t SkSwizzle_Color_to_PMColor(SkColor c) {
     return SkPackARGB32NoCheck(SkColorGetA(c), SkColorGetR(c), SkColorGetG(c), SkColorGetB(c));
 }
 
 SkLinearGradient::LinearGradientContext::LinearGradientContext(
         const SkLinearGradient& shader, const ContextRec& ctx)
     : INHERITED(shader, ctx)
 {
     // setup for Sk4f
-    int count = shader.fColorCount;
+    const int count = shader.fColorCount;
+    SkASSERT(count > 1);
+
     fRecs.setCount(count);
     Rec* rec = fRecs.begin();
     if (shader.fOrigPos) {
         rec[0].fPos = 0;
         SkDEBUGCODE(rec[0].fPosScale = SK_FloatNaN;)   // should never get used
         for (int i = 1; i < count; ++i) {
             rec[i].fPos = SkTPin(shader.fOrigPos[i], rec[i - 1].fPos, 1.0f);
             float diff = rec[i].fPos - rec[i - 1].fPos;
             if (diff > 0) {
                 rec[i].fPosScale = 1.0f / diff;
             } else {
                 rec[i].fPosScale = 0;
             }
         }
-        rec[count - 1].fPos = 1;    // overwrite the last value just to be sure we end at 1.0
     } else {
         // no pos specified, so we compute evenly spaced values
         const float scale = float(count - 1);
-        float invScale = 1.0f / scale;
+        const float invScale = 1.0f / scale;
         for (int i = 0; i < count; ++i) {
             rec[i].fPos = i * invScale;
             rec[i].fPosScale = scale;
         }
     }
+    rec[count - 1].fPos = 1;    // overwrite the last value just to be sure we end at 1.0
 
     fApplyAlphaAfterInterp = true;
     if ((shader.getGradFlags() & SkGradientShader::kInterpolateColorsInPremul_Flag) ||
         shader.colorsAreOpaque())
     {
         fApplyAlphaAfterInterp = false;
     }
 
     if (fApplyAlphaAfterInterp) {
         // Our fColor values are in PMColor order, but are still unpremultiplied, allowing us to
@@ skipping 607 matching lines @@
             this->shade4_dx_clamp<false, true>(dstC, count, fx, dx, invDx, dither);
         }
     } else {
         if (fApplyAlphaAfterInterp) {
             this->shade4_dx_clamp<true, false>(dstC, count, fx, dx, invDx, dither);
         } else {
             this->shade4_dx_clamp<false, false>(dstC, count, fx, dx, invDx, dither);
         }
     }
 }