clamp matrix-translate before converting to pmcolor

src/effects/SkColorMatrixFilter.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkColorMatrixFilter.h"
 #include "SkColorMatrix.h"
 #include "SkColorPriv.h"
@@ skipping 254 matching lines @@
 #endif
 
     return pm;
 }
 
 static Sk4s unpremul(const SkPMFloat& pm) {
     float scale = 255 / pm.a(); // candidate for fast/approx invert?
     return Sk4s(pm) * Sk4s(scale, scale, scale, 1);
 }
 
+static Sk4f clamp_0_255(const Sk4f& value) {
+    return Sk4f::Max(Sk4f::Min(value, Sk4f(255)), Sk4f(0));
+}
+
 void SkColorMatrixFilter::filterSpan(const SkPMColor src[], int count, SkPMColor dst[]) const {
     Proc proc = fProc;
     if (NULL == proc) {
         if (src != dst) {
             memcpy(dst, src, count * sizeof(SkPMColor));
         }
         return;
     }
 
 #ifdef SK_SUPPORT_LEGACY_INT_COLORMATRIX
     const bool use_floats = false;
 #else
     const bool use_floats = true;
 #endif
 
     if (use_floats) {
         const Sk4s c0 = Sk4s::Load(fTranspose + 0);
         const Sk4s c1 = Sk4s::Load(fTranspose + 4);
         const Sk4s c2 = Sk4s::Load(fTranspose + 8);
         const Sk4s c3 = Sk4s::Load(fTranspose + 12);
         const Sk4s c4 = Sk4s::Load(fTranspose + 16);  // translates
 
-        SkPMColor matrix_translate_pmcolor = SkPMFloat(premul(c4)).clamped();
+        // todo: we could cache this in the constructor...
+        SkPMColor matrix_translate_pmcolor = SkPMFloat(premul(clamp_0_255(c4))).clamped();
 
         for (int i = 0; i < count; i++) {
             const SkPMColor src_c = src[i];
             if (0 == src_c) {
                 dst[i] = matrix_translate_pmcolor;
                 continue;
             }
 
             SkPMFloat srcf(src_c);
 
             if (0xFF != SkGetPackedA32(src_c)) {
                 srcf = unpremul(srcf);
             }
 
             Sk4s r4 = Sk4s(srcf.r());
             Sk4s g4 = Sk4s(srcf.g());
             Sk4s b4 = Sk4s(srcf.b());
             Sk4s a4 = Sk4s(srcf.a());
 
             // apply matrix
             Sk4s dst4 = c0 * r4 + c1 * g4 + c2 * b4 + c3 * a4 + c4;
 
-            // pin before re-premul (convention for color-matrix???)
-            dst4 = Sk4s::Max(Sk4s(0), Sk4s::Min(Sk4s(255), dst4));
-
-            // re-premul and write
-            dst[i] = SkPMFloat(premul(dst4)).get();
+            // clamp, re-premul, and write
+            dst[i] = SkPMFloat(premul(clamp_0_255(dst4))).get();
         }
     } else {
         const State& state = fState;
         int32_t result[4];
         const SkUnPreMultiply::Scale* table = SkUnPreMultiply::GetScaleTable();
 
         for (int i = 0; i < count; i++) {
             SkPMColor c = src[i];
 
             unsigned r = SkGetPackedR32(c);
@@ skipping 240 matching lines @@
     str->append("matrix: (");
     for (int i = 0; i < 20; ++i) {
         str->appendScalar(fMatrix.fMat[i]);
         if (i < 19) {
             str->append(", ");
         }
     }
     str->append(")");
 }
 #endif