add test for opaque-preserving colormatrixfilters

BUG=skia:

Review URL: https://codereview.chromium.org/1069463002

tests/ColorFilterTest.cpp

@@ -147,3 +147,89 @@ DEF_TEST(LumaColorFilter, reporter) {
         REPORTER_ASSERT(reporter, SkGetPackedB32(out) == 0);
     }
 }
+
+///////////////////////////////////////////////////////////////////////////////
+
+#include "SkColorMatrixFilter.h"
+
+static void get_brightness_matrix(float amount, float matrix[20]) {
+    // Spec implementation
+    // (http://dvcs.w3.org/hg/FXTF/raw-file/tip/filters/index.html#brightnessEquivalent)
+    // <feFunc[R|G|B] type="linear" slope="[amount]">
+    memset(matrix, 0, 20 * sizeof(SkScalar));
+    matrix[0] = matrix[6] = matrix[12] = amount;
+    matrix[18] = 1.f;
+}
+
+static void get_grayscale_matrix(float amount, float matrix[20]) {
+    // Note, these values are computed to ensure MatrixNeedsClamping is false
+    // for amount in [0..1]
+    matrix[0] = 0.2126f + 0.7874f * amount;
+    matrix[1] = 0.7152f - 0.7152f * amount;
+    matrix[2] = 1.f - (matrix[0] + matrix[1]);
+    matrix[3] = matrix[4] = 0.f;
+    
+    matrix[5] = 0.2126f - 0.2126f * amount;
+    matrix[6] = 0.7152f + 0.2848f * amount;
+    matrix[7] = 1.f - (matrix[5] + matrix[6]);
+    matrix[8] = matrix[9] = 0.f;
+    
+    matrix[10] = 0.2126f - 0.2126f * amount;
+    matrix[11] = 0.7152f - 0.7152f * amount;
+    matrix[12] = 1.f - (matrix[10] + matrix[11]);
+    matrix[13] = matrix[14] = 0.f;
+    
+    matrix[15] = matrix[16] = matrix[17] = matrix[19] = 0.f;
+    matrix[18] = 1.f;
+}
+
+static SkColorFilter* make_cf0() {
+    SkScalar matrix[20];
+    get_brightness_matrix(0.5f, matrix);
+    return SkColorMatrixFilter::Create(matrix);
+}
+static SkColorFilter* make_cf1() {
+    SkScalar matrix[20];
+    get_grayscale_matrix(1, matrix);
+    return SkColorMatrixFilter::Create(matrix);
+}
+static SkColorFilter* make_cf2() {
+    SkColorMatrix m0, m1;
+    get_brightness_matrix(0.5f, m0.fMat);
+    get_grayscale_matrix(1, m1.fMat);
+    m0.preConcat(m1);
+    return SkColorMatrixFilter::Create(m0);
+}
+static SkColorFilter* make_cf3() {
+    SkColorMatrix m0, m1;
+    get_brightness_matrix(0.5f, m0.fMat);
+    get_grayscale_matrix(1, m1.fMat);
+    m0.postConcat(m1);
+    return SkColorMatrixFilter::Create(m0);
+}
+typedef SkColorFilter* (*CFProc)();
+
+// Test that a colormatrix that "should" preserve opaquness actually does.
+DEF_TEST(ColorMatrixFilter, reporter) {
+    const CFProc procs[] = {
+        make_cf0, make_cf1, make_cf2, make_cf3,
+    };
+
+    for (size_t i = 0; i < SK_ARRAY_COUNT(procs); ++i) {
+        SkAutoTUnref<SkColorFilter> cf(procs[i]());
+
+        // generate all possible r,g,b triples
+        for (int r = 0; r < 256; ++r) {
+            for (int g = 0; g < 256; ++g) {
+                SkPMColor storage[256];
+                for (int b = 0; b < 256; ++b) {
+                    storage[b] = SkPackARGB32(0xFF, r, g, b);
+                }
+                cf->filterSpan(storage, 256, storage);
+                for (int b = 0; b < 256; ++b) {
+                    REPORTER_ASSERT(reporter, 0xFF == SkGetPackedA32(storage[b]));
+                }
+            }
+        }
+    }
+}