Luminance-to-alpha color filter (SkLumaColorFilter).

tests/ColorFilterTest.cpp

Index: tests/ColorFilterTest.cpp
diff --git a/tests/ColorFilterTest.cpp b/tests/ColorFilterTest.cpp
index 4016f2193d58a3e14cc3bddf0c33cb2f8b19bfc3..b333ad68f090af838ecf604e829e4fca9bad56db 100644
--- a/tests/ColorFilterTest.cpp
+++ b/tests/ColorFilterTest.cpp
@@ -7,7 +7,9 @@
  */
 #include "Test.h"
 #include "SkColor.h"
+#include "SkColorPriv.h"
 #include "SkColorFilter.h"
+#include "SkLumaColorFilter.h"
 #include "SkRandom.h"
 #include "SkXfermode.h"
 #include "SkOrderedReadBuffer.h"
@@ -93,5 +95,38 @@ static void test_asColorMode(skiatest::Reporter* reporter) {
     }
 }
 
+///////////////////////////////////////////////////////////////////////////////
+
+static void test_lumaColorFilter(skiatest::Reporter* reporter) {
+    SkPMColor in, out;
+    SkAutoTUnref<SkColorFilter> lf(SkLumaColorFilter::Create());
+
+    // Applying luma to white is a nop (luminance(white) == 1.0)
+    for (unsigned i = 0; i < 256; ++i) {
+        in = SkPackARGB32(i, i, i, i);
+        lf->filterSpan(&in, 1, &out);
+        REPORTER_ASSERT(reporter, out == in);
+    }
+
+    // Applying luma to black yields transparent black (luminance(black) == 0)
+    for (unsigned i = 0; i < 256; ++i) {
+        in = SkPackARGB32(i, 0, 0, 0);
+        lf->filterSpan(&in, 1, &out);
+        REPORTER_ASSERT(reporter, out == SK_ColorTRANSPARENT);
+    }
+
+    // For general colors, a luma filter has an attenuating effect.
+    for (unsigned i = 1; i < 256; ++i) {
+        in = SkPackARGB32(i, i, i / 2, i / 3);
+        lf->filterSpan(&in, 1, &out);
+        REPORTER_ASSERT(reporter, out != in);
+        REPORTER_ASSERT(reporter, SkGetPackedA32(out) <= i);
+        REPORTER_ASSERT(reporter, SkGetPackedR32(out) <= i);
+        REPORTER_ASSERT(reporter, SkGetPackedG32(out) <= i / 2);
+        REPORTER_ASSERT(reporter, SkGetPackedB32(out) <= i / 3);
+    }
+}
+
 #include "TestClassDef.h"
 DEFINE_TESTCLASS("ColorFilter", ColorFilterTestClass, test_asColorMode)
+DEFINE_TESTCLASS("LumaColorFilter", LumaColorFilterTestClass, test_lumaColorFilter)