extend compose-colorfilter to 4f

src/core/SkColor.cpp

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkColor.h"
 #include "SkColorPriv.h"
 #include "SkFixed.h"
@@ skipping 93 matching lines @@
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 #include "SkNx.h"
 
 SkPM4f SkPM4f::FromPMColor(SkPMColor c) {
     Sk4f value = SkNx_cast<float>(Sk4b::Load(&c));
     SkPM4f c4;
     (value * Sk4f(1.0f / 255)).store(&c4);
     return c4;
 }
 
+SkColor4f SkPM4f::unpremul() const {
+    float alpha = fVec[A];
+    if (0 == alpha) {
+        return { 0, 0, 0, 0 };
+    } else {
+        float invAlpha = 1 / alpha;
+        return { alpha, fVec[R] * invAlpha, fVec[G] * invAlpha, fVec[B] * invAlpha };
+    }
+}
+
 SkColor4f SkColor4f::FromColor(SkColor c) {
     Sk4f value = SkNx_shuffle<3,2,1,0>(SkNx_cast<float>(Sk4b::Load(&c)));
     SkColor4f c4;
     (value * Sk4f(1.0f / 255)).store(&c4);
     return c4;
 }
 
 SkColor4f SkColor4f::Pin(float a, float r, float g, float b) {
     SkColor4f c4;
     Sk4f::Min(Sk4f::Max(Sk4f(a, r, g, b), Sk4f(0)), Sk4f(1)).store(c4.vec());
@@ skipping 17 matching lines @@
     dst.store(&pm4);
     return pm4;
 }
 
 #ifdef SK_DEBUG
 void SkPM4f::assertIsUnit() const {
     auto c4 = Sk4f::Load(fVec);
     SkASSERT((c4 >= Sk4f(0)).allTrue() && (c4 <= Sk4f(1)).allTrue());
 }
 #endif