add SkLerpXfermode

src/effects/SkLerpXfermode.cpp

Index: src/effects/SkLerpXfermode.cpp
diff --git a/src/effects/SkLerpXfermode.cpp b/src/effects/SkLerpXfermode.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..d73ecf4c5771bd425d6104ec2a51a86c700ec6f1
--- /dev/null
+++ b/src/effects/SkLerpXfermode.cpp
@@ -0,0 +1,110 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkLerpXfermode.h"
+#include "SkColorPriv.h"
+#include "SkFlattenableBuffers.h"
+#include "SkString.h"
+
+SkXfermode* SkLerpXfermode::Create(SkScalar scale) {
+    int scale256 = SkScalarRoundToInt(scale * 256);
+    if (scale256 >= 256) {
+        return SkXfermode::Create(SkXfermode::kSrc_Mode);
+    } else if (scale256 <= 0) {
+        return SkXfermode::Create(SkXfermode::kDst_Mode);
+    }
+    return SkNEW_ARGS(SkLerpXfermode, (scale256));
+}
+
+SkLerpXfermode::SkLerpXfermode(unsigned scale256) : fScale256(scale256) {}
+
+SkLerpXfermode::SkLerpXfermode(SkFlattenableReadBuffer& buffer)
+    : INHERITED(buffer) {
+    fScale256 = buffer.readUInt();
+}
+
+void SkLerpXfermode::flatten(SkFlattenableWriteBuffer& buffer) const {
+    this->INHERITED::flatten(buffer);
+    buffer.writeUInt(fScale256);
+}
+
+void SkLerpXfermode::xfer32(SkPMColor dst[], const SkPMColor src[], int count,
+                             const SkAlpha aa[]) const {
+    const int scale = fScale256;
+
+    if (aa) {
+        for (int i = 0; i < count; ++i) {
+            unsigned a = aa[i];
+            if (a) {
+                SkPMColor dstC = dst[i];
+                SkPMColor resC = SkFastFourByteInterp256(src[i], dstC, scale);
+                if (a < 255) {
+                    resC = SkFastFourByteInterp256(resC, dstC, a + (a >> 7));
+                }
+                dst[i] = resC;
+            }
+        }
+    } else {
+        for (int i = 0; i < count; ++i) {
+            dst[i] = SkFastFourByteInterp256(src[i], dst[i], scale);
+        }
+    }
+}
+
+void SkLerpXfermode::xfer16(uint16_t dst[], const SkPMColor src[], int count,
+                             const SkAlpha aa[]) const {
+    const int scale = fScale256;
+
+    if (aa) {
+        for (int i = 0; i < count; ++i) {
+            unsigned a = aa[i];
+            if (a) {
+                SkPMColor dstC = SkPixel16ToPixel32(dst[i]);
+                SkPMColor resC = SkFastFourByteInterp256(src[i], dstC, scale);
+                if (a < 255) {
+                    resC = SkFastFourByteInterp256(resC, dstC, a + (a >> 7));
+                }
+                dst[i] = SkPixel32ToPixel16(resC);
+            }
+        }
+    } else {
+        for (int i = 0; i < count; ++i) {
+            SkPMColor dstC = SkPixel16ToPixel32(dst[i]);
+            SkPMColor resC = SkFastFourByteInterp256(src[i], dstC, scale);
+            dst[i] = SkPixel32ToPixel16(resC);
+        }
+    }
+}
+
+void SkLerpXfermode::xferA8(SkAlpha dst[], const SkPMColor src[], int count,
+                             const SkAlpha aa[]) const {
+    const int scale = fScale256;
+
+    if (aa) {
+        for (int i = 0; i < count; ++i) {
+            unsigned a = aa[i];
+            if (a) {
+                unsigned dstA = dst[i];
+                unsigned resA = SkAlphaBlend(SkGetPackedA32(src[i]), dstA, scale);
+                if (a < 255) {
+                    resA = SkAlphaBlend(resA, dstA, a + (a >> 7));
+                }
+                dst[i] = resA;
+            }
+        }
+    } else {
+        for (int i = 0; i < count; ++i) {
+            dst[i] = SkAlphaBlend(SkGetPackedA32(src[i]), dst[i], scale);
+        }
+    }
+}
+
+#ifdef SK_DEVELOPER
+void SkLerpXfermode::toString(SkString* str) const {
+    str->printf("SkLerpXfermode: scale: %g", fScale256 / 256.0);
+}
+#endif