add SkLerpXfermode

include/core/SkColorPriv.h

 
 /*
  * 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.
  */
 
 
 #ifndef SkColorPriv_DEFINED
@@ skipping 255 matching lines @@
                                          U8CPU srcWeight) {
     unsigned scale = SkAlpha255To256(srcWeight);
     return SkFourByteInterp256(src, dst, scale);
 }
 
 /**
  * 32b optimized version; currently appears to be 10% faster even on 64b
  * architectures than an equivalent 64b version and 30% faster than
  * SkFourByteInterp(). Third parameter controls blending of the first two:
  *   (src, dst, 0) returns dst
- *   (src, dst, 0xFF) returns src
- * ** Does not match the results of SkFourByteInterp() because we use
+ *   (src, dst, 256) returns src
+ * ** Does not match the results of SkFourByteInterp256() because we use
  * a more accurate scale computation!
  * TODO: migrate Skia function to using an accurate 255->266 alpha
  * conversion.
  */
-static inline SkPMColor SkFastFourByteInterp(SkPMColor src,
-                                             SkPMColor dst,
-                                             U8CPU srcWeight) {
-    SkASSERT(srcWeight < 256);
+static inline SkPMColor SkFastFourByteInterp256(SkPMColor src,
+                                                SkPMColor dst,
+                                                unsigned scale) {
+    SkASSERT(scale <= 256);
 
     // Reorders ARGB to AG-RB in order to reduce the number of operations.
     const uint32_t mask = 0xFF00FF;
     uint32_t src_rb = src & mask;
     uint32_t src_ag = (src >> 8) & mask;
     uint32_t dst_rb = dst & mask;
     uint32_t dst_ag = (dst >> 8) & mask;
 
-    // scale = srcWeight + (srcWeight >> 7) is more accurate than
-    // scale = srcWeight + 1, but 7% slower
-    int scale = srcWeight + (srcWeight >> 7);
-
     uint32_t ret_rb = src_rb * scale + (256 - scale) * dst_rb;
     uint32_t ret_ag = src_ag * scale + (256 - scale) * dst_ag;
 
     return (ret_ag & ~mask) | ((ret_rb & ~mask) >> 8);
 }
 
+static inline SkPMColor SkFastFourByteInterp(SkPMColor src,
+                                             SkPMColor dst,
+                                             U8CPU srcWeight) {
+    SkASSERT(srcWeight <= 255);
+    // scale = srcWeight + (srcWeight >> 7) is more accurate than
+    // scale = srcWeight + 1, but 7% slower
+    return SkFastFourByteInterp256(src, dst, srcWeight + (srcWeight >> 7));
+}
+
 /**
  *  Same as SkPackARGB32, but this version guarantees to not check that the
  *  values are premultiplied in the debug version.
  */
 static inline SkPMColor SkPackARGB32NoCheck(U8CPU a, U8CPU r, U8CPU g, U8CPU b) {
     return (a << SK_A32_SHIFT) | (r << SK_R32_SHIFT) |
            (g << SK_G32_SHIFT) | (b << SK_B32_SHIFT);
 }
 
 static inline
@@ skipping 540 matching lines @@
     int srcG = SkColorGetG(color);
     int srcB = SkColorGetB(color);
 
     for (int i = 0; i < width; i++) {
         dst[i] = SkBlendLCD16Opaque(srcR, srcG, srcB, dst[i], src[i],
                                     opaqueDst);
     }
 }
 
 #endif