Skip memcpy() swizzles in SkPngCodec

src/codec/SkSwizzler.cpp

Index: src/codec/SkSwizzler.cpp
diff --git a/src/codec/SkSwizzler.cpp b/src/codec/SkSwizzler.cpp
index debcd45c207048b5e96279a7ed5001e0695628cb..04560095bd0fd06936460cc3c48d6688874d4c18 100644
--- a/src/codec/SkSwizzler.cpp
+++ b/src/codec/SkSwizzler.cpp
@@ -11,13 +11,11 @@
 #include "SkSwizzler.h"
 #include "SkTemplates.h"
 
-static void copy(void* dst, const uint8_t* src, int width, int bpp, int deltaSrc, int offset,
+static void noop(void* dst, const uint8_t* src, int width, int bpp, int deltaSrc, int offset,

[msarett, 2016/02/05 20:48:18]

This is broken as is.
It works for PNG, but I would need to modify other users of SkSwizzler as well.

         const SkPMColor ctable[]) {
     // This function must not be called if we are sampling.  If we are not
     // sampling, deltaSrc should equal bpp.
     SkASSERT(deltaSrc == bpp);
-
-    memcpy(dst, src + offset, width * bpp);
 }
 
 static void sample1(void* dst, const uint8_t* src, int width, int bpp, int deltaSrc, int offset,
@@ -400,7 +398,7 @@ static void fast_swizzle_bgra_to_n32_unpremul(
 #ifdef SK_PMCOLOR_IS_RGBA
     SkOpts::RGBA_to_BGRA((uint32_t*) dst, src + offset, width);
 #else
-    memcpy(dst, src + offset, width * bpp);
+    // Nothing needs to be done here.
 #endif
 }
 
@@ -525,7 +523,7 @@ static void fast_swizzle_rgba_to_n32_unpremul(
     SkASSERT(deltaSrc == bpp);
 
 #ifdef SK_PMCOLOR_IS_RGBA
-    memcpy(dst, src + offset, width * bpp);
+    // Nothing needs to be done here.
 #else
     SkOpts::RGBA_to_BGRA((uint32_t*) dst, src + offset, width);
 #endif
@@ -714,7 +712,7 @@ SkSwizzler* SkSwizzler::CreateSwizzler(SkSwizzler::SrcConfig sc,
                     break;
                 case kIndex_8_SkColorType:
                     proc = &sample1;
-                    fastProc = ©
+                    fastProc = &noop;
                     break;
                 default:
                     break;
@@ -728,7 +726,7 @@ SkSwizzler* SkSwizzler::CreateSwizzler(SkSwizzler::SrcConfig sc,
                     break;
                 case kGray_8_SkColorType:
                     proc = &sample1;
-                    fastProc = ©
+                    fastProc = &noop;
                     break;
                 case kRGB_565_SkColorType:
                     proc = &swizzle_gray_to_565;
@@ -854,15 +852,15 @@ SkSwizzler* SkSwizzler::CreateSwizzler(SkSwizzler::SrcConfig sc,
             break;
         case kNoOp8:
             proc = &sample1;
-            fastProc = ©
+            fastProc = &noop;
             break;
         case kNoOp16:
             proc = sample2;
-            fastProc = ©
+            fastProc = &noop;
             break;
         case kNoOp32:
             proc = &sample4;
-            fastProc = ©
+            fastProc = &noop;
             break;
         default:
             break;
@@ -883,6 +881,7 @@ SkSwizzler* SkSwizzler::CreateSwizzler(SkSwizzler::SrcConfig sc,
         srcOffset = options.fSubset->left();
         srcWidth = options.fSubset->width();
         dstWidth = srcWidth;
+        fastProc = nullptr;

[msarett, 2016/02/05 20:48:18]

Problem:

We need the swizzler to do a copy for us on subset decodes.  We can get this by
turning off fastProc.

The result is that subset decodes will be slower.

     } else if (frame) {
         dstOffset = frame->left();
         srcWidth = frame->width();