Skip memcpy() swizzles in SkPngCodec

src/codec/SkSwizzler.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCodecPriv.h"
 #include "SkColorPriv.h"
 #include "SkOpts.h"
 #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,
         const SkPMColor ctable[]) {
     src += offset;
     uint8_t* dst8 = (uint8_t*) dst;
     for (int x = 0; x < width; x++) {
         dst8[x] = *src;
         src += deltaSrc;
     }
@@ skipping 362 matching lines @@
         void* dst, const uint8_t* src, int width, int bpp, int deltaSrc, int offset,
         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);
 
 #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
 }
 
 static void swizzle_bgra_to_n32_premul(
         void* SK_RESTRICT dstRow, const uint8_t* SK_RESTRICT src, int dstWidth,
         int bpp, int deltaSrc, int offset, const SkPMColor ctable[]) {
 
     src += offset;
     SkPMColor* SK_RESTRICT dst = (SkPMColor*)dstRow;
     for (int x = 0; x < dstWidth; x++) {
@@ skipping 104 matching lines @@
 
 static void fast_swizzle_rgba_to_n32_unpremul(
         void* dst, const uint8_t* src, int width, int bpp, int deltaSrc, int offset,
         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);
 
 #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
 }
 
 // kCMYK
 //
 // CMYK is stored as four bytes per pixel.
 //
 // We will implement a crude conversion from CMYK -> RGB using formulas
@@ skipping 168 matching lines @@
                     } else {
                         proc = &swizzle_index_to_n32;
                         break;
                     }
                     break;
                 case kRGB_565_SkColorType:
                     proc = &swizzle_index_to_565;
                     break;
                 case kIndex_8_SkColorType:
                     proc = &sample1;
-                    fastProc = &copy;
+                    fastProc = &noop;
                     break;
                 default:
                     break;
             }
             break;
         case kGray:
             switch (dstInfo.colorType()) {
                 case kN32_SkColorType:
                     proc = &swizzle_gray_to_n32;
                     fastProc = &fast_swizzle_gray_to_n32;
                     break;
                 case kGray_8_SkColorType:
                     proc = &sample1;
-                    fastProc = &copy;
+                    fastProc = &noop;
                     break;
                 case kRGB_565_SkColorType:
                     proc = &swizzle_gray_to_565;
                     break;
                 default:
                     break;
             }
             break;
         case kGrayAlpha:
             switch (dstInfo.colorType()) {
@@ skipping 105 matching lines @@
                     break;
                 case kRGB_565_SkColorType:
                     proc = &swizzle_cmyk_to_565;
                     break;
                 default:
                     break;
             }
             break;
         case kNoOp8:
             proc = &sample1;
-            fastProc = &copy;
+            fastProc = &noop;
             break;
         case kNoOp16:
             proc = sample2;
-            fastProc = &copy;
+            fastProc = &noop;
             break;
         case kNoOp32:
             proc = &sample4;
-            fastProc = &copy;
+            fastProc = &noop;
             break;
         default:
             break;
     }
 
     // Store bpp in bytes if it is an even multiple, otherwise use bits
     int srcBPP = SkIsAlign8(BitsPerPixel(sc)) ? BytesPerPixel(sc) : BitsPerPixel(sc);
     int dstBPP = SkColorTypeBytesPerPixel(dstInfo.colorType());
 
     int srcOffset = 0;
     int srcWidth = dstInfo.width();
     int dstOffset = 0;
     int dstWidth = srcWidth;
     if (options.fSubset) {
         // We do not currently support subset decodes for image types that may have
         // frames (gif).
         SkASSERT(!frame);
         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();
     }
 
     return new SkSwizzler(fastProc, proc, ctable, srcOffset, srcWidth, dstOffset, dstWidth,
             srcBPP, dstBPP);
 }
 
 SkSwizzler::SkSwizzler(RowProc fastProc, RowProc proc, const SkPMColor* ctable, int srcOffset,
@@ skipping 32 matching lines @@
     }
 
     return fAllocatedWidth;
 }
 
 void SkSwizzler::swizzle(void* dst, const uint8_t* SK_RESTRICT src) {
     SkASSERT(nullptr != dst && nullptr != src);
     fActualProc(SkTAddOffset<void>(dst, fDstOffsetBytes), src, fSwizzleWidth, fSrcBPP,
             fSampleX * fSrcBPP, fSrcOffsetUnits, fColorTable);
 }