Allow sampling GIF images during decode.

src/images/SkScaledBitmapSampler.cpp

 /*
  * Copyright 2007 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 "SkScaledBitmapSampler.h"
 #include "SkBitmap.h"
@@ skipping 558 matching lines @@
 SkScaledBitmapSampler::SkScaledBitmapSampler(int width, int height,
                                              int sampleSize) {
     fCTable = NULL;
     fDstRow = NULL;
     fRowProc = NULL;
 
     if (width <= 0 || height <= 0) {
         sk_throw();
     }
 
+    SkDEBUGCODE(fSampleMode = kUninitialized_SampleMode);
+
     if (sampleSize <= 1) {
         fScaledWidth = width;
         fScaledHeight = height;
         fX0 = fY0 = 0;
         fDX = fDY = 1;
         return;
     }
 
     int dx = SkMin32(sampleSize, width);
     int dy = SkMin32(sampleSize, height);
@@ skipping 115 matching lines @@
     } else {
         fRowProc = chooser(decoder);
     }
     fDstRow = (char*)dst->getPixels();
     fDstRowBytes = dst->rowBytes();
     fCurrY = 0;
     return fRowProc != NULL;
 }
 
 bool SkScaledBitmapSampler::next(const uint8_t* SK_RESTRICT src) {
+    SkASSERT(kInterlaced_SampleMode != fSampleMode);
+    SkDEBUGCODE(fSampleMode = kConsecutive_SampleMode);
     SkASSERT((unsigned)fCurrY < (unsigned)fScaledHeight);
 
     bool hadAlpha = fRowProc(fDstRow, src + fX0 * fSrcPixelSize, fScaledWidth,
                              fDX * fSrcPixelSize, fCurrY, fCTable);
     fDstRow += fDstRowBytes;
     fCurrY += 1;
     return hadAlpha;
 }
 
+bool SkScaledBitmapSampler::sampleInterlaced(const uint8_t* SK_RESTRICT src, int srcY) {
+    SkASSERT(kConsecutive_SampleMode != fSampleMode);
+    SkDEBUGCODE(fSampleMode = kInterlaced_SampleMode);
+    // Any line that should be a part of the destination can be created by the formula:
+    // fY0 + (some multiplier) * fDY
+    // so if srcY - fY0 is not an integer multiple of fDY that srcY will be skipped.
+    const int srcYMinusY0 = srcY - fY0;
+    if (srcYMinusY0 % fDY != 0) {
+        // This line is not part of the output, so return false for alpha, since we have
+        // not added an alpha to the output.
+        return false;
+    }
+    // Unlike in next(), where the data is used sequentially, this function skips around,
+    // so fDstRow and fCurrY are never updated. fDstRow must always be the starting point
+    // of the destination bitmap's pixels, which is used to calculate the destination row
+    // each time this function is called.
+    const int dstY = srcYMinusY0 / fDY;
+    SkASSERT(dstY < fScaledHeight);
+    char* dstRow = fDstRow + dstY * fDstRowBytes;
+    return fRowProc(dstRow, src + fX0 * fSrcPixelSize, fScaledWidth,
+                    fDX * fSrcPixelSize, dstY, fCTable);
+}
+
 #ifdef SK_DEBUG
 // The following code is for a test to ensure that changing the method to get the right row proc
 // did not change the row proc unintentionally. Tested by ImageDecodingTest.cpp
 
 // friend of SkScaledBitmapSampler solely for the purpose of accessing fRowProc.
 class RowProcTester {
 public:
     static SkScaledBitmapSampler::RowProc getRowProc(const SkScaledBitmapSampler& sampler) {
         return sampler.fRowProc;
     }
@@ skipping 79 matching lines @@
                     SkScaledBitmapSampler::RowProc actual = RowProcTester::getRowProc(sampler);
                     SkASSERT(expected == actual);
                     procCounter++;
                 }
             }
         }
     }
     SkASSERT(SK_ARRAY_COUNT(gTestProcs) == procCounter);
 }
 #endif // SK_DEBUG