Scanline decoding for gifs

src/codec/SkGifInterlaceIter.cpp

-/*
- * Copyright 2015 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 "SkGifInterlaceIter.h"
-
-static const uint8_t kStartingInterlaceYValues[] = { 0, 4, 2, 1 };
-static const uint8_t kDeltaInterlaceYValues[] = { 8, 8, 4, 2 };
-
-SkGifInterlaceIter::SkGifInterlaceIter(int height) : fHeight(height) {
-    fStartYPtr = kStartingInterlaceYValues;
-    fDeltaYPtr = kDeltaInterlaceYValues;
-
-    fCurrY = *fStartYPtr++;
-    fDeltaY = *fDeltaYPtr++;
-}
-
-void SkGifInterlaceIter::prepareY() {
-    int32_t y = fCurrY + fDeltaY;
-
-    // Iterate through fStartYPtr until a valid row is found.
-    // This ensures that we do not move past the height of the small images.
-    while (y >= fHeight) {
-        if (kStartingInterlaceYValues +
-                SK_ARRAY_COUNT(kStartingInterlaceYValues) == fStartYPtr) {
-            // Now we have iterated over the entire image.  Forbid any
-            // subsequent calls to nextY().
-            SkDEBUGCODE(fStartYPtr = NULL;)
-            SkDEBUGCODE(fDeltaYPtr = NULL;)
-            y = 0;
-        } else {
-            y = *fStartYPtr++;
-            fDeltaY = *fDeltaYPtr++;
-        }
-    }
-    fCurrY = y;
-}
-
-int32_t SkGifInterlaceIter::nextY() {
-    SkASSERT(fStartYPtr);
-    SkASSERT(fDeltaYPtr);
-    int32_t y = fCurrY;
-    prepareY();
-    return y;
-}