Correct GIF frame dependencies and track alpha

Add SkCodec::FrameInfo::fAlphaType. The SkImageInfo for the SkCodec
specifies the SkAlphaType for the first frame, but the opacity can vary
from frame to frame.

When determining the required frame, also compute whether a frame has
alpha. Update how we determine the required frame, which had bugs.
(Update a test that had an incorrect required frame as a result.)

Add new test images covering cases that have been fixed:
- randPixelsAnim2.gif
It has the following frames:
A (keep)
B (keep) (subset)
C (disposePrevious) (covers B)
D (any) (does *not* cover B)

B and C depend on A, but D depends on B, since after disposing C, B
should be visible again.

- alphabetAnim.gif
Includes frames which fill the image size, with different disposal
methods and transparencies.

Change-Id: Ie086167711c4cac4931ed8c4ddaeb9c9b0b91fdb
Reviewed-on: https://skia-review.googlesource.com/9810
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Matt Sarett <msarett@google.com>

1 files changed, 9 insertions, 1 deletions

diff --git a/third_party/gif/SkGifImageReader.h b/third_party/gif/SkGifImageReader.h
index 24c917af2a..9d69e48823 100644
--- a/third_party/gif/SkGifImageReader.h
+++ b/third_party/gif/SkGifImageReader.h
@@ -201,6 +201,7 @@ public:
         , m_width(0)
         , m_height(0)
         , m_transparentPixel(SkGIFColorMap::kNotFound)
+        , m_hasAlpha(false)
         , m_disposalMethod(SkCodecAnimation::Keep_DisposalMethod)
         , m_requiredFrame(kUninitialized)
         , m_dataSize(0)
@@ -240,6 +241,8 @@ public:
     unsigned height() const { return m_height; }
     size_t transparentPixel() const { return m_transparentPixel; }
     void setTransparentPixel(size_t pixel) { m_transparentPixel = pixel; }
+    bool hasAlpha() const { return m_hasAlpha; }
+    void setHasAlpha(bool alpha) { m_hasAlpha = alpha; }
     SkCodecAnimation::DisposalMethod getDisposalMethod() const { return m_disposalMethod; }
     void setDisposalMethod(SkCodecAnimation::DisposalMethod disposalMethod) { m_disposalMethod = disposalMethod; }
 
@@ -282,6 +285,11 @@ private:
     unsigned m_width;
     unsigned m_height;
     size_t m_transparentPixel; // Index of transparent pixel. Value is kNotFound if there is no transparent pixel.
+    // Cached value, taking into account:
+    // - m_transparentPixel
+    // - frameRect
+    // - previous required frame
+    bool m_hasAlpha;
     SkCodecAnimation::DisposalMethod m_disposalMethod; // Restore to background, leave in place, etc.
     size_t m_requiredFrame;
     int m_dataSize;
@@ -407,7 +415,7 @@ private:
 
     void addFrameIfNecessary();
     // Must be called *after* the SkGIFFrameContext's color table (if any) has been parsed.
-    void setRequiredFrame(SkGIFFrameContext*);
+    void setAlphaAndRequiredFrame(SkGIFFrameContext*);
     // This method is sometimes called before creating a SkGIFFrameContext, so it cannot rely
     // on SkGIFFrameContext::localColorMap().
     bool hasTransparentPixel(size_t frameIndex, bool hasLocalColorMap, size_t localMapColors);