Make SkCodec more flexible about its required frame

SkCodec sets fRequiredFrame to be the earliest possible frame that a
given frame can depend on. e.g.

- Frame A fills the screen, Keep
- Frame B does not cover A, Keep
- Frame C covers B but not A, and is opaque

Frame C can depend on either A or B. SkCodec already reports that C
depends on A. This CL allows a client of SkCodec to use either A or
B to create C.

Also expose the DisposalMethod. Since any frame between A and C can
be used to create C except for DisposePrevious frames, the client
needs to be able to know the disposal method so they do not try to
use such a frame to create C.

Further, the disposal method can be used to give the client a better
idea whether they will continue to need a frame. (e.g. if frame i is
DisposePrevious and depends on i-1, the client may not want to steal
i-1 to create i, since i+1 may also depend on i-1.)

TODO: Share code for decoding prior frames between GIF and WEBP

Change-Id: I91a5ae22ba3d8dfbe0bde833fa67ae3da0d81ed6
Reviewed-on: https://skia-review.googlesource.com/13722
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Chris Blume <cblume@chromium.org>
Reviewed-by: Matt Sarett <msarett@google.com>
Commit-Queue: Leon Scroggins <scroggo@google.com>

1 files changed, 5 insertions, 5 deletions

diff --git a/third_party/gif/SkGifImageReader.cpp b/third_party/gif/SkGifImageReader.cpp
index 0666fedbc8..76f3edcef0 100644
--- a/third_party/gif/SkGifImageReader.cpp
+++ b/third_party/gif/SkGifImageReader.cpp
@@ -616,11 +616,11 @@ bool SkGifImageReader::parse(SkGifImageReader::SkGIFParseQuery query)
             case 4:
                 // Some specs say that disposal method 3 is "overwrite previous", others that setting
                 // the third bit of the field (i.e. method 4) is. We map both to the same value.
-                currentFrame->setDisposalMethod(SkCodecAnimation::RestorePrevious_DisposalMethod);
+                currentFrame->setDisposalMethod(SkCodecAnimation::DisposalMethod::kRestorePrevious);
                 break;
             default:
                 // Other values use the default.
-                currentFrame->setDisposalMethod(SkCodecAnimation::Keep_DisposalMethod);
+                currentFrame->setDisposalMethod(SkCodecAnimation::DisposalMethod::kKeep);
                 break;
             }
             currentFrame->setDuration(GETINT16(currentComponent + 1) * 10);
@@ -903,7 +903,7 @@ static bool independent(const SkFrame& frame) {
 }
 
 static bool restore_bg(const SkFrame& frame) {
-    return frame.getDisposalMethod() == SkCodecAnimation::RestoreBGColor_DisposalMethod;
+    return frame.getDisposalMethod() == SkCodecAnimation::DisposalMethod::kRestoreBGColor;
 }
 
 bool SkGIFFrameContext::onReportsAlpha() const {
@@ -935,7 +935,7 @@ void SkFrameHolder::setAlphaAndRequiredFrame(SkFrame* frame) {
     }
 
     const SkFrame* prevFrame = this->getFrame(i-1);
-    while (prevFrame->getDisposalMethod() == SkCodecAnimation::RestorePrevious_DisposalMethod) {
+    while (prevFrame->getDisposalMethod() == SkCodecAnimation::DisposalMethod::kRestorePrevious) {
         const int prevId = prevFrame->frameId();
         if (0 == prevId) {
             frame->setHasAlpha(true);
@@ -992,7 +992,7 @@ void SkFrameHolder::setAlphaAndRequiredFrame(SkFrame* frame) {
         return;
     }
 
-    SkASSERT(prevFrame->getDisposalMethod() == SkCodecAnimation::Keep_DisposalMethod);
+    SkASSERT(prevFrame->getDisposalMethod() == SkCodecAnimation::DisposalMethod::kKeep);
     frame->setRequiredFrame(prevFrame->frameId());
     frame->setHasAlpha(prevFrame->hasAlpha() || (reportsAlpha && !blendWithPrevFrame));
 }