Tweak SkPictureShader's tile semantics.

Currently, the tile offset is added when drawing the picture. This might
have made a tiny bit of sense when the picture was always positioned at
origin, but with a picture cull rect offset things looks really strange.

For example, to specify a tile == the picture cull rect we have to pass
in [-cullrect.x, -cullrect.y, cullrect.width, cullrect.height]. Yikes.

(there's also a bug when not passing a tile, as we use a default tile
== cullrect but don't compensate for the above oddity)

This changes the semantics of the tile offset: it is now subtracted when
drawing the picture tile. As a consequence, one can pass in a tile equal
to the cull rect and get the expected behavior (same when not passing
a tile).

This will require a minor Blink change with the roll, as one client
works around the current behavior:
https://codereview.chromium.org/789503003

R=reed@google.com,robertphillips@google.com
BUG=440046

Review URL: https://codereview.chromium.org/733203005

1 files changed, 1 insertions, 1 deletions

diff --git a/src/core/SkPictureShader.cpp b/src/core/SkPictureShader.cpp
index 5fded935cc..198a2a9e49 100644
--- a/src/core/SkPictureShader.cpp
+++ b/src/core/SkPictureShader.cpp
@@ -185,7 +185,7 @@ SkShader* SkPictureShader::refBitmapShader(const SkMatrix& matrix, const SkMatri
 
         SkCanvas canvas(bm);
         canvas.scale(tileScale.width(), tileScale.height());
-        canvas.translate(fTile.x(), fTile.y());
+        canvas.translate(-fTile.x(), -fTile.y());
         canvas.drawPicture(fPicture);
 
         SkMatrix shaderMatrix = this->getLocalMatrix();