Changeset 15470

Timestamp:

07/16/06 17:25:56 (2 years ago)

Author:

bdakin

Message:

Reviewed by Maciej.

Fix for <rdar://problem/4616595> REGRESSION: Problems with world
clock widget clock hand motion on 9A211 + 4604574

The second hand on the widget was jiggling because the rotation was
messing up the use of the affine transformation matrix while
rounding to pixel boundaries in device space. We are mainly
concerned with rounding to pixel boundaries with the scale in mind,
so this patch extracts the scale to device space from the matrix,
and rounds to pixel boundaries using only the scale. This doesn't
seem like it is a perfect solution, but it definitely solves the
immediate problem. We will probably need to re-address what should
happen to avoid pixel cracks with rotations at non-integral scale
factors.

• platform/cg/GraphicsContextCG.cpp: (WebCore::GraphicsContext::roundToDevicePixels):

Location:

trunk/WebCore

Files:

• ChangeLog (modified) (1 diff)
• platform/cg/GraphicsContextCG.cpp (modified) (2 diffs)

trunk/WebCore/ChangeLog

@@ +1 @@
+2006-07-16  Beth Dakin  <bdakin@apple.com>
+
+        Reviewed by Maciej.
+
+        Fix for <rdar://problem/4616595> REGRESSION: Problems with world 
+        clock widget clock hand motion on 9A211 + 4604574
+
+        The second hand on the widget was jiggling because the rotation was 
+        messing up the use of the affine transformation matrix while 
+        rounding to pixel boundaries in device space. We are mainly 
+        concerned with rounding to pixel boundaries with the scale in mind, 
+        so this patch extracts the scale to device space from the matrix, 
+        and rounds to pixel boundaries using only the scale. This doesn't 
+        seem like it is a perfect solution, but it definitely solves the 
+        immediate problem. We will probably need to re-address what should 
+        happen to avoid pixel cracks with rotations at non-integral scale 
+        factors. 
+
+        * platform/cg/GraphicsContextCG.cpp:
+        (WebCore::GraphicsContext::roundToDevicePixels):
+
 2006-07-15  Darin Adler  <darin@apple.com>
 

trunk/WebCore/platform/cg/GraphicsContextCG.cpp

@@ -637 +637 @@
 FloatRect GraphicsContext::roundToDevicePixels(const FloatRect& rect)
 {
-    // It's important to separately transform the two corners, as transforming the whole rect
-    // will grab bounding boxes, and so will enlarge the rect when there is any rotation or skew
-    // in the current transform
-    CGPoint deviceOrigin = CGContextConvertPointToDeviceSpace(platformContext(), rect.location());
-    CGPoint deviceLowerRight = CGContextConvertPointToDeviceSpace(platformContext(), rect.location() + rect.size());
+    // It is not enough just to round to pixels in device space. The rotation part of the 
+    // affine transform matrix to device space can mess with this conversion if we have a
+    // rotating image like the hands of the world clock widget. We just need the scale, so 
+    // we get the affine transform matrix and extract the scale.
+    CGAffineTransform deviceMatrix = CGContextGetUserSpaceToDeviceSpaceTransform(platformContext());
+    float deviceScaleX = sqrtf(deviceMatrix.a * deviceMatrix.a + deviceMatrix.b * deviceMatrix.b);
+    float deviceScaleY = sqrtf(deviceMatrix.c * deviceMatrix.c + deviceMatrix.d * deviceMatrix.d);
+
+    CGPoint deviceOrigin = CGPointMake(rect.x() * deviceScaleX, rect.y() * deviceScaleY);
+    CGPoint deviceLowerRight = CGPointMake((rect.x() + rect.width()) * deviceScaleX,
+        (rect.y() + rect.height()) * deviceScaleY);
 
     deviceOrigin.x = roundf(deviceOrigin.x);
@@ -653 +659 @@
     if (deviceOrigin.x == deviceLowerRight.x && rect.width() != 0)
         deviceLowerRight.x += 1;
-    
-    FloatPoint roundedOrigin = CGContextConvertPointToUserSpace(platformContext(), deviceOrigin);
-    FloatPoint roundedLowerRight = CGContextConvertPointToUserSpace(platformContext(), deviceLowerRight);
-
+
+    FloatPoint roundedOrigin = FloatPoint(deviceOrigin.x / deviceScaleX, deviceOrigin.y / deviceScaleY);
+    FloatPoint roundedLowerRight = FloatPoint(deviceLowerRight.x / deviceScaleX, deviceLowerRight.y / deviceScaleY);
     return FloatRect(roundedOrigin, roundedLowerRight - roundedOrigin);
 }