Jochen,
The behavioral differences you're observing is the result of
NSCompositingOperation setting.
NSRectFill() uses NSCompositeCopy whereas NSBezierPath does not modify
the current setting that is accessible via -[NSGraphicsContext
compositingOperation].
Aki
On 2008/10/15, at 4:56, Jochen Moeller wrote:
Hello List,
in the sample code Movie_Overlay (here with Xcode 3.1.1)
<http://developer.apple.com/samplecode/Movie_Overlay/index.html>
both subviews (AnimationView and ImageView) are filled with -
whiteColor in -drawRect:.
- (void)drawRect:(NSRect)rect { // original AnimationView.m
[[NSColor whiteColor] set];
NSRectFill(rect);
[self doStarAnimation];
}
This is not what I want because the movie is dimmed with increasing
alpha values in the overlay. So I replaced the -whiteColor by -
clearColor in both -drawRect: and used bounds instead of rect.
Additionally I set the alpha value to 0.5 (instead 0.3) in MyDocument.
- (void)drawRect:(NSRect)rect { // 1st modification
[[NSColor clearColor] set]; // in AnimationView.m
NSRectFill([self bounds]);
[self doStarAnimation];
}
1st Issue:
This worked fine in ImageView but in AnimationView remained a light
grey shape of the animation figure which was not erased by
NSRectFill(). Therefore I replaced NSRectFill() by -fillRect: in the
next step.
- (void)drawRect:(NSRect)rect { // 2nd modification
[[NSColor clearColor] set]; // in AnimationView.m
[NSBezierPath fillRect:[self bounds]];
[self doStarAnimation];
}
2nd Issue:
The remaining shape had gone but the movie was dimmed under the
AnimationView. So -fillRect: seems not to be able to handle alpha
values correct.
Next I tried to fill once with -whiteColor to erase the remaining
shape.
- (void)drawRect:(NSRect)rect { // 3rd modification
static int counter = 0; // in AnimationView.m
if ( counter == 0 ) {
[[NSColor whiteColor] set];
counter++ ;
}
else [[NSColor clearColor] set];
NSRectFill([self bounds]);
[self doStarAnimation];
}
That almost worked. The shape had gone but a line between the views
appeared.
I have the suspicion that the first call to NSBezierPath "stamps"
the path in the background which is somewhere buffered and the
rectangle is then always replaced by that buffer. So I tried a first
call with an empty bezierpath object:
- (void)drawRect:(NSRect)rect { // 4th modification
static int counter = 0; // in AnimationView.m
[[NSColor clearColor] set];
NSRectFill([self bounds]);
if ( counter == 0 ) {
NSBezierPath *bezierPath = [NSBezierPath bezierPath];
[bezierPath stroke]; // empty bezierpath
counter++;
}
else [self doStarAnimation];
}
And that worked !! A clear underlaying movie.
So my questions. Are that known issues of NSBezierPath?
1. -fillRect: cannot handle alpha values correct,
2. The "stamp" in the background by the first call to NSBezierPath.
And is there another workaround, e.g. to clear the buffer which is
used by NSRectFill() ?
Regards
Jochen Moeller
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