CoreAnimation doesn't work with -setAlphaValue on QTMovieView

Question

Hello

I have some basic code for adding a QTMovieView. I want it to fade in, so I add an animation on setAlphaValue. Only issue is that it doesn't work. The alpha value is instantly set to whatever it was supposed to animate to. If I try animating e.g. setFrame: it works fine. You'll find my code below. This is on 10.5.7 with the Mac OS X 10.5 SDK.

    - (void)addMovie:(NSString *)aFile
    {
            QTMovieView     *aMovieView;
            QTMovie         *aMovie;
            NSRect          contentFrame;

            contentFrame = [[self contentView] frame];

            aMovieView = [[QTMovieView alloc]
                            initWithFrame:contentFrame];
            [aMovieView setWantsLayer:YES];
            [aMovieView setControllerVisible:NO];
            [aMovieView setPreservesAspectRatio:YES];

            aMovie = [[QTMovie alloc]
                            initWithFile:aFile error:nil];

            [aMovieView setMovie:aMovie];

            [aMovieView setAlphaValue:0.4];

            [[self contentView] addSubview:aMovieView];

            [NSAnimationContext beginGrouping];
            [[NSAnimationContext currentContext] setDuration:2.0];
            [[aMovieView animator] setAlphaValue:0.9];
            [NSAnimationContext endGrouping];

    }

Any ideas?

Answer 1

I don't know for sure but it sounds like QTMovieView may not support alpha compositing. One further test I would try would be to call setWantsLayer on the superview of the QTMovieView to see if that affects the QTMovieViews ability to composite correctly. Probably will not work.

You could try using QTMovieLayer instead. One way to incorporate QTMovieLayer would be to make your own NSView subclass that created and managed a QTMovieLayer that was added inside its root layer. Be aware though that when mixing layer backed views with non layer backed views in the same window you may get funny ordering if the layer backed views are not all in front or are behind and overlapping.

Answer 2

I began on QTMovieLayer, but being less powerfull (of course) than QTMovieView it opened another box of issues. The solution was to use NSAnimation on the QTMovieView. I have a NSAnimation class looking somewhat like this:

AlphaAnimation.h

    #import <Cocoa/Cocoa.h>

    NSString * const AAFadeIn;
    NSString * const AAFadeOut;

    @interface AlphaAnimation : NSAnimation {
            NSView          *animatedObject;
            NSString        *effect;
    }
    - (id)initWithDuration:(NSTimeInterval)duration effect:(NSString *)effect object:(NSView *)object;
    @end

AlphaAnimation.m

    #import "AlphaAnimation.h"

    NSString * const AAFadeIn = @"AAFadeIn";
    NSString * const AAFadeOut = @"AAFadeOut";

    @implementation AlphaAnimation
    - (id)initWithDuration:(NSTimeInterval)aDuration effect:(NSString *)anEffect object:(NSView *)anObject
    {
            self = [super initWithDuration:aDuration animationCurve:0];

            if (self) {
                    animatedObject = anObject;
                    effect = anEffect;
            }

            return self;
    }

    - (void)setCurrentProgress:(NSAnimationProgress)progress
    {
            if ([effect isEqual:AAFadeIn])
                    [animatedObject setAlphaValue:progress];
            else
                    [animatedObject setAlphaValue:1 - progress];
    }
    @end

Which can then be used like this:

animation = [[AlphaAnimation alloc] initWithDuration:0.5 effect:AAFadeIn object:movieView];

[animation setAnimationBlockingMode:NSAnimationNonblocking];
[animation startAnimation];

If your QTMovieViews are in full screen it isn't very smooth, though.

Answer 3

I suggest NSViewAnimation. It's a subclass of NSAnimation that will do the fading in and out for you.