Hi everyone,
I have a NSView in which I am drawing a waveform from a buffer. This
NSView has a child playhead element, that I want to move across the
waveform as it plays. The problem is, drawRect: is expensive and anytime
the playhead moves, the waveform has to draw itself all over again,
causing terrible performance problems.
My thought was to draw the waveform once, save it as an NSImage, and
then have drawRect: draw itself from the saved image, and when a new
buffer is loaded, discard the image and let drawRect: draw the new
waveform and save it as an NSImage, etc.
However, when drawRect: is called subsequent times (after new buffers
are set), the image appears to be garbage and therefore this strategy is
not quite working as planned... What am I doing wrong?
@property (nonatomic, strong) NSImage *image;
...
-(void)drawRect:(NSRect)dirtyRect {
if (self.image) {
[self.image drawInRect:dirtyRect];
return;
}
[[NSColor blackColor] setFill];
NSRectFill(dirtyRect);
[super drawRect:dirtyRect];
float zero = self.bounds.size.height / 2;
[[NSColor blueColor] set];
NSPoint pointA = NSMakePoint(0, zero);
NSPoint pointB = NSMakePoint(self.bounds.size.width, zero);
[self drawLineFromPointA:pointA toPointB:pointB];
if (self.buffer) {
float spacing = self.bounds.size.width / self.buffer.size;
for (int i = 0; i < self.buffer.size - 1; i++) {
NSPoint pointA = NSMakePoint(i * spacing, zero -
(self.buffer.samples[i] * zero));
NSPoint pointB = NSMakePoint((i + 1) * spacing, zero -
(self.buffer.samples[i + 1] * zero));
[self drawLineFromPointA:pointA toPointB:pointB];
}
}
[self lockFocus];
NSBitmapImageRep *rep = [[NSBitmapImageRep alloc]
initWithFocusedViewRect:[self bounds]];
self.image = [[NSImage alloc] initWithData:[rep TIFFRepresentation]];
[self unlockFocus];
}
-(void)setBuffer:(Buffer *)buffer {
_buffer = buffer;
self.image = nil;
[self setNeedsDisplay:YES];
}
I tried asking this question on Stack Overflow, but it's gotten no love..
http://stackoverflow.com/questions/43177850/trying-to-use-cached-image-as-background-in-nsview
Patrick J. Collins
http://collinatorstudios.com
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