The right way to make a continuously redrawn Metal NSView - macos

Question

I'm learning Metal and Cocoa and trying to make a boilerplate application as a platform for future experiments. As part of the process, I'm implementing a view which will redraw itself (or, more accurately, contents of its CAMetalLayer) on 60fps. Also for educational purposes Im avoiding MTKView (for "learning Cocoa part"). Here's an abbreviated code snippet of how I'm tackling the problem:
#implementation MyMetalView // which is a subclass of NSView
- (BOOL) isOpaque {
return YES;
}
- (NSViewLayerContentsRedrawPolicy) layerContentsRedrawPolicy {
return NSViewLayerContentsRedrawOnSetNeedsDisplay;
}
- (CALayer *) makeBackingLayer {
// create CAMetalLayer with default device
}
- (BOOL) wantsLayer {
return YES;
}
- (BOOL) wantsUpdateLayer {
return YES;
}
- (void) displayLayer:(CALayer *)layer {
id<MTLCommandBuffer> cmdBuffer = [_commandQueue commandBuffer];
id<CAMetalDrawable> drawable = [((CAMetalLayer *) layer) nextDrawable];
[cmdBuffer enqueue];
[cmdBuffer presentDrawable:drawable];
// rendering
[cmdBuffer commit];
}
#end
int main() {
// init app, window and MyMetalView instance
// invocation will call [myMetalViewInstance setNeedsDisplay:YES]
[NSTimer scheduledTimerWithTimeInterval:1./60. invocation:setNeedsDisplayInvokation repeats:YES];
[NSApp run];
return 0;
}
Is it the right way to do what I want? Or have I chosen a long and not recommended approach?

Answer 1

It is strongly preferred to use CVDisplayLink rather than a generic NSTimer to drive animations that need to match the refresh rate of the display.
You'll want to create an ivar or property to hold a CVDisplayLinkRef:
CVDisplayLinkRef displayLink;
Then, when your view is going onto the screen and you want to start animating, you'll create, configure, and start your display link:
CVDisplayLinkCreateWithActiveCGDisplays(&displayLink);
CVDisplayLinkSetOutputCallback(displayLink, &MyDisplayLinkCallback, self);
CVDisplayLinkStart(displayLink);
The display link callback should be a static function. It will be invoked at the beginning of the display's v-blank period (on modern displays where there is no physical v-blank, this still happens at a regular 60Hz cadence):
static CVReturn MyDisplayLinkCallback(CVDisplayLinkRef displayLink, const CVTimeStamp* now, const CVTimeStamp* outputTime, CVOptionFlags flagsIn, CVOptionFlags* flagsOut, void* displayLinkContext)
{
[(MyMetalView *)displayLinkContext setNeedsDisplay:YES];
return kCVReturnSuccess;
}
When your view leaves the display, or if you want to pause, you can release the display link and nil it out:
CVDisplayLinkRelease(displayLink);

Answer 2

following #warrenm solution adding dispatch_sync to refresh and other minor :
#import "imageDrawer.h"
#import "image/ImageBuffer.h"
#import "common.hpp"
#implementation imageDrawer {
CVDisplayLinkRef displayLink;
}
CVReturn MyDisplayLinkCallback(CVDisplayLinkRef displayLink, const CVTimeStamp* now, const CVTimeStamp* outputTime, CVOptionFlags flagsIn, CVOptionFlags* flagsOut, void* displayLinkContext)
{
dispatch_sync(dispatch_get_main_queue(), ^{
[(__bridge imageDrawer*)displayLinkContext setNeedsDisplay:YES];
});
return kCVReturnSuccess;
}
-(void)setContDisplay {
CVDisplayLinkCreateWithActiveCGDisplays(&displayLink);
CVDisplayLinkSetOutputCallback(displayLink, &MyDisplayLinkCallback, (__bridge void*)self);
CVDisplayLinkStart(displayLink);
}
-(void)awakeFromNib {
[self setContDisplay];
}
- (void)drawRect:(NSRect)rect {
[super drawRect:rect];
int w=rect.size.width, h=rect.size.height;
// do the drawing...
}
#end