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Recreates display link upon a screen change.

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Different screens may have different refresh rates, and I can find no guarantees about how Apple handles that.
This commit is contained in:
Thomas Harte 2020-01-26 23:23:33 -05:00
parent 6bcdd3177d
commit 52e49439a6
1 changed files with 46 additions and 7 deletions
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53
OSBindings/Mac/Clock Signal/Views/CSOpenGLView.m
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@ -30,12 +30,35 @@
// Note the initial screen.
_currentScreen = self.window.screen;
// Synchronize buffer swaps with vertical refresh rate
// Synchronize buffer swaps with vertical refresh rate.
// TODO: discard this, once scheduling is sufficiently intelligent?
GLint swapInt = 1;
[[self openGLContext] setValues:&swapInt forParameter:NSOpenGLCPSwapInterval];
// set the clear colour
[self.openGLContext makeCurrentContext];
glClearColor(0.0, 0.0, 0.0, 1.0);
// Setup the [initial] display link.
[self setupDisplayLink];
}
- (void)setupDisplayLink {
// Kill the existing link if there is one, then wait until its final shout is definitely done.
if(_displayLink) {
const double duration = CVDisplayLinkGetActualOutputVideoRefreshPeriod(_displayLink);
CVDisplayLinkStop(_displayLink);
// This is a workaround; I could find no way to ensure that a callback from the display
// link is not currently ongoing.
usleep((useconds_t)ceil(duration * 1000000.0));
CVDisplayLinkRelease(_displayLink);
}
// Create a display link capable of being used with all active displays
CVDisplayLinkCreateWithActiveCGDisplays(&_displayLink);
NSNumber *const screenNumber = self.window.screen.deviceDescription[@"NSScreenNumber"];
CVDisplayLinkCreateWithCGDisplay(screenNumber.unsignedIntValue, &_displayLink);
// Set the renderer output callback function
CVDisplayLinkSetOutputCallback(_displayLink, DisplayLinkCallback, (__bridge void * __nullable)(self));
@ -45,27 +68,42 @@
CGLPixelFormatObj cglPixelFormat = [[self pixelFormat] CGLPixelFormatObj];
CVDisplayLinkSetCurrentCGDisplayFromOpenGLContext(_displayLink, cglContext, cglPixelFormat);
// set the clear colour
[self.openGLContext makeCurrentContext];
glClearColor(0.0, 0.0, 0.0, 1.0);
// Activate the display link
CVDisplayLinkStart(_displayLink);
}
static CVReturn DisplayLinkCallback(CVDisplayLinkRef displayLink, const CVTimeStamp *now, const CVTimeStamp *outputTime, CVOptionFlags flagsIn, CVOptionFlags *flagsOut, void *displayLinkContext) {
CSOpenGLView *const view = (__bridge CSOpenGLView *)displayLinkContext;
[view drawAtTime:now frequency:CVDisplayLinkGetActualOutputVideoRefreshPeriod(displayLink)];
/*
Do not touch the display link from after this call; there's a bit of a race condition with setupDisplayLink.
Specifically: Apple provides CVDisplayLinkStop but a call to that merely prevents future calls to the callback,
it doesn't wait for completion of any current calls. So I've set up a usleep for one callback's duration,
so code in here gets one callback's duration to access the display link.
In practice, it should do so only upon entry, and before calling into the view. The view promises not to
access the display link itself as part of -drawAtTime:frequency:.
*/
return kCVReturnSuccess;
}
- (void)drawAtTime:(const CVTimeStamp *)now frequency:(double)frequency {
// Test now whether the screen this view is on has changed since last time it was checked.
// There's likely a callback available for this, on NSWindow if nowhere else, or an NSNotification,
// but since this method is going to be called repeatedly anyway, and the test is cheap, polling
// feels fine.
if(self.window.screen != _currentScreen) {
_currentScreen = self.window.screen;
// Issue a reshape, in case a switch to/from a Retina display has
// happened, changing the results of -convertSizeToBacking:, etc.
[self reshape];
// Also switch display links, to make sure synchronisation is with the display
// the window is actually on, and at its rate.
[self setupDisplayLink];
}
[self redrawWithEvent:CSOpenGLViewRedrawEventTimer];
@ -87,7 +125,8 @@ static CVReturn DisplayLinkCallback(CVDisplayLinkRef displayLink, const CVTimeSt
}
- (void)dealloc {
// Release the display link
// Stop and release the display link
CVDisplayLinkStop(_displayLink);
CVDisplayLinkRelease(_displayLink);
}