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65 lines
1.7 KiB
Objective-C
65 lines
1.7 KiB
Objective-C
//
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// CSBestEffortUpdater.m
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// Clock Signal
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//
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// Created by Thomas Harte on 16/06/2016.
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// Copyright © 2016 Thomas Harte. All rights reserved.
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//
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#import "CSBestEffortUpdater.h"
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@implementation CSBestEffortUpdater
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{
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// these are inherently handled only by thread-safe constructions
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uint32_t _updateIsOngoing;
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dispatch_queue_t _serialDispatchQueue;
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// these are permitted for modification on _serialDispatchQueue only
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NSTimeInterval _previousTimeInterval;
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NSTimeInterval _cyclesError;
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BOOL _hasSkipped;
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}
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- (instancetype)init
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{
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if(self = [super init])
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{
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_serialDispatchQueue = dispatch_queue_create("Best Effort Updater", DISPATCH_QUEUE_SERIAL);
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}
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return self;
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}
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- (void)update
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{
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const uint32_t processingMask = 0x01;
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// Always post an -openGLView:didUpdateToTime: if a previous one isn't still ongoing. This is the hook upon which the substantial processing occurs.
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if(!OSAtomicTestAndSet(processingMask, &_updateIsOngoing))
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{
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dispatch_async(_serialDispatchQueue, ^{
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NSTimeInterval timeInterval = [NSDate timeIntervalSinceReferenceDate];
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if(_previousTimeInterval > DBL_EPSILON)
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{
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NSTimeInterval timeToRunFor = timeInterval - _previousTimeInterval;
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double cyclesToRunFor = timeToRunFor * self.clockRate + _cyclesError;
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_cyclesError = fmod(cyclesToRunFor, 1.0);
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NSUInteger integerCyclesToRunFor = (NSUInteger)cyclesToRunFor;
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[self.delegate bestEffortUpdater:self runForCycles:integerCyclesToRunFor didSkipPreviousUpdate:_hasSkipped];
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}
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_previousTimeInterval = timeInterval;
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_hasSkipped = NO;
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OSAtomicTestAndClear(processingMask, &_updateIsOngoing);
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});
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}
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else
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{
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dispatch_async(_serialDispatchQueue, ^{
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_hasSkipped = YES;
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});
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}
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}
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@end
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