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dragging an object along a CGPath on iOS demo
#import <UIKit/UIKit.h>
@interface UIBezierPath (forEachElement)
- (void)forEachElement:(void (^)(CGPathElement const *element))block;
@end
#import "UIBezierPath+forEachElement.h"
typedef void (^UIBezierPath_forEachElement_Block)(CGPathElement const *element);
@implementation UIBezierPath (forEachElement)
static void applyBlockToPathElement(void *info, CGPathElement const *element) {
__unsafe_unretained UIBezierPath_forEachElement_Block block =(__bridge UIBezierPath_forEachElement_Block)info;
block(element);
}
- (void)forEachElement:(void (^)(const CGPathElement *))block {
CGPathApply(self.CGPath, (__bridge void *)block, applyBlockToPathElement);
}
@end
// This code is described here:
// http://stackoverflow.com/questions/13664615/drag-uiview-around-oval-shape-comprised-of-cgmutablepaths
#import "ViewController.h"
#import "UIBezierPath+forEachElement.h"
@interface ViewController ()
@end
@implementation ViewController {
UIBezierPath *path_;
CAShapeLayer *pathLayer_;
NSMutableData *pathPointsData_;
CGPoint const *pathPoints_;
NSInteger pathPointsCount_;
UIView *handleView_;
NSInteger handlePathPointIndex_;
CGPoint desiredHandleCenter_;
}
- (void)viewDidLoad {
[super viewDidLoad];
[self initPathLayer];
[self initHandleView];
[self initHandlePanGestureRecognizer];
}
- (void)initPathLayer {
pathLayer_ = [CAShapeLayer layer];
pathLayer_.lineWidth = 1;
pathLayer_.fillColor = nil;
pathLayer_.strokeColor = [UIColor blackColor].CGColor;
pathLayer_.lineCap = kCALineCapButt;
pathLayer_.lineJoin = kCALineJoinRound;
[self.view.layer addSublayer:pathLayer_];
}
- (void)initHandleView {
handlePathPointIndex_ = 0;
CGRect rect = CGRectMake(0, 0, 30, 30);
CAShapeLayer *circleLayer = [CAShapeLayer layer];
circleLayer.fillColor = nil;
circleLayer.strokeColor = [UIColor redColor].CGColor;
circleLayer.lineWidth = 2;
circleLayer.path = [UIBezierPath bezierPathWithOvalInRect:CGRectInset(rect, circleLayer.lineWidth, circleLayer.lineWidth)].CGPath;
circleLayer.frame = rect;
handleView_ = [[UIView alloc] initWithFrame:rect];
[handleView_.layer addSublayer:circleLayer];
[self.view addSubview:handleView_];
}
- (void)initHandlePanGestureRecognizer {
UIPanGestureRecognizer *recognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handleWasPanned:)];
[handleView_ addGestureRecognizer:recognizer];
}
- (void)viewDidLayoutSubviews {
[super viewDidLayoutSubviews];
[self createPath];
[self createPathPoints];
[self layoutPathLayer];
[self layoutHandleView];
}
- (void)layoutHandleView {
// Make sure the index is in bounds.
handlePathPointIndex_ = [self handlePathPointIndexWithOffset:0];
handleView_.center = [pathLayer_ convertPoint:pathPoints_[handlePathPointIndex_] toLayer:self.view.layer];
}
- (void)createPath {
CGRect bounds = self.view.bounds;
CGFloat const radius = bounds.size.height / 6;
CGFloat const offset = 2 * radius * M_SQRT1_2;
CGPoint const topCenter = CGPointMake(CGRectGetMidX(bounds), CGRectGetMidY(bounds) - offset);
CGPoint const bottomCenter = { topCenter.x, CGRectGetMidY(bounds) + offset };
path_ = [UIBezierPath bezierPath];
[path_ addArcWithCenter:topCenter radius:radius startAngle:M_PI_4 endAngle:-M_PI - M_PI_4 clockwise:NO];
[path_ addArcWithCenter:bottomCenter radius:radius startAngle:-M_PI_4 endAngle:M_PI + M_PI_4 clockwise:YES];
[path_ closePath];
}
static CGPoint *lastPointOfPathElement(CGPathElement const *element) {
int index;
switch (element->type) {
case kCGPathElementMoveToPoint: index = 0; break;
case kCGPathElementAddCurveToPoint: index = 2; break;
case kCGPathElementAddLineToPoint: index = 0; break;
case kCGPathElementAddQuadCurveToPoint: index = 1; break;
case kCGPathElementCloseSubpath: index = NSNotFound; break;
}
return index == NSNotFound ? 0 : &element->points[index];
}
- (void)createPathPoints {
CGPathRef cgDashedPath = CGPathCreateCopyByDashingPath(path_.CGPath, NULL, 0, (CGFloat[]){ 1.0f, 1.0f }, 2);
UIBezierPath *dashedPath = [UIBezierPath bezierPathWithCGPath:cgDashedPath];
CGPathRelease(cgDashedPath);
static CGFloat const kMinimumDistance = 0.1f;
__block CGPoint priorPoint = { HUGE_VALF, HUGE_VALF };
pathPointsData_ = [[NSMutableData alloc] init];
[dashedPath forEachElement:^(const CGPathElement *element) {
CGPoint *p = lastPointOfPathElement(element);
if (!p)
return;
if (hypotf(p->x - priorPoint.x, p->y - priorPoint.y) < kMinimumDistance)
return;
[pathPointsData_ appendBytes:p length:sizeof *p];
priorPoint = *p;
}];
pathPoints_ = (CGPoint const *)pathPointsData_.bytes;
pathPointsCount_ = pathPointsData_.length / sizeof *pathPoints_;
if (pathPointsCount_ > 1 && hypotf(pathPoints_[0].x - priorPoint.x, pathPoints_[0].y - priorPoint.y) < kMinimumDistance) {
pathPointsCount_ -= 1;
}
}
- (void)layoutPathLayer {
pathLayer_.path = path_.CGPath;
pathLayer_.frame = self.view.bounds;
}
- (void)handleWasPanned:(UIPanGestureRecognizer *)recognizer {
switch (recognizer.state) {
case UIGestureRecognizerStateBegan: {
desiredHandleCenter_ = handleView_.center;
break;
}
case UIGestureRecognizerStateChanged:
case UIGestureRecognizerStateEnded:
case UIGestureRecognizerStateCancelled: {
CGPoint translation = [recognizer translationInView:self.view];
desiredHandleCenter_.x += translation.x;
desiredHandleCenter_.y += translation.y;
[self moveHandleTowardPoint:desiredHandleCenter_];
break;
}
default:
break;
}
[recognizer setTranslation:CGPointZero inView:self.view];
}
- (void)moveHandleTowardPoint:(CGPoint)point {
CGFloat earlierDistance = [self distanceToPoint:point ifHandleMovesByOffset:-1];
CGFloat currentDistance = [self distanceToPoint:point ifHandleMovesByOffset:0];
CGFloat laterDistance = [self distanceToPoint:point ifHandleMovesByOffset:1];
if (currentDistance <= earlierDistance && currentDistance <= laterDistance)
return;
NSInteger direction;
CGFloat distance;
if (earlierDistance < laterDistance) {
direction = -1;
distance = earlierDistance;
} else {
direction = 1;
distance = laterDistance;
}
NSInteger offset = direction;
while (true) {
NSInteger nextOffset = offset + direction;
CGFloat nextDistance = [self distanceToPoint:point ifHandleMovesByOffset:nextOffset];
if (nextDistance >= distance)
break;
distance = nextDistance;
offset = nextOffset;
}
handlePathPointIndex_ += offset;
[self layoutHandleView];
}
- (CGFloat)distanceToPoint:(CGPoint)point ifHandleMovesByOffset:(NSInteger)offset {
int index = [self handlePathPointIndexWithOffset:offset];
CGPoint proposedHandlePoint = pathPoints_[index];
return hypotf(point.x - proposedHandlePoint.x, point.y - proposedHandlePoint.y);
}
- (NSInteger)handlePathPointIndexWithOffset:(NSInteger)offset {
NSInteger index = handlePathPointIndex_ + offset;
while (index < 0) {
index += pathPointsCount_;
}
while (index >= pathPointsCount_) {
index -= pathPointsCount_;
}
return index;
}
@end
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