I have created a simple drawing project,the code works fine, but I want to cache the drawing into CGlayer, because I read that its more efficient way in drawing . I have read through the documents, but not able to understand it properly. So friends, I request you to please help me in this regard.
Below is my code, I want to know how to use CgLayer in this
- (void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
if(myLayerRef == nil)
{
myLayerRef = CGLayerCreateWithContext(context, self.bounds.size, NULL);
}
CGContextRef layerContext = CGLayerGetContext(myLayerRef);
CGContextDrawLayerAtPoint(context, CGPointZero, myLayerRef);
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *mytouch=[[touches allObjects] objectAtIndex:0];
m_previousPoint2 = m_previousPoint1;
m_previousPoint1 = [mytouch previousLocationInView:self];
m_currentPoint = [mytouch locationInView:self];
CGPoint mid1 = midPoint(m_previousPoint1, m_previousPoint2);
CGPoint mid2 = midPoint(m_currentPoint, m_previousPoint1);
testpath = CGPathCreateMutable();
CGPathMoveToPoint(testpath, NULL, mid1.x, mid1.y);
CGPathAddQuadCurveToPoint(testpath, NULL, m_previousPoint1.x, m_previousPoint1.y, mid2.x, mid2.y);
CGContextRef context = UIGraphicsGetCurrentContext();
context = CGLayerGetContext(myLayerRef);
CGRect bounds = CGPathGetBoundingBox(testpath);
CGPathRelease(testpath);
CGRect drawBox = bounds;
//Pad our values so the bounding box respects our line width
drawBox.origin.x -= self.lineWidth * 2;
drawBox.origin.y -= self.lineWidth * 2;
drawBox.size.width += self.lineWidth * 4;
drawBox.size.height += self.lineWidth * 4;
[self setNeedsDisplayInRect:drawBox];
}
- (void) drawingOperations
{
CGContextRef context1 = CGLayerGetContext(myLayerRef);
CGPoint mid1 = midPoint(m_previousPoint1, m_previousPoint2);
CGPoint mid2 = midPoint(m_currentPoint, m_previousPoint1);
CGContextMoveToPoint(context1, mid1.x, mid1.y);
CGContextAddQuadCurveToPoint(context1, m_previousPoint1.x, m_previousPoint1.y, mid2.x, mid2.y);
CGContextSetLineCap(context1, kCGLineCapRound);
CGContextSetLineWidth(context1, self.lineWidth);
CGContextSetStrokeColorWithColor(context1, self.lineColor.CGColor);
CGContextSetFlatness(context1, 2.0);
CGContextSetAllowsAntialiasing(context1, true);
CGContextStrokePath(context1);
}
Regards
Ranjit
The link posted by #hfossli is now dead, but here is the archived content:
CGLayer no longer recommended
Posted by robnapier on Jul 13, 2012 in Book Updates
I spend a lot of time in the labs at WWDC asking questions and talking with the developers. I sat down the Core Graphics engineers this time and asked them about one of my favorite underused tools: CGLayer, which I discuss at the end of Chapter 6. CGLayer sounds like a great idea: a drawing context optimized specifically for drawing on the screen, with hardware optimization. What could go wrong?
I started to have doubts, though, that CGLayer was always a great win. What if your layers were too large to store in GPU textures? CGLayer is advertised for use as a “stamp” that you repeatedly draw. Moving data to and from the GPU is expensive. Maybe CGLayer doesn’t make sense unless you draw it a certain number of times. The docs give no guidance on this.
So I asked the Core Graphics team “When should I be using CGLayer?”
“Never.”
… ??? Never? But for stamping right?
Never.
So we talked some more. It appears that CGLayer was one of those things that sounded great on paper, but just doesn’t always work in practice. Sometimes it’s faster. Sometimes its slower. There’s no easy rule for when it’s going to be faster. Over time it seems they’ve quietly abandoned it without actually deprecating it. I’ve asked that the docs be updated to match Apple’s current recommendation. The CGLayer Reference hasn’t been updated since 2006.
The recommendation I received was to use CGBitmapContext or CALayer for stamping. For the specific example given on pages 131-132, CATextLayer would probably be the best tool. Remember that you can easily clone a CALayer using initWithLayer:. (John Mueller points out below that this isn’t actually supported.)
Not optimal to use CGLayer anymore
http://iosptl.com/posts/cglayer-no-longer-recommended/
Related
I would like to draw a "disappearing stroke" on a UIImageView, which follows a touch event and self-erases after a fixed time delay. Here's what I have in my ViewController.
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *touch = [touches anyObject];
CGPoint currentPoint = [touch locationInView:self.view];
CGPoint lp = lastPoint;
UIColor *color = [UIColor blackColor];
[self drawLine:5 from:lastPoint to:currentPoint color:color blend:kCGBlendModeNormal];
double delayInSeconds = 1.0;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
[self drawLine:brush from:lp to:currentPoint color:[UIColor clearColor] blend:kCGBlendModeClear];
});
lastPoint = currentPoint;
}
- (void)drawLine:(CGFloat)width from:(CGPoint)from to:(CGPoint)to color:(UIColor*)color blend:(CGBlendMode)mode {
UIGraphicsBeginImageContext(self.view.frame.size);
CGContextRef context = UIGraphicsGetCurrentContext();
[self.tempDrawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
CGContextMoveToPoint(context, from.x, from.y);
CGContextAddLineToPoint(context, to.x, to.y);
CGContextSetLineCap(context, kCGLineCapRound);
CGContextSetLineWidth(context, width);
CGContextSetStrokeColorWithColor(context, [color CGColor]);
CGContextSetBlendMode(context, mode);
CGContextStrokePath(context);
self.tempDrawImage.image = UIGraphicsGetImageFromCurrentImageContext();
[self.tempDrawImage setAlpha:1];
UIGraphicsEndImageContext();
}
The draw phase works nicely, but there are a couple problems with the subsequent erase phase.
While the line "fill" is correctly cleared, a thin stroke around the path remains.
The "erase phase" is choppy, nowhere near as smooth as the drawing phase. My best guess is that this is due to the cost of UIGraphicsBeginImageContext run in dispatch_after.
Is there a better approach to drawing a self-erasing line?
BONUS: What I'd really like is for the path to "shrink and vanish." In other words, after the delay, rather than just clearing the stroked path, I'd like to have it shrink from 5pt to 0pt while simultaneously fading out the opacity.
I would just let the view draw continuously with 60 Hz, and each time draw the entire line using points stored in an array. This way, if you remove the oldest points from the array, they will not be drawn anymore.
to hook up your view to display refresh rate (60 Hz), try this:
displayLink = [CADisplayLink displayLinkWithTarget:self selector:#selector(update)];
[displayLink addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
Store an age property along with each point, then just loop over the array and remove points which are older than your threshold.
e.g.
#interface AgingPoint <NSObject>
#property CGPoint point;
#property NSTimeInterval birthdate;
#end
// ..... later, in the draw call
NSTimeInterval now = CACurrentMediaTime();
AgingPoint *p = [AgingPoint new];
p.point = touchlocation; // get yr touch
p.birthdate = now;
// remove old points
while(myPoints.count && now - [myPoints[0] birthdate] > 1)
{
[myPoints removeObjectAtIndex: 0];
}
myPoints.add(p);
if(myPoints.count < 2)
return;
UIBezierPath *path = [UIBezierPath path];
[path moveToPoint: [myPoints[0] point]];
for (int i = 1; i < myPoints.count; i++)
{
[path lineToPoint: [myPoints[i] point];
}
[path stroke];
So on each draw call, make a new bezierpath, move to the first point, then add lines to all other points. Finally, stroke the line.
To implement the "shrinking" line, you could draw just short lines between consecutive pairs of points in your array, and use the age property to calculate stroke width. This is not perfect, as the individual segments will have the same width at start and end point, but it's a start.
Important: If you are going to draw a lot of points, performance will become an issue. This kind of path rendering with Quartz is not exactly tuned to render real fast. In fact, it is very, very slow.
Cocoa arrays and objects are also not very fast.
If you run into performance issues and you want to continue this project, look into OpenGL rendering. You will be able to have this run a lot faster with plain C structs pushed into your GPU.
There were a lot of great answers here. I think the ideal solution is to use OpenGL, as it'll inevitably be the most performant and provide the most flexibility in terms of sprites, trails, and other interesting visual effects.
My application is a remote controller of sorts, designed to simply provide a small visual aid to track motion, rather than leave persistent or high fidelity strokes. As such, I ended up creating a simple subclass of UIView which uses CoreGraphics to draw a UIBezierPath. I'll eventually replace this quick-fix solution with an OpenGL solution.
The implementation I used is far from perfect, as it leaves behind white paths which interfere with future strokes, until the user lifts their touch, which resets the canvas. I've posted the solution I used here, in case anyone might find it helpful.
I use the code below for masking image to remove a part using touch. This works properly using CGContextSetBlendMode.
Now I want to re-draw that image using this touch event. Can you help me for re-draw erased part of the image?
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [touches anyObject];
currentTouch = [touch locationInView:Second_IMG];
CGFloat brushSize = 35;
CGColorRef strokeColor = [UIColor whiteColor].CGColor;
UIGraphicsBeginImageContext(Second_IMG.frame.size);
CGContextRef context = UIGraphicsGetCurrentContext();
[Second_IMG.image drawInRect:CGRectMake(0, 0, Second_IMG.frame.size.width, Second_IMG.frame.size.height)];
CGContextSetLineCap(context, kCGLineCapRound);
CGContextSetLineWidth(context, brushSize);
CGContextSetStrokeColorWithColor(context, strokeColor);
CGContextSetBlendMode(context, kCGBlendModeClear);
CGContextBeginPath(context);
CGContextMoveToPoint(context, lastTouch.x, lastTouch.y);
CGContextAddLineToPoint(context, currentTouch.x, currentTouch.y);
CGContextStrokePath(context);
Second_IMG.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
lastTouch = [touch locationInView:Second_IMG];
}
I use the code below for masking image
No, you're not masking at all. You are drawing a new image that lacks the touched area (because you "erased" that part of the image using kCGBlendModeClear). And you are then replacing the image of Second_IMG with this new partially erased image. So there is no "erased part" to "redraw" - you have thrown the information away.
Thus, to do what you are asking to do, you will need first to have access to a copy of the original Second_IMG.image. If you then replace the partially erased Second_IMG.image with the original, all the erased material will magically reappear - because you will return to the image with nothing erased.
But let's say that that isn't your goal: you don't want to bring back all the erased material, but only the material most recently erased. Then you would need to save off each generated intermediate image. You don't want to do this on every touchesMoved:, obviously, because you would end up with thousands of intermediate images. But if you save off the current state of the image on touchesEnded:, for example, then if you want to go back to before the most recent touchesMoved: sequence, you'll be able to, because you saved it on the previous occasion.
It would be simpler, however, if you were really using masking! In other words, if each stroke were expressed as an actual mask layer sitting on top of the image view, then the stroke could be removed simply by removing that mask layer. You would thus be working with masks layers expressing the strokes, rather than replacing the images as you are doing now. You will fine, in any case, that replacing the image repeatedly does not hold up well on the device - it's a very inefficient way to proceed.
I am trying to use CAShapeLayer to mask a CALayer in my iOS app as it takes a fraction of the CPU time to mask an image vs manually masking one in a bitmap context;
When I have several dozen or more images layered over each other, the CAShapeLayer masked UIImageView is slow to move to my touch.
Here is some example code:
UIImage *image = [UIImage imageWithContentsOfFile:[[NSBundle mainBundle]pathForResource:#"SomeImage.jpg" ofType:nil]];
CGMutablePathRef path = CGPathCreateMutable();
CGPathAddEllipseInRect(path, NULL, CGRectMake(0.f, 0.f, image.size.width * .25, image.size.height * .25));
for (int i = 0; i < 200; i++) {
SLTUIImageView *imageView = [[SLTUIImageView alloc]initWithImage:image];
imageView.frame = CGRectMake(arc4random_uniform(CGRectGetWidth(self.view.bounds)), arc4random_uniform(CGRectGetHeight(self.view.bounds)), image.size.width * .25, image.size.height * .25);
CAShapeLayer *shape = [CAShapeLayer layer];
shape.path = path;
imageView.layer.mask = shape;
[self.view addSubview:imageView];
[imageView release];
}
CGPathRelease(path);
With the above code, imageView is very laggy. However, it reacts instantly if I mask it manually in a bitmap context:
UIImage *image = [UIImage imageWithContentsOfFile:[[NSBundle mainBundle]pathForResource:#"3.0-Pad-Classic0.jpg" ofType:nil]];
CGMutablePathRef path = CGPathCreateMutable();
CGPathAddEllipseInRect(path, NULL, CGRectMake(0.f, 0.f, image.size.width * .25, image.size.height * .25));
for (int i = 0; i < 200; i++) {
UIGraphicsBeginImageContextWithOptions(CGSizeMake(image.size.width * .25, image.size.height * .25), NO, [[UIScreen mainScreen]scale]);
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextAddPath(ctx, path);
CGContextClip(ctx);
[image drawInRect:CGRectMake(-(image.size.width * .25), -(image.size.height * .25), image.size.width, image.size.height)];
UIImage *finalImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
SLTUIImageView *imageView = [[SLTUIImageView alloc]initWithImage:finalImage];
imageView.frame = CGRectMake(arc4random_uniform(CGRectGetWidth(self.view.bounds)), arc4random_uniform(CGRectGetHeight(self.view.bounds)), finalImage.size.width, finalImage.size.height);
[self.view addSubview:imageView];
[imageView release];
}
CGPathRelease(path);
By the way, here is the code to SLTUIImageView, it's just a simple subclass of UIImageView that responds to touches (for anyone who was wondering):
-(id)initWithImage:(UIImage *)image{
self = [super initWithImage:image];
if (self) {
self.userInteractionEnabled = YES;
}
return self;
}
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
[self.superview bringSubviewToFront:self];
}
-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
UITouch *touch = [touches anyObject];
self.center = [touch locationInView:self.superview];
}
Is it possible to somehow optimize how the CAShapeLayer is masking the UIImageView so that the performance is improved? I have tried to find out where the bottle-neck is using the Time Profiler in Instruments, but I can't tell exactly what is causing it.
I have tried setting shouldRasterize to YES on both layer and on layer.mask but neither seem to have any effect. I'm not sure what to do.
Edit:
I have done more testing and find that if I use just a regular CALayer to mask another CALayer (layer.mask = someOtherLayer) I have the same performance issues. It seems that the problem isn't specific to CAShapeLayer—rather it is specific to the mask property of CALayer.
Edit 2:
So after learning more about using the Core Animation tool in Instruments, I learned that the view is being rendered offscreen each time it moves. Setting shouldRaster to YES when the touch begins and turning it off when the touch ends makes the view stay green (thus keeping the cache) in instruments, but performance is still terrible. I believe this is because even though the view is being cached, if it isn't opaque, than it still has to be re-rendered with each frame.
One thing to emphasize is that if there are only a few views being masked (say even around ten) the performance is pretty good. However, when you increase that to 100 or more, the performance lags. I imagine this is because when one moves over the others, they all have to be re-rendered.
My conclusion is this, I have one of two options.
First, there must be someway to permanently mask a view (render it once and call it good). I know this can be done via the graphic or bitmap context route as I show in my example code, but when a layer masks its view, it happens instantly. When I do it in a bitmap context as shown, it is quite slow (as in it almost can't even be compared how much slower it is).
Second, there must be some faster way to do it via the bitmap context route. If there is an expert in masking images or views, their help would be very much appreciated.
You've gotten pretty far along and I believe are almost to a solution. What I would do is simply an extension of what you've already tried. Since you say many of these layers are "ending up" in final positions that remain constant relative to the other layers, and the mask.. So simply render all those "finished" layers to a single bitmap context. That way, every time you write out a layer to that single context, you'll have one less layer to worry about that is slowing down the animation/rendering process.
Quartz (drawRect:) is slower than CoreAnimation for many reasons: CALayer vs CGContext drawRect vs CALayer. But it is necessary to use it correctly.
In the documentation you can see some advices. ImprovingCoreAnimationPerformance
If you want a hight performance, maybe you can try using AsyncDisplayKit. This framework allows to create smooth and responsive apps.
I'm trying to add a feature in my iPhone app that allows users to record the screen. To do this, I used an open source class called ScreenCaptureView that compiles a series of screenshots of the main view through the renderInContext: method. However, this method ignores masked CALayers, which is key to my app.
EDIT:
I need a way to record the screen so that the masks are included. Although this question specifically asks for a way to create the illusion of an image mask, I'm open to any other modifications I can make to record the screen successfully.
APP DESCRIPTION
In the app, I take a picture and create the effect of a moving mouth by animating the position of the jaw region, as shown below.
Currently, I have the entire face as one CALayer, and the chin region as a separate CALayer. To make the chin layer, I mask the chin region from the complete face using a CGPath. (This path is an irregular shape and must be dynamic).
- (CALayer *)getChinLayerFromPic:(UIImage *)pic frame:(CGRect)frame {
CGMutablePathRef mPath = CGPathCreateMutable();
CGPathMoveToPoint(mPath, NULL, p0.x, p0.y);
CGPoint midpt = CGPointMake( (p2.x + p0.x)/2, (p2.y+ p0.y)/2);
CGPoint c1 = CGPointMake(2*v1.x - midpt.x, 2*v1.y - midpt.y); //control points
CGPoint c2 = CGPointMake(2*v2.x - midpt.x, 2*v2.y - midpt.y);
CGPathAddQuadCurveToPoint(mPath, NULL, c1.x, c1.y, p2.x, p2.y);
CGPathAddQuadCurveToPoint(mPath, NULL, c2.x, c2.y, p0.x, p0.y);
CALayer *chin = [CALayer layer];
CAShapeLayer *chinMask = [CAShapeLayer layer];
chin.frame = frame;
chin.contents = (id)[pic CGImageWithProperOrientation];
chinMask.path = mPath;
chin.mask = chinMask;
CGPathRelease(mPath);
return chin;
}
I then animate the chin layer with a path animation.
As mentioned before, the renderInContext: method ignores the mask, and returns an image of the entire face instead of just the chin. Is there any way I can create an illusion of masking the chin? I would like to use CALayers if possible, since it would be most convenient for animations. However, I'm open to any ideas, including other ways to capture the video. Thanks.
EDIT:
I'm turning the cropped chin into a UIImage, and then setting that new image as the layers contents, instead of directly masking the layer. However, the cropped region is the reverse of the specified path.
CALayer *chin = [CALayer layer];
chin.frame = frame;
CGImageRef imageRef = [pic CGImage];
CGColorSpaceRef colorSpaceInfo = CGImageGetColorSpace(imageRef);
int targetWidth = frame.size.width;
int targetHeight = frame.size.height;
CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);
CGContextRef bitmap = CGBitmapContextCreate(NULL, targetWidth, targetHeight, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);
CGContextAddPath(bitmap, mPath);
CGContextClip(bitmap);
CGContextDrawImage(bitmap, CGRectMake(0, 0, targetWidth, targetHeight), imageRef);
CGImageRef ref = CGBitmapContextCreateImage(bitmap);
UIImage *chinPic = [UIImage imageWithCGImage:ref];
chin.contents = (id)[chinPic CGImageWithProperOrientation];
Why don't you draw the CALayer of the chin into a seperate CGImage and make a new UIImage with that?
Then you can add this CGImage to a seperate UIImageView, which you can just move around with a PanGestureRecognizer for example?
I suggest that you draw each part alone(you don't need masks), the face without a chin, and the chin, both with alpha pixels around, then just draw the chin over and move it on your path ..
Please inform me if this wasn't helpful to you, regards
If you just need this in order to capture the screen, it is much easier to use a programme such as
http://www.airsquirrels.com/reflector/
that connects your device to the computer via AirPlay, and then record the stream on the computer. This particular programme has screen recording built in, extremely convenient. I think there is a trial version you can use for recordings of up to 10 minutes.
Have you tried taking a look at layer.renderInContext doesn't take layer.mask into account? ?
In particular (notice the coordinate flip):
//Make the drawing right with coordinate switch
CGContextTranslateCTM(context, 0, cHeight);
CGContextScaleCTM(context, 1.0, -1.0);
CGContextClipToMask(context, CGRectMake(maskLayer.frame.origin.x * mod, maskLayer.frame.origin.y * modTwo, maskLayer.frame.size.width * mod,maskLayer.frame.size.height * modTwo), maskLayer.image.CGImage);
//Reverse the coordinate switch
CGAffineTransform ctm = CGContextGetCTM(context);
ctm = CGAffineTransformInvert(ctm);
CGContextConcatCTM(context, ctm);
I have a "palette" of paths that I will draw many times; perhaps 100.
I'd like to draw these at a specified location like this:
CGPathRef foo = ...
CGPathRef bar = ...
// do this dozens of times at differing points
[self draw:context path:foo atX:100 andY:50];
[self draw:context path:bar atX:200 andY:50];
What I'm doing now is translating. It works, but I'm not sure that this is the most performant solution. Something like this:
- (CGRect) draw:(CGContextRef) context path:(CGPathRef) path atX:(CGFloat) x andY: (CGFloat)y
{
CGContextSaveGState(context);
CGContextTranslateCTM(context, x, y);
CGRect pathBoundingRect = CGPathGetBoundingBox(path);
CGContextSetFillColorWithColor(context, drawColor);
CGContextAddPath(context, path);
CGContextDrawPath(context, kCGPathFill);
CGContextRestoreGState(context);
return pathBoundingRect;
}
Do you have any suggestions for improvement?
If they move, it would probably be much faster to draw each one in its own UIView (so in the beginning, they would all be identical), and position the view itself.
That way, the translation (of the views) would automatically be done on the GPU instead of the CPU, and drawRect: would only need to be called once for each path object.