I'm writing an application that uses your finger to draw simple diagrams. I have it working for the most part but now I'm trying to optimize its performance. When the user swipes their finger fast, I can't capture enough touch events to draw a smooth path.
Here's my current approach:
1) I subclassed a UIView and added a poroperty to a CGLayer (gets created lazily and is the same size as my UIView).
2) My UIView subclass responds to touch events by storing the current and last touch points in instance variables.
3) My view's setNeedsDisplay is called and in the draw rect , do the following:
- draw a line from the previous touch location to the current touch location to the CGLayer
- draw the entire CGLayer to my views context in one go
The main problem is when a user swipes fast I get relatively few touch events, so the lines I draw between the touches are long and makes the path look jagged not smooth.
My questions:
1) Does drawRect (on my UIView subclass) and my touch event handlers on my UIView subclass get called in the same thread? I.e. could I have to threads executing (one in a touch event and the second in my draw rect)?
If no - do touch events get queued up while drawRect is being called? And how can I improve performance - simply improve performance of drawRect?
If yes - how can I get more touch events to happen so I can draw a smoother path?
Thanks.
Another approach is to interpolate the curve between the sample points. When the finger drag starts, begin collecting sample points. As the number of points increase, redraw the line. With two points, draw a straight line, with three or more draw a curve. You can re-start the process when two points are sampled that lie within a defined distance. This would allow you to draw two arcs (like a 'm') in one motion - you naturally pause in the middle as you change direction, possibly long enough for two or more samples.
drawRect gets called on the main thread. But you don't have to do this. You can use the main thread to collect UI events and do the drawing on a background thread. The background thread gets notified whenever there are new touches and starts a drawing operation in its own CGBitmapContext. Then you create a CGImage and hand it over to the View: view.layer.contents = drawingImage.
If you need even more performance, consider drawing using OpenGL.
Aloo, did you have find a solution to his as I've got the same problem. I also found agreat tutorial http://www.ipodtouchfans.com/forums/showthread.php?t=132024 but it also has the same problem that if you draw fast, say a circle, the drawing isn't very smooth. It;s almost like the iPhone just can't keep up, unfortunately this has to use the core graphics stuff.
Have you tried this?
http://developer.apple.com/library/ios/#samplecode/GLPaint/Introduction/Intro.html#//apple_ref/doc/uid/DTS40007328-Intro-DontLinkElementID_2
I tried adding
CGContextSetLineJoin(UIGraphicsGetCurrentContext(), kCGLineJoinRound);
but this did nothing. Looks like we'll have to figure out bezier curves
Related
I just want to draw point and line as per finger touch and moved in iphone screen.
What is the best way to draw point in iphone?
Can anyboday tell me how to draw point as per finger touch and moved in iphone ?
Thanks,
You can't "just draw" on the screen. Closest approximation might be to save some coordinates from some view's touch delegate methods and call setNeedsDisplay. When the view's drawRect is called, you can then use some Core Graphics (CG) drawing commands with those saved coordinates into the given drawing context. The OS will shortly then composite that view context onto the display screen.
check with this tutorial,i am sure it will definetly help you.
http://mobile.tutsplus.com/tutorials/iphone/ios-sdk_freehand-drawing/
you can draw line on Image or on UIView using UIBezierPath class.. in this class object you can store the user touch points and draw line using this points array..
for more details see the tutorial and demo from this link..
Drawing on View and Image
I have a UIScrollView that contains a custom UIView. In my UIView I am overriding drawRect to draw a path using CGContextStrokePath. I would like to slightly alter the way the zoom works. Pinch zooming out will show more of the paths on the screen. This is what I want but i want the line width to stay the same not shrink as you zoom out so that they are still clear to the user.
I thought I would just do this (myUIView zoom target is called _lineView)
-(void)scrollViewDidZoom:(UIScrollView *)pScrollView
{
_lineView.zoomScale = _scrollView.zoomScale;
[_lineView setNeedsDisplay];
}
and then just calculate an appropriate line stroke size in my _lineView drawRect method to give the effect of constant line width as you zoom out.
This is really slow and I have read that this is expected as drawrect is not optimised to be called many times a second.
I then started looking at using a GLKView instead and just rendering the whole thing in opengl directly. The problem with this is I will have to implement all of the zooming and panning myself (with all the lovely zoom and pan bounce effects you get for free in UiScrollView). I will also have to implement all the controls I want to use in opengl, buttons etc.
Is there a way to do this whilst still using Quartz2d? I feel like opengl will give me lots of power but it will take me much longer to get the rest of my app done if I go down that route.
I figured this out. I found a simple way to do this that does not slow down the zoom / bouncing animations at all and is very fast and fluid.
Quartz has a class called CAShapeLayer that lets you do some pretty cool stuff. Among these is being able to set a CGPath property and specify a linewidth. Changes are reflected in the view.
So i basically call shapeLayer.lineWidth from my scrollViewDidZoom method and it does exactly what i need.
What I would do if I were you is to use default zooming behavior while zooming (which does not redraw, but instead just applies a transform to the zoomed view, which can be done by the GPU very, very quickly, but as you have noticed can lead to inferior quality).
Then, when the user finished zooming, redraw the whole view as you do now. The appropriate delegate method is scrollViewDidEndZooming:withView:atScale:.
This way, you have fast (but slightly ugly) zooming, and nice (but slightly, probably unnoticeably, slower) display after the zoom is finished.
My question might be answered somewhere but I just couldn't find solution after a long research.
I need to draw visually shapes (curves, lines, rectangles etc.) on iPhone one on top of the previous. I did that using CGContext to draw over an image and it's working fine. However in my app the drawing view resizes on device rotation and the lines become blurred because of the different image size.
That's why I subclassed UIView and to call setNeedsDisplay from touchesMoved and touchesEnded. In drawRect I'm passing the point and... almost everything works OK.
However I have two problems:
1. Every time drawRect is called it clears previous drawing and starts over so I can't add a new shape.
2. Second is followed by same thing - I can't make a curve as on every move drawRect is called and the previous point is dismissed and a line is added from the starting point to the current.
So am I doing the whole thing wrong and is there some other better approach to this.
Thanks in advance!
My whole app uses touchesMoved for drawing (Coregraphics). Should I be calling [self setNeedsDisplay] from within touchesMoved instead of performing the drawing code in there? Would that stop some lag that I am experiencing? The only reason I didn't try this before posting is because it is going to take me a few hours to convert all drawing to within drawRect and I wanted to know if it would be more would efficient than drawing in touchesMoved?
Yes. You should always keep your drawing in drawRect and use setNeedsDisplay to trigger the actual drawing. This is key to the rendering of views in Cocoa Touch.
For example, if you didn't use this method, you could potentially have drawing code scattered around your class in multiple methods. In addition, this also ensures that your drawing code executes only once during a render cycle. Essentially, calling setNeedsDisplay triggers an invalidation flag that lets your UIView know to redraw itself. Without this, you could be performing extra drawing operations that aren't actually needed due to the render cycle.
You should not do drawing inside a UI callback. It will slow down or freeze the UI responsiveness, and you won't have the proper drawing context if you want to draw directly into a UIView.
Instead save, schedule or queue the information required for drawing for later, either into your own bitmap drawing context, or during the drawRect callback for that view.
Depending on the frame rate required, you many not even need to do a setNeedsDisplay on every touchesMoved event, but can queue the data and set a flag for an animation rate timer or CADisplayLink callback to do the setNeedsDisplay at a more constant rate (say only 15 or 30 frames per second). This will also help eliminate extra drawing operations.
I have drawn 5 circles in in my app one above the other . But i want to perform different operations when i touch each circle and there is only one touches began where I can perform touches for the entire view.. can anyone help me how to do that.
Either process the coordinates of the touch to "grab" a specific circle (you know their coordinates if you have the origins and radii), or put each circle into its own view, and make five subviews/circles of a parent view. Pass the touch down the view chain until the coordinates overlap.