When I'm using a UIBezierPath to draw where the user is touching if the user moves to fast sometimes I get really hard points like the tip of a triangle. Any clue what might be causing this? Or how I can fix it?
I am capturing the points using touchesBegan/Moved/Ended and placing them into an NSArray of UIBezierPaths.
Despite the name, UIBezierPath doesn't just draw curves. In fact, by default it won't - presumably you're simply passing the coordinates returned by touchesBegan etc, into the addLineToPoint method.
Instead of simply passing all the touch coordinates directly into a UIBezierPath you should first interpolate them to avoid these sharp lines that occur when you rapidly move your finger across the screen. This is not too difficult, although does require some knowledge of how bezier curves work and spline interpolation.
If you are looking for a slightly easier way out, there are a couple of open source libraries that will do this for you, like this one: http://cocoacontrols.com/platforms/ios/controls/smooth-line-view
Related
My Question is something similar to this.
I have 2 CGPathRef and 1 will be moved by finger touch. I want to find that whether the 2 CGPathRef are intersected? That question was asked almost 2 years ago and I want to know whether something has been found in the mean time.
This is fairly old, but I found it looking for a similar solution, in my problem I wanted to find when a circle overlapped with a path (a special case of your question).
I solved this by using CGPathCreateCopyByStrokingPath to create a stroked version of the original path using the radius of the circle as the stroke width. If the center point of the circle overlaps the stroked path then the original path overlaps the circle.
BOOL CGPathIntersectsCircle(CGPathRef path, CGPoint center, CGFloat radius)
{
CGPathRef fuzzyPath;
fuzzyPath = CGPathCreateCopyByStrokingPath(path, NULL, radius,
kCGLineCapRound,
kCGLineJoinRound, 0.0);
if (CGPathContainsPoint(fuzzyPath, NULL, center, NO))
{
CGPathRelease(fuzzyPath);
return YES;
}
CGPathRelease(fuzzyPath);
return NO;
}
Edit: A minor bug where the fuzzyPath was not released.
I have written a small pixel based path collision detection API for CGPathRefs. It requires that you add a few source directories to your project, and it only works with ARC, but it should at least show you how one might do something like this. It basically draws the two paths on two separate contexts, and then does pixel-by-pixel checks to see if any pixels are on both paths. Obviously this would be slow to run every time the user drags their finger, but it certainly could be done once every half second or so, maybe not even on the main thread.
This is the easiest way I've found of doing something like this, and it may easily be that there's no better way, besides using lots of math.
The source on Github
A quick Youtube demo.
Generally speaking, finding the intersection of two arbitrary CGPaths is going to be very complex.
There are ways to do approximations. Checking the intersections of the bounding boxes is a good first step. You can also subdivide the curve and repeat the process to get better approximations. Another option is to flatten the paths and see if any of the line segments of the flattened paths intersect.
For the general case, however, things get very nasty very fast. Consider, for example, the fact that two cubic bezier segments (never mind an entire path... just one segment) can intersect with another segment at up to 6 points. The more segments in your path, the more potential intersections. There is also the problem of degenerate bezier curves where a segment has a cusp that just touches one point of another segment. Does that count as an intersection? (sometimes yes, sometimes no)
It's not clear from your question, but you might also want to consider the intersections of the strokes that are applied to the curves, and correctly account for line joins and miters. That that gets even harder. Macromedia FreeHand (a drawing program similar to Adobe Illustrator) had a very large, complex, intensely mathematical library for discovering arbitrary bezier curve intersections. The problem is not easily solved.
To find the intersection of two CAShapeLayers, we can use below method, CAShapeLayer won't return frame. But we can get the refPath frame using CGPathGetBoundingBox. But this one will give the frame in rectangle.I thing you may understand.
if (CGRectIntersectsRect(CGPathGetBoundingBox(layer.path), CGPathGetBoundingBox(layer.path)))
I am tearing my hair out trying to figure out what seems to be a very easy problem. I know a lot of this stuff has been talked about tangentially, so apologies if this treads on well-covered ground, but I can't find anything specific to my solution (believe me, I've looked).
Basically I want to drag an object/sprite along a pre-defined, curved path (not just move it, but DRAG IT). Think of the iPhone's "Slide to unlock" thing, but instead of just dragging the slider left-to-right, make the path an arc or a wavy line.
My basic thinking was:
define a bezier path, set the object at the start point.
if the object is touched, check for hit detection on the bezier path in touchesMoved (or some similar function). if touches stay on the path, advance the sprite along the path until the path ends (in which case, task is finished) or the user's finger goes off the path (in which case, the object should go back to the beginning).
None of this is trivial (at least, that's how it seems). For example:
Doing hit detection on a Bezier path is a royal pain since you actually need to do it on the stroked portion, not the fill portion. And even then, I can't seem to find a way to do it on a path of any width -- only on the 1-point-wide path of the Bezier.
Moving an object partially along a path doesn't even seem possible: all of the animation methods move the sprite along the ENTIRE path. Also, doing this requires you to find the point on the path closest to the user's touch, which, if you've ever looked this up involves astoundingly complicated math.
I've thought of using rigid bodies to occupy all of the space EXCEPT the path, so the object can only move in the path. However, this requires the definition of curved rigid bodies some of which must be concave. Dead end.
Am I making this too hard? It doesn't seem that complicated. I don't need a whole solution, just a new way to think about this and kick in the right direction. Any help would be really appreciated.
How about this?
Consider the X Axis of your bezier
path.
Each time the user taps or interacts with the screen just look at the x portion of the touch
Map that X Coordinate with your path and move the object to the right position.
Yes, you are making this too hard.
Take the simplification suggested above (or along a circle, line, etc) if it works for, or if you really want to do it against a bézier curve, consider the following:
Look at the definition of the bézier curve
What you're looking for is to define a new object position P' from a current position P and a change in touch position D.
If you rephrase the original P(x,y) in terms of t (bézier curves are parametric), then the problem becomes finding how much t offset to add based on D.
Something involving the differential of the bezier fn at P might be a good way to do that. Ie, how much t would have been added had the curve just been a straight line coming from point P along the curve.
EDIT:
Transition between segments:
If each segment has t in [0,1), then you can detect t >= 1 and move on to the next segment, setting P to the end of the previous segment, and evaluating the movement again in relation to that point. There might have to be some heuristics involved if you have a lot of small points, etc.
I'm trying to implement "hand draw tool".
At the moment algorythm looks like that (I don't insert any code because methods are quite big, will try to explain an idea):
Drawing
In touchesStarted: method I create NSMutableArray *pointsArray and add point into it. Call setNeedsDisplay: method.
In touchesMoved: method I calculate points between last added point from the pointsArray and current point. Add all points to the pointsArray. Call setNeedsDisplay: method.
In touchesFinished: event I calculate points between last added point from the array and current point. Set flag touchesWereFinished. Call setNeedsDisplay:.
Render:
drawRect: method checks is pointsArray != nil and is there any data in it. If there is - it starts to traw circles in each point of this array. If flag touchesWereFinished is set - save current context to the UIImage, release pointsArray, set it to nil and reset the flag.
There are a lot disadvantages of this method:
It is slow
It becomes extremely slow when user touches and move finger for long time. Array becomes enormous
"Lines" composed by circles are ugly
I would like to change my algorithm to make it bit faster and line smoother.
In result I would like to have lines like on the picture at following URL (sorry, not enough reputation to insert an image): http://2.bp.blogspot.com/_r5VzEAUYXJ4/SrOYp8tJCPI/AAAAAAAAAMw/ZwDKXiHlhV0/s320/SketchBook+Mobile(4).png
Can you advice me, ho I can draw lines this way (smooth and slim on the edges)? I thought to draw circles with alpha gradient on the edges (to make lines smoother), but it will be extremely slowly IMHO.
Thanks for help
Update
I changed draw algorithm. Now every event I save UITouch and in the drawRect: method I draw path from prev. point to the current one. And dump UIImage from context every drawRect: invocation.
But I still have 2 questions:
Is it possible to draw more smooth. I mean if I draw quite fast, I easily can see that path path is a set of straight lines. But I want to draw curves, to make path smooth. Probably Bezier curves will help but I don't understand how they can help in this.
situation.
I want to start path with thiner line and finish with thiner line too. How I can do this line transform?
Thanks!
How would I smooth a line (UIBeizerPath) or a set of points? Right now it draws it jagged. I read about spline interpolation, could anyone point me to an implementation of this in cocoa or C or give me an alternate line smoothing algorithm.
I don't think you need to do Bezier paths with curves. You can keep drawing straight line segments but add more data points with interpolation. This is especially important because I'm assuming you want to smooth only on one axis so you don't end up with odd things like loops in your graph.
So you want to add more points to your source data, between the existing points, and use an interpolation algorithm that's more sophisticated than a linear interpolation. There are many to choose from. Quadratic? Sine-based? Many, and it depends on what kind of data you're using.
Quartz (which UIKit uses for drawing, and in many places makes you use directly for drawing) has anti-aliasing support built-in. Most contexts have it turned on already, so you should not have aliased (jagged) drawing unless you're turning anti-aliasing off. So, stop doing that. :-)
The contexts that don't have it turned on by default are mostly those where it isn't appropriate, such as PDF contexts and CGLayer contexts. The documentation implies that those contexts don't even support anti-aliasing, which makes some amount of sense.
CGContext provides a couple of functions for turning anti-aliasing on and off, but you should never need to call them except when you want aliasing, which you don't. You could try turning it on using those functions; if that works, then you should investigate why it was ever off in the first place.
Are you drawing the path from within a CALayer? That may be why it's off; there's an Info.plist key you have to turn on to get anti-aliasing turned on by default in such contexts.
I've found that if you draw a line or an image on the edge of your frame that it will appear jagged. Move the line in a few (or grow your frame) and it should appear nice and crisp. Again, not sure if that's your question or not but it has bit me a few times.
For instance if you are displaying an image inside a CALayer, make sure there is space between the image and the frame if you are doing anything but 90 degree angles.
I have a NSArray of points that make up a path. I can detect when it self-intersects. When this happens, I try to fill the path.
First I used CoreGraphics, now I'm using openGl to draw a triangle array. Doesn't work well as you can see in the image.
How do I fill only the circular area while leaving the "tail" alone? I was thinking of a reverse flood fill but don't think CG has any API functions for this...
Maybe instead of actually drawing the path you can just approximate the diameter of the path and draw a circle with your approximation.
Here is some code to detect a circle gesture on the iPhone:
http://www.mobileorchard.com/iphone-circle-gesture-detection/
Record all of the points in a doubly-linked list. When it comes time to fill, walk the list from the start and find the point that's closest to the end. Then, lineto that point, then lineto each point in reverse order, stopping with the second point in the list. The fill will implicitly close the path, which will jump from where you left off (the second point) back to the start (first) point.
This is just off the top of my head; you can play with a couple of variations on this to see what works best. You might record the closest previous node in each node, but this could get expensive for many nodes.