I want to check the drawn shape matches a letter from the alphabet. It's a kids app for learning.
When any one draw the shape then how can i detect it's a correct letter?
I don't have any sample code for you but this is how I'd do this, I think.
You need to define or get a bezier path describing the shape of each letter - this would be an outline of a solid letter, not just a line drawing the letter shape. There may be a way to get this from the api, obtaining a bezier path from a glyph, or you may have to design them yourself.
You then need to scale the bezier path so it is roughly the same size as the drawing on the screen.
Then, check how many of the points in the drawn path fall within your standard font glyph. If its over a certain threshold, you can count that as a successful draw.
This is assuming you've asked the user to draw an A and you are checking against that one path. If you're trying to find out what theyve drawn without anything to go on, you need a handwriting recognition library, try searching for one of those.
Related
Is it possible to have irregularly shaped images positioned adjacent to each other, where each individual image is clickable within its own boundaries?
For example, if I had a map of the US and I want to click each state and have a separate segue for each:
(https://upload.wikimedia.org/wikipedia/commons/thumb/a/a5/Map_of_USA_with_state_names.svg/2000px-Map_of_USA_with_state_names.svg.png)
I appreciate any tips/pointers in the right direction. Thanks!
Whether the map is really a bunch of irregularly shaped images, or just one image, is immaterial. (The latter will be easier.) You can just define a separate UIBezierPath objects that outline each of the states, and then you can use the UIBezierPath method containsPoint to determine whether some tap point is contained within the respective state.
Frankly, you might consider how much accuracy you really need. For example, if looking at map of US from continental scale, you really don't need extremely accurate bezier paths. Often a simple irregular polygon shape can approximate the boundaries and is more than sufficient for hit tests.
In fact, you sometimes deliberately use a much bigger bezier path. For example, you might draw a single path that goes around all of the Hawaiian islands, with some leeway, so that you don't have to tap right on the actual island, but just somewhere close. Or, for Rhode Island, you might allow a tap on the text "Rhode Island", as well as the state itself.
I am able to draw shapes using the UIBezierPath object. Now I want to identify different shapes drawn using this eg. Rectangle , Square , Triangle , Circle etc. Then next thing I want to do is that user should be able to select a particular shape and should be able to move the whole shape to different location on the screen. The actual requirement is even more complex , but If I could make this much then I can work out on the rest.
Any suggestion or links or points on how do I start with this is welcome . I am thinking of writing a separate view to handle every shape but not getting how do I do that..
Thank You all in advance !!
I recommend David Gelphman’s Programming with Quartz.
In his chapter “Drawing with Paths” he has a section on “Path Construction Primitives” which provides a crossroads:
If you use CGContextAddLineToPoint your user could make straight lines defined by known Cartesian points. You would use basic math to deduce the geometric shapes defined by those points.
If you use CGContextAddCurveToPoint your user could make curved lines defined by known points, and I’m pretty sure that those lines would run through the points, so you could still use basic math to determine at least an approximation of the types of shapes formed.
But if you use CGContextAddQuadCurveToPoint, the points define a framework outside of the drawn curve. You’d need more advanced math to determine the shapes formed by curves along tangents.
Gelphman also discusses “Path Utility Functions,” like getting a bounding box and checking whether a given point is inside the path.
As for moving the completed paths, I think you would use CGContextTranslateCTM.
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 have a rectangular CGMutablePathRef and I want to subtract a circle which lays exactly on centered on one edge of that rectangle, so the edge does not cross the circle anymore.
There seem to be no functions to intersect or subtract paths from another. How can I do it?
You need to look at the CGContext you are drawing into and use the clipping on the context rather than the path.
Apple's documentation is here.
If I understand your question, you can draw your rectangle into the context and then "clip out" the circle path. If you are filling the paths, you'll need to pay attention to the winding rules.
Alternatively, you can make your path with a series of commands such as CGPathAddLineToPoint, CGPathAddArcToPoint, etc and then stoke the path in your context. If you use this approach, you can then apply transforms to the final path for scaling and rotating as needed. Depending on what you are trying to accomplish, this may be the better approach.
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.