I've been having a little success with NSAffineTransform but have come across AffineTransform which is presumably more Swifty. However it doesn't have a concat method, so how do you use it? I'm aiming to draw the same little BezierPath rotated several times round the centre.
Sorry if it's obvious; I guess others might find this useful.
Here's how I see it. If you're drawing with an NSBezierPath you apply it to the path with myPath.transform(using: tr), e.g.:
let tr1 = AffineTransform(translationByX: 20, byY: 20)
bez = NSBezierPath()
// add some elements to the path here
bez.transform(using: tr1)
bez.stroke()
As I see it, the transform affects all the elements already in the path, but not any elements subsequently added. Transforms are cumulative, in that re-applying a transform, or applying another will affect all the elements so far entered.
You can also use the AffineTransform's own methods to transform individual points or sizes.
Related
i have the requirement to perform a redaction in itext7. We have several rectangles which have been selected by the user. Some of these have been rotated. I have not found the ability to rotate rectangles in itext7. Usually, how we draw "rotated" rectangles is to perform some mathematical operations on a "fake" rectangle we draw in the code, and then draw them either using a series of lines like so:
if (rect.mRotation > 0)
{
r.Rotate(DegreeToRadian(rect.mRotation));
}
c.MoveTo(r.TopLeft.X, r.TopLeft.Y);
c.LineTo(r.TopRight.X, r.TopRight.Y);
c.LineTo(r.BottomRight.X, r.BottomRight.Y);
c.LineTo(r.BottomLeft.X, r.BottomLeft.Y);
c.LineTo(r.TopLeft.X, r.TopLeft.Y);
c.Stroke();
In the case of images, or something similar, we are unable to do the above. In this case we use an affinetransform to simulate the movement, which is applied to the image before it is added to the document. Both of the previous methods work perfectly.
Unfortunately for us, the pdfSweep tool only accepts (iText.Kernel.Geom) rectangles. We are looking for a way to be able to still pass an iText.Kernel.Geom.Rectangle which has had transforms applied (ie. a rectangle which has been rotated). We have tried setting the llx/urx values manually using the setBBox method, but this wont affect the rotation.
Does anyone know how we can go about redacting items over a given rectangular area which has been rotated?
Thanks
I'm using CGAffineTransformMakeRotation to rotate a subview using its transform property. Later, I need to find out how far the subview has been rotated. I realize that I could simply use an int to keep track of this, but is there a simple way to get the current rotation of the subview?
CGAffineTransformMakeRotation is explicitly defined to return a matrix with cos(angle) in the transform's a value, sin(angle) in b, etc (and, given the way the transform works, that's the only thing it really could do).
Hence you can work out the current rotation by doing some simple inverse trigonometry. atan2 is probably the thing to use, because it'll automatically figure out the quadrants appropriately.
So, e.g.
- (float)currentAngleOfView:(UIView *)view
{
CGAffineTransform transform = view.transform;
return atan2f(transform.b, transform.a);
}
Because that'll do an arctangent that'll involve dividing the a and b fields in an appropriate manner, that method will continue to work even if you apply scaling (as long as it's the same to each axis) or translation.
If you want to apply more complex or arbitrary transformations then things get a lot more complicated. You'll want to look how to calculate normal matrices. From memory I think you'd want the adjugate, which is about as much fun to work out as it sounds.
How would I efficiently draw a CGPath on a CATiledLayer? I'm currently checking if the bounding box of the tile intersects the bounding box of the path like this:
-(void)drawLayer:(CALayer*)layer inContext:(CGContextRef)context {
CGRect boundingBox = CGPathGetPathBoundingBox(drawPath);
CGRect rect = CGContextGetClipBoundingBox(context);
if( !CGRectIntersectsRect(boundingBox, rect) )
return;
// Draw path...
}
This is not very efficient as the drawLayer:inContext: is called multiple times from multiple threads and results in drawing the path many times.
Is there a better, more efficient way to do this?
The simplest option is to draw your curve into a large image and then tile the image. But if you're tiling, it probably means the image would be too large, or you would have just drawn the path in the first place, right?
So you probably need to split your path up. The simplest approach is to split it up element by element using CGPathApply. For each element, you can check its bounding box and determine if that element falls in your bounds. If not, just keep track of the last end point. If so, then move to the last end point you saw and add the element to a new path for this tile. When you're done, each tile will draw its own path.
Technically you will "draw" things that go outside your bounds here (such as a line that extends beyond the tile), but this is much cheaper than it sounds. Core Graphics is going to clip single elements very easily. The goal is to avoid calculating elements that are not in your bounding box at all.
Be sure to cache the resulting path. You don't need to calculate the path for every tile; just the ones you're drawing. But avoid recalculating it every time the tile draws. Whenever the data changes, dump your cache. If there are a very large number of tiles, you can also use NSCache to optimize this even better.
You don't show where the path gets created. If possible, you might try building the path up in the -drawLayer:inContext: method, only creating the portion of it needed for the tile being drawn.
As with all performance problems, you should use Instruments to profile your code and find out exactly where the bottlenecks are. Have you tried that already, and if so, what did you find?
As a side note, is there a reason you're using CGPath instead of UIBezierPath? From Apple's documentation:
For creating paths in iOS, it is recommended that you use UIBezierPath
instead of CGPath functions unless you need some of the capabilities
that only Core Graphics provides, such as adding ellipses to paths.
For more on creating and rendering paths in UIKit, see “Drawing Shapes
Using Bezier Paths.”
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 made a quad curve path using the method CGPathAddQuadCurveToPoint. I got the path perfectly. But, I want to know all the coordinate points which are participated in the path.
Is there a way to retrieve all the coordinate points in a path?
If not do u have any other solution for retrieving all the points in a curve mathematically.
Thanks in advance,
Vamshi
You can do this using the wykobi C++ library routine for cubic bezier curves. Wykobi's library supports quadratic Bezier curves also.
Of course as someone pointed out you don't want all the points (although not impossible, it would just take infinite time :). Wykobi makes it easy to get a certain number of points -- if your start, c1, c2, and end points (where c1, c2 are the control points) are exactly the same as the ones given to CGContextAddCurveToPoint then the points will lie perfectly on the line drawn by core graphics -- so you can do things like draw a pattern at several points on the path.
See: http://www.codeproject.com/Articles/22568/Computational-Geometry-C-and-Wykobi
Also, after I started using wykobi I heard that there is a similar, maybe even better library that is part of Boost, but have not checked it out yet.
I created a C++ Class WPoint as a bridge between wykobi points and CGPoints (C++ fun!). Here's some code (without WPoint, but you can imagine that it is exactly the same layout as a CGPoint so if you do the right cast you can convert easily.
NSMutableArray* result = [[NSMutableArray alloc] init];
wykobi::cubic_bezier<CGFloat,2> bezier;
bezier[0] = (WPoint)p1; // start point, in CG we did a CGMoveToPoint
bezier[1] = (WPoint)b1i; // control 1
bezier[2] = (WPoint)b2i; // control 2
bezier[3] = (WPoint)p2; // end point
std::vector<WPoint> point_list;
int numPoints = p2.dist(p3) * pointDensity;
// *** here's the magic ***
wykobi::generate_bezier(bezier,std::back_inserter(point_list), numPoints);
for (int i=0; i<numPoints; i++) {
CGPoint p = (CGPoint)(point_list[i]);
[result addObject:[NSValue valueWithCGPoint:p]];
}
// result has your points!
Here's a link to the Boost geometry library:
http://www.boost.org/doc/libs/1_47_0/libs/geometry/doc/html/geometry/introduction.html
Use CGContextSetLineDash
The purpose of this function is to create a dashed line, but You can use it to get smaller segments.
starting point of each segment can be treated as points.
CGSize bbSize = CGPathGetBoundingBox(path).size;
UIGraphicsBeginImageContext(bbSize);
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(ctx, 1.0);
CGContextAddPath(ctx, path);
CGContextSetLineDash(ctx, phase, lengths, count);
CGContextReplacePathWithStrokedPath(ctx);
result = CGContextCopyPath(ctx);
UIGraphicsEndImageContext();
If you want to work on the moveto, lineto, and curveto elements of the path, use CGPathApply. You pass this a pointer to a function in your program, and it calls that function once per element of the path.
Unfortunately, there's no way to just ask for each element like there is with AppKit's NSBezierPath. The function is the only way.
If you want to determine every pixel intersected by the path, too bad—that's not practical, and I can't even think of why you'd want that information. Some contexts, such as PDF contexts, don't even have pixels; in those cases, any question involving pixels is a non sequitur.
A quadratic curve is just that -- a curve. It's impossible to get a list of all of the points on it because there are infinitely many points, and it's not a simple line segment.
See Getting Information about Quartz Paths for a list of the functions you can use to query a CGPath object. Unfortunately, it seems like the most useful information you're going to get is with CGPathContainsPoint(), which only tells you if a given point is contained within the area of the path.
If not do u have any other solution for retrieving all the points in a curve mathematically.
What do you need them for, i.e. what problem are you trying to solve? If it is to intersect two curves, you can do this mathematically. Just set the two curve equations equal to each other and solve for the unknown.
I guess you're after something equivalent to the Java2D FlatteningPathIterator class. For example Java2D's path.getPathIterator(null, 1.0) returns an iterator of only 'lineTo' segments even if the original path had curveTo and quadTo, the double argument controls the 'flatness', giving you an easy way to calculate any point on the curve.
I'm searching for the same thing in Cocoa, but have found nothing. If you find a solution please let me know.
There are curve implmentations around (e.g. http://sourceforge.net/projects/curves/) that could be ported, but there's always a risk that if you don't use the same algorithm as Cocoa then there could be errors between your interpolation and the stroked NSBezierPath/CGPath.