In my custom control I have defined a few CGMutablePathRefs with the needed lines and arcs to draw my control; one draws the overall fill shape and others provide specular highlights. I have also defined two CGMutablePathRefs which contain the paths needed as clipping masks for the active and inactive state of the control.
What I'm struggling with is applying the clipping paths. I have previously used clipping paths for applying gradients to an image, but those drawing commands were of the CGContext... variety, not the CGPath... variety.
For testing purposes I have removed the specular highlight drawing aspects, just trying to get a large path clipped to a smaller path. This is what I had been testing with:
- (void)drawRect:(CGRect)rect
{
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextBeginPath(ctx);
CGContextAddPath(ctx, inactiveClip);
CGContextClosePath(ctx);
CGContextClip(ctx);
CGContextAddPath(ctx, frontFace);
CGContextSetLineWidth(ctx, 1.0);
CGContextSetFillColorWithColor(ctx, [[UIColor blackColor] CGColor]);
CGContextFillPath(ctx);
}
By putting the clipping command before any drawing, I thought I was saying to CoreGraphics, "Here's the region you should actually draw into."
Alas, nothing is drawn.
So assuming I had that ordering backwards I tried:
- (void)drawRect:(CGRect)rect
{
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextAddPath(ctx, frontFace);
CGContextSetLineWidth(ctx, 1.0);
CGContextSetFillColorWithColor(ctx, [[UIColor blackColor] CGColor]);
CGContextFillPath(ctx);
CGContextBeginPath(ctx);
CGContextAddPath(ctx, inactiveClip);
CGContextClosePath(ctx);
CGContextClip(ctx);
}
This was to say to CoreGraphics, "Okay before you actually color bits, check them against this clipping region."
Alas, nothing is clipped.
Since it is the case that my clipping path uses some of the same points and control points, in the same order, as the fill path, I have also replaced the call to CGContextClip with a call to CGContextEOClip to see if I was really struggling with the even-odd rule, but that doesn't seem to have had any visual affect.
I don't really know if I needed to bracket the CGContextAddPath call with CGContextBeginPath/CGContextClosePath calls, but what I was trying to do was minimize the differences between Apple's example code and my code. In theirs they do their CGContext... drawing calls between begin/close calls so I was too.
What am I misunderstanding here?
Related
I am drawing a shape in a UIView drawRect function that involves clipping a path, and then adding coloured blocks behind so that the colors have the shape of the clipped path. However, for some reason the lines of the path are not coming out smoothly; its if the antialiasing isn't working properly.
CGContextSetStrokeColorWithColor(context, [UIColor clearColor].CGColor);
CGContextSetLineWidth(context, 1.0);
CGContextSetShouldAntialias(context, true);
CGContextSetAllowsAntialiasing(context, true);
CGContextBeginPath (context);
CGContextMoveToPoint(context, xStart, yStart);
for (int i=0; i<points.count; i++) {
CGContextAddLineToPoint(context, xPoint, yPoint);
}
}
CGContextAddLineToPoint(context, xStart, yStart );
CGContextClip(context);
CGRect colorRect = CGRectMake(0, 0 , rectWidth, rectHeight);
CGContextSetFillColorWithColor(context, blockColor.CGColor);
CGContextFillRect(context, colorRect);
CGContextRestoreGState(context);
The result should have smooth lines, but it comes out jagged with visible pixels as in this image:
Any idea what the problem is and how to fix it?
Thanks in advance
Okey. So, there is no problem in your code. The problem is that antialiasing works a little different. You drawing a vertical slopes expecting that edge of resulting histogram will be smoothed. But actually antialiasing doesn't smooth the resulting figure. It works with path elements (curves, lines) one by one. So, for example if you draw a circle, its edges will be smoothed.
There is a simple solution of your problem: just create a curve, enveloping the histogram. Add it to your context. It will look more smooth.
Sorry for bad english.
First off, here's an image of my current situation.
To accomplish this I am using a subclassed UIView with the following method:
-(void)drawRect:(CGRect)rect
{
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextBeginPath(ctx);
CGContextMoveToPoint (ctx, CGRectGetMinX(rect), CGRectGetMinY(rect)); // top left
CGContextAddLineToPoint(ctx, CGRectGetMaxX(rect), CGRectGetMidY(rect)); // mid right
CGContextAddLineToPoint(ctx, CGRectGetMinX(rect), CGRectGetMaxY(rect)); // bottom left
CGContextClosePath(ctx);
CGContextSetRGBFillColor(ctx, 0, 1, 0, 1);
CGContextFillPath(ctx);
}
My ultimate goal is to clip the colored regions so that only the neon green remains. (I'll flip the colors later). I want it to look like a pie chart. I'm guessing there's a way to clip the colored corners out but I have no clue. CGContextClip(ctx) doesn't work.
I am using the Pixate framework as well. If anyone knows a way to accomplish a triangle shape with Pixate that would be even better.
The easiest way to clip a UIView to a path is to create a CAShapeLayer, add a path to the layer, and add the shape layer as a mask of your view's layer.
Or with a CGPathRef, essentially the same thing but at core foundation level
eg..
{
// before existing drawing code..
CGMutablePathRef clipTriangle = CGPathCreateMutable();
CGPathMoveToPoint (clipTriangle, nil, startX, startY);
CGPathAddLineToPoint(clipTriangle, nil, secondPointX, secondPointY);
CGPathAddLineToPoint(clipTriangle, nil, thirdPointX, thirdPointY);
CGPathCloseSubpath(clipTriangle);
CGContextSaveGstate(ctx);
CGContextAddPath(ctx, clipTriangle); /// this is the essential line I left out, we drew the triangle and forgot to use it, clipping to nothing instead, sorry mate
CGContextClip(ctx);
//draw stuff that you wanted clipped here...
CGContextRestoreGstate(ctx);
CGPathRelease(clippingTriangle); //CFstuff still needs manual memory management regardless of ARC
}
I want to achieve the shape shown in image using UIBezier Path, and too the shape is filled with blocks in image it shows one block is filled, how to achieve this.
I have tried the following code taken from here
UIBezierPath *path = [UIBezierPath bezierPath];
[path moveToPoint:CGPointMake(0, 10)];
[path addQuadCurveToPoint:CGPointMake(200, 10) controlPoint:CGPointMake(100, 5)];
[path addLineToPoint:CGPointMake(200, 0)];
[path addLineToPoint:CGPointMake(0, 0)];
[path closePath];
Thanks.
It looks to me like both the outline and also each block has the same shape. What you would probably do is to make one shape for the outline, and stroke it, and one shape for each cell and fill it.
Creating the shape
Each shape could be created something like this (as I've previously explained in this answer). It's done by stroking one path (the orange arc) which is a simple arc from one angle to another to get another path (the dashed outline)
Before we can stroke the path we to create it. CGPath's work just like UIBezierPath but with a C API. First we move to the start point, then we add an arc around the center from the one angle to another angle.
CGMutablePathRef arc = CGPathCreateMutable();
CGPathMoveToPoint(arc, NULL,
startPoint.x, startPoint.y);
CGPathAddArc(arc, NULL,
centerPoint.x, centerPoint.y,
radius,
startAngle,
endAngle,
YES);
Now that we have the centered arc, we can create one shape path by stroking it with a certain width. The resulting path is going to have the two straight lines (because we specify the "butt" line cap style) and the two arcs (inner and outer). As you saw in the image above, the stroke happens from the center an equal distance inwards and outwards.
CGFloat lineWidth = 10.0;
CGPathRef strokedArc =
CGPathCreateCopyByStrokingPath(arc, NULL,
lineWidth,
kCGLineCapButt,
kCGLineJoinMiter, // the default
10); // 10 is default miter limit
You would do this a couple of times to create one path for the stroked outline and one path for each cell.
Drawing the shape
Depending on if it's the outline or a cell you would either stroke it or fill it. You can either do this with Core Graphics inside drawRect: or with Core Animation using CAShapeLayers. Choose one and don't between them :)
Core Graphics
When using Core Graphics (inside drawRect:) you get the graphics context, configure the colors on it and then stroke the path. For example, the outline with a gray fill color and a black stroke color would look like this:
I know that your shape is filled white (or maybe it's clear) with a light blue stroke but I already had a gray and black image and I didn't want to create a new one ;)
CGContextRef c = UIGraphicsGetCurrentContext();
CGContextAddPath(c, strokedArc); // the path we created above
CGContextSetFillColorWithColor(c, [UIColor lightGrayColor].CGColor);
CGContextSetStrokeColorWithColor(c, [UIColor blackColor].CGColor);
CGContextDrawPath(c, kCGPathFillStroke); // both fill and stroke
That will put something like this on screen
Core Animation
The same drawing could be done with a shape layer like this:
CAShapeLayer *outline = [CAShapeLayer layer];
outline.fillColor = [UIColor lightGrayColor].CGColor;
outline.strokeColor = [UIColor blackColor].CGColor;
outline.lineWidth = 1.0;
outline.path = strokedArc; // the path we created above
[self.view.layer addSublayer: outline];
I draw line like this:
- (void)drawRect:(CGRect)rect {
_lineColor = [UIColor blackColor];
[_lineColor setStroke];
[_lineColor setFill];
CGContextRef c = UIGraphicsGetCurrentContext();
CGContextClearRect(c, rect);
[[UIColor clearColor] setFill];
CGContextAddRect(c, rect);
CGContextSetLineWidth(c, 1);
CGContextDrawPath(c, kCGPathFill);
CGContextBeginPath(c);
CGContextMoveToPoint(c, 0, 0);
CGContextAddLineToPoint(c, x1, y1);
CGContextStrokePath(c);
}
but, my line is have different width which angle is 90 or 45 degrees. How I can draw line with same width
I whipped up something that may make the effect here more visible. Here's the code:
- (void)drawRect:(CGRect)rect
{
CGContextRef c = UIGraphicsGetCurrentContext();
// Get us a gray background
CGContextSetFillColorWithColor(c, [[UIColor grayColor] CGColor]);
CGContextFillRect(c, CGRectInfinite);
CGContextSetStrokeColorWithColor(c, [[UIColor blackColor] CGColor]);
CGContextSetLineWidth(c, 1.0);
CGContextBeginPath(c);
// Draw some lines at various angles
for (CGFloat i = -10.; i <= 10.; i += 1.0)
{
CGContextMoveToPoint(c, CGRectGetMidX(self.bounds), CGRectGetMidY(self.bounds));
CGContextAddLineToPoint(c, CGRectGetMidX(self.bounds) + i * 10., CGRectGetMidY(self.bounds) + 100);
}
CGContextStrokePath(c);
}
Here's the output from that code on a retina device: (This should display at 100% in the standard StackOverflow format, but you can look at it full size to be sure)
Now here's a piece of that blown up:
What you're seeing here is anti-aliasing at work. For starters the vertical line is 2.0 pixels across, all the time, with no anti-aliasing (assuming you draw it on a pixel boundary). Now think about a 45deg line drawn using the same pixel grid, and employ the Pythagorean theorem. Here's another diagram:
At it's narrowest (i.e. in the dimension perpendicular to the line itself), a 45 deg line will appear 1.414px wide, and at it's widest opaque section (not counting the mostly transparent pixel that's bridging the space in the jaggy gaps) it's going to appear 2.828px across. When blown up, you can see how the work that's being done to anti-alias these lines is effecting the optical appearance of the lines.
Someone is probably going to come along and suggest that you turn off anti-aliasing, but for reference, that makes the optical effect even worse (because then the rasterizer is going to make every pixel with coverage completely opaque):
In short, this is expected behavior, and if you need to adjust how you draw each line to achieve some desired optical appearance that the default anti-aliasing code doesn't provide, then you just have to do that work. There's not a "make all my lines optically similar" setting in CoreGraphics -- they've done the best they can for the general case, and if you need something more specific that's up to you. FWIW, many many applications simply use the default, and people seem pretty satisfied with the results, so you might ask yourself if this is really the place in your app where you want to put in a bunch of extra work.
It occurred to me: I'm not sure you'll like the effect, but one possible approach for achieving optical similarity might be to draw your vertical lines not on pixel boundaries. This will cause them to appear anti-aliased too, which (depending on how you look at it) may make them appear more consistent with the angled, anti-aliased lines. Here's what that looks like:
What you lose doing this is a certain "crispness" to the lines. Drawing off pixel-boundaries can most easily be achieved by translating the context by 0.25pt in the X direction (for retina -- for non-retina, 0.5pt will have a similar effect) like this:
CGContextTranslateCTM(c, 0.25, 0);
Hope this helps.
I'm currently drawing on the screen. I get smooth lines, I can change the color of my drawings. But I can't find how to apply a shadow to that line.
To draw it, I use :
[path strokeWithBlendMode:[path blendMode] alpha:1.0];
I saw that I could use CGContextSetShadowWithColor() but even though, I'm not sure how to use it since here's what's said in the CGPath reference for strokeWithBlendMode:
This method automatically saves the current graphics state prior to
drawing and restores that state when it is done, so you do not have to
save the graphics state yourself.
So I don't really know where to put that CGContextSetShadowWithColor() or anything else if I can use it.
Regards
If you want to use CGContextSetShadowwithColor() then you will need to change the way to draw your bezierpath to the view so that you draw the CGPath representation to the CGContext. An example is below:
UIBezierPath *path; // this is your path as before
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextAddPath(context, path.CGPath);
CGContextSetLineWidth(context, 2.0);
CGContextSetBlendMode(context, path.blendMode);
CGContextSetShadowWithColor(context, CGSizeMake(1.0, 1.0), 2.0, [UIColor blackColor].CGColor);
CGContextStrokePath(context);
Another way you could do this is to create a new CAShapeLayer and draw you path to that by setting it as the path property. This will easily allow you to add a shadow that will only shadow your path.