I'm the new one in Core Graphics and I try to draw circles. They can be transparent (only stroke) and filled with the stroke color. So the method looks like this:
+ (UIImage *)iconImageWithColor: (UIColor *)markColor strokeOnly:(BOOL)strokeOnly
{
CGRect rect = CGRectMake(0.0f, 0.0f, 20.0f, 20.0f);
UIGraphicsBeginImageContext(rect.size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGPathRef clippingPath = [UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:7.5f].CGPath;
CGContextAddPath(context, clippingPath);
CGContextClip(context);
CGContextSetFillColorWithColor(context, strokeOnly == YES ? [[UIColor clearColor] CGColor] : [markColor CGColor]);
CGContextFillRect(context, rect);
CGPathRef path = CGPathCreateWithRoundedRect(rect, 10.f, 10.f, NULL);
[markColor setStroke];
CGContextAddPath(context, path);
CGContextDrawPath(context, kCGPathFillStroke);
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
The result is strange - it looks like the resolution of the image is very low. Is it possible to make the result image looks good on retina display?
UIGraphicsBeginImageContext creates a context with a scale of 1, so non retina.
What you want to use is
UIGraphicsBeginImageContextWithOptions(rect.size, NO, 0.0f)
scale 0 means it will use the device screen scale
Use UIGraphicsBeginImageContextWithOptions(rect.size, YES, 0.0);
Last parameter means the resulting pixel density (scale). When you pass 0 it picks it up automatically from device native screen scale.
Related
I have a function where I fill the image with a color and use a UIBezierPath to erase a point for corners.
CGRect rect = CGRectMake(0.0f, 0.0f, width, height);
UIGraphicsBeginImageContext(rect.size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetBlendMode(context, kCGBlendModeCopy);
// Fill image
CGContextSetFillColorWithColor(context, [[UIColor redColor] CGColor]);
CGContextFillRect(context, rect);
// Round corners
UIBezierPath *bezierPath = [UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:15.0];
CGContextSetStrokeColorWithColor(context, [[UIColor clearColor] CGColor]);
[bezierPath stroke];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
With the above, I get an image that does have the Bézier path cut out, and the background filled.
However, how can I remove the corners outside of the path, or get at least some way to reference where they are so I can clear them?
A couple of options:
Use CoreGraphics, like you have, but clip it to a path:
CGRect rect = CGRectMake(0.0f, 0.0f, width, height);
UIGraphicsBeginImageContextWithOptions(rect.size, false, 0);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetBlendMode(context, kCGBlendModeCopy);
// Round corners
UIBezierPath *bezierPath = [UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:15.0];
CGContextAddPath(context, bezierPath.CGPath);
CGContextClip(context);
// Fill image
CGContextSetFillColorWithColor(context, [[UIColor redColor] CGColor]);
CGContextFillRect(context, rect);
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
Alternatively, eliminate CoreGraphics and just fill the UIBezierPath:
UIGraphicsBeginImageContextWithOptions(rect.size, false, 0);
[[UIColor redColor] setFill];
[[UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:15.0] fill];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
Note, in both of those examples, I used UIGraphicsBeginImageContextWithOptions, supplying a scale of 0 (a scale optimized for display on the device in question). If you really want, you can supply a scale of 1, which obviously will be a bit pixelated when rendered on a retina device, but that's up to you.
I want create image using CGcontext. This is simple image with white or black background. also I want to add transperent part which is in circle ( check attached image). I know how to do this in rect. But i want to make it circle. Please anyone help me in this.
Use the below code to clear circle in your context
-(UIImage *) getImageWithcenterClear:(CGPoint) center{
CGRect frame = [[UIScreen mainScreen] bounds];
UIGraphicsBeginImageContextWithOptions([[UIScreen mainScreen] bounds].size,
NO, [UIScreen mainScreen].scale);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(context, [[UIColor colorWithRed:0 green:0 blue:0 alpha:0.5 ] CGColor]);
CGContextFillRect(context, frame);
float radius = 50 * 2;
// Clear Circle
CGContextSetFillColorWithColor(context, [UIColor clearColor].CGColor);
CGContextSetBlendMode(context, kCGBlendModeClear);
CGContextAddArc(context, center.x, center.y, radius - 0.54, 0, 2 * M_PI, 0);
CGContextDrawPath(context, kCGPathFill);
CGContextSetBlendMode(context, kCGBlendModeNormal);
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
I am looking for the way how to draw a hollow circle using Core Graphics (CGContext) in iOS. I tried to do it using the code:
- (void)drawRect:(CGRect)rect {
[super drawRect:rect];
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(ctx, 8.0);
CGContextSetStrokeColor(ctx, CGColorGetComponents([[UIColor redColor] CGColor]));
CGContextSetFillColor(ctx, CGColorGetComponents([[UIColor blueColor] CGColor]));
CGContextFillEllipseInRect(ctx, rect);
CGContextFillPath(ctx);
}
but it draws the filled circle.
Since this question is over discussed here but other examples like this give me only filled circles.
If you want to draw a circle within the rect, using Stroke methods and the rect in parameter you will draw a part of the cercle outside the rect.
You then have two choices, assuming you know the width of the circle you want to draw.
First, you can stroke the line, but you have to draw it in a smaller rect :
-(void)drawRect:(CGRect)rect {
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGFloat innerWidth = 8;
[[UIColor redColor] setStroke];
CGContextSetLineWidth(ctx, innerWidth);
// We add an ellipsis shifted by half the inner Width
CGContextAddEllipseInRect(ctx, CGRectInset(rect, innerWidth, innerWidth));
// Stroke the path
CGContextStrokePath(ctx);
}
You can also fill the circles using the even-odd rule (Apple docs)
-(void)drawRect:(CGRect)rect {
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGFloat innerWidth = 8;
[[UIColor redColor] setStroke];
// Add the outer circle
CGContextAddEllipseInRect(ctx, rect);
// Add the inner circle
CGContextAddEllipseInRect(ctx, CGRectInset(rect, innerWidth, innerWidth));
// Fill the path using the EO rule
CGContextEOFillPath(ctx);
}
If you only want the circle outline, don't fill it.
- (void)drawRect:(CGRect)rect {
[super drawRect:rect];
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(ctx, 8.0);
[[UIColor redColor] set];
CGContextStrokeEllipseInRect(ctx, rect);
}
Use CGContextStrokeEllipseInRect instead of CGContextFillEllipseInRect. And since you haven't built a path in the current context, get rid of CGContextFillPath.
One way you could do it is draw a filled circle and then draw a slightly smaller circle with CGContextSetBlendMode(UIGraphicsGetCurrentContext(),kCGBlendModeClear)
After your code add something like
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(ctx, 5.0);
CGContextSetBlendMode(ctx,kCGBlendModeClear)
CGContextSetFillColor(ctx, CGColorGetComponents([[UIColor blueColor] CGColor]));
CGContextFillEllipseInRect(ctx, rect);
CGContextFillPath(ctx);
UIGraphicsEndImageContext();
I use CGContextSetBlendMode(UIGraphicsGetCurrentContext(),kCGBlendModeClear) in my drawing application, which is probably a better use. Stroking the path will probably work for you.
This code results in the image below. As far as I understand CGContextClipToMask, the red rectangle should not be visible, since it is outside of the clipped area. What am I missing here? Thanks for any help!
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(context, [UIColor blackColor].CGColor);
CGContextFillRect(context, rect);
CGContextSetLineWidth(context, 20);
CGContextSetStrokeColorWithColor(context, [UIColor whiteColor].CGColor);
// draw partial circle
UIBezierPath *arc = [UIBezierPath bezierPathWithArcCenter:center radius:radius startAngle:startAngle endAngle:endAngle clockwise:NO];
CGContextAddPath(context, [arc CGPath]);
CGContextStrokePath(context);
// create mask
CGImageRef mask = CGBitmapContextCreateImage(context);
self.maskCreated(mask);
// save state
CGContextSaveGState(context);
// clip with mask
CGContextClipToMask(context, rect, mask);
// draw test rect
CGContextSetFillColorWithColor(context, [UIColor redColor].CGColor);
CGContextFillRect(context, CGRectMake(0, 0, 100, 100));
// restore state
CGContextRestoreGState(context);
The documentation for CGContextClipToMask says:
If mask is an image, then it must be in the DeviceGray color space,
may not have an alpha component, and may not be masked by an image
mask or masking color.
I'm assuming your code is in a the -drawRect: method of a subclass of UIView, so you are using the CGContext which was provided to you, which is in an RGB color space and probably has an alpha component. Your mask image is created from that context, so it gets the same attributes.
To fix this, use a separate bitmap context to generate the mask, using a gray colorspace with no alpha. Here's a self-contained example that does something similar to your code.
- (void)drawRect:(CGRect)rect
{
// Create a context for the mask
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
CGContextRef maskContext = CGBitmapContextCreate(NULL, rect.size.width, rect.size.height, 8, 0, colorSpace, kCGImageAlphaNone | kCGBitmapByteOrderDefault);
CGColorSpaceRelease(colorSpace);
// Fill with black
CGContextSetFillColorWithColor(maskContext, [UIColor blackColor].CGColor);
CGContextFillRect(maskContext, rect);
// Draw an arc in white
CGContextSetLineWidth(maskContext, 20);
CGContextSetStrokeColorWithColor(maskContext, [UIColor whiteColor].CGColor);
CGContextAddArc(maskContext, CGRectGetMidX(rect), CGRectGetMidY(rect), 50, M_PI, 0, false);
CGContextStrokePath(maskContext);
// Create the mask image from the context, and discard the context
CGImageRef mask = CGBitmapContextCreateImage(maskContext);
CGContextRelease(maskContext);
// Now draw into the view itself
CGContextRef context = UIGraphicsGetCurrentContext();
// Apply the mask
CGContextClipToMask(context, rect, mask);
// Then draw something that overlaps the mask
CGContextSetFillColorWithColor(context, [UIColor redColor].CGColor);
CGContextFillRect(context, rect);
// Make sure to clean up when we're done
CGImageRelease(mask);
}
Actually don't understand your concern, but you can hide rectangle in your method like this:
// draw a test rect
CGContextSetFillColorWithColor(context, [UIColor redColor].CGColor);
CGRect rect = CGRectZero;
CGContextFillRect(context, rect);
I am trying to apply a color fill to the MKAnnotation. I found some code that pretty much works but for some reason the filled image is upside down after applying the fill to it.
Here is the current code that I am running on a map pin.
CGRect rect = CGRectMake(0, 0, self.image.size.width, self.image.size.height);
UIGraphicsBeginImageContext(self.image.size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextClipToMask(context, rect, self.image.CGImage);
CGContextSetFillColorWithColor(context, [[UIColor grayColor] CGColor]);
CGContextFillRect(context, rect);
CGContextRotateCTM(context, 90);
UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
UIImage *flippedImage = [UIImage imageWithCGImage:img.CGImage
scale:1.0 orientation:self.image.imageOrientation];
self.image = flippedImage;
Here is what the pins look like after this code runs.
http://d.pr/i/UaPU
I was thinking that if I applied the current image orientation to the flippedImage that would do the trick but that did not work. I also tried setting self.image = img; and removing the flippedImage var completely but the result is still the same.
CGContext coordinate system is flipped vertically in regard to UIView coordinate system.
Just flip it like this:
CGContextTranslateCTM(ctx, 0, imageHeight);,
CGContextScaleCTM(ctx, 1, -1);