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Questions tagged [cgcontext]

The CGContextRef opaque type represents a Quartz 2D drawing destination.

977 questions
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Remove alpha channel from UIImage

I use the following method to get a decompressed uiimage from file system. However the UIImageView is colored as red when I turn on the color blended layer, even though the UIImageView is set to Opaque. The images on file system don't have alpha…
Jensen
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Drawing a polygon with one color for stroke, and a different one for fill?

I'm having trouble with drawing some lines that are stroked with a color and then filling their insides (they make a polygon) with another one. UIColor *houseBorderColor = [UIColor colorWithRed:(170/255.0) green:(138/255.0) blue:(99/255.0)…
Morgan Wilde
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Iphone CGContextShowTextAtPoint for Japanese characters

I am working on an app where I am using CGContextShowTextAtPoint to display text to the screen. I want to also display Japanese characters, but CGContextShowTextAtPoint takes as its input a C string. So either A) How do I change Japanese characters…
kiyoshi
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How can I render line faster than CGContextStrokePath?

I'm plotting ~768 points for a graph using CGContextStrokePath. The problem is that every second I get a new data point, and thus redraw the graph. This is currently taking 50% CPU in what's already a busy App. Graph drawing is done in drawRect…
Peter
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How to take high-quality screenshot with UIGraphicsImageRenderer programmatically?

PROBLEM: After I take screenshot the image is blurry when check by zooming. The text inside image seems to be blurred when zoomed. I know this question have been raised many a times but none of them have desired solution. I already checked quite a…
Parvez Belim
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How to get rid of this "points" between my lines when I am drawing?

is there an easy way to not draw this points in my lines? I don't know why this points are there because i never release my finger from screen during drawing of a line. I got the code from a drawing example. // draw a line -…
madmax
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Crazy rounded rect UIBezierPath behavior on iOS 7. What is the deal?

The simple UIView below draws a rounded rectangle. When I pass a corner radius of 65 or below it rounds correctly, but 66 and above and it generates a perfect circle! What is going on here? It should only show a circle when the corner radius is…
Steveo
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How can I reset or clear the clipping mask associated with a CGContext?

I'm drawing to a CGContext and using a CGImageRef-based mask: CGContextRef context = UIGraphicsGetCurrentContext(); CGContextClipToMask(context, rect, _firstMaskImageRef); CGContextSetFillColorWithColor(context, color); CGContextFillRect(context,…
WiseOldDuck
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CGContextAddArc counterclockwise instead of clockwise

I'm having an issue when drawing an arc inside of my drawing function inside of a CALayer subclass. The implementation for that drawing function is as follows: -(void)drawInContext:(CGContextRef)ctx { CGPoint center =…
J Kagney
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Quartz2D: How to convert a clipping rect to an inverted mask at runtime?

Given: a CGContextRef (ctx) with frame {0,0,100,100} and a rect (r), with frame {25,25,50,50} It's easy to clip the context to that rect: CGContextClipToRect(ctx, r); to mask out the red area below (red == mask): But I want to invert this…
Todd Ditchendorf
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Drawing a dashed line with CGContextSetLineDash

I'm trying to draw a dashed line with CGContextSetLineDash. Here's my code: float dashPhase = 0.0; float dashLengths[] = {30, 30}; CGContextSetLineDash(context, dashPhase, dashLengths, 20.0); self.previousPoint2 =…
James Anderson
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Filling a shape with a gradient in CGContext

I want to fill a polygon shape that I have drawn via Core Graphics with a linear CGGradient. The CGContextDrawLinearGradient function draws a gradient from one point to another but it fills the entire view. How can I display the gradient only…
titaniumdecoy
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Changing the background colour of a CGContext

i'm really new to dealing with CGContexts and i'm just trying to get my head around things by following a simple touch paint & sketch tutorial (http://blog.effectiveui.com/?p=8105) I have hit a brick wall when it's come to changing the background…
DaveDee
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How could I get CGContextRef from UIImage?

CGContextRef context = ??; // get from UIImage *oldImage CGContextSaveGState(context); CGRect drawRect = CGRectMake(0, 0, 320, 480); CGContextConcatCTM(context, transform); UIImage *newImage = [[UIImage alloc] init]; …
Kordan Ou
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Adding text in a bitmap graphic context (on macOS) with Swift

My project is to paste some image crops on a bitmap graphic context to add some text to save the bitmap as a JPEG image I have no problem for 1) and 3) but I can’t find a way for adding text to the bitmap graphic context. I spent many hours…
Jean-Pierre
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