I've got a weird issue with quartz. The first time I run the piece of code below, the line will be drawn like the line to the right in the image. The second time (and every time after) these lines are executed, the line will look like the line to the left. Why does it look like that? It's all jaggy and seems to have a dark border. If you'd draw the curve with opacity, it would be rather bright the first time, and very dark the second.
CGContextSetRGBFillColor(context, 0.0,0.0,0.0,0.0);
CGContextClearRect(context, CGRectMake( 0, 0, 320, 480));
CGContextSetRGBFillColor(context, 0, 0, 0, 0);
CGContextSetBlendMode(context, kCGBlendModeNormal);
CGContextSetRGBStrokeColor(context, 1.0, 1.0, 1.0, 1.0);
CGContextSetLineWidth(context, 4.0);
CGContextMoveToPoint(context, p1.x, p1.y);
CGContextAddCurveToPoint(context, cp1.x, cp1.y, cp2.x, cp2.y, p2.x, p2.y);
CGContextDrawPath(context, kCGPathStroke);
(source: pici.se)
antialiasing OFF?
also, you might want to make sure the x and y values are rounded as the Quartz Framework doesn't handle well the half point.
Related
I'm trying to draw a L shape, the code works but the lines are not of the right width and is 5 pixels thick for vertical lines and some are 3 pixels thick despite me explicitly telling it to use 3 pixel as line width,what am I doing wrong? here's my code:
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextClearRect(ctx, rect);
CGContextAddPath(ctx, pathi);
CGContextSetStrokeColorWithColor(ctx, [UIColor redColor].CGColor);
CGContextSetLineWidth(ctx, 3.0);
CGContextSetLineCap(ctx, kCGLineCapRound);
CGContextSetShouldAntialias(ctx, NO);
CGContextStrokePath(ctx);
I have already calculated path "pathi" The path is working fine.
The lines are actually not thick, the half of the lines gets cutoff while drawing.
You should apply padding equal to the half of the width( inn your case, 3/2 => 1.5) because the drawing always start from the mid of the points provided.
I drew rectangle diagram with boarder dotted blue line. I would like to rectangle diagram with same images as a boarder line. That means i want to replace dots with images
My Code:
- (void)drawRect:(CGRect)rect
{
context =UIGraphicsGetCurrentContext();
CGContextSetRGBStrokeColor(context, 0.0, 0.0, 1.0, 1.0);
CGFloat dashPattern[10] = {3.0, 2.0};
CGContextSetLineDash(context, 0, dashPattern, 2);
CGContextSetRGBFillColor(context, 0.0, 1.0, 0.0, 1.0);
CGContextSetLineWidth(context, 10.0);
CGContextAddRect(context, self.bounds);
CGContextDrawPath(context, kCGPathFillStroke);
CGContextClosePath(context);
CGContextStrokePath(context);
}
Can i set image instead of dots? Please give any suggestions to me. Thanks in advance.
I don't try yet, but maybe you can use:
CGContextSetStrokeColorWithColor(context, [UIColor colorWithPatternImage:myImage].CGColor);
I am new to Objective-C and iOS development. I have a view with some figures drawn by core drawing. Now I want to fill those shapes with color and I don't know the path or context of shape. Does Objective-C have any function like flood-fill or put-pixel so that by having only the stroke color I can fill any shape inside my view.
-(void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(context, 4.0);
CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
CGFloat components[] = {1.0, 0.0, 0.0, 1.0};
CGColorRef color = CGColorCreate(colorspace, components);
CGContextSetStrokeColorWithColor(context, color);
CGContextMoveToPoint(context, 50, 0);
CGContextAddLineToPoint(context, 0,320);
CGContextStrokePath(context);
CGColorSpaceRelease(colorspace);
CGColorRelease(color);
CGContextSetLineWidth(context, 2.0);
CGContextSetStrokeColorWithColor(context, [UIColor blueColor].CGColor);
CGContextSetRGBFillColor(context, 0, 255, 0, 1.0);
CGContextMoveToPoint(context, 100, 100);
CGContextAddLineToPoint(context, 150, 150);
CGContextAddLineToPoint(context, 100, 200);
CGContextAddLineToPoint(context, 50, 150);
CGContextAddLineToPoint(context, 100, 100);
CGContextStrokePath(context);
CGContextSetLineWidth(context, 2.0);
CGContextSetStrokeColorWithColor(context, [UIColor blueColor].CGColor);
CGRect rectangle = CGRectMake(60,170,200,80);
CGContextAddEllipseInRect(context, rectangle);
CGContextStrokePath(context);
}
This will make a circle and a square with some common region. I want a particular region to fill with color when a user taps that region.
So you are looking for flood fill in Objective C.
This is my implementation of Scan Line Flood Fill Algorithm.
Github : UIImageScanlineFloodfill
If you want to learn basic of flood fill:
Lode's Computer Graphics Tutorial Flood Fill
I hope this will help you.
Put your drawing code in the question and I can give you a specific answer.
Normally you just need to set a fill color using
[[UIColor redColor] setFill];
And any shapes you draw your core graphics will be filled with that color automatically.
Try this command:-
CGContextSetStrokeColorWithColor(context, [UIColor blueColor].CGColor);
Core Graphics is closely tied to UIView and its drawRect: method and has a C interface. As you point out, you always draw in the current graphics context. I can think of 2 approaches: (1) When the user taps myView, set a property like myView.pointTapped, and in drawRect: find the shape to fill, set a fill color, and fill the closed path using GGGeometry methods.
There is an objective-C alternative: (2) Take a look at UIBezierPath. It's not as comprehensive as drawing in Core Graphics but it can be used in your ViewController implementation.
When I draw some text using CGContext, it is drawn mirrored.
I tried to apply some transformations, then it is draw well, but then the rest of the drawing and all coordinates seems to be draw bad.
I tried to save and restore the context, before and ater drawing the text (and aplying transformation), but that does not help.
How some text must be drawn onto a View using CGContext without affecting the rest of the drawing, nor the onscreen CGPoint coords for that text ?
Can you clarify what you mean as 'mirrored'? Here is some code for drawing some black text. It should not be 'mirrored'.
CGRect viewBounds = self.bounds;
CGContextTranslateCTM(ctx, 0, viewBounds.size.height);
CGContextScaleCTM(ctx, 1, -1);
CGContextSetRGBFillColor(ctx, 0.0, 1.0, 0.0, 1.0);
CGContextSetLineWidth(ctx, 2.0);
CGContextSelectFont(ctx, "Helvetica", 10.0, kCGEncodingMacRoman);
CGContextSetCharacterSpacing(ctx, 1.7);
CGContextSetTextDrawingMode(ctx, kCGTextFill);
CGContextShowTextAtPoint(ctx, 100.0, 100.0, "SOME TEXT", 9);
I think you have to reverse the text matrix :
CGAffineTransform transform = CGAffineTransformMake(1.0, 0.0, 0.0, -1.0, 0.0, 0.0);
CGContextSetTextMatrix(context, transform);
I have code in my iPhone app to draw a pie chart in a UIView. All is great but I need to be able to use a chalk-like texture to draw the outlines and then to fill in the different colours of the pie chart.
Here are extracts from the existing code for each area:
Drawing the circle around the pie chart:
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextSetRGBStrokeColor(ctx, 1.0, 1.0, 1.0, 1.0);
CGContextSetLineWidth(ctx, 8.0);
// Draw a thin line around the circle
CGContextAddArc(ctx, x, y, r, 0.0, 360.0*M_PI/180.0, 0);
CGContextClosePath(ctx);
CGContextDrawPath(ctx, kCGPathStroke);
... and drawing a segment of the pie:
CGContextSetRGBStrokeColor(ctx, 1.0, 1.0, 1.0, 1.0);
CGContextSetLineWidth(ctx, 8.0);
CGContextMoveToPoint(ctx, x, y);
CGContextAddArc(ctx, x, y, r, (startDeg-90)*M_PI/180.0, (endDeg-90)*M_PI/180.0, 0);
CGContextClosePath(ctx);
CGContextDrawPath(ctx, kCGPathStroke);
... then filling it with a colour fill:
CGContextSetRGBFillColor(ctx, color.red, color.green, color.blue, color.alpha );
CGContextMoveToPoint(ctx, x, y);
CGContextAddArc(ctx, x, y, r, (startDeg-90)*M_PI/180.0, (endDeg-90)*M_PI/180.0, 0);
CGContextClosePath(ctx);
CGContextFillPath(ctx);
Ignoring the fact that I haven't pasted in the variable declarations for many of the variables used, I hope the code is fairly self-explanatory.
Now: How could I change the code to use a texture for the actual drawing of the lines/arcs?
Similarly, how can I use a texture fill instead of a colour fill?
I'm trying to get this app finished off and this is my last stumbling block. Other questions on SO and elsewhere on the web just don't seem to answer the question in a way I can follow.
Any help will be gratefully received!
Robert
Know this is outdated but one can set fill or stroke patterns using this simple code snippet:
// Somewhere in initialization code.
UIColor *pattern = [UIColor colorWithPatternImage:[UIImage imageNamed:#"pattern.png"]];
CGColorRef fillColor = [pattern CGColor];
CGColorRef strokeColor = [pattern CGColor];
// Probably in |draw| method call.
CGContextSetStrokeColorWithColor(context, strokeColor);
CGContextSetFillColorWithColor(context, fillColor);
Hope it will help someone. There are also other great advanced possibilities - you can manipulate patterns in many ways: shift, scale, rotate, use colored or stencil patters and many many others, but this requires deep digging in api docs.