I want to draw a line of 2 pixels..I have written the following code but it does not draw any line or anything on the view..Plzz help me regarding this or tell me the error in this code...In code pointToBeShown is CGPoint.....
- (void)drawRect:(CGRect)rect {
// Drawing code.
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(context, 2.0);
CGContextSetStrokeColor(context, currentColor.CGColor);
pointToBeShown.x = 30;
pointToBeShown.y = 449;
CGContextMoveToPoint(context, pointToBeShown.x, pointToBeShown.y);
CGContextAddLineToPoint(context, (pointToBeShown.x + 1),( pointToBeShown.y + 1));
CGContextStrokePath(context);
}
Are you not getting any warning?
Replace the line
CGContextSetStrokeColor(context, currentColor.CGColor);
with
CGContextSetStrokeColorWithColor(context, currentColor.CGColor);
Update:
Update as you mentioned in the comments
CGContextRef context = UIGraphicsGetCurrentContext();
[currentColor set];
CGContextSetLineWidth(context, 2.0);
CGContextFillEllipseInRect(context, CGRectMake(pointToBeShown.x, pointToBeShown.y, 10, 10));
Related
How can I increase size of CGContextRef after its creation.
if(UIGraphicsBeginImageContextWithOptions != NULL) {
UIGraphicsBeginImageContextWithOptions(CGSizeMake(width, height), NO, 0);
}
else {
UIGraphicsBeginImageContext(CGSizeMake(width, height));
}
CGContextRef ctr = UIGraphicsGetCurrentContext();
Can i change size of ctr?
Try doing it without the if-else conditions. Create a CGContext using that last line of code only.
Here's a simple example
- (void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetStrokeColorWithColor(context, [UIColor blueColor].CGColor);
CGContextSetLineWidth(context, 2.0);
CGContextMoveToPoint(context, 100,100);
CGContextAddLineToPoint(context, 200, 200);
CGContextStrokePath(context);
}
I want to draw line between two points. Here is my code. but context memory is 0.
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(context, 2.0);
CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
CGFloat components[] = {0.0, 0.0, 1.0, 1.0};
CGColorRef color = CGColorCreate(colorspace, components);
CGContextSetStrokeColorWithColor(context, color);
CGContextMoveToPoint(context, 0, 0);
CGContextAddLineToPoint(context, 300, 400);
CGContextStrokePath(context);
CGColorSpaceRelease(colorspace);
CGColorRelease(color);
You need to call your code within a UIView subclass in the method drawRect:.
UIGraphicsGetCurrentContext() will get NULL (0) when your are not in a drawing context.
You might also check the docs.
Here is a very useful tutorial for your need.
http://trailsinthesand.com/exploring-iphone-graphics-part-1/
Go through it once..!
I want to draw 15 horizontal lines, with 20 points space between them. I can't understand why this code doesn't work.
- (void)drawRect:(CGRect)rect
{
// Drawing code
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetStrokeColorWithColor(context, [UIColor redColor].CGColor);
CGContextSetLineWidth(context, 2.0);
for (int i=20;i+=20;i<=20*15) {
CGContextBeginPath(context);
CGContextMoveToPoint(context, 10, i);
CGContextAddLineToPoint(context, 310, i);
CGContextStrokePath(context);
}
}
Thank you!
Yes, the for loop should be:
for (int i=20; i<=20*15; i+=20) {
...
}
I want to draw a curved line with arrow between two points using the Quartz Core framework in an iPhone Application. How to do that or any what classes are available to do that ?
You can change the co-ordinates as you want
- (void)drawRect:(CGRect)rect {
//DRAW CURVE
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(context, 2.0);
CGContextSetStrokeColorWithColor(context, [UIColor blueColor].CGColor);
CGContextMoveToPoint(context, 100, 100);
CGContextAddArcToPoint(context, 100,200, 300,200, 100);
CGContextStrokePath(context);
//DRAW LINE
CGContextSetLineWidth(context, 2.0);
CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
CGFloat components[] = {0.0, 0.0, 1.0, 1.0};
CGColorRef color = CGColorCreate(colorspace, components);
CGContextSetStrokeColorWithColor(context, color);
CGContextMoveToPoint(context, 0, 0);
CGContextAddLineToPoint(context, 300, 400);
CGContextStrokePath(context);
CGColorSpaceRelease(colorspace);
CGColorRelease(color);
}
I am having some troubles using the CGContext with an iPhone app. I am trying to draw several lines with different colors, but all the lines always end up having the color which was used last. I tried several approaches, but haven't been lucky.
I set up a small sample project to deal with that issue. This is my code, I use in the drawRect method. I am trying to draw a red and a blue line:
- (void)drawRect:(CGRect)rect{
NSLog(#"drawrect!");
CGContextRef bluecontext = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(bluecontext, 2.0);
CGContextSetStrokeColorWithColor(bluecontext, [UIColor blueColor].CGColor);
CGContextMoveToPoint(bluecontext, 1, 1);
CGContextAddLineToPoint(bluecontext, 100, 100);
CGContextSetStrokeColorWithColor(bluecontext, [UIColor redColor].CGColor);
CGContextAddLineToPoint(bluecontext, 200, 100);
CGContextStrokePath(bluecontext);
}
thanks for your help
Insert this code just before you set the stroke color the second time:
CGContextStrokePath(bluecontext);
CGContextBeginPath(bluecontext);
All the AddLine and AddOther calls are building a path. The path is drawn with a call like StrokePath, using the most recently set colors and other attributes. You are trying to draw two separate paths, so you must call Begin and Stroke for each path. Begin is sort of implicit when you start drawing, although it does not hurt to call it yourself. The basic flow of drawing is:
CGContextBeginPath(bluecontext); // clears any previous path
// add lines, curves, rectangles, etc...
CGContextStrokePath(bluecontext); // renders the path
Thats what you need.
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextClearRect(context, rect);
CGContextSetLineWidth(context, 2.0);
CGContextBeginPath(context);
CGContextSetStrokeColorWithColor(context, [UIColor orangeColor].CGColor);
CGContextMoveToPoint(context, 1, 1);
CGContextAddLineToPoint(context, 100, 100);
CGContextStrokePath(context); // and draw orange line}
CGContextBeginPath(context);
CGContextSetStrokeColorWithColor(context, [UIColor blueColor].CGColor);
CGContextMoveToPoint(context, 100, 100);
CGContextAddLineToPoint(context, 200, 100);
CGContextStrokePath(context); // draw blue line
I think this could be working.
CGContextRef bluecontext = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(bluecontext, 2.0);
CGContextSetStrokeColorWithColor(bluecontext, [UIColor blueColor].CGColor);
CGContextMoveToPoint(bluecontext, 1, 1);
CGContextAddLineToPoint(bluecontext, 100, 100);
CGContextStrokePath(bluecontext); // draw blue line
CGContextSetStrokeColorWithColor(bluecontext, [UIColor redColor].CGColor);
CGContextAddLineToPoint(bluecontext, 200, 100);
CGContextStrokePath(bluecontext); // and draw red line
If you are interested in the way it looks in a loop:
- (void)drawRect:(CGRect)rect {
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(context, 2.0);
CGPoint startingPoint = [[pointsArray objectAtIndex:0] CGPointValue];
CGContextMoveToPoint(context, startingPoint.x, startingPoint.y); //start at this point
for (int i = 1; i < [pointsArray count]; i++) {
CGContextBeginPath(context);
//start at the previous point
CGContextMoveToPoint(context,
[[pointsArray objectAtIndex:i-1] CGPointValue].x,
[[pointsArray objectAtIndex:i-1] CGPointValue].y);
CGPoint point = [[pointsArray objectAtIndex:i] CGPointValue];
if (point.y < 50) { // if y is less then 50 use red color
CGContextSetStrokeColorWithColor(context, [UIColor redColor].CGColor);
} else { // else use blue color
CGContextSetStrokeColorWithColor(context, [UIColor blueColor].CGColor);
}
CGContextAddLineToPoint(context, point.x, point.y); //draw to this point
CGContextStrokePath(context);
}
}