I used below code for free hand drawing on the whole view:
UIGraphicsBeginImageContext(self.view.frame.size);
[drawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 5.0);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0, 0.0, 0.0, 1.0);
CGContextBeginPath(UIGraphicsGetCurrentContext());
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
CGContextStrokePath(UIGraphicsGetCurrentContext());
drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
Now my requirement is something like this .. I should be able to draw on particular area of a view. So I modified the code like this ..
UIGraphicsBeginImageContext(CGSizeMake(300, 100));
[drawImage.image drawInRect:CGRectMake(0, 0, 400, 100)];
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 5.0);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0, 0.0, 0.0, 1.0);
CGContextBeginPath(UIGraphicsGetCurrentContext());
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
CGContextStrokePath(UIGraphicsGetCurrentContext());
drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
but the drawing is not proper. Please suggest me how to do this.
Create custome view like :
UIView *drawingView = [[UIView alloc] initWithFrame:CGRectMake(x, y,
300, 300)];
[self.view addSubView:drawingView];
And Then modify your code something like below :
UIGraphicsBeginImageContext(drawingView.frame.size);
[drawImage.image drawInRect:CGRectMake(0, 0, drawingView.frame.size.width, drawingView.frame.size.height)];
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 5.0);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0, 0.0, 0.0, 1.0);
CGContextBeginPath(UIGraphicsGetCurrentContext());
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
CGContextStrokePath(UIGraphicsGetCurrentContext());
drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
Related
Hi want to choose colors in a coloring project that I am trying out.
I am new at this so this might be a silly question. I am using buttons to select different colors. But when the button is pressed the only thing that happens is that the last pixel of the line that was drawn changes to the selected color. In the code below the first tag erases the drawing and the second should change to color for the next line that will be drawn...
-(IBAction)buttonClicked:(UIButton *)sender {
switch (sender.tag)
{
case 1: {
drawImage.image = nil;
return;
}
//lastPoint.y -= 0;
break;
case 2: {
UIGraphicsBeginImageContext(self.view.frame.size);
[drawImage.image drawInRect:CGRectMake(0, 0, drawImage.frame.size.width, drawImage.frame.size.height)];
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 3.0);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 0.0, 1.0, 2.0, 1.0);
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
CGContextStrokePath(UIGraphicsGetCurrentContext());
CGContextFlush(UIGraphicsGetCurrentContext());
drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
}
break;
default:
break;
}
}
The code:
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
does not reallydraw a line since the start of the line CGContextMoveToPoint and the end of the line CGContextAddLineToPoint are the same point.
A couple of points, less code is better:
Eliminate the switch statement by having a target for each button.
Call UIGraphicsGetCurrentContext() once and save it in a var, just for clarity.
Example:
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineCap(context, kCGLineCapRound);
CGContextSetLineWidth(context, 3.0);
CGContextSetRGBStrokeColor(context, 0.0, 1.0, 2.0, 1.0);
CGContextMoveToPoint(context, firstPoint.x, firstPoint.y);
CGContextAddLineToPoint(context, lastPoint.x, lastPoint.y);
CGContextStrokePath(context);
I use this code to draw a line in quartz2d
CGPoint currentPoint = CGPointMake(rascalImage.center.x, rascalImage.center.y);
currentPoint.y += 10;
UIGraphicsBeginImageContext(self.view.frame.size);
[drawingView.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 5.0);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0, 0.0, 0.0, 1.0);
CGContextBeginPath(UIGraphicsGetCurrentContext());
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
CGContextStrokePath(UIGraphicsGetCurrentContext());
drawingView.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
lastPoint = currentPoint;
Now how would I go about making an erase function for just where the eraser intersects? I know that I have to erase a certain point from the line (where the eraser touches), I just don't know how to do this so please help!!
UIGraphicsBeginImageContext(imgBlankView.frame.size);
[imgBlankView.image drawInRect:CGRectMake(0, 0, imgBlankView.frame.size.width, imgBlankView.frame.size.height)];
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(),lineWidth);
CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeClear);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, 1.0);
CGContextBeginPath(UIGraphicsGetCurrentContext());
CGContextSetShouldAntialias(UIGraphicsGetCurrentContext(), YES);
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint1.x, lastPoint1.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
CGContextStrokePath(UIGraphicsGetCurrentContext());
imgBlankView.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
I assume you are not drawing on a solid colored background? If you are, just use the same function to draw background-colored lines over the contrasting lines.
But, since you most likely have a complex background: Once you end the graphics context, and get a UIImage from the lines you have drawn, there is no way to erase just the lines. If you are creating some sort of complex drawing app, I would suggest that you use layers, and simply "stack up" layers one on top of the other to create the drawing environment.
Check out this post also:
How to erase some portion of a UIImageView's image on iOS?
UIGraphicsBeginImageContext(self.view.frame.size);
[drawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 8.0);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 135.0,213.0,0.0,1.0);
CGContextBeginPath(UIGraphicsGetCurrentContext());
CGContextMoveToPoint(UIGraphicsGetCurrentContext(),currentPoint.x, currentPoint.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
CGContextStrokePath(UIGraphicsGetCurrentContext());
drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
I am draw a line use RGB(135,213,0),RGB(135,213,0) should be green. but iOS display yellow line!! why?
You need to have the values in the range of [0,1]. Therefore you need to divide each value by 255.
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 135.0/255.0,213.0/255.0,0.0,1.0);
Divide each value by 255 ie RGB(135/255,213/255,0)
max value is 1.0, divide each argument by 255.0
i want to erase image in view (like erase drawing with Eraser).i did if view frame is 0,0,320,480 ,but i worry if the view frame has different size:
here my code:
UIGraphicsBeginImageContext(self.view.frame.size);
[myImageView.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
CGContextSetLineCap(UIGraphicsGetCurrentContext(),kCGImageAlphaNone);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 10);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1, 0, 0, 10);
CGContextBeginPath(UIGraphicsGetCurrentContext());
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), point.x, point.y);
//this line code for erasing select the part of the image
CGContextClearRect (UIGraphicsGetCurrentContext(), CGRectMake(point.x, point.y, 30, 30));
//End the code
CGContextStrokePath(UIGraphicsGetCurrentContext());
myImageView.image = UIGraphicsGetImageFromCurrentImageContext();
Try the below code ..
UIGraphicsBeginImageContext(self.frame.size);
[imageView.image drawInRect:CGRectMake(0, 0, imageView.frame.size.width, imageView.frame.size.height)];
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 30.0);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0, 1.0, 1.0, 1.0);
CGContextBeginPath(UIGraphicsGetCurrentContext());
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastTouch.x, lastTouch.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
CGContextStrokePath(UIGraphicsGetCurrentContext());
imageView.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
IS it possible to draw line with special shape for example like dotted(China Point) ? i draw line with below code
UIGraphicsBeginImageContext(self.view.frame.size);
[drawImage.image drawInRect:CGRectMake(0, 0, 320, 480)];
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 5.0);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 0.867, 0.867, 0.867, 1.0);
CGContextBeginPath(UIGraphicsGetCurrentContext());
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), startPoint.x, startPoint.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), endPoint.x, endPoint.y);
CGContextStrokePath(UIGraphicsGetCurrentContext());
CGContextFlush(UIGraphicsGetCurrentContext());
drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
Maybe CGContextSetLineDash is what you want.
It sets the pattern for dashed lines in a graphics context.
void CGContextSetLineDash (
CGContextRef c,
CGFloat phase,
const CGFloat lengths[],
size_t count
);
This example draws a line with circles (diameter: 20 points, distance: 40 points):
CGContextSetLineWidth(context, 20.0);
CGFloat dash[] = {0.0, 40.0};
CGContextSetLineCap(context, kCGLineCapRound);
CGContextSetLineDash(context, 0.0, dash, 2);
CGContextMoveToPoint(context, 10.0, 30.0);
CGContextAddLineToPoint(context, 310.0, 30.0);
CGContextStrokePath(context);