Basic drawing with Quartz 2D on iPhone
- by wwrob
My goal is to make a program that will draw points whenever the screen is touched. This is what I have so far:
The header file:
#import <UIKit/UIKit.h>
@interface ElSimView : UIView
{
CGPoint firstTouch;
CGPoint lastTouch;
UIColor *pointColor;
CGRect *points;
int npoints;
}
@property CGPoint firstTouch;
@property CGPoint lastTouch;
@property (nonatomic, retain) UIColor *pointColor;
@property CGRect *points;
@property int npoints;
@end
The implementation file:
//@synths etc.
- (id)initWithFrame:(CGRect)frame
{
return self;
}
- (id)initWithCoder:(NSCoder *)coder
{
if(self = [super initWithCoder:coder])
{
self.npoints = 0;
}
return self;
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [touches anyObject];
firstTouch = [touch locationInView:self];
lastTouch = [touch locationInView:self];
}
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [touches anyObject];
lastTouch = [touch locationInView:self];
points = (CGRect *)malloc(sizeof(CGRect) * ++npoints);
points[npoints-1] = CGRectMake(lastTouch.x-15, lastTouch.y-15,30,30);
[self setNeedsDisplay];
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [touches anyObject];
lastTouch = [touch locationInView:self];
[self setNeedsDisplay];
}
- (void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(context, 2.0);
CGContextSetStrokeColorWithColor(context, [UIColor blackColor].CGColor);
CGContextSetFillColorWithColor(context, pointColor.CGColor);
for(int i=0; i<npoints; i++)
CGContextAddEllipseInRect(context, points[i]);
CGContextDrawPath(context, kCGPathFillStroke);
}
- (void)dealloc {
free(points);
[super dealloc];
}
@end
When I load this and click some points, it draws the first points normally, then then next points are drawn along with random ellipses (not even circles).
Also I have another question: When is exactly drawRect executed?
