I've got a custom view with the following drawRect method
- (void)drawRect:(CGRect)rect
{
CGContextRef ctx = UIGraphicsGetCurrentContext();
float w = rect.size.width;
CGContextSetFillColorWithColor(ctx, [UIColor blackColor].CGColor);
CGContextAddArc(ctx, w / 2, w / 2, w / 2 - 10, 0, 2 * M_PI, 0);
CGContextDrawPath(ctx, kCGPathFill);
}
I'm expecting to see a black circle, however, for some reason it draws a black rectangle instead. I guess the whole view is just getting filled with black. Where is the problem?
Perhaps your view's backgroundColor is also black (which is the default for opaque views)?
Also, you shouldn't assume that the rect parameter covers the whole view, it could be only a part of the view that has been marked as needing to be redrawn. You should base your geometry calculations on the view's bounds instead.
You need to add....
[super drawRect:rect];
as the first line, this will then render the background as per the views background property, OR if you prefer you can fill the context with the background colour yourself, I prefer the former.
Maybe if you clip it that it will be shaped into the right size?
CGContextClip(context);
(Why aren't you using CGMutablePathRef btw?)
Related
This is a code snippet for creating a thumbnail sized image (from an original large image) and placing it appropriately on top of a tableviewcell. As i was studying the code i got stuck at the part where the thumbnail is being given a position by setting its abscissa and ordinate. In the method -(void)setThumbDataFromImage:(UIImage *)image they're setting the dimensions and coordinate for project thumbnail—
-(void)setThumbnailDataFromImage:(UIImage *)image{
CGSize origImageSize= [image size];
// the rectange of the thumbnail
CGRect newRect= CGRectMake(0, 0, 40, 40);
// figure out a scaling ratio to make sure we maintain the same aspect ratio
float ratio= MAX(newRect.size.width/origImageSize.width, newRect.size.height/origImageSize.height);
// Create a transparent bitmap context with a scaling factor equal to that of the screen
UIGraphicsBeginImageContextWithOptions(newRect.size, NO, 0.0);
// create a path that is a rounded rectangle
UIBezierPath *path= [UIBezierPath bezierPathWithRoundedRect:newRect cornerRadius:5.0];
// make all the subsequent drawing to clip to this rounded rectangle
[path addClip];
// center the image in the thumbnail rectangle
CGRect projectRect;
projectRect.size.width=ratio * origImageSize.width;
projectRect.size.height= ratio * origImageSize.height;
projectRect.origin.x= (newRect.size.width- projectRect.size.width)/2;
projectRect.origin.y= (newRect.size.height- projectRect.size.height)/2;
// draw the image on it
[image drawInRect:projectRect];
// get the image from the image context, keep it as our thumbnail
UIImage *smallImage= UIGraphicsGetImageFromCurrentImageContext();
[self setThumbnail:smallImage];
// get the PNG representation of the image and set it as our archivable data
NSData *data= UIImagePNGRepresentation(smallImage);
[self setThumbnailData:data];
// Cleanup image context resources, we're done
UIGraphicsEndImageContext();
}
I got the width and height computation wherein we multiply the origImageSize with scaling factor/ratio.
But then we use the following to give the thumbnail a position—
projectRect.origin.x= (newRect.size.width- projectRect.size.width)/2;
projectRect.origin.y= (newRect.size.height- projectRect.size.height)/2;
This i fail to understand. I cannot wrap my head around it. :?
Is this part of the centering process. I mean, are we using a mathematical relation here to position the thumbnail or is it some random calculation i.e could have been anything.. Am i missing some fundamental behind these two lines of code??
Those two lines are standard code for centering something, although they aren’t quite written in the most general way. You normally want to use:
projectRect.origin.x = newRect.origin.x + newRect.size.width / 2.0 - projectRect.size.width / 2.0;
projectRect.origin.y = newRect.origin.y + newRect.size.height / 2.0 - projectRect.size.height / 2.0;
In your case the author knows the origin is 0,0, so they omitted the first term in each line.
Since to center a rectangle in another rectangle you want the centers of the two axes to line up, you take, say, half the container’s width (the center of the outer rectangle) and subtract half the inner rectangle’s width (which takes you to the left side of the inner rectangle), and that gives you where the inner rectangle’s left side should be (e.g.: its x origin) when it is correctly centered.
I'm trying to implement a custom slider in Cocoa with 5 values. See my demo project, which can be downloaded here: http://s000.tinyupload.com/index.php?file_id=07311576247413689572.
I've subclassed the NSSliderCell and implemented methods like drawKnob:(NSRect)knobRect and drawBarInside:(NSRect)cellFrame flipped:(BOOL)flipped etc.
I'm facing some issues:
I'm not able to position the knob correctly regarding to the background image. I know that I'm able to change the knob's frame, and I've tried doing some calculation to position the knob correctly, but I'm not able to make it work for my custom slider. Could someone please help me with this?
The height of my custom slider background is 41px. In the drawBarInside:(NSRect)cellFrame flipped:(BOOL)flipped I change the height of the frame to 41px as well, but the entire background is not visible. Why?
I've noticed that the included images (the background and knob) are flipped vertically. Why? Note that the border top is darker in the background compared to the bottom, but this is reversed when I draw the background.
I found a mistake in your calculation of the x position of the knob rectangle: You used the height of the image where you should have used the width.
The cell drawing is being clipped to the frame of the control. Maybe you could expand the control frame when your cell awakes.
You need to use the NSImage method drawInRect:fromRect:operation:fraction:respectFlipped:hints:, and pass YES for the respectFlipped: parameter. Apple's controls generally do use flipped coordinates.
Added: Expanding the frame in awakeFromNib doesn't seem to work, the frame gets set back. Here's something that does work. Instead of overriding drawBarInside:flipped:, add this override:
- (void)drawWithFrame:(NSRect)cellFrame inView:(NSView *)controlView
{
NSRect controlFrame = [controlView frame];
float bgHeight = self.backgroundImage.size.height;
if (controlFrame.size.height < bgHeight)
{
controlFrame.size.height = bgHeight;
[controlView setFrame: controlFrame];
}
[self.backgroundImage
drawInRect: [controlView bounds]
fromRect: NSZeroRect
operation: NSCompositeSourceOver
fraction: 1.0
respectFlipped: YES
hints: NULL];
[self drawKnob];
}
I want to do some custom drawing with CoreGraphics. I need a linear gradient on my view, but the thing is that this view is a rounded rectangle so I want my gradient to be also rounded at angles. You can see what I want to achieve on the image below:
So is this possible to implement in CoreGraphics or some other programmatic and easy way?
Thank you.
I don't think there is an API for that, but you can get the same effect if you first draw a radial gradient, say, in an (N+1)x(N+1) size bitmap context, then convert the image from the context to a resizable image with left and right caps set to N.
Pseudocode:
UIGraphicsBeginImageContextWithOptions(CGSizeMake(N+1,N+1), NO, 0.0f);
CGContextRef context = UIGraphicsGetCurrentContext();
// <draw the gradient into 'context'>
UIImage* gradientBase = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
UIImage* gradientImage = [gradientBase resizableImageWithCapInsets:UIEdgeInsetsMake(0,N,0,N)];
In case you want the image to scale vertically as well, you just have to set the caps to UIEdgeInsetsMake(N,N,N,N).
I just want to add more sample code for this technique, as some things weren't obvious for. Maybe it will be useful for somebody:
So, let's say, we have our custom view class and in it's drawRect: method we put this:
// Defining the rect in which to draw
CGRect drawRect=self.bounds;
Float32 gradientSize=drawRect.size.height; // The size of original radial gradient
CGPoint center=CGPointMake(0.5f*gradientSize,0.5f*gradientSize); // Center of gradient
// Creating the gradient
Float32 colors[4]={0.f,1.f,1.f,0.2f}; // From opaque white to transparent black
CGGradientRef gradient=CGGradientCreateWithColorComponents(CGColorSpaceCreateDeviceGray(), colors, nil, 2);
// Starting image and drawing gradient into it
UIGraphicsBeginImageContextWithOptions(CGSizeMake(gradientSize, gradientSize), NO, 1.f);
CGContextRef context=UIGraphicsGetCurrentContext();
CGContextDrawRadialGradient(context, gradient, center, 0.f, center, center.x, 0); // Drawing gradient
UIImage* gradientImage=UIGraphicsGetImageFromCurrentImageContext(); // Retrieving image from context
UIGraphicsEndImageContext(); // Ending process
gradientImage=[gradientImage resizableImageWithCapInsets:UIEdgeInsetsMake(0.f, center.x-1.f, 0.f, center.x-1.f)]; // Leaving 2 pixels wide area in center which will be tiled to fill whole area
// Drawing image into view frame
[gradientImage drawInRect:drawRect];
That's all. Also if you're not going to ever change the gradient while app is running, you would want to put everything except last line in awakeFromNib method and then in drawRect: just draw the gradientImage into view's frame. Also don't forget to retain the gradientImage in this case.
I was wondering if it is possible to create an NSRect with maybe an NSMakeRect to make a simple square that will display on the screen without a window or any view behind it, just made all in code.
This is what I have as an example
-(void)drawRect
{
NSRect myNewRect
myNewRect = NSMakeRect(100, 100, 50, 50);
}
Thats just a simple starting point but it will not show up on the screen by itself. what do i need to add?
Thanks
Every drawing operation on Mac OS X requires some window of sort. So no, you cannot draw a rect without a window. But you can create a transparent window without any borders to draw into.
First of all, you can't "display on the screen without a window or any view behind it".
You will always be drawing on some layer-backed object (UIView, etc).
And UIViews must eventually be part of some UIWindow hierarchy to display them.
So you can't "[draw] on main screen without window" at all. That's not how Core Graphics works.
However, I believe this is what you're trying to do:
-(void)drawRect
{
CGRect myNewRect = CGRectMake(100, 100, 50, 50);
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(ctx, [[UIColor redColor] CGColor]);
CGContextFillRect(ctx, myNewRect);
}
Which draws a rectangle in the UIView implementing the above drawRect method.
I'm trying to figure out what i'm doing wrong but i just don't get it. Here is what i want to do:
I want to draw a circle somewhere on the screen of the iPhone and then i want the circle always to be displayed at the position where the user currently taps on the screen.
I started by creating a subclass of UIView and adding the following lines into the "drawRect" method:
- (void)drawRect:(CGRect)rect {
//Create the main view!
CGContextRef mainscreen = UIGraphicsGetCurrentContext();
//Draw the dot
//will be a circle cause rectangle is a square
CGRect dotRect = CGRectMake(50, 80, 100, 100);
[[UIColor blueColor] set];
CGContextStrokeEllipseInRect(mainscreen, dotRect);
CGContextFillEllipseInRect(mainscreen, dotRect);
}
The appears just fine but now I have no idea how to make it move around on the screen I've tried several things and nothing worked.
To draw the dot in a different location, change the origin of dotRect. To figure out where to draw it, implement -touchesBegan:withEvent: and -touchesMoved:withEvent: and record the location where the touches are occuring.