I am trying to draw a box/path in drawRect in one of my view's, the path rect is:
CGRect pathRect = CGRectMake(self.buttonSize_ + 25, commentYOffset, rect.size.width - 80, 40);
and before this I have:
CGContextSetTextMatrix(context, CGAffineTransformIdentity);
CGContextTranslateCTM(context, 0.0, rect.size.height);
CGContextScaleCTM(context, 1.0, -1.0);
I wanted this path to be drawn 100 pixels from the top, so what I did is set that commentYOffset to 100, however this doesn't do it. What am I doing wrong so that when I draw this path it starts at 100 pixels from the top?
CGContextTranslateCTM(context,…) applies a translation transform to context. The translation is applied after any existing transform in the drawing context. Those last two lines in the code you posted effectively flip the vertical on your drawing context. Just leave them out and the path will be drawn where you want.
Edit: adit says he needs the transforms to keep some text drawing right side up, so: If you need to flip the vertical on your drawing context (as you're doing) then just remember that after applying these transformations zero-y is at the bottom of rect and the positive y-axis points towards the top of rect. So to draw your path 100 pixels from the top you should make
commentYOffset = CGRectGetMaxY(rect) - 40.0 - 100.0;
and that 40 is because your rect is 40 points tall. Actually it's better practice to make these named constants so you don't have to copy magic numbers all over the place going forward. Then your code will look something like this:
commentYOffset = CGRectGetMaxY(rect) - kPathRectHeight - kPathTopMargin;
Related
I'm drawing several circles within my view by means of the drawRect function.
I'd like to have my circles pop up (scale to 1.2 -> scale to 1.0)
I've used coreanimation in the past but using OpenGL takes different functions.
Here's a snippit of my code which draws a circle in my view:
//calling draw function
CGContextRef contextRef = UIGraphicsGetCurrentContext();
//setting a specific fill color
CGContextSetRGBFillColor(contextRef, 0.0, 255.0, 0.0, 1.0);
//drawing the circle with a specific height, weight and x,y location
CGContextFillEllipseInRect(contextRef, CGRectMake(30 ,30, 20,20));
How can I animate this circle that it 'pops up'.
"Pops up" is not telling me that much.
if you want it to go from small to big modify width and height of rect.use a global int variable
I'm making a legend for a graph that will basically look like this:
[ ] Line 1
[ ] Line 2
[ ] Line 3
The boxes on the left need to be the same color as the lines on the graph.
Anyhow, all I need to know, is whether it's faster to draw the boxes with Core Graphics or just make some pngs with GIMP for the squares and include them.
Use UIView for each legend and set their background color to the color you want.
Both approaches are fast enough that it shouldn't make a difference. However, using Core Graphics has the advantage that you're a lot more flexible, e.g. when you later decide that you need additional colors. Plus, your app will be smaller, because you don't have to include the PNG files.
Drawing boxes is a snap! I would go with Core Graphics everyday, especially since you get retina support for free.
As can be seen in this example you can do it using UIKit only classes:
// Setup colors
[myBoxColor setFill];
[myBoxBorderColor set];
// Setup a path for the box
UIBezierPath* path = [UIBezierBath bezierPathWithRect:rectOfTheBox];
path.lineWidth = 2;
// Draw!
[path fill];
[path stroke];
One warning; stroke fills using the edges of the path as the center of the line. So you will get a blurry line if you stroke a path with integral rect with a 1 point line width.
You can remedy this is you want a 1 point line for the border by doing something like this:
CGRect strokeRect = UIEdgeInsetsInsetRect(rectOfTheBox,
UIEdgeInsetsMake(0.5f,0.5f,0.5f,0.5f));
UIBezierPath* path = [UIBezierPath bezierPathWithRect:strokeRect];
[path stroke];
On iOS, Core Graphics is quite simple to use. In your view's drawRect: method, just do this to draw a square:
- (void)drawRect:(CGRect)frame {
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetRGBFillColor(context, 0.5, 0.5, 0.5, 1); // gray
CGContextFillRect(context, CGRectMake(10, 10, 20, 20)); // our rect is {10,10,20,20)
// draw a line
CGContextSetRGBStrokeColor(context, 1, 0, 0, 1);
CGContextBeginPath(context);
CGContextMoveToPoint(context, startX, startY);
CGContextAddLineToPoint(context, endX, endY);
CGContextStrokePath(context);
}
Hope this helps!
I'm trying to add a little red line on the bottom of my UIView.
I want the line to be a 1px line.
Can someone tell me why the following code:
- (void)drawRect:(CGRect)rect {
CGContextRef currentContext = UIGraphicsGetCurrentContext();
CGContextSaveGState(currentContext);
CGContextSetRGBFillColor(currentContext, 0.0f, 0.0f, 0.0f, 1.0f);
CGContextFillRect(currentContext, RECT(0, 0, rect.size.width, rect.size.height - 8));
CGContextSetLineWidth(currentContext, 1);
CGContextSetRGBStrokeColor(currentContext, 1.0f, 0.0f, 0.0f, 1.0f);
CGContextBeginPath(currentContext);
CGContextMoveToPoint(currentContext, 0, rect.size.height - 7);
CGContextAddLineToPoint(currentContext, rect.size.width, rect.size.height - 7);
CGContextStrokePath(currentContext);
CGContextRestoreGState(currentContext);
}
Draws a line that spans 2px in height?
The integral coordinates indicate places half-way between pixels; that is, (0,0) is in the upper-left corner, above and to the left of the upper-left pixel; similarly, (1,0) is between the first and second pixels; finally, (0.5,0.5) is at the center of the upper-left pixel.
According to the documentation for CGContextSetLineWidth, "when stroked, the line straddles the path, with half of the total width on either side." Thus, if the path is lying precisely in between the pixels, the line will be stroked half on one row of pixels, half on the other.
Hence, to get a sharp pixel line, you must offset your coordinates by half a pixel: for your x coordinate, use rect.size.height - 7.5 instead of - 7.
By the way, when drawing rectangles, it is handy to use CGRectInset(rect, 0.5, 0.5) to achieve this.
Do you use an iPhone 4? The iPhone 4 uses a coordinate system with a scale factor of 2. So you would need to set the line width to 0.5 in order to get what you want.
(The coordinate system is set up that way so the same code produces the same output on all models.)
Lines are by default drawn antialiased (unless you configure otherwise). Thus any line that's not strictly vertical or horizontal and starting and ending on a pixel will likely partially cover multiple pixels in some rows and/or columns, making it look like a wider grey line instead of a thin higher-contrast line.
It's really a pain, but always when I draw an UIImage in -drawRect:, it's upside-down.
When I flip the coordinates, the image draws correctly, but at the cost of all other CG functions drawing "wrong" (flipped).
What's your strategy when you have to draw images and other things? Is there any rule of thumb how to not get stuck in this problem over and over again?
Also, one nasty thing when I flip the y-axis is, that my CGRect from the UIImageView frame is wrong. Instead of the origin appearing at 10,10 upper left as expected, it appears at the bottom.
But at the same time, all those normal line drawing functions of CGContext take correct coordinates. drawing a line in -drawRect with origin 10,10 upper left, will really start at upper left. But at the same time that's strange, because core graphics actually has a flipped coordinate system with y 0 at the bottom.
So it seems like something is really inconsistent there. Drawing with CGContext functions takes coordinates as "expected" (cmon, nobody thinks in coordinates starting from bottom left, that's silly), while drawing any kind of image still works the "wrong" way.
Do you use helper methods to draw images? Or is there anything useful that makes image drawing not a pain in the butt?
Problem: Origin is at lower-left corner; positive y goes upward (negative y goes downward).
Goal: Origin at upper-left corner; positive y going downward (negative y going upward).
Solution:
Move origin up by the view's height.
Negate (multiply by -1) the y axis.
The way to do this in code is to translate up by the view bounds' height and scale by (1, -1), in that order.
There are a couple of portions of the Quartz 2D Programming Guide that are relevant to this topic, including “Drawing to a Graphics Context on iPhone OS” and the whole chapter on Transforms. Of course, you really should read the whole thing.
You can do that by apply affinetransform on the point you want to convert in UIKit related coordinates. Following is example.
// Create a affine transform object
CGAffineTransform transform = CGAffineTransformMakeScale(1, -1);
// First translate your image View according to transform
transform = CGAffineTransformTranslate(transform, 0, - imageView.bounds.size.height);
// Then whenever you want any point according to UIKit related coordinates apply this transformation on the point or rect.
// To get tranformed point
CGPoint newPointForUIKit = CGPointApplyAffineTransform(oldPointInCGKit, transform);
// To get transformed rect
CGRect newRectForUIKit = CGRectApplyAffineTransform(oldPointInCGKit, transform);
The better answer to this problem is to use the UIImage method drawInRect: to draw your image. I'm assuming you want the image to span the entire bounds of your view. This is what you'd type in your drawRect: method.
Instead of:
CGContextRef ctx = UIGraphicsGetCurrentContext();
UIImage *myImage = [UIImage imageNamed:#"theImage.png"];
CGImageRef img = [myImage CGImage];
CGRect bounds = [self bounds];
CGContextDrawImage(ctx, bounds, img);
Write this:
UIImage *myImage = [UIImage imageNamed:#"theImage.png"];
CGRect bounds = [self bounds];
[myImage drawInRect:bounds];
It's really a pain, but always when I draw an UIImage in -drawRect:, it's upside-down.
Are you telling the UIImage to draw, or getting its CGImage and drawing that?
As noted in “Drawing to a Graphics Context on iPhone OS”, UIImages are aware of the difference in co-ordinate spaces and should draw themselves correctly without you having to flip your co-ordinate space yourself.
CGImageRef flip (CGImageRef im) {
CGSize sz = CGSizeMake(CGImageGetWidth(im), CGImageGetHeight(im));
UIGraphicsBeginImageContextWithOptions(sz, NO, 0);
CGContextDrawImage(UIGraphicsGetCurrentContext(),
CGRectMake(0, 0, sz.width, sz.height), im);
CGImageRef result = [UIGraphicsGetImageFromCurrentImageContext() CGImage];
UIGraphicsEndImageContext();
return result;
}
Call the above method using the code below:
This code deals with getting the left half of an image from an existing UIImageview and setting the thus generated image to a new imageview - imgViewleft
CGContextRef con = UIGraphicsGetCurrentContext();
CGContextDrawImage(con,
CGRectMake(0,0,sz.width/2.0,sz.height),
flip(leftReference));
imgViewLeft = [[UIImageView alloc] initWithImage:UIGraphicsGetImageFromCurrentImageContext()];
My usercase is an iphone application where I do an animation on the scale, rotation and translation of an image.
So, I concat everything and feed it to the transform property, but there is one problem:
Since my images vary in size, it is a problem to position them correctly. I'm used to an inverted y axis coordinate system, so I want my image to positioned exactly at 60 pixels in the y axis.
So, how do I change from the original cartesian y axis to an inverted y axis point of view?
As smacl points out, the easiest way to do this is to shift your origin to the bottom-left of the screen by using (screenheight - viewheight - y) instead of y in the origins of your views.
However, you can flip the coordinate system of your main view's layers using a CATransform3D. I do this so that I can share the same Core Animation CALayer layout code between my iPhone application and a Mac client (the iPhone inverts the normal Quartz coordinate system for CALayers to match that of the UIViews). All you need to do to enable this is to place the line
self.layer.sublayerTransform = CATransform3DMakeScale(1.0f, -1.0f, 1.0f);
in your initialization code for your layer-hosting UIView. Remember that this will flip your CALayers, so any UIKit text rendering in those layers may also need to be flipped using code similar to the following:
CGContextSaveGState(context);
CGContextTranslateCTM(context, 0.0f, self.frame.size.height);
CGContextScaleCTM(context, 1.0f, -1.0f);
UIFont *theFont = [UIFont fontWithName:#"Helvetica" size:fontSize];
[text drawAtPoint:CGPointZero withFont:theFont];
CGContextRestoreGState(context);
You can do a similar sort of inversion using a CGAffineTransform, but you will also need to apply a translation to make that work:
CGAffineTransform flipTransform = CGAffineTransformMakeTranslation(0.0f, self.frame.size.height);
flipTransform = CGAffineTransformScale(flipTransform, 1.0f, -1.0f);
You may be able to use the affine transform to convert your origin coordinates using CGPointApplyAffineTransform().
For every y ordinate, y = top-y, where top is the y ordinate of the top of the bounding box you are drawing in.