I'm trying to draw a small image on a UIScrollView for my iPhone app. I started with a UIImage created from a png I included in my bundle and that works ok. Every time the zooming/panning stops the delegate of the scrollview recalculates the frame of that UIImage (which is a subview of the UIScrollView's contentView) and calls setNeedsDisplay. The frame gets smaller and smaller in width/height measurements as you zoom into the scrollview because I want the image to stay the same size on the screen. While the user is zooming the image is the wrong size but as soon as the zooming stops it gets corrected. Not great but not the worst thing either.
The problem is now that I want to draw the image myself rather than have a static png. I've subclassed UIView and got into the drawRect method but I can't get the maths right to draw a smooth looking path when the view is zoomed in. I thought I could just scale the line width down and the radius of the circle I'm drawing (CGContextAddArc) but it looks as if the iPhone has tried to draw a thin lined circle over two or three pixels and then enlarged those pixels, rather than zoomed the view in and drawn a highly accurate circle over it.
This is the ViewController resizing the UIView (which is a subview of the UIScrollView's contentView)
float scaler = (1/scrollView.zoomScale);
[targetView setFrame:CGRectMake(viewCoords.x-11*scaler, viewCoords.y-11*scaler, 22*scaler,22*scaler)];
[targetView setNeedsDisplay];
This is the drawRect of the UIView
float x = rect.origin.x + rect.size.width/2.0;
float y = rect.origin.y + rect.size.height/2.0;
float radius = (rect.size.width-2.0*lineWidth)/2.0;
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(ctx,lineWidth );
CGContextSetRGBStrokeColor(ctx, 1.0, 0.0, 0.0, 1.0);
CGContextAddArc(ctx, x, y, radius , 0, 2* M_PI, 1);
CGContextClosePath(ctx);
CGContextStrokePath(ctx);
I'm open to the idea of placing the UIView subclass elsewhere, but I must have it move in sync with the UIScrollView's contentview
See my answer to this question. The UIScrollView applies a transform to your content view when it does the pinch zooming, which is what's causing your blurriness. You can override this to draw your own content sharply if you follow the method I describe.
Related
I have an UIImageView 3 levels deep in a super view. (The white region on top of the gray rectangle is my superview, the gray elongated rectangle is one subview, the black square is another subview of the elongated gray rectangle, the cog is the image of the UIImageView which is a subview of the black square). The frame rectangle of the UIImageView is calculate as follows, where _normalImage is a UIImage object. I do this inside the subclass that represents the black square
CGFloat xPoint = self.bounds.size.width/2 - _normalImage.size.width/2;
CGFloat yPoint = self.bounds.size.height/2 - _normalImage.size.height/2;
CGRect frameRect = CGRectMake(xPoint, yPoint, _normalImage.size.width, _normalImage.size.height);
self.imageHolder = [[UIImageView alloc] initWithFrame:frameRect];
The _normalImage is 26X26 and should be a perfect square. However the image is rendering as distorted as if there is an aspect ratio loss.
Whats wrong ?
try using floorf() function for your coordinates to prevent them contain the fractional part.
Image is stretched because by default it use UIViewContentModeScaleToFill content mode.
self.imageHolder.contentMode = UIViewContentModeScaleAspectFit;
I have a simple custom UIView (a rectangle) that is implemented with drawRect.
The view is drawn from two values; currentValue and maxValue
From drawRect:
The height of the rect represents how much currentValue is of maxValue:
if(currentValue > maxValue)
currentValue = maxValue;
float scale = currentValue/maxValue;
//Draw the rect
CGContextBeginPath(context);
CGContextMoveToPoint(context, self.bounds.origin.x, self.bounds.size.height);
CGContextAddLineToPoint(context, self.bounds.size.width, self.bounds.size.height);
CGContextAddLineToPoint(context, self.bounds.size.width, self.bounds.size.height-(self.bounds.size.height*scale));
CGContextAddLineToPoint(context, self.bounds.origin.x, self.bounds.size.height-(self.bounds.size.height*scale));
CGContextClosePath(context);
CGContextSetRGBFillColor(context, 1.0, 0.0, 0.0, 1.0);
CGContextFillPath(context);
CGContextStrokePath(context);
I've setup a ViewController with a UISlider that changes the currentValue and each time it's changed setNeedsDisplay gets called. This part works just fine. The rect changes height when the slider is used, exactly as planned.
My question is.. I would like this transition between heights to be animated. What's the best way to do it?
Thanks
Instead of having UIView with custom drawing your can add CAShapeLayer object to your view's layer. CAShapeLayer class allows to specify path to draw and draw attributes - and also changes for those properties are easily animatable.
If your view is just a rect filled with solid color as in question your second option is either adjust view's frame or set appropriate affine transform to get required heights - both those properties are also easily animatable using animation methods in UIView class.
If you really just want a simple shape that can be drawn by a Core Animation layer (like CAShapeLayer or CAGradientLayer), you should just use a Core Animation layer and a CABasicAnimation to animate the layer's frame.
If you plan to draw something more complex, and you want to animate changes to the shape, then you need to do more work. You need to give your object properties or instance variables to store the current and final values, and maybe to store the velocity of the value. You need to create a CADisplayLink object and use it to drive calls to your animation method. Your animation method should update the current value based on how much time has passed and then call setNeedsDisplay.
You'll probably want to do this with Core Animation. The relevant docs are on Apple's developer site. There is also a good source of links on Core Animation with iOS on this other SO question.
Background: I have a custom scrollview (subclassed) that has uiimageviews on it that are draggable, based on the drags I need to draw some lines dynamically in a subview of the uiscrollview. (Note I need them in a subview as at a later point i need to change the opacity of the view.)
So before I spend ages developing the code (i'm a newbie so it will take me a while) I looked into what i need to do and found some possible ways. Just wondering what the right way to do this.
Create a subclass of UIView and use the drawRect method to draw the line i need (but unsure how to make it dynamically read in the values)
On the subview use CALayers and draw on there
Create a draw line method using CGContext functions
Something else?
Cheers for the help
Conceptually all your propositions are similar. All of them would lead to the following steps (some of them done invisibly by UIKit):
Setup a bitmap context in memory.
Use Core Graphics to draw the line into the bitmap.
Copy this bitmap to a GPU buffer (a texture).
Compose the layer (view) hierarchy using the GPU.
The expensive part of the above steps are the first three points. They lead to repeated memory allocation, memory copying, and CPU/GPU communication. On the other hand, what you really want to do is lightweight: Draw a line, probably animating start/end points, width, color, alpha, ...
There's an easy way to do this, completely avoiding the described overhead: Use a CALayer for your line, but instead of redrawing the contents on the CPU just fill it completely with the line's color (setting its backgroundColor property to the line's color. Then modify the layer's properties for position, bounds, transform, to make the CALayer cover the exact area of your line.
Of course, this approach can only draw straight lines. But it can also be modified to draw complex visual effects by setting the contents property to an image. You could, for example have fuzzy edges of a glow effect on the line, using this technique.
Though this technique has its limitations, I used it quite often in different apps on the iPhone as well as on the Mac. It always had dramatically superior performance than the core graphics based drawing.
Edit: Code to calculate layer properties:
void setLayerToLineFromAToB(CALayer *layer, CGPoint a, CGPoint b, CGFloat lineWidth)
{
CGPoint center = { 0.5 * (a.x + b.x), 0.5 * (a.y + b.y) };
CGFloat length = sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
CGFloat angle = atan2(a.y - b.y, a.x - b.x);
layer.position = center;
layer.bounds = (CGRect) { {0, 0}, { length + lineWidth, lineWidth } };
layer.transform = CATransform3DMakeRotation(angle, 0, 0, 1);
}
2nd Edit: Here's a simple test project which shows the dramatical difference in performance between Core Graphics and Core Animation based rendering.
3rd Edit: The results are quite impressive: Rendering 30 draggable views, each connected to each other (resulting in 435 lines) renders smoothly at 60Hz on an iPad 2 using Core Animation. When using the classic approach, the framerate drops to 5 Hz and memory warnings eventually appear.
First, for drawing on iOS you need a context and when drawing on the screen you cannot get the context outside of drawRect: (UIView) or drawLayer:inContext: (CALayer). This means option 3 is out (if you meant to do it outside a drawRect: method).
You could go for a CALayer, but I'd go for a UIView here. As far as I have understood your setup, you have this:
UIScrollView
| | |
ViewA ViewB LineView
So LineView is a sibling of ViewA and ViewB, would need be big enough to cover both ViewA and ViewB and is arranged to be in front of both (and has setOpaque:NO set).
The implementation of LineView would be pretty straight forward: give it two properties point1 and point2 of type CGPoint. Optionally, implement the setPoint1:/setPoint2: methods yourself so it always calls [self setNeedsDisplay]; so it redraws itself once a point has been changed.
In LineView's drawRect:, all you need to is draw the line either with CoreGraphics or with UIBezierPath. Which one to use is more or less a matter of taste. When you like to use CoreGraphics, you do it like this:
- (void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
// Set up color, line width, etc. first.
CGContextMoveToPoint(context, point1);
CGContextAddLineToPoint(context, point2);
CGContextStrokePath(context);
}
Using NSBezierPath, it'd look quite similar:
- (void)drawRect:(CGRect)rect
{
UIBezierPath *path = [UIBezierPath bezierPath];
// Set up color, line width, etc. first.
[path moveToPoint:point1];
[path addLineToPoint:point2];
[path stroke];
}
The magic is now getting the correct coordinates for point1 and point2. I assume you have a controller that can see all the views. UIView has two nice utility methods, convertPoint:toView: and convertPoint:fromView: that you'll need here. Here's dummy code for the controller that would cause the LineView to draw a line between the centers of ViewA and ViewB:
- (void)connectTheViews
{
CGPoint p1, p2;
CGRect frame;
frame = [viewA frame];
p1 = CGPointMake(CGRectGetMidX(frame), CGRectGetMidY(frame));
frame = [viewB frame];
p2 = CGPointMake(CGRectGetMidX(frame), CGRectGetMidY(frame));
// Convert them to coordinate system of the scrollview
p1 = [scrollView convertPoint:p1 fromView:viewA];
p2 = [scrollView convertPoint:p2 fromView:viewB];
// And now into coordinate system of target view.
p1 = [scrollView convertPoint:p1 toView:lineView];
p2 = [scrollView convertPoint:p2 toView:lineView];
// Set the points.
[lineView setPoint1:p1];
[lineView setPoint2:p2];
[lineView setNeedsDisplay]; // If the properties don't set it already
}
Since I don't know how you've implemented the dragging I can't tell you how to trigger calling this method on the controller. If it's done entirely encapsulated in your views and the controller is not involved, I'd go for a NSNotification that you post every time the view is dragged to a new coordinate. The controller would listen for the notification and call the aforementioned method to update the LineView.
One last note: you might want to call setUserInteractionEnabled:NO on your LineView in its initWithFrame: method so that a touch on the line will go through to the view under the line.
Happy coding !
My goal is simple; I want to create a program that displays an UIImage, and when swiped from bottom to top, displays another UIImage. The images here could be a happy face/sad face. The sad face should be the starting point, the happy face the end point. When swiping your finger the part below the finger should be showing the happy face.
So far I tried solving this with the frame and bounds properties of the UIImageview I used for the happy face image.
What this piece of code does is wrong, because the transition starts in the center of the screen and not the bottom. Notice that the origin of both frame and bounds are at 0,0...
I have read numerous pages about frames and bounds, but I don't get it. Any help is appreciated!
The loadimages is called only once.
- (void)loadImages {
sadface = [UIImage imageNamed:#"face-sad.jpg"];
happyface = [UIImage imageNamed:#"face-happy.jpg"];
UIImageView *face1view = [[UIImageView alloc]init];
face1view.image = sadface;
[self.view addSubview:face1view];
CGRect frame;
CGRect contentRect = self.view.frame;
frame = CGRectMake(0, 0, contentRect.size.width, contentRect.size.height);
face1view.frame = frame;
face2view = [[UIImageView alloc]init];
face2view.layer.masksToBounds = YES;
face2view.contentMode = UIViewContentModeScaleAspectFill;
face2view.image = happyface;
[self.view addSubview:face2view];
frame = CGRectMake(startpoint.x, 0, contentRect.size.width, contentRect.size.height);
face2view.frame = frame;
face2view.clipsToBounds = YES;
}
-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
CGPoint movepoint = [[touches anyObject] locationInView: self.view];
NSLog(#"movepoint: %f %f", movepoint.x, movepoint.y);
face2view.bounds = CGRectMake(0, 0, 320, 480 - movepoint.y);
}
The UIImages and UIImageViews are properly disposed of in the dealloc function.
Indeed, you seem to be confused about frames and bounds. In fact, they are easy. Always remember that any view has its own coordinate system. The frame, center and transform properties are expressed in superview's coordinates, while the bounds is expressed in the view's own coordinate system. If a view doesn't have a superview (not installed into a view hierarchy yet), it still has a frame. In iOS the frame property is calculated from the view's bounds, center and transform. You may ask what the hell frame and center mean when there's no superview. They are used when you add the view to another view, allowing to position the view before it's actually visible.
The most common example when a view's bounds differ from its frame is when it is not in the upper left corner of its superview: its bounds.origin may be CGPointZero, while its frame.origin is not. Another classic example is UIScrollView, which frequently modifies its bounds.origin to make subviews scroll (in fact, modifying the origin of the coordinate system automatically moves every subview without affecting their frames), while its own frame is constant.
Back to your code. First of all, when you already have images to display in image views, it makes sense to init the views with their images:
UIImageView *face1view = [[UIImageView alloc] initWithImage: sadface];
That helps the image view to immediately size itself properly. It is not recommended to init views with -init because that might skip some important code in their designated initializer, -initWithFrame:.
Since you add face1view to self.view, you should really use its bounds rather than its frame:
face1view.frame = self.view.bounds;
Same goes for the happier face. Then in -touchesMoved:… you should either change face2view's frame to move it inside self.view or (if self.view does not contain any other subviews besides faces) modify self.view's bounds to move both faces inside it together. Instead, you do something weird like vertically stretching the happy face inside face2view. If you want the happy face to slide from the bottom of self.view, you should initially set its frame like this (not visible initially):
face2view.frame = CGRectOffset(face2view.frame, 0, CGRectGetHeight(self.view.bounds));
If you choose to swap faces by changing image views' frames (contrasted with changing self.view's bounds), I guess you might want to change both the views' frame origins, so that the sad face slides up out and the happy face slides up in. Alternatively, if you want the happy face to cover the sad one:
face2view.frame = face1view.frame;
Your problem seems to have something to do with the face2view.bounds in touchesMoved.
You are setting the bounds of this view to the rect, x:0, y:0, width:320, height:480 - y
x = 0 == left on the x axis
y = 0 == top on the y axis
So you are putting this image frame at the upper left corner, and making it fill the whole view. That's not what you want. The image simply becomes centered in this imageView.
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()];