On my iPhone app, I would need to draw a kind of full gauge with a dynamic indicator.
I was thinking of using a gauge image (a .png, that I would draw in an external tool) without any indicator, and then draw the dynamic indicator on top of the image.
I was thinking of using a UIView with this image in background and then then use CoreGraphics (that I've never tried) to draw the indicator.
Do you think it's the easiest way to do this ?
thanks a lot,
Luc
I think you can't have a background image in the same view.
1°) You draw the image each time drawRect() is called
2°) You have two UIView, one who have the background image, and the other one which draw your gauge ;-)
Good Luck !
(I think the easiest method is the second one which don't re-draw the background each time :-))
Luc,
Your approach should work fine. Create a custom UIView and override -drawRect: to first draw the background PNG of the gauge, then draw the indicators.
- (void) drawRect: (CGRect) rect {
\\ draw the gauge PNG into the view bounds
...;
\\ Now use Quartz to draw the indicators
...;
}
Related
I am in the process of creating an app where I have a background image (a UIImageView with the frame set to the UIView's bounds and added as a subview).
I would like to now add a UIView that will be over the background image but will apply gaussian blur to the image behind, only over the area where the UIView is.
I have just tried to use GPUImage to create a blur, which looks good but it uses 2 UIImageViews (one large background and one behind the UIView, which is blurred). Unfortunately the image no longer matches up with the background.
Is there any way to get the UIView to blur only the area behind it? A bit like the UIView is frosting the image behind.
Thanks!
Try FXBlurView from here - https://github.com/nicklockwood/FXBlurView
It should work.
I hope that makes sense. I'll try to explain it.
I have a UIImageView on screen, and am wondering how I can take the area after "drawing" on it with a finger, and remove that section from the UImage, or, create a separate UIImage from the selection.
I'm not looking for code (unless you have it =] ), just an idea of how to go about doing it. If you have tips, I'd be very grateful, thanks.
If I understand your question,
I think I would add a transparent UIView as a subview over the top of the UIImageView. And draw on that. Then you can remove/hide the subview when your done.
you need to create a UIGestureRecognizer with target and a action like -imageIsPressed, in this -imagePressed method you can call something to make the image disappear. I would suggest placing the UIImage into a UIImageView and calling imageview.hidden = YES; to hide the image, and set it back to "NO" once its not held by the finger.
You'd need to implement something that captures the area the user 'selected' (maybe be creating a CGPath. Then you create a CALayer of the size of the imageView. In it you create, draw and fill the captured path with some arbitrary color while leaving the rest transparent. Finally you apply your generated CALayer as a mask to the UIImageView:
imageView.layer.mask = maskLayer;
Hope that gets you started.
For more info on how to draw that custom CALayer pls refer to Quartz Programming Guide
So basically you want to implement freehand erasing of an image? You will need to use core graphics and the various CGContext methods (with blend mode set to clear) to achieve this. There are two approaches, but both start with drawing your image as the first part of drawRect, and then
1) Store your strokes in an array, and stroke all of them over top of the image.
2) Stroke one stroke over the image and then store the resulting image into a UIImage. Use this UIImage as the next image that you draw in drawRect. This one is difficult for undo/redo functionality.
I recently implemented this myself and made the source available here. Basically I used the same methods described here with this change when setting up the graphics context:
CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeClear);
I have a custom view for which I've (in the XIB) created a UIImageView as a subview. How can I make the image view appear in the background? (i.e. so that in the custom view I can create the hands of a clock that will appear over the top)
Do I need to make my background image have alpha areas for transparency? (if I have the terms correct) Or is it OK to have an image with it's background just set to white or black or whatever it needs to be (on the basis it will be in the background so this will be ok)
You can't: views are composited on top of their superviews, which means if your custom view is drawing in -drawRect:, it will always appear under the UIImageView.
The easiest way to achieve the effect you're looking for is to put the image view under your custom view in IB.
Background images generally do not need to have transparency (and there's a slight speedup if the PNG has no alpha channel).
An alternate approach to using UIImageView objects if you are drawing the rest of stuff in drawRect: is to use the image directly. Draw the image in drawRect: before you do any of the drawing.
Example
- (void)drawRect:(CGRect)rect {
[backgroundImage drawInRect:rect];
/* Do rest of your drawing */
}
Now this is only if you are using a complex image. If it is a texture, you would rather use UIColor's colorWithPatternImage: method to get a color from the UIImage object and set your custom view's backgroundColor. Remember that using the colorWithPatternImage: will not scale the image while drawing and will tile if the source image is smaller the frame of the view.
basic question, but I'm unsure. Not looking for code as an answer.
I want to draw 4 short lines 1px lines on a view. What is the best way to approach this task? Options:-
Load an image of the line, then create 4 UIImageViews with it.
Create my own subclass of a UIView that draws a line in the draw rect method.
Draw elsewhere on another view, another UIImageView that has an UIImage inside it (is this possible?)
Another way?
Thanks
Ross
Simplest way is to create a UIView subclass and perform your drawing in drawRect:. See the CoreGraphics guide for details on how to draw a line.
Quick and dirty way to achieve this is to just create a UIView and set it's height (or width, depending on its orientation) to 1px, and then set a background colour and slap it onto your view as a subview.
I've created a NIB file with some button controls on it, and as a background it has an ImageView which contains a PNG file loaded from my project.
What I want to do is to draw on top of the ImageView - imagine that my UI is a clockface and I want to draw the hands of the clock on top of the background image.
Is it the correct approach to try to subclass the UIImageView and use its DrawRect as when I use the DrawRect of the default view I don't see anything on the screen?
I'm a little lost as I'm finding this particular bit of the documentation hard to follow.
Thanks.
Create a new custom UIView (e.g. named HandsView) that sits on top of your background view (by adding it as a subview of the UIImageView). In the custom view, you can use the drawRect method. Make sure, you clear the context to transparent, so that the background image can be seen below the HandsView.
If you just want to draw turning hands, you can also try to use two fixed UIImageViews with the images of the hands and use the transform property to apply a rotation.