I'm working on a drawing app, where user should be able to both fill locked areas and simply draw lines on finger moves.
Locked areas are provided as SVGs (paths), so I'm using SVGKit library to render them on the screen (as CAShapeLayers within a view). Then basically use fillColor on proper layer to fill it on touch.
However, for lines drawing then Core Graphics comes into play (CGContextStrokePath), and lines are always drawn below everything contained within CALayers hierarchy. So basically below filled areas.
What I'm trying to reach is a system where last applied drawing is always on top. So that applying fill overrides any lines in the area, and next drawing a line shows it above filled zone.
Seems that CGLayer's z-index is less than CALayer's one, and I need some other approach for my goal...
CAShapeLayer is designed to hold CGPath instances and render them, so I'd add a CAShapeLayer at the point in your layer-hierarchy where you want it to appear, and modify the CGPath property on that.
Related
On my table view, I want to display small circles of certain colors that will provide context for the information. The circles should be in the location that the image would usually be in (the left hand side). Is there an easy way to do this? I was thinking that I could create a new image view and simply draw on it using some drawing routines. The problem is I don't know any of these drawing routines, or at least I don't know how to use them outside of a drawRect function.
Well, the easiest way would be to include the different images in your bundle and conditionally set them to the cell's imageView's image property in cellForRowAtIndexPath:.
However, if you're looking for alternative's you could subclass UITableViewCell, and use CAShapeLayers to draw them programmatically and add them to the cells layer in what ever position you want.
Here's an example of how to use CAShapeLayer to draw a circle:
iPhone Core Animation - Drawing a Circle
I'm working on a graphing application which I wrote using Core Graphics. I have a buffer which accumulates data, and I render it on the screen. It's super slow and I want to avoid going to openGL if possible. According to the profiler, drawing my graph data is what's killing me (which consists of a number of points which are converted to a path, followed by the calls AddPath, DrawPath)..
This is what I want to do, my question is how to best implement it using layers / views / etc..
I have a grid and some text. I want this to be rendered in a CALayer (or some other layer/view?) and only update when required (the graph is rescaled).
Only a portion of the data needs to be refreshed. I want to take the previous screen buffer, erase a rectangle's worth of data (or cover it with a white box) and then draw only the portion of the graphs that have changed.
I then want to merge the background layer with the foreground graphs to generate the composite image. This requires the graph layer to have a transparent background so as not to obscure the grid.
I've looked at using CAlayer as a sublayer, but it doesn't seem to provide a simple way to draw a line. CAShapeLayer seems a bit better, but it looks like it can only draw a single line. I want the grid to be composed of multiple lines.
What's the best approach and combination of objects to allow me to do this?
Thanks,
Reza
I'd have a CGLayerRef that was used for drawing the path into. For each new point I'd draw just the new segment. When the graph got to full width I'd create a new CGLayerRef and start drawing the new line segments into that.
What happens to the previous layer as it's drawn over by the new layer depends on how your graph is displayed, but you could clear the section which is now underneath the new layer (using CGContextSetBlendMode(context, kCGBlendModeClear);) or you could choose to blend them together in some other way.
Drawing the layers each time you make a change to the lines they contain is relatively cheap compared to drawing all of the line segments themselves.
Technically, there would also be CALayers used to manage the drawing of the CGLayerRefs to the screen (via the delegate relationship drawLayer:inContext:), but all of the line drawing is done using the CGLayerRefs context and then the CGLayerRef is drawn as a whole into the CALayers context (CGContextDrawLayerInRect(context, frame, backingCGLayer);).
I have been trying so much but have no solution find out yet. I have to implement the painting and erasing on iOS so I successfully implemented the painting logic using UIBezierPath. The problem is that for erasing, I implemented the same logic as for painting by using kCGBlendModeClear but the problem is that I cant redraw on the erased area and this is because in each pass in drawRect i have to stroke both the painting and erasing paths. So is there anyway that we can subtract erasing path from drawing path to get the resultant path and then stroke it. I am very new to Core Graphics and looking forward for your reply and comments. Or any other logic to implement the same. I can't use eraser as background color because my background is textured.
You don't need to stroke the path every time, in fact doing so is a huge performance hit. I guarantee if you try it on an iPad 3 you will be met with a nearly unresponsive screen after a few strokes. You only need to add and stroke the path once. After that, it will be stored as pixel data. So don't keep track of your strokes, just add them, stroke them, and get rid of them. Also look into using a CGLayer (you can draw to that outside the main loop, and only render it to your rect in the main loop so it saves lots of time).
These are the steps that I use, and I am doing the exact same thing (I use a CGPath instead of UIBezierPath, but the idea is the same):
1) In touches began, store the touch point and set the context to either erase or draw, depending on what the user has selected.
2) In touches moved, if the point is a certain arbitrary distance away from the last point, then move to the last point (CGContextMoveToPoint) and draw a line to the new point (CGContextAddLineToPoint) in my CGLayer. Calculate the rectangle that was changed (i.e. contains the two points) and call setNeedsDisplayInRect: with that rectangle.
3) In drawRect render the CGLayer into the current window context ( UIGraphicsGetCurrentContext() ).
On an iPad 3 (the one that everyone has the most trouble with due to its enormous pixel count) this process takes between 0.05 ms and 0.15ms per render (depending on how fast you swipe). There is one caveat though, if you don't take the proper precautions, the entire frame rectangle will be redrawn even if you only use setNeedsDisplayInRect: My hacky way to combat this (thanks to the dev forums) is described in my self answered question here, Otherwise, if your view takes a long time to draw the entire frame (mine took an unacceptable 150 ms) you will get a short stutter under certain conditions while the view buffer gets recreated.
EDIT With the new info from your comments, it seems that the answer to this question will benefit you -> Use a CoreGraphic Stroke as Alpha Mask in iPhone App
Hai here is the code for making painting, erasing, undo, redo, saving as picture. you can check sample code and implement this on your project.
Here
I'm working on yet another drawing app with canvas that is many times bigger than screen.
I need some advice/direction on how to that.
Basically what i want is to scroll around this big canvas, drawing only in visible region.
I was thinking of two approaches:
Have 64x64 (or whatever) "tiles" to draw on, and then on scroll just load new tiles.
Record all user strokes (points) and on scroll calculate which are in specified region, and draw them, using only screen-size canvas.
If this matters, i'm using cocos2d for prototype.
Forget the 2000x200 limitation, I have an open source project that draws 18000 x 18000 NASA images.
I suggest you break this task into two parts. First, scrolling. As was suggested by CodaFi, when you scroll you will provide CATiledLayers. Each of those will be a CGImageRef that you create - a sub image of your really huge canvas. You can then easily support zooming in and out.
The second part is interacting with the user to draw or otherwise effect the canvas. When the user stops scrolling, you then create an opaque UIView subclass, which you add as a subview to your main view, overlaying the view hosting the CATiledLayers. At the moment you need to show this view, you populate it with the proper information so it can draw that portion of your larger canvas properly (say a circle at this point of such and such a color, etc).
You would do your drawing using the drawRect: method of this overlay view. So as the user takes action that changes the view, you do a "setDisplayInRect:" as needed to force iOS to call your drawRect:.
When the user decides to scroll, you need to update your large canvas model with whatever changes the user has made, then remove the opaque overlay, and let the CATiledLayers draw the proper portions of the large image. This transition is probably the most tricky part of the process to avoid visual glitches.
Supposing you have a large array of object definitions used for your canvas. When you need to create a CGImageRef for a tile, you scan through it looking for overlap between the object's frame and the tile's frame, and only then draw those items that are required for that tile.
Many mobile devices don't support textures over 2048x2048. So I would recommend:
make your big surface out of large 2048x2048 tiles
draw only the visible part of the currently visible tile to the screen
you will need to draw up to 4 tiles per frame, in case the user has scrolled to a corner of four tiles, but make sure you don't draw anything extra if there is only one visible tile.
This is probably the most efficient way. 64x64 tiles are really too small, and will be inefficient since there will be a large repeated overhead for the "draw tile" calls.
There is a tiling example in Apples ScrollViewSuite Doesn't have anything to do with the drawing part but it might give you some ideas about how to manage the tile part of things.
You can use CATiledLayer.
See WWDC2010 session 104
But for cocos2d, it might not work.
I'm working on an app that lets the user stack graphics on top of each other.
The graphics are instantiated as a UIImageView, and is transparent outside of the actual graphic. I'm also using pan gestures to let the user drag them around the screen.
So when you have a bunch of graphics of different sizes and shapes on top of one another, you may have the illusion that you are touching a sub-indexed view, but you're actually touching the top one because some transparent part of it its hovering over your touch point.
I was wondering if anyone had ideas on how we could accomplish ONLY listening to the pan gesture on the solid part of the imageview. Or something that would tighten up the user experience so that whatever they touched was what they select. Thanks
Create your own subclass of UIImageView. In your subclass, override the pointInside:withEvent: method to return NO if the point is in a transparent part of the image.
Of course, you need to determine if a point is in a transparent part. :)
If you happen to have a CGPath or UIBezierPath that outlines the opaque parts of your image, you can do it easily using CGPathContainsPoint or -[UIBezierPath containsPoint:].
If you don't have a handy path, you will have to examine the image's pixel data. There are many answers on stackoverflow.com already that explain how to do that. Search for get pixel CGImage or get pixel UIImage.