I am drawing a graph with UIKIT and I want to show before it is finished a preloader (spinning circle)
Another solution should be before start drawing set the alpha of my view to 0.0 and when it's done fade it to 1.0.
Someone did this before and/or know how to do this?
If using UIKit, you could draw the path, fill and stroke, then draw another path. This is resource-intensive as you will be calling drawRect: often.
The other way is to create animation. I'll let someone else as I have no experience in creating animation in iOS.
You could add an activity indicator to the view, send the view setNeedsDisplay and remove the activity indicator at the end of the drawRect:, but I doubt you will see the activity indicator at all. Activity indicators are only useful when you are performing some lengthy operations, taking at least several seconds to complete. If drawing the graph is that long, you should either optimize it or consider drawing it on a secondary thread into a CGImage. In the latter case, I'm afraid, you restrict yourself to Core Graphics.
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I am using CADisplayLink to draw frames using the EAGLView method in a game at 60 times per second.
When I call UIView animateWithDuration: the framerate drops down to exactly half, from 60 to 30 fps for the duration of the animation. Once the animation is over, the fps rises instantly back up to 60.
I also tried using NSTimer animation method instead of CADisplayLink and still get the same result.
The same behavior happens when I press the volume buttons while the speaker icon is fading out, so it may be using animateWithDuration. As I would like to be able to handle the speaker icon smoothly in my app, this means I can't just rewrite my animation code to use a different method other than animateWithDuration, but need to find a solution that works with it.
I am aware that there is an option to slow down animations for debug on the simulator, however, I am experiencing this on the device and no such option is enabled. I also tried using various options for animateWithDuration such as the linear one and the user interaction, but none had an improvement.
I am also aware I can design an engine that can still work with a frame rate that varies widely. However, this is not an ideal solution to this problem, as high fps is desirable for games.
Has someone seen this problem or solved it before?
The solution to this is to do your own animation and blit during the CADisplayLink callback.
1) for the volume issue, put a small volume icon in the corner, or show it if the user takes some predefined touch action, and give them touch controls. With that input you can use AVAudioPlayer to vary the volume, and just avoid the system control altogether. you might even be able to determine the user has pressed the volume buttons, and pop some note saying do it your way. This gets you away from any animations happening by the system.
2) When you have an animation you want to do, well, create a series of images in code (either then or before hand), and every so many callbacks in the displayLink blit the image to the screen.
Here's an old thread that describes similar drops in frame rate. In that case, the cause of the problem was adding two or more semi-transparent sprites, but I'd guess that any time you try to composite several layers together you may be doing enough work to cut the frame rate, and animateWithDuration very likely does exactly that kind of thing.
Either use OpenGL or CoreAnimation. They are not compatible.
To test this remove any UIView animation, the frame rate will be what you expect. Add back UIView animation, it will drop to 30fps.
You said:
When I call UIView animateWithDuration: the framerate drops down to exactly half, from 60 to 30 fps for the duration of the animation. Once the animation is over, the fps rises instantly back up to 60
I dont know why your not accepting my answer, this is exactly what happens when you combine UIView animation with CA animation not using a UIView.
So in my XIB I have a few graphics that need to reveal in order.. say every one second, the next thing will reveal..
I assume I am going to need something involving viewdidload, starting an NSTimer, then animate the revealing of my graphics with the timer. Can anyone please drop me a few ideas, hints or lines of code to get started?
Thanks!
You could use Quartz Composer to build your image sequence, and then render that to a QCView or OpenGL context.
I know that the CGContext cannot call it to draw directly, and it needs to fill the drawing logic in the drawInContext, and call the CGContext to draw using "setNeedsDisplay", so, I designed a cmd to execute, but it cause some problems... like this :
Why I can't draw in a loop? (Using UIView in iPhone)
I think the CGContext is very different from my previous programming experience....(I used HTML5 canvas, that allow me add more details, after I draw, so do the Java Swing)
Actually, I want to know what is the suitable to implement these kind of thing in Apples' programmer mind. Thz.
There are three approaches to what you're asking. You can draw everything in drawRect:, you can manage multiple layers, or you can draw in an image. Each has advantages, but first you need to think correctly about the problem so that you don't destroy performance.
Drawing happens constantly. Every time anything changes, there may be quite a lot of drawing that has to be done. Not the whole screen usually, but still a lot of drawing. Since drawRect: and drawInContext: can be called many times, they need to be efficient. That means that you don't want to do a lot of expensive calculations, and you don't want to do a lot of useless drawing. "Useless" means "won't actually be displayed because it's off screen or obscured by other drawing."
So in the usual case, you put your actual drawing code in drawRect:, but you do all your calculations elsewhere, generally when your data changes. For example, you read your files, figure out your coordinates, create CGPaths, etc whenever your data changes (which should be much less frequent then drawing). You save all the results into ivars, and then in drawRect: you just draw the final result. So in your loop example, you would probably have an NSArray of images in your view object, and in drawRect: you would draw them all in order.
Another approach is to create a separate layer for each image, set the image as the content, and then attach the layer to the view. You're done at that point. There is no more drawing code you need to write. Quartz handles layers very efficiently, so this can be a very good solution to a wide variety of problems.
Finally, you can composite everything into an image, and then stick that image in an image view, or draw the image directly in the view, or attach the image to a layer. This is a good solution if you have very complicated drawing (particularly using CGPath). This can be expensive if you're constantly changing things, since you have to create a new image context, draw the old image into the new context, draw on top of it, and then create a new image from the context. But it's good for a complicated drawing that doesn't change often.
But you're correct, CGContext is not like a canvas. It needs to be redrawn every draw cycle. You can do that yourself, or you can use another view object (like UIImageView) to do it for you. But it has to be done one way or another.
I would like to create a custom NSView that takes a layered approach to painting. I imagine the majority of the layers would be the same width and height as the backing view.
Is it appropriate to use the Core Animation classes like CALayer for this task, even though I don't expect to need much animation? Is there a more appropriate approach?
To clarify, the view is not meant to be like a canvas in a Photoshop-like application. It more of a data display that should allow for user interaction (selecting, moving, scrolling, etc.)
If it's display and layout you're after, I'd say that a CALayer-based architecture is a good choice. For the open source Core Plot framework, we construct all of our graphs and plot elements out of CALayers, and organize them in a regular hierarchy. CALayers are lightweight and use almost identical APIs between Mac and iPhone. They can even be made to respond to touch or mouse events.
For another example of a CALayer-based user interface, my iPhone application's entire equation entry interface is composed of CALayers, including the menu that slides up from below. Performance is slightly better than that of my previous UIView-based implementation, but the same code also works within my preliminary desktop version of the application.
For a drawing program, I would imagine it would be important to hold a buffer of the bitmap data. The only issue with using a CALayer is that the contents property is a CGImageRef. To turn that back into a graphics context for doing further drawing can be a bit of a pain. You'd have to initialize a new context, draw the bitmap data into it, then do whatever drawing operations you wanted to do, and finally turn that back into a CGImageRef. You probably wouldn't be able to avoid doing a number of pretty large memory allocations, which is virtually guaranteed to slow your program way down.
I would consider holding an off-screen buffer for each layer. Take a look at the Quartz CGLayerRef object. I think it probably does what you want to do: it's an off-screen buffer that holds things you might want to draw repeatedly. You can also quickly get a CGContextRef whenever you need it so you can do additional drawing. And you can always use that CGContextRef with NSGraphicsContext if you want to use Cocoa drawing methods.
We're working on a couple simple games and we have some performance problems that we keep running into, and I was curious if it was a code issue or a "we're using the wrong objects" issue.
Our games are basically simple ones that work as follows:
We have a custom view that we load, and a custom object that is our game engine. The view has a timer that fires like such:
[NSTimer scheduledTimerWithTimeInterval:1.0 / 30.0 target:self selector:#selector(animationTimerMethod) userinfo:nil repeats:YES];
and in our timer method, we have the following:
- (void)animationTimerMethod:(NSTimer*)timer
{
if([gameEngine doGameLoop]) //only redraw if we need to
[self setNeedsDisplay];
}
Our drawing code is very simple, we're just drawing a couple of images on the screen, using code similar to the following:
- (void)drawRect:(CGRect)rect
{
CGGraphicsContext ctx = UIGraphicsGetCurrentContext();
CGContextDrawImage(ctx, someRect, someImage);
}
The main problem we have is responsiveness to touch. Our code will not get a response in the touchesBegan method many times. Is this just a limitation of the Core Graphics library? Should we be using OpenGL? Are there other ways to do simple animations (not even objects moving on screen, just 6 or so frames of animation for an object in the same place) that would be more responsive?
Thanks so much!
There are definitely ways to speed this up. Manually redrawing the images every frame means you are redrawing textures you could be reusing. You could reuse them either by moving to OpenGL, or moving the images into a CALayer and then just repositioning the layer instead of redrawing the image.
If you do not want to move to OpenGL you would probably also see a significant performance win by moving to CAAnimation instead of having your code calculate each frame, but that might require significant changes to your engine.
Also, if you can avoid avoid alpha compositing it is a big speed up.
My first question is do your images have transparency?
Images with transparency with HIGHLY effect performance.
In Apple's doc's they make reference to this point several times.
The second thing I would ask is, have you tried running your app in Instruments and/or Shark? Both these apps can help give you an idea of where your problems are happening.