few months ago I've found a really awesome sample code from Apple site. The sample is called "LargeImageDownsizing" the wonderful thing is that it explain a lot about how image are read from resources and then rendered on screen. Digging into that code I've found something that is disturbing me a little. The downsized image is passed to a view that has a CATiledLayer, but without giving a piece of image at each tile to improve memory performance, it just set the tile size and then load image (I'm making things simple to go to the concept). So my question basically is why?Why use a CATiledLayer if it is not feed in the right way, they could have used a normal UIImageView... So I made few tests to understand if I was right. Modifing the code simple adding a scrollview with an image view as subview and responding to the delegate scrollview for zoom. I went to those conclusions testing on device and sim:
-The memory impact and footprint is exactly the same, even during zooming scrolling operation and it doesn't surprise me at all, the image is decompressed in memory
-Time profile say that a tileview take more time to be drawn during scrolling zoom operation instead of a uiimageview and that doesn't surprise me at all again the uiimageview is already drawn
-If I send memory warning nothing change between the two solution(only on sim)
-Testing Core Animation performance I get the same results around 60FPS
So what's the deal between those two views/layers why should I pick one instead of the other in these specific case? UIImageView seems to win the battle.
I hope that someone could help me to understand that.
They might perform the same for small images because ghen the only difference in terms os performance is that CATiledLayer draws on a background thread. Depending on the tile size CATiledLayer would even be slower because it has to draw multiple tiles for one image.
BUT ...
the point of CATiledLayer is that you don't need to draw all tiles, especially when zooming into a very very large image. It is smart to know which parts are actually needed. It also is smart about evicting tiles that are not needed any more.
Or this mechanism to work you need to provide the individual parts of the image separately. We're talking a total size of an image that probably cannot be held in memory uncompressed.
Related
I'm loading a very large image (8000x8000) into an UIImageView that's in a UIScrollView. This works but it consumes a lot of memory and takes a couple of seconds to load.
I've looked into a better approach and all the examples I have found are based on a 2010 WWDC example called PhotoScroller. This example uses a custom UIView with CATiledLayer to break the large image into smaller tiles and draw them to the screen.
https://github.com/master-nevi/WWDC-2010/tree/master/PhotoScroller
Is there a more modern way to do this in iOS 13 or is this still the best approach?
It is still the best approach. 8000x8000 is huge. You cannot load the whole image at once. CATiledLayer means you only need a few tiles loaded at a time — just the portion of the image that the user is looking at at the moment.
I am making a game, and it involves a sandstorm. I decided that the basic concept would be that I would make an image that looks roughly like a sandstorm, and then decorate it with some particles/whatever else it takes.
I ran into an issue at step one. I threw together a simple image for testing purposes:
I added that to my game, and the FPS dropped by 60%. I was surprised by the effect one image had, but I wasn't too worried about it. I cut the resolution of the image in half, and again, lots of lag.
Is spritekit/iOS really that bad at handling moderately sized images with alpha? I read on another question that the simulator is bad at rendering, but that can't be the entire problem.
Is there any hope for getting this to render without slicing my performance? The particles work well, everything else runs at 60fps just fine, but the addition of this image is apparently a severe drain on resources.
EDIT: I tested my game out on my phone, and I got no lag. So apparently, the simulator is just really bad at rendering after all. At the same time, I am curious as to how to speed up performance, as there is clearly some kind of lag going on.
I'm no expert on SpriteKit, but I had similar experiences with plain core animation and layering.
The issue is that an image with alpha, even for the "opaque" parts of it, it introduces a redrawing call on all the sublayers underneath it for every time it moves. First check if this is actually the problem, and then, try one of this, and see if it improves:
SKCropNode could prevent for rendering the underneath elements
Tile the image so only the border has alpha
Snapshot the underneath layers.
Reduce the amount of nodes being rendered, hide the ones that are "under the sandstorm".
And you should be using real devices to test performance of your game, you cannot rely on the simulator for that.
I'm looking for any advice on ways to have a rather large scrollview (let's say 8192x8192) which is essentially a grid and it has subviews of about 5-100 buttons placed in it.
The brute force approach runs out of memory as CALayer seems to be allocating a bitmap for the size of the scrollview's content (the memory issue is especially prominent when zooming is used)
I next added CATiledLayer to it, that's fixed the memory issue but there is a blurry effect on the grid as tiles are generated asynchronously and is still not ideal in that it's using a lot of memory for what is essentially a trivial 'draw some lines' task.
It seems like if I could somehow get control to draw my own grid via OpenGL each frame and tell UIKit not to create a bitmap buffer for the scrollview it would be perfect but not sure if this is feasible or even the right approach?
On Android I just took control of the entire drawing/zooming/panning but this seems vastly overkill on iOS which seems to offer most of this already?
You should check out the WWDC 2009 video session 102: "Mastering iPhone Scroll Views" along with the ScrollViewSuite sample project from Apple. They explain how to do a tiled scroll view with different zoom levels, which sounds like it is what you need.
I have a custom view (inherited from UIView) in my app. The custom view overrides
- (void) drawRect:(CGRect) rect
The problem is: the drawRect: executes many times longer on iPad 3 than on iPad 2 (about 0.1 second on iPad 3 and 0.003 second on iPad 2). It's about 30 times slower.
Basically, I am using some pre-created layers and draw them in the drawRect:. The last call
CGContextDrawLayerAtPoint(context, CGPointZero, m_currentLayer);
takes most of the time (about 95% of total time in drawRect:)
What might be slowing things so much and how should I fix the cause?
UPDATE:
There are no threads directly involved. I do call setNeedsDisplay: in one thread and drawRect: gets called from another but that's it. The same goes for locks (there are no locks used).
The view gets redrawn in response to touches (it's a coloring book app). On iPad 2 I get reasonable delay between a touch and an update of the screen. I want to achieve the same on iPad 3.
So, the iPad 3 is definitely slower in a lot of areas. I have a theory about this. Marco Arment noted that the method renderInContext is ridiculously slow on the new iPad. I also found this to be the case when trying to create a magnifying glass for a custom text view. In the end I had to forego renderInContext for custom Core Graphics drawing.
I've also been having problem hitting the dreaded wait_fences errors on my core graphics drawing here: Only on new iPad 3: wait_fences: failed to receive reply: 10004003.
This is what I've figured out so far. The iPad 3 obviously has 4 times the pixels to drive. This can cause problems in two place:
First, the CPU. All core graphics drawing is done by the CPU. In the case of rotational events, if the CPU takes too long to draw, it hits the wait_fences error, which I believe is simply a call that tells the device to wait a little longer to actually perform the rotation, thus the delay.
Transferring images to the GPU. The GPU obviously handles the retina resolution just fine (see Infinity Blade 2). But when core graphics draws, it draws its images directly to the GPU buffers to avoid memcpy. However, either the GPU buffers haven't changes since the iPad 2 or they just didn't make them large enough, because it's remarkably easy to overload those buffers. When that happens, I believe the CPU writes the images to standard memory and then copies them to the GPU when the GPU buffers can handle it. This, I think is what causes the performance problems. That extra copy is time consuming with so many pixels and slows things down considerably.
To avoid memcpy I recommend several things:
Only draw what you need. Avoid drawing anything offscreen at all costs. If you're drawing a large view, but only display part of that view (subviews covering it, for example) try to find a way to only draw what is visible.
If you have to draw a large view, consider breaking the view up in to parts either as subviews or sublayers (probably sublayers in your case). And only redraw what you need. Take the notability app, for example. When you zoom in, you can literally watch it redraw one square at a time. Or in safari you can watch it update squares as you scroll. Unfortunately, I haven't had to do this so I'm uncertain of the methodology.
Try to keep your drawings simple. I had an awesome looking custom core text view that had to redraw on every character entered. Very slow. I changed the background to simple white (in core graphics) and it sped up well. Even better would be for me to not redraw the background.
I would like to point out that my theory is conjecture. Apple doesn't really explain what exactly they do. My theory is just based on what they have said and how the iPad responds as well as my own experimentation.
UPDATE
So Apple has now released the 2012 WWDC Developer videos. They have two videos that may help you (requires developer account):
iOS App Performance: Responsiveness
iOS App Performance: Graphics and Animation
One thing they talk about I think may help you is using the method: setNeedsDisplayInRect:(CGRect)rect. Using this method instead of the normal setNeedsDisplay and making sure that your drawRect method only draws the rect given to it can greatly help performance. Personally, I use the function: CGContextClipToRect(context, rect); to clip my drawing only to the rect provided.
As an example, I have a separate class I use to draw text directly to my views using Core Text. My UIView subclass keeps a reference to this object and uses it to draw it's text rather than use a UILabel. I used to refresh the entire view (setNeedsDisplay) when the text change. Now I have my CoreText object calculate the changed CGRect and use setNeedsDisplayInRect to only change the portion of the view that contains the text. This really helped my performance when scrolling.
I ended up using approach described in #Kurt Revis answer for similar question.
I minimized number of layers used, added UIImageView and set its image to an UIImage wrapping my CGImageRef. Please read the mentioned answer to get more details about the approach.
In the end my application become even simpler than before and works with almost identical speed on iPad 2 and iPad 3.
I'm developing a game in as3 for iPhone, and I've gotten it running reasonably well (consistanty 24fps on iPhone 3G), but I've noticed that when the "character" goes partly off the screen, the frame rate drops to 10-12fps. Does anyone know why this is and what I can do to remedy it?
Update - Been through the code pretty thoroughly, even made a new project just to test animations. Started a image offscreen and moved it across the screen and back off. Any time the image is offscreen, even partially, the frame rates are terrible. Once the image is fully on the screen, things pick back up to a solid 24fps. I'm using cacheAsBitmap, I've tried masking the stage, I've tried placing the image in a movieclip and using scrollRect. I would keep objects from going off the screen, except that the nature of the game I'm working on has objects dropping from the top down (yes, I'm using object pooling. No, I'm not scaling anything. Striclt x,y translations). And yes, I realize that Obj-C is probably the best answer, but I'd really like to avoid that if I can. AS3 is so much nicer to write in
Try and take a look at the 'blitmasking' technique: http://www.greensock.com/blitmask
From Doyle himself:
A BlitMask is basically a rectangular Sprite that acts as a high-performance mask for a DisplayObject by caching a bitmap version of it and blitting only the pixels that should be visible at any given time, although its bitmapMode can be turned off to restore interactivity in the DisplayObject whenever you want. When scrolling very large images or text blocks, BlitMask can greatly improve performance, especially on mobile devices that have weaker processorst