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POReducing the cost of native <-> managed interactions in monotouch
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copied!<p>I'm playing with a native library for which I wrote monotouch (are we supposed to name that Xamarin.iOS now?) bindings.</p> <p>Overriding some often used methods in C# shows a severe performance downgrade, even if the core of the function do nothing or return base.X (). Instruments confirms the problem and the time spend in managed<->native interactions.</p> <p>Is there a way to speed that up, from one side or the other (native or managed) ? Or is this a tax to pay when P/Invoking in MT ?</p> <p>The glass ceiling I'm hitting is about 50000 calls/sec. </p> <p><strong>[UPDATE 2013/02/22]</strong> To give some context or example, here's what I'm doing. I'm playing with cocos2d kinematics (without chipmunk). To manage my own position of sprites, I have to override</p> <pre><code>CGAffineTransform NodeToParentTransform { get; } </code></pre> <p>and </p> <pre><code>bool Dirty { get; } </code></pre> <p>The former returns a matrices, and poke the native side to get parameters like ScaleX, ScaleY, RotationX. RotationY and AnchorPointInPoints, the latter return <code>true</code> unconditionally.</p> <p>My attempt in reducing the cost is partly successful at this moment as, by changing the native code to have a single point to override which doesn't poke to any properties, I get a 25% to 50% speedup.</p> <pre><code>-(BOOL) dirty:(CGAffineTransform*)nodeToParentTransform rotationX:(float)rotX rotationY:(float)rotY scaleX:(float)scaleX scaleY:(float)scaleY anchorPointInPoints:(CGPoint)anchorPointInPoints; </code></pre> <p>I'm now getting an almost acceptable 25-30fps for my 3500 sprites, but I'd still like to go further. And also not have to patch the native sources.</p> <p><strong>[UPDATE 2013/02/22 2]</strong> Here's a sample that you could use to test <a href="https://github.com/StephaneDelcroix/mt-speed" rel="nofollow noreferrer">https://github.com/StephaneDelcroix/mt-speed</a>. It contains an over simplified first order kinematic engine, 3501 bodies and sprites.</p> <p>The interesting class here is <code>KinematicSprite</code>. The code as is works on a modified version of cocos2d (included in Cocos2D.dll). You can make it work on stock cocos2d and cocos2d bindings by commenting out the new <code>Dirty</code> function and uncommenting <code>NodeToParentTransform</code> and the old <code>Dirty</code>. As per <a href="https://stackoverflow.com/questions/14962741/subclassing-bound-type-in-mono-touch">Subclassing bound type in mono touch</a>, it only works on devices. I get 20 to 22.5 fps on an iPad mini.</p>

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