CODEWITHSUNDEEP
iphoneipadcore-graphicsquartz-2d
johnbakers
johnbakers

Reputation: 24770

Continuous drawing with Quartz? frame by frame possible?

I've been working on custom drawings using drawRect in UIView subclasses. That's cool, but you have to wait until the end of the run loop for drawRect to be called and I'm wondering how you can control frame by frame animations where you change the drawings over time, or if this is possible? Perhaps Quartz isn't really designed for this type of animated graphics? I gather that perhaps it is designed for static drawings that don't change so frequently.

Upvotes: 1

Views: 660

Answers (2)

hotpaw2
hotpaw2

Reputation: 70703

Your app should exit to the run loop before each frame. Do all your custom frame animation setup between each frame. So frame-by-frame drawing in drawRect should work just fine. This can work in iOS apps at a 60 Hz frame update rate, not just for static views, as long as all your methods between frame times, as well as your drawRects, are fast enough. Chop them up if needed.

Upvotes: 1

viggio24
viggio24

Reputation: 12366

Quartz by itself its not able to sustain a high frame rate, due to its need to redraw everything each time. But you can have Quartz work together with CoreAnimation to have Quartz based animations. The idea behind this is that you can cache previously drawn content inside CALayer objects and then use CoreAnimation to create the continuous drawing effect.

A good example of this technique can be see in the AccelerometerGraph sample code provided by Apple. Inside this sample the UIView subclass that uses this technique is the "GraphView" object. Basically this object draws as completely new only a portion of the graph (the newly generated segments), backs it in a dedicated layer and then animates the layers in order to provide the "scrolling graph" animation.

Clearly this technique works only when you have full control of the drawing elements and can manage this incremental way of adding objects in the screen. Of course things become much more complicated when you must redraw many different parts of the screen and you need to modify previously generated layers.

Anyway have a look at the mentioned code: it is quite interesting.

Upvotes: 2

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