CODEWITHSUNDEEP
iosobjective-ccocoa-touchios6
nserror
nserror

Reputation: 857

Best Practice for Rendering Context of free hand drawing on iPad 3

I currently have a free hand drawing iPad app, that adds lines to a mutable path via quad curves in the touches methods then calls setNeedsDisplayInRect on the new area.

Problem is when the drawing (path) gets rather large, it takes longer to redraw, and begins to bog down. As well as whenever the user changes the brush size or color, it applies this to overlapping parts of the previously drawn path on redraw.

To counter this, I call renderInContext in a background thread in touchesEnded, and merge this with another UIImage in an imageview behind the draw view. Then clear the draw view.

This also helps so when the user hits save, the drawing is usually already rendered in a single UIImage - ready to go.

This works fine on other devices, but on he iPad 3 retina display, the performance is really awful and tends to crash whenever the user lifts his finger multiple times when drawing quickly.

I am seeking any type of advice for best practice in handling this type of situation? Aside from adding additional views to render off of in the background to prevent the main and background thread from accessing the same view at a time - which sounds rather hack-ish - I feel like I'm beating a dead horse?

Upvotes: 1

Views: 380

Answers (1)

borrrden
borrrden

Reputation: 33423

In my current app, I made a working implementation that works fine on iPad 2 as well as 3, regardless of path length or number of paths. It seems that the graphics card is better at drawing lots of small paths then a few large paths, and either one is faster than rendering an image into a context. So, what I do is even if the user is continuously drawing, I break the path into many smaller paths and add those to an array. This approach gives me one advantage, and one disadvantage.

Advantage: The ability to zoom and redraw the image crisply
Disadvantage: Can't do pixel perfect erasing

As far as multiple colors, I made a subclass of UIBezierPath that includes a color property. Since colors are now serializable via NSCoding, they are easily saveable. In addition, I have a "stroke" object, which holds all of the paths the user created in one continuous stroke. This way I can handle undo / redo correctly.

Hope this info helps.

Upvotes: 4

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