Wiggler

Υου’ll wonder why is that useful… Well for a number of reasons and for creating the shadowPath of a path!
If you want to render some paths with their shadow, you can set the CALayer‘s properties:

mycalayer.shadowOpacity = 0.8;

But if you don’t specify a shadowPath, the layer’s alpha channel will be used which is slow for real time changes. The solution is to specify a CGpath as the shadowPath. But apple doesn’t give you a function that creates a shadowPath around your path. So… I’ve written one!

The function accepts an open or closed  CGpath and the desirable width for the outline and returns the outline as a closed CGpath. It uses the Acclerate Framework for faster calculations.

I have created a demo that animates the outline’s width as well as the rotation of a path. The outline of one of the paths is used as a shadowPath. You can find the function inside this demo project here: https://github.com/Petrakeas/outlineDEMO

A video of the demo follows and some technical details.

UPDATE: I have added some more functions that help in the creation of bezier curves and updated the demo accordingly. Read the post here.

• My function is a class method function so that it can be used without initializing a class instance first.
• The animation in this demo is done using CABasicAnimation for custom properties. A very good guide for the topic is here. Generally you have to synthesize your properties, override “needsDisplayForKey:” , override “initWithLayer” in order to copy your custom variables and custom properties (because CA creates copies of your layer)
• You can’t alter the shadowPath of an animated CAlayer,! So I created an external CAlayer for shadows and passed its reference to the animated CALayer so that it can change the shadowPath.
• I use CGAffineTransform to rotate one of the paths and then created the outline of its path with my funtion.
• The CAlayer sets its contentsScale in order to render properly in retina displays.