We're repetitively making a CGLayer, doing processing, and then releasing it. This happens a lot in real time. Surely there is a lot of overhead in making a whole new CGLayer each time. So...

Surely it would be better to just keep the layer around, and erase all the data from it each time -- rather than creating a new one from scratch.

Note: if you paint in a blank or clear rectangle covering everything, that just adds even more data on top of your extant paths.

So, how to actually "erase" or "start again" a CGLayer?

There is a function CGContextBeginPath(cc) but it's confusing: it seems to only clear out "that" path, it does not appear to erase all of the CGLayer back to no-data state.

How to return a CGLayer to a state of no-data? Does anyone know?

Update...

It turns out there is actually NO WAY TO DO THIS.

After conside开发者_运维技巧rable experimentation, we have determined that there appears to be no way to clear out all the data from a CGLayer (which is disappointing really).

Note that adding a new white or clear rectangle, only does that - it actually adds more data.

So unfortunately no known way to do this. If you are building these at high hz (perhaps for a calculation), you just have to start with a fresh one each time. Or, you can apparently delete (actually delete, not just cover) just the one path using CGContextBeginPath().

Hopefully this will help someone in the future.

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Once you have the context call CGContextClearRect( cc, someRect ) to clear the contents.

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Why don't you just fill it with a rectangle of (clear/white) color? Make sure the layer is not opaque if you wanna clear it with clearColor (transparent).