Thanks for the suggestion Mike.

Cheers, solly

On Fri, 27 May 2005, Mike Tammerman wrote:

> 1. Retrieve all items from the canvas with QCanvas.allItems() method,
> then make a set with the points of the item. Call it A.
>
> 2. Make a full set with all the points in the canvas. Call it B.
>
> 3. Get the difference. (B - A)
>
> If your items are as simple as rectangels, it would be trivial.
>
> Mike
>
> On 5/27/05, Solly Brown <sollyb@cse.unsw.edu.au> wrote:
>> I've got a qcanvas with a number of canvasitems moving about on it. I need
>> to efficiently identify which areas of the canvas are empty (ie. don't
>> have any objects on them).
>>
>> The simplest implementation is to lay down a grid of qpoints on the
>> canvas, and then just check whether there are collisions with each point
>> -- if there are no collisions then that particular point area is empty.
>>
>> The problem with this is that it's really slow... a 40x40 grid has 1600
>> points and looping through all of them and calling 'collisions' on each
>> one makes my display slow to a crawl.
>>
>> Can anyone suggest an efficient way of identifying which points on a grid
>> are clear (don't have collisions above them)?
>>
>> Thanks for your help....!
>>
>> Solly
>>
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