On Mar 12, 2008, at 6:23 AM, Scott Thompson wrote: On Mar 11, 2008, at 11:55 PM, Luigi Castelli wrote: Hi all,
I have a 16x16 matrix made by rectangular CGPaths.
The exact shape of the paths is actually a rounded rectangle.
All the CGPaths in the matrix are NOT adjacent to each other.
In other words there is some space between the paths - or cells of the matrix.
Now I want to implement 2D interpolation when the user drags on the matrix in an attempt to select its cells.
This would have the effect that even during fast drags the cells over which the mouse has passed will be selected.
So, if a line is drawn on top of the matrix how would I know which paths (cells) it intersected ?
What would be the best strategy to tackle such a problem ?
Any advice or suggestion is highly appreciated.
Track the mouse in a mouseMoved handler and at each mouse position use CGPathContainsPoint to determine if the mouse is in a particular cell.
If that's not sufficient, you could use bressenham's algorithm or even simple interpolation to calculate intermediate points on a line and check whether they are in the path(s). If you know how big your cells are you simply have to sample at half that distance to feel confident that you hit everything you might have hit.
Given near-rectangular paths, as in this case, you should use "CGRectContainsPoint" first — it's much faster than any other approach. Once you know that the point is within the rectangle, you can then call "CGPathContainsPoint" (which is possibly faster than doing the work yourself). On the other hand, with a rounded rectangle, the only problematic areas are at the corners — it would easy to do a check for that case first and only call "CGPathContainsPoint" if you end up in a corner.
Derek
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