Re: Hit detection for GWT canvas - which strategy for drawings?

First option is definitely best, but you need to expand it slightly:

Use a bounding box around every shape, so you can do an O(1) check if the click is inside the bounding box (click.x < box.left, click.x > box.right, etc)
If the click is inside the bounding box, then you can run normal edge detect O(number of lines per poly) -- (drop a line to the axis, count number of line intersections - check stackoverflow or similar for code)

If you have Z index on your shapes, then start from the biggest Z index and take the first match.
If you are drawing in a list, then start from the bottom of the list and work upwards and take the first match.

On Thursday, December 20, 2012 1:14:43 PM UTC+2, membersound wrote:

I'm creating some kind of drawings/flowchart/UML-diagram like tool with GWT Canvas (Java).
For hit-detection of my drawings I could imagine 3 different strategies, but I do not know which would work best for my goal.

-  Just keep track of all Shape coordinates and iterate all objects on mouseclick
-  draw all objects on a ghost-canvas on mouseclick, and use isPointInPath() after every object drawing
- using a ghost-canvas and draw each object with its own color (like #000001, #000002), and keep reference of them in a Map<Color, Shape>. Then just detecting the mouseclick on the ghost-canvas and get the object belonging to the pixelcolor under mouse

What would you prefer, and why?

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