pixlpa
pixlpa
/ draggablecanvasshapes.js
Last active
August 29, 2015 13:57
— forked from anonymous/Draggable-Shapes.markdown
For each shape drawn into a canvas, an offscreen canvas is painted with the same shape, with the red color channel storing an ID. Shape click-testing is done by querying the color of the clicked position in the offscreen canvas. For UI with a lot of shapes (data viz for example) this is much more efficient than looping through and hit testing ba…
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| var canvas = document.getElementById('cvs'), | |
| c = canvas.getContext('2d'), | |
| ocan = document.createElement("canvas"), | |
| oc = ocan.getContext('2d'); | |
| ocan.width=canvas.width; | |
| ocan.height=canvas.height; | |
| var offx = canvas.offsetLeft; | |
| var offy = canvas.offsetTop; | |
| var lastX = 0,lastY=0; | |
| var active = 0; |