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function trim(c) { | |
var ctx = c.getContext('2d'), | |
copy = document.createElement('canvas').getContext('2d'), | |
pixels = ctx.getImageData(0, 0, c.width, c.height), | |
l = pixels.data.length, | |
i, | |
bound = { | |
top: null, | |
left: null, | |
right: null, | |
bottom: null | |
}, | |
x, y; | |
for (i = 0; i < l; i += 4) { | |
if (pixels.data[i+3] !== 0) { | |
x = (i / 4) % c.width; | |
y = ~~((i / 4) / c.width); | |
if (bound.top === null) { | |
bound.top = y; | |
} | |
if (bound.left === null) { | |
bound.left = x; | |
} else if (x < bound.left) { | |
bound.left = x; | |
} | |
if (bound.right === null) { | |
bound.right = x; | |
} else if (bound.right < x) { | |
bound.right = x; | |
} | |
if (bound.bottom === null) { | |
bound.bottom = y; | |
} else if (bound.bottom < y) { | |
bound.bottom = y; | |
} | |
} | |
} | |
var trimHeight = bound.bottom - bound.top, | |
trimWidth = bound.right - bound.left, | |
trimmed = ctx.getImageData(bound.left, bound.top, trimWidth, trimHeight); | |
copy.canvas.width = trimWidth; | |
copy.canvas.height = trimHeight; | |
copy.putImageData(trimmed, 0, 0); | |
// open new window with trimmed image: | |
return copy.canvas; | |
} |
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