subPixelOptimize.js
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/**
* Sub-pixel optimize for canvas rendering, prevent from blur
* when rendering a thin vertical/horizontal line.
*/
var round = Math.round;
/**
* Sub pixel optimize line for canvas
*
* @param {Object} outputShape The modification will be performed on `outputShape`.
* `outputShape` and `inputShape` can be the same object.
* `outputShape` object can be used repeatly, because all of
* the `x1`, `x2`, `y1`, `y2` will be assigned in this method.
* @param {Object} [inputShape]
* @param {number} [inputShape.x1]
* @param {number} [inputShape.y1]
* @param {number} [inputShape.x2]
* @param {number} [inputShape.y2]
* @param {Object} [style]
* @param {number} [style.lineWidth]
*/
function subPixelOptimizeLine(outputShape, inputShape, style) {
var lineWidth = style && style.lineWidth;
if (!inputShape || !lineWidth) {
return;
}
var x1 = inputShape.x1;
var x2 = inputShape.x2;
var y1 = inputShape.y1;
var y2 = inputShape.y2;
if (round(x1 * 2) === round(x2 * 2)) {
outputShape.x1 = outputShape.x2 = subPixelOptimize(x1, lineWidth, true);
} else {
outputShape.x1 = x1;
outputShape.x2 = x2;
}
if (round(y1 * 2) === round(y2 * 2)) {
outputShape.y1 = outputShape.y2 = subPixelOptimize(y1, lineWidth, true);
} else {
outputShape.y1 = y1;
outputShape.y2 = y2;
}
}
/**
* Sub pixel optimize rect for canvas
*
* @param {Object} outputShape The modification will be performed on `outputShape`.
* `outputShape` and `inputShape` can be the same object.
* `outputShape` object can be used repeatly, because all of
* the `x`, `y`, `width`, `height` will be assigned in this method.
* @param {Object} [inputShape]
* @param {number} [inputShape.x]
* @param {number} [inputShape.y]
* @param {number} [inputShape.width]
* @param {number} [inputShape.height]
* @param {Object} [style]
* @param {number} [style.lineWidth]
*/
function subPixelOptimizeRect(outputShape, inputShape, style) {
var lineWidth = style && style.lineWidth;
if (!inputShape || !lineWidth) {
return;
}
var originX = inputShape.x;
var originY = inputShape.y;
var originWidth = inputShape.width;
var originHeight = inputShape.height;
outputShape.x = subPixelOptimize(originX, lineWidth, true);
outputShape.y = subPixelOptimize(originY, lineWidth, true);
outputShape.width = Math.max(subPixelOptimize(originX + originWidth, lineWidth, false) - outputShape.x, originWidth === 0 ? 0 : 1);
outputShape.height = Math.max(subPixelOptimize(originY + originHeight, lineWidth, false) - outputShape.y, originHeight === 0 ? 0 : 1);
}
/**
* Sub pixel optimize for canvas
*
* @param {number} position Coordinate, such as x, y
* @param {number} lineWidth Should be nonnegative integer.
* @param {boolean=} positiveOrNegative Default false (negative).
* @return {number} Optimized position.
*/
function subPixelOptimize(position, lineWidth, positiveOrNegative) {
// Assure that (position + lineWidth / 2) is near integer edge,
// otherwise line will be fuzzy in canvas.
var doubledPosition = round(position * 2);
return (doubledPosition + round(lineWidth)) % 2 === 0 ? doubledPosition / 2 : (doubledPosition + (positiveOrNegative ? 1 : -1)) / 2;
}
exports.subPixelOptimizeLine = subPixelOptimizeLine;
exports.subPixelOptimizeRect = subPixelOptimizeRect;
exports.subPixelOptimize = subPixelOptimize;