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Set minimum opacity, rather than minimum (percent of _max) value with minOpacity #32

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Set minimum opacity, rather than minimum (percent of _max) value with minOpacity #32

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dba8d75
add slider for minOpacity to demo
nhamer Nov 4, 2017
4328553
handle minOpacity as opacity instead of minimum scaled value
nhamer Nov 4, 2017
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10 changes: 7 additions & 3 deletions demo/index.html
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Original file line number Diff line number Diff line change
Expand Up @@ -23,7 +23,8 @@
<div class="container">
<div class="options">
<label>Radius </label><input type="range" id="radius" value="25" min="10" max="50" /><br />
<label>Blur </label><input type="range" id="blur" value="15" min="10" max="50" />
<label>Blur </label><input type="range" id="blur" value="15" min="10" max="50" /><br />
<label>Opacity </label><input type="range" id="minOpacityPct" value="5" min="0" max="100" />
</div>
<canvas id="canvas" width="1000" height="600"></canvas>
</div>
Expand All @@ -40,11 +41,12 @@
}

var heat = simpleheat('canvas').data(data).max(18),
minOpacity = 0,
frame;

function draw() {
console.time('draw');
heat.draw();
heat.draw(minOpacity);
console.timeEnd('draw');
frame = null;
}
Expand All @@ -58,10 +60,12 @@

var radius = get('radius'),
blur = get('blur'),
minOpacityPct = get('minOpacityPct'),
changeType = 'oninput' in radius ? 'oninput' : 'onchange';

radius[changeType] = blur[changeType] = function (e) {
radius[changeType] = blur[changeType] = minOpacityPct[changeType] = function (e) {
heat.radius(+radius.value, +blur.value);
minOpacity = +minOpacityPct.value / 100;
frame = frame || window.requestAnimationFrame(draw);
};

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8 changes: 5 additions & 3 deletions simpleheat.js
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Original file line number Diff line number Diff line change
Expand Up @@ -106,26 +106,28 @@ simpleheat.prototype = {
// draw a grayscale heatmap by putting a blurred circle at each data point
for (var i = 0, len = this._data.length, p; i < len; i++) {
p = this._data[i];
ctx.globalAlpha = Math.min(Math.max(p[2] / this._max, minOpacity === undefined ? 0.05 : minOpacity), 1);
ctx.globalAlpha = Math.min(p[2] / this._max, 1);
ctx.drawImage(this._circle, p[0] - this._r, p[1] - this._r);
}

// colorize the heatmap, using opacity value of each pixel to get the right color from our gradient
var colored = ctx.getImageData(0, 0, this._width, this._height);
this._colorize(colored.data, this._grad);
this._colorize(colored.data, this._grad, minOpacity);
ctx.putImageData(colored, 0, 0);

return this;
},

_colorize: function (pixels, gradient) {
_colorize: function (pixels, gradient, minOpacity) {
var minAlpha = 255 * (minOpacity || 0);
for (var i = 0, len = pixels.length, j; i < len; i += 4) {
j = pixels[i + 3] * 4; // get gradient color from opacity value

if (j) {
pixels[i] = gradient[j];
pixels[i + 1] = gradient[j + 1];
pixels[i + 2] = gradient[j + 2];
pixels[i + 3] = Math.max(pixels[i + 3], minAlpha);
}
}
},
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