80 lines
2.9 KiB
Markdown
80 lines
2.9 KiB
Markdown
# bitmap-sdf [](http://github.com/badges/stability-badges)
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Calculate signed distance field for an image / bw-data. Fork of [tiny-sdf](https://github.com/mapbox/tiny-sdf) with reduced API.
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[Demo](https://dy.github.io/bitmap-sdf/)
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## Usage
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[](https://npmjs.org/package/bitmap-sdf/)
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```js
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let calcSdf = requrie('bitmap-sdf')
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//draw image
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let canvas = document.body.appendChild(document.createElement('canvas'))
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let w = canvas.width = 200, h = canvas.height = 200
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let ctx = canvas.getContext('2d')
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ctx.fillStyle = 'white'
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ctx.font = 'bold 30px sans-serif'
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ctx.fillText('X', 20, 20)
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//calculate distances
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let distances = calcSdf(canvas)
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//show distances
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let imgArr = new Uint8ClampedArray(w*h*4)
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for (let i = 0; i < w; i++) {
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for (let j = 0; j < h; j++) {
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imgArr[j*w*4 + i*4 + 0] = arr[j*w+i]*255
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imgArr[j*w*4 + i*4 + 1] = arr[j*w+i]*255
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imgArr[j*w*4 + i*4 + 2] = arr[j*w+i]*255
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imgArr[j*w*4 + i*4 + 3] = 255
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}
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}
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var data = new ImageData(imgArr, w, h)
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ctx.putImageData(data, 0, 0)
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```
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### dist = calcSdf(source, options?)
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Calculate distance field for the input `source` data, based on `options`. Returns 1-channel array with distance values from `0..1` range.
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#### Source:
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Type | Meaning
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---|---
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_Canvas_, _Context2D_ | Calculates sdf for the full canvas image data based on `options.channel`, by default `0`, ie. red channel.
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_ImageData_ | Calculates sdf for the image data based on `options.channel`
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_Uint8ClampedArray_, _Uint8Array_ | Handles raw pixel data, requires `options.width` and `options.height`. Stride is detected from `width` and `height`.
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_Float32Array_, _Array_ | Handles raw numbers from `0..1` range, requires `options.width` and `options.height`. Stride is detected from `width` and `height`.
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#### Options:
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Property | Default | Meaning
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---|---|---
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`cutoff` | `0.25` | Cutoff parameter, balance between SDF inside `1` and outside `0` of glyph
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`radius` | `10` | Max length of SDF, ie. the size of SDF around the `cutoff`
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`width` | `canvas.width` | Width of input data, if array
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`height` | `canvas.height` | Height of input data, if array
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`channel` | `0` | Channel number, `0` is red, `1` is green, `2` is blue, `3` is alpha.
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`stride` | `null` | Explicitly indicate number of channels per pixel. Not needed if `height` and `width` are provided.
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## See also
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* [font-atlas-sdf](https://github.com/hughsk/font-atlas-sdf) − generate sdf atlas for a font.
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* [tiny-sdf](https://github.com/mapbox/tiny-sdf) − fast glyph signed distance field generation.
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* [optical-properties](https://github.com/dfcreative/optical-properties) − glyph optical center and bounding box calculation
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## Alternatives
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* [disttransform.wat](https://github.com/LingDong-/wasm-fun/blob/master/wat/disttransform.wat)
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## License
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(c) 2017 Dima Yv. MIT License
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Development supported by plot.ly.
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