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Helper to test how the browser blends overlayed semi-transparent colors
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| /** | |
| * Helper to test how alpha-transparent colors are layered in the browser. | |
| * | |
| * @example | |
| * blendColors('255 0 0 / 20%', '60 60 40 / 30%', '128 96 44 / 60%') | |
| * // -> {r: 128, g: 84, b: 40, a: 0.7764705882352941} | |
| */ | |
| function overlayColors(...colors) { | |
| let canvas; | |
| if (typeof OffscreenCanvas === 'function') { | |
| canvas = new OffscreenCanvas(1, 1); | |
| } else { | |
| canvas = document.createElement('canvas'); | |
| canvas.width = canvas.height = 1; | |
| } | |
| const ctx = canvas.getContext('2d'); | |
| colors.forEach(col => { | |
| ctx.fillStyle = `rgb(${col})`; | |
| ctx.rect(0, 0, 1, 1) | |
| ctx.fill(); | |
| }); | |
| const [r,g,b,a] = ctx.getImageData(0,0,1,1).data; | |
| return {r, g, b, a: (a / 255) } | |
| } |
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