Created
May 12, 2017 16:06
-
-
Save leekelleher/babff2d3f8d8f61d69394533dd28218c to your computer and use it in GitHub Desktop.
Playing around with HTML Canvas to tint the colour of a white logo (on transparent background) PNG
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| <html> | |
| <head> | |
| <title>canvas</title> | |
| </head> | |
| <body bgcolor="white"> | |
| <h1>canvas</h1> | |
| <canvas id="logo"></canvas> | |
| <script> | |
| var can = document.getElementById("logo"); | |
| can.width = 32; | |
| can.height = 32; | |
| var ctx = can.getContext("2d"); | |
| img = new Image(); | |
| img.src = "logo_white.png"; | |
| img.onload = function() { | |
| ctx.drawImage(img, 0, 0); | |
| var map = ctx.getImageData(0, 0, can.width, can.height); | |
| var imdata = map.data; | |
| // convert image to grayscale | |
| var r,g,b,avg; | |
| for(var p = 0, len = imdata.length; p < len; p += 4) { | |
| r = imdata[p] | |
| g = imdata[p + 1]; | |
| b = imdata[p + 2]; | |
| // alpha channel (p+3) is ignored | |
| avg = Math.floor((r + g + b) / 3); | |
| imdata[p] = imdata[p + 1] = imdata[p + 2] = avg; | |
| } | |
| ctx.putImageData(map, 0, 0); | |
| // overlay filled rectangle using composition | |
| ctx.globalCompositeOperation = "source-in"; | |
| ctx.globalAlpha = 1; | |
| ctx.fillStyle = "#991d1d"; | |
| ctx.fillRect(0, 0, can.width, can.height); | |
| }; | |
| </script> | |
| </body> | |
| </html> |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment