Distort Image into Isosceles Trapezoid with Canvas
One option might be to use the 3D transforms of WebGL in a browser, but that’s a really heavy solution and there currently aren’t any WebGL canvas libraries for Node.JS. It would be better if we could use just a 2D canvas drawing context.
So how can we accomplish this without 3D transforms? Read on to find out!
It’s best begin with the end in mind, and a pictures worth a thousand works, so essentially we’re looking to be able to turn an image like this:
Into an image like this:
In theory, an isosceles trapezoid transform seems simple enough. Take a canvas, make another canvas of equal size, and draw the first canvas to the second canvas row-by-row, calculating the width and x position of each row based on the y position in the image. Let’s try that.
Note: In these examples, I’m using Automattic’s canvas library on NPM, but this can easily be adapted to work in a browser.