Created attachment 465824 [details]
repo of canvas drawImage issue

Here's an example where a canvas is 400x200

It sets the scale to 2x2  eg: ctx.scale(2,2)
It then copies the canvas to itself with

    ctx.drawImage(ctx.canvas
      2, 0, 398, 200,    // these values are in source pixels (ie, 400x200)
      0, 0, 199, 100);   // these values are in transformed pixels (ie, 200x100)

this works in Firefox and Chrome but fails in Safari

https://jsgist.org/?src=fedaf98f88bb57622af24481944bbefc

Attached a stand alone repo