When I create a custom fragment shader and attach it to some sprite, the fragment shader works with some bounding rectangle of the sprite but not with the transformed quad.
When sprited rotated, this rectangle remains perpendicular to the coordinate axis. You can take a look at this example: https://jsfiddle.net/q2rux5wc/ (the red zone is this "bounding rectangle").
In my understanding, when we rotate the sprite, a different matrix should be passed into the vertex shader, it should transform the input quad, then the fragment shader works with transformed quad.
But looks like PixiJS uses another approach. So can somebody explain (or give some links) how it's implemented in PixiJS and why?