Canvas's don't necessarily draw right-side-up.

[icefoxen]

See https://github.com/ggez/ggez/blob/master/examples/shadows.rs#L375-L383 for an example of such.

This is Yet Another Little Coordinate Goof that needs to be fixed. Once you fix it, make sure that things drawn on canvases such as text and images get drawn right-side-up still!

[icefoxen]

They totally don't draw right-side up, sigh. And fixing that means they flip on awkward axes for some stupid reason. I suspect the exciting stuff happens on DrawParams::into_matrix() IIRC, but it's still a PITA.

The following code makes render_to_image draw in the right spot, but breaks shadows even when you remove the existing hack to make things draw upright:

impl Drawable for Canvas {
    fn draw_ex(&self, ctx: &mut Context, param: DrawParam) -> GameResult<()> {
        let mut flipped_param = param;
        flipped_param.scale.y *= -1.0;
        flipped_param.dest.y += self.image.height() as f32 / 2.0;
        self.image.draw_ex(ctx, flipped_param)
    }
    ...
}

[termhn]

Hmm. I think this could be caused by a coordinate transformation happening twice. IIRC: we do the first coordinate transformation when we draw onto the canvas by making it have "top left = 0,0 with pixel coordinates", then we apply that same transformation again when drawing the canvas onto the main render target. Perhaps we should disable the first set of coordinate transformations for canvases. I've only thought about this for a couple minutes and haven't been in the ggez world for a little while but this is what I suspect is the root cause of the issue.

[icefoxen]

Started working on this in commit d6ef5b7

I hate coordinate transforms so so much. augh.