Incorrect linear gradients

[Yevhenii Reizner]

use raqote::*;

fn main() {
    let mut dt = DrawTarget::new(200, 200);

    let mut pb = PathBuilder::new();
    pb.move_to( 20.0,  20.0);
    pb.line_to(180.0,  20.0);
    pb.line_to(180.0, 180.0);
    pb.line_to( 20.0, 180.0);
    pb.close();
    let path = pb.finish();

    let gradient = Source::LinearGradient(
        Gradient {
            stops: vec![
                GradientStop {
                    position: 0.0,
                    color: 0xff000000,
                },
                GradientStop {
                    position: 1.0,
                    color: 0xffffffff,
                },
            ],
        },
        Transform::default(),
    );
    dt.fill(&path, &gradient, &DrawOptions::new());

    dt.write_png("test.png").unwrap();
}

Produces:

But if we swap colors, we will get:

[Jeff Muizelaar]

I'm pretty sure this is just an artifact of the implicit with of a linear gradient being 256 device pixels. You should use the 'new_linear_gradient' and 'new_radial_gradient' helpers to get more reasonable results. I suspect we'll eventually want to make Source opaque and just have the helper api's around that do the conversion to the internal representation.