Invert Stencil for Non-Convex Polygons

[tyehle]

looks like Blend::Invert will not work when drawing to the stencil buffer. This is one of the easiest ways I've found of drawing non-convex polygons.

Could this be supported? I took a look at the draw_state code and I wasn't sure how to go about implementing such support.

[bvssvni]

There is a "draw_state" example which might help: https://github.com/PistonDevelopers/opengl_graphics/blob/master/examples/draw_state.rs

[tyehle]

Yeah I saw that, but I don't think anything in there is quite what I'd like to do. I was trying to do something like this:

|triangles, transform, g| {
    // create the stencil
    g.clear_stencil(0);
    let clip = DrawState::new_clip().blend(Blend::Invert);
    for triangle in triangles {
        Polygon::new([1.0, 1.0, 1.0, 1.0])
            .draw(triangle, &clip, transform, g);
    }

    // fill the stenciled area
    Rectangle::new([1.0, 0.0, 0.0, 1.0])
        .draw([0.0, 0.0, 100.0, 100.0], &DrawState::new_inside(), transform, g);
}

But it looks like the blend mode for the stencil drawing is always just adding because the StencilOp is always bound as gl::StencilOp(gl::REPLACE, gl::KEEP, gl::KEEP); if the stencil is Clip(val).