render borders using shader

[debris]

This pr enables quad shader to render borders. This enables iced to easily add border param to all elements (e.g. Button) and makes the border more smooth than 2 quads rendered on top of each other.

e.g.

before:

now:

[hecrj]

This is great, @debris. Besides improving quality, it should reduce the amount of primitives too. Thank you!

I have noticed the border color was affecting the background color when the border width was 0. I have been able to fix it, but I am not sure it's the best way to do it. I know GPUs do not like branching.

Please, take a look and let me know!

[debris]

I have noticed the border color was affecting the background color when the border width was 0. I have been able to fix it, but I am not sure it's the best way to do it. I know GPUs do not like branching.

good catch! but it's easily solvable even without branching :)

[debris]

I forced push to this branch, I hope you don't mind.

changes overwritten by the push

    vec4 c = bg_color;
    float alpha = d > 0 ? clamp(radius + s - d, 0, 1) : 1;

    if(frame_width > 0) {
        float inner_radius = radius - frame_width;
        float mix_factor = smoothstep(inner_radius - s, inner_radius + s, d);
        c = mix(c, frame_color, mix_factor);
    }

    return vec4(c.xyz, c.w * alpha);

now

    float inner_radius = radius - frame_width;
    float alpha = 1.0 - smoothstep(radius - s, radius + s, d);
    float mix_factor = smoothstep(inner_radius - s, inner_radius + s, d);
    vec4 c = mix(bg_color, frame_color, min(frame_width, mix_factor));
    return vec4(c.xyz, c.w * alpha);

[debris]

Ah, I just realised that border_radius affects the rendering in a similar way. Fix on the way :)

[hecrj]

Oh, I see. I thought min and max also performed branching, but I guess they are way easier to optimize by the compiler.

Ah, I just realised that border_radius affects the rendering in a similar way. Fix on the way :)

Yeah, I think this is currently a bug present in master 😅

[debris]

I think it should be fine now