Wish the GPU compiles pipeline "circle" {
    {vec2 center float radius float thickness vec4 color int filled} {
        float r = radius + thickness;
        vec2 vertices[4] = vec2[4](
            center - r,
            vec2(center.x + r, center.y - r),
            vec2(center.x - r, center.y + r),
            center + r
        );
        return vertices[gl_VertexIndex];
    } {
        float dist = length(gl_FragCoord.xy - center) - radius;
        if (filled == 1) {
            return (dist < thickness) ? color : vec4(0, 0, 0, 0);
        } else {
            return (dist < thickness && dist > 0.0) ? color : vec4(0, 0, 0, 0);
        }
    }
}

When /someone/ wishes to draw a circle with /...options/ {
    set center [dict_getdef $options center ""]
    if {$center eq ""} { set center [list [dict get $options x] [dict get $options y]] }
    set radius [dict get $options radius]
    set thickness [dict get $options thickness]
    set color [getColor [dict get $options color]]
    set filled [dict_getdef $options filled false]
    set layer [dict_getdef $options layer 0]

    Wish the GPU draws pipeline "circle" with arguments \
        [list $center $radius $thickness $color [expr {$filled eq false ? 0 : 1}]] \
        layer $layer
}