Constant CLIPPED_SURFACE 

pub const CLIPPED_SURFACE: &str = r"#version 100

//_DEFINES_

#if defined(EXTERNAL)
#extension GL_OES_EGL_image_external : require
#endif

#ifdef GL_FRAGMENT_PRECISION_HIGH
precision highp float;
#else
precision mediump float;
#endif
#if defined(EXTERNAL)
uniform samplerExternalOES tex;
#else
uniform sampler2D tex;
#endif

uniform float alpha;
uniform mat3 input_to_geo;
uniform vec2 geo_size;
uniform vec4 corner_radius;
uniform float geo_px;
varying vec2 v_coords;

#if defined(DEBUG_FLAGS)
uniform float tint;
#endif

void main() {
    vec4 colour = texture2D(tex, v_coords);
#if defined(NO_ALPHA)
    colour = vec4(colour.rgb, 1.0) * alpha;
#else
    colour = colour * alpha;
#endif
#if defined(DEBUG_FLAGS)
    if (tint == 1.0)
        colour = vec4(0.0, 0.2, 0.0, 0.2) + colour * 0.8;
#endif
    // Into the client's own pixels, then ROUNDED_CORNERS' field, unchanged.
    vec2 geo = (input_to_geo * vec3(v_coords, 1.0)).xy;
    vec2 half_size = geo_size * 0.5;
    float picked = (geo.x < half_size.x)
        ? ((geo.y < half_size.y) ? corner_radius.x : corner_radius.z)
        : ((geo.y < half_size.y) ? corner_radius.y : corner_radius.w);
    float r = min(picked, min(half_size.x, half_size.y));
    vec2 p = abs(geo - half_size) - (half_size - vec2(r));
    float away = min(max(p.x, p.y), 0.0) + length(max(p, 0.0)) - r;
    float band = 0.5 / max(geo_px, 0.0001);
    gl_FragColor = colour * (1.0 - smoothstep(-band, band, away));
}
";

Rounded corners for one client surface, drawn where it is: the surface’s texture coordinate is taken into the client’s rectangle through input_to_geo, and the distance field is ROUNDED_CORNERS’ own, measured there. So a subsurface’s corner that coincides with the client’s is cut and its others are not, and the band is one screen pixel at any zoom (geo_px), which the old shader’s own comment could not promise. tests::the_clipped_program_is_shaped_the_way_smithay_requires, and wirecheck’s case 11h, which draws a root surface and a subsurface through it.