bevy/crates/bevy_ui_render/src/ui.wgsl

#define_import_path bevy_ui::ui_node

#import bevy_render::view::View

const TEXTURED = 1u;
const RIGHT_VERTEX = 2u;
const BOTTOM_VERTEX = 4u;
// must align with BORDER_* shader_flags from bevy_ui/render/mod.rs
const BORDER_LEFT: u32 = 256u;
const BORDER_TOP: u32 = 512u;
const BORDER_RIGHT: u32 = 1024u;
const BORDER_BOTTOM: u32 = 2048u;
const BORDER_ANY: u32 = BORDER_LEFT + BORDER_TOP + BORDER_RIGHT + BORDER_BOTTOM;

fn enabled(flags: u32, mask: u32) -> bool {
    return (flags & mask) != 0u;
}

@group(0) @binding(0) var<uniform> view: View;

struct VertexOutput {
    @location(0) uv: vec2<f32>,
    @location(1) color: vec4<f32>,

    @location(2) @interpolate(flat) size: vec2<f32>,
    @location(3) @interpolate(flat) flags: u32,
    @location(4) @interpolate(flat) radius: vec4<f32>,    
    @location(5) @interpolate(flat) border: vec4<f32>,    

    // Position relative to the center of the rectangle.
    @location(6) point: vec2<f32>,
    @builtin(position) position: vec4<f32>,
};

@vertex
fn vertex(
    @location(0) vertex_position: vec3<f32>,
    @location(1) vertex_uv: vec2<f32>,
    @location(2) vertex_color: vec4<f32>,
    @location(3) flags: u32,

    // x: top left, y: top right, z: bottom right, w: bottom left.
    @location(4) radius: vec4<f32>,

    // x: left, y: top, z: right, w: bottom.
    @location(5) border: vec4<f32>,
    @location(6) size: vec2<f32>,
    @location(7) point: vec2<f32>,
) -> VertexOutput {
    var out: VertexOutput;
    out.uv = vertex_uv;
    out.position = view.clip_from_world * vec4(vertex_position, 1.0);
    out.color = vertex_color;
    out.flags = flags;
    out.radius = radius;
    out.size = size;
    out.border = border;
    out.point = point;

    return out;
}

@group(1) @binding(0) var sprite_texture: texture_2d<f32>;
@group(1) @binding(1) var sprite_sampler: sampler;

// The returned value is the shortest distance from the given point to the boundary of the rounded 
// box.
// 
// Negative values indicate that the point is inside the rounded box, positive values that the point 
// is outside, and zero is exactly on the boundary.
//
// Arguments: 
//  - `point`        -> The function will return the distance from this point to the closest point on 
//                    the boundary.
//  - `size`         -> The maximum width and height of the box.
//  - `corner_radii` -> The radius of each rounded corner. Ordered counter clockwise starting 
//                    top left:
//                      x: top left, y: top right, z: bottom right, w: bottom left.
fn sd_rounded_box(point: vec2<f32>, size: vec2<f32>, corner_radii: vec4<f32>) -> f32 {
    // If 0.0 < y then select bottom left (w) and bottom right corner radius (z).
    // Else select top left (x) and top right corner radius (y).
    let rs = select(corner_radii.xy, corner_radii.wz, 0.0 < point.y);
    // w and z are swapped above so that both pairs are in left to right order, otherwise this second 
    // select statement would return the incorrect value for the bottom pair.
    let radius = select(rs.x, rs.y, 0.0 < point.x);
    // Vector from the corner closest to the point, to the point.
    let corner_to_point = abs(point) - 0.5 * size;
    // Vector from the center of the radius circle to the point.
    let q = corner_to_point + radius;
    // Length from center of the radius circle to the point, zeros a component if the point is not 
    // within the quadrant of the radius circle that is part of the curved corner.
    let l = length(max(q, vec2(0.0)));
    let m = min(max(q.x, q.y), 0.0);
    return l + m - radius;
}

fn sd_inset_rounded_box(point: vec2<f32>, size: vec2<f32>, radius: vec4<f32>, inset: vec4<f32>) -> f32 {
    let inner_size = size - inset.xy - inset.zw;
    let inner_center = inset.xy + 0.5 * inner_size - 0.5 * size;
    let inner_point = point - inner_center;

    var r = radius;

    // Top left corner.
    r.x = r.x - max(inset.x, inset.y);

    // Top right corner.
    r.y = r.y - max(inset.z, inset.y);

    // Bottom right corner.
    r.z = r.z - max(inset.z, inset.w); 

    // Bottom left corner.
    r.w = r.w - max(inset.x, inset.w);

    let half_size = inner_size * 0.5;
    let min_size = min(half_size.x, half_size.y);

    r = min(max(r, vec4(0.0)), vec4<f32>(min_size));

    return sd_rounded_box(inner_point, inner_size, r);
}

fn nearest_border_active(point_vs_mid: vec2<f32>, size: vec2<f32>, width: vec4<f32>, flags: u32) -> bool {
    if (flags & BORDER_ANY) == BORDER_ANY {
        return true;
    }
 
    // get point vs top left
    let point = clamp(point_vs_mid + size * 0.49999, vec2(0.0), size);
 
    let left = point.x / width.x;
    let top = point.y / width.y;
    let right = (size.x - point.x) / width.z;
    let bottom = (size.y - point.y) / width.w;
 
    let min_dist = min(min(left, top), min(right, bottom));
 
    return (enabled(flags, BORDER_LEFT) && min_dist == left) ||
        (enabled(flags, BORDER_TOP) && min_dist == top) || 
        (enabled(flags, BORDER_RIGHT) && min_dist == right) || 
        (enabled(flags, BORDER_BOTTOM) && min_dist == bottom);
}

// get alpha for antialiasing for sdf
fn antialias(distance: f32) -> f32 {
    // Using the fwidth(distance) was causing artifacts, so just use the distance.
    return saturate(0.5 - distance);
}

fn draw_uinode_border(
    color: vec4<f32>,
    point: vec2<f32>,
    size: vec2<f32>,
    radius: vec4<f32>,
    border: vec4<f32>,
    flags: u32,
) -> vec4<f32> {
    // Signed distances. The magnitude is the distance of the point from the edge of the shape.
    // * Negative values indicate that the point is inside the shape.
    // * Zero values indicate the point is on the edge of the shape.
    // * Positive values indicate the point is outside the shape.

    // Signed distance from the exterior boundary.
    let external_distance = sd_rounded_box(point, size, radius);

    // Signed distance from the border's internal edge (the signed distance is negative if the point 
    // is inside the rect but not on the border).
    // If the border size is set to zero, this is the same as the external distance.
    let internal_distance = sd_inset_rounded_box(point, size, radius, border);

    // Signed distance from the border (the intersection of the rect with its border).
    // Points inside the border have negative signed distance. Any point outside the border, whether 
    // outside the outside edge, or inside the inner edge have positive signed distance.
    let border_distance = max(external_distance, -internal_distance);

    // check if this node should apply color for the nearest border
    let nearest_border = select(0.0, 1.0, nearest_border_active(point, size, border, flags));

#ifdef ANTI_ALIAS
    // At external edges with no border, `border_distance` is equal to zero. 
    // This select statement ensures we only perform anti-aliasing where a non-zero width border 
    // is present, otherwise an outline about the external boundary would be drawn even without 
    // a border.
    let t = select(1.0 - step(0.0, border_distance), antialias(border_distance), external_distance < internal_distance);
#else
    let t = 1.0 - step(0.0, border_distance);
#endif

    // Blend mode ALPHA_BLENDING is used for UI elements, so we don't premultiply alpha here.
    return vec4(color.rgb, saturate(color.a * t * nearest_border));
}

fn draw_uinode_background(
    color: vec4<f32>,
    point: vec2<f32>,
    size: vec2<f32>,
    radius: vec4<f32>,
    border: vec4<f32>,
) -> vec4<f32> {
    // When drawing the background only draw the internal area and not the border.
    let internal_distance = sd_inset_rounded_box(point, size, radius, border);

#ifdef ANTI_ALIAS
    let t = antialias(internal_distance);
#else
    let t = 1.0 - step(0.0, internal_distance);
#endif

    return vec4(color.rgb, saturate(color.a * t));
}

@fragment
fn fragment(in: VertexOutput) -> @location(0) vec4<f32> {
    let texture_color = textureSample(sprite_texture, sprite_sampler, in.uv);

    // Only use the color sampled from the texture if the `TEXTURED` flag is enabled. 
    // This allows us to draw both textured and untextured shapes together in the same batch.
    let color = select(in.color, in.color * texture_color, enabled(in.flags, TEXTURED));

    if enabled(in.flags, BORDER_ANY) {
        return draw_uinode_border(color, in.point, in.size, in.radius, in.border, in.flags);
    } else {
        return draw_uinode_background(color, in.point, in.size, in.radius, in.border);
    }
}