1// TODO use common view binding
2#import bevy_render::{view::View, maths::affine3_to_square}
3
4@group(0) @binding(0) var<uniform> view: View;
5
6
7struct LineGizmoUniform {
8    world_from_local: mat3x4<f32>,
9    line_width: f32,
10    depth_bias: f32,
11    _joints_resolution: u32,
12    gap_scale: f32,
13    line_scale: f32,
14#ifdef SIXTEEN_BYTE_ALIGNMENT
15    // WebGL2 structs must be 16 byte aligned.
16    _padding: vec3<f32>,
17#endif
18}
19
20@group(1) @binding(0) var<uniform> line_gizmo: LineGizmoUniform;
21
22struct VertexInput {
23    @location(0) position_a: vec3<f32>,
24    @location(1) position_b: vec3<f32>,
25    @location(2) color_a: vec4<f32>,
26    @location(3) color_b: vec4<f32>,
27    @builtin(vertex_index) index: u32,
28};
29
30struct VertexOutput {
31    @builtin(position) clip_position: vec4<f32>,
32    @location(0) color: vec4<f32>,
33    @location(1) uv: f32,
34    @location(2) line_fraction: f32,
35};
36
37const EPSILON: f32 = 4.88e-04;
38
39@vertex
40fn vertex(vertex: VertexInput) -> VertexOutput {
41    var positions = array<vec2<f32>, 6>(
42        vec2(-0.5, 0.),
43        vec2(-0.5, 1.),
44        vec2(0.5, 1.),
45        vec2(-0.5, 0.),
46        vec2(0.5, 1.),
47        vec2(0.5, 0.)
48    );
49    let position = positions[vertex.index];
50
51    let world_from_local = affine3_to_square(line_gizmo.world_from_local);
52
53    // algorithm based on https://wwwtyro.net/2019/11/18/instanced-lines.html
54    var clip_a = view.clip_from_world * world_from_local * vec4(vertex.position_a, 1.);
55    var clip_b = view.clip_from_world * world_from_local * vec4(vertex.position_b, 1.);
56
57    // Manual near plane clipping to avoid errors when doing the perspective divide inside this shader.
58    clip_a = clip_near_plane(clip_a, clip_b);
59    clip_b = clip_near_plane(clip_b, clip_a);
60    let clip = mix(clip_a, clip_b, position.y);
61
62    let resolution = view.viewport.zw;
63    let screen_a = resolution * (0.5 * clip_a.xy / clip_a.w + 0.5);
64    let screen_b = resolution * (0.5 * clip_b.xy / clip_b.w + 0.5);
65
66    let y_basis = normalize(screen_b - screen_a);
67    let x_basis = vec2(-y_basis.y, y_basis.x);
68
69    var color = mix(vertex.color_a, vertex.color_b, position.y);
70
71    var line_width = line_gizmo.line_width;
72    var alpha = 1.;
73
74    var uv: f32;
75#ifdef PERSPECTIVE
76    line_width /= clip.w;
77
78    // get height of near clipping plane in world space
79    let pos0 = view.view_from_clip * vec4(0, -1, 0, 1); // Bottom of the screen
80    let pos1 = view.view_from_clip * vec4(0, 1, 0, 1); // Top of the screen
81    let near_clipping_plane_height = length(pos0.xyz - pos1.xyz);
82
83    // We can't use vertex.position_X because we may have changed the clip positions with clip_near_plane
84    let position_a = view.world_from_clip * clip_a;
85    let position_b = view.world_from_clip * clip_b;
86    let world_distance = length(position_a.xyz - position_b.xyz);
87
88    // Offset to compensate for moved clip positions. If removed dots on lines will slide when position a is ofscreen.
89    let clipped_offset = length(position_a.xyz - vertex.position_a);
90
91    uv = (clipped_offset + position.y * world_distance) * resolution.y / near_clipping_plane_height / line_gizmo.line_width;
92#else
93    // Get the distance of b to the camera along camera axes
94    let camera_b = view.view_from_clip * clip_b;
95
96    // This differentiates between orthographic and perspective cameras.
97    // For orthographic cameras no depth adaptment (depth_adaptment = 1) is needed.
98    var depth_adaptment: f32;
99    if (clip_b.w == 1.0) {
100        depth_adaptment = 1.0;
101    }
102    else {
103        depth_adaptment = -camera_b.z;
104    }
105    uv = position.y * depth_adaptment * length(screen_b - screen_a) / line_gizmo.line_width;
106#endif
107
108    // Line thinness fade from https://acegikmo.com/shapes/docs/#anti-aliasing
109    if line_width > 0.0 && line_width < 1. {
110        color.a *= line_width;
111        line_width = 1.;
112    }
113
114    let x_offset = line_width * position.x * x_basis;
115    let screen = mix(screen_a, screen_b, position.y) + x_offset;
116
117    var depth: f32;
118    if line_gizmo.depth_bias >= 0. {
119        depth = clip.z * (1. - line_gizmo.depth_bias);
120    } else {
121        // depth * (clip.w / depth)^-depth_bias. So that when -depth_bias is 1.0, this is equal to clip.w
122        // and when equal to 0.0, it is exactly equal to depth.
123        // the epsilon is here to prevent the depth from exceeding clip.w when -depth_bias = 1.0
124        // clip.w represents the near plane in homogeneous clip space in bevy, having a depth
125        // of this value means nothing can be in front of this
126        // The reason this uses an exponential function is that it makes it much easier for the
127        // user to chose a value that is convenient for them
128        depth = clip.z * exp2(-line_gizmo.depth_bias * log2(clip.w / clip.z - EPSILON));
129    }
130
131    var clip_position = vec4(clip.w * ((2. * screen) / resolution - 1.), depth, clip.w);
132
133    let line_fraction = 2.0 * line_gizmo.line_scale / (line_gizmo.gap_scale + line_gizmo.line_scale);
134    uv /= (line_gizmo.gap_scale + line_gizmo.line_scale) / 2.0;
135    return VertexOutput(clip_position, color, uv, line_fraction);
136}
137
138fn clip_near_plane(a: vec4<f32>, b: vec4<f32>) -> vec4<f32> {
139    // Move a if a is behind the near plane and b is in front.
140    // equivalent to `a.z / a.w > 1.0 && b.z / b.w <= 1.0` but avoids divs
141    if a.z * sign(a.w) > abs(a.w) && b.z * sign(b.w) <= abs(b.w) {
142        // Interpolate a towards b until it's at the near plane.
143        let distance_a = a.z - a.w;
144        let distance_b = b.z - b.w;
145        // Add an epsilon to the interpolator to ensure that the point is
146        // not just behind the clip plane due to floating-point imprecision.
147        let t = distance_a / (distance_a - distance_b) + EPSILON;
148        return mix(a, b, t);
149    }
150    return a;
151}
152
153struct FragmentInput {
154    @builtin(position) position: vec4<f32>,
155    @location(0) color: vec4<f32>,
156    @location(1) uv: f32,
157    @location(2) line_fraction: f32,
158};
159
160struct FragmentOutput {
161    @location(0) color: vec4<f32>,
162};
163
164@fragment
165fn fragment_solid(in: FragmentInput) -> FragmentOutput {
166    return FragmentOutput(in.color);
167}
168@fragment
169fn fragment_dotted(in: FragmentInput) -> FragmentOutput {
170    var alpha: f32;
171#ifdef PERSPECTIVE
172    alpha = 1 - floor(in.uv % 2.0);
173#else
174    alpha = 1 - floor((in.uv * in.position.w) % 2.0);
175#endif
176    
177    return FragmentOutput(vec4(in.color.xyz, in.color.w * alpha));
178}
179
180@fragment
181fn fragment_dashed(in: FragmentInput) -> FragmentOutput {
182#ifdef PERSPECTIVE
183    let uv = in.uv;
184#else
185    let uv = in.uv * in.position.w;
186#endif
187    let alpha = 1.0 - floor(min((uv % 2.0) / in.line_fraction, 1.0));
188    
189    return FragmentOutput(vec4(in.color.xyz, in.color.w * alpha));
190}