1import bevy_render::{view::View, maths::affine3_to_square};
2
3@group(0) @binding(0) var<uniform> view: View;
4
5
6struct LineGizmoUniform {
7    world_from_local: mat3x4<f32>,
8    line_width: f32,
9    depth_bias: f32,
10    resolution: u32,
11    @if(SIXTEEN_BYTE_ALIGNMENT)
12    // WebGL2 structs must be 16 byte aligned.
13    _padding: f32,
14}
15
16@group(1) @binding(0) var<uniform> joints_gizmo: LineGizmoUniform;
17
18struct VertexInput {
19    @location(0) position_a: vec3<f32>,
20    @location(1) position_b: vec3<f32>,
21    @location(2) position_c: vec3<f32>,
22    @location(3) color: vec4<f32>,
23    @builtin(vertex_index) index: u32,
24};
25
26struct VertexOutput {
27    @builtin(position) clip_position: vec4<f32>,
28    @location(0) color: vec4<f32>,
29};
30
31const EPSILON: f32 = 4.88e-04;
32
33@vertex
34fn vertex_bevel(vertex: VertexInput) -> VertexOutput {
35    var positions = array<vec2<f32>, 3>(
36        vec2(0, 0),
37        vec2(0, 0.5),
38        vec2(0.5, 0),
39    );
40    var position = positions[vertex.index];
41
42    let world_from_local = affine3_to_square(joints_gizmo.world_from_local);
43
44    var clip_a = view.clip_from_world * world_from_local * vec4(vertex.position_a, 1.);
45    var clip_b = view.clip_from_world * world_from_local * vec4(vertex.position_b, 1.);
46    var clip_c = view.clip_from_world * world_from_local * vec4(vertex.position_c, 1.);
47
48    // Manual near plane clipping to avoid errors when doing the perspective divide inside this shader.
49    clip_a = clip_near_plane(clip_a, clip_c);
50    clip_b = clip_near_plane(clip_b, clip_a);
51    clip_c = clip_near_plane(clip_c, clip_b);
52    clip_a = clip_near_plane(clip_a, clip_c);
53
54    let resolution = view.viewport.zw;
55    let screen_a = resolution * (0.5 * clip_a.xy / clip_a.w + 0.5);
56    let screen_b = resolution * (0.5 * clip_b.xy / clip_b.w + 0.5);
57    let screen_c = resolution * (0.5 * clip_c.xy / clip_c.w + 0.5);
58
59    var color = vertex.color;
60    var line_width = joints_gizmo.line_width;
61
62    @if(PERSPECTIVE)
63    line_width /= clip_b.w;
64
65    // Line thinness fade from https://acegikmo.com/shapes/docs/#anti-aliasing
66    if line_width > 0.0 && line_width < 1. {
67        color.a *= line_width;
68        line_width = 1.;
69    }
70
71    let ab = normalize(screen_b - screen_a);
72    let cb = normalize(screen_b - screen_c);
73    let ab_norm = vec2(-ab.y, ab.x);
74    let cb_norm = vec2(cb.y, -cb.x);
75    let tangent = normalize(ab - cb);
76    let normal = vec2(-tangent.y, tangent.x);
77    let sigma = sign(dot(ab + cb, normal));
78
79    var p0 = line_width * sigma * ab_norm;
80    var p1 = line_width * sigma * cb_norm;
81
82    let screen = screen_b + position.x * p0 + position.y * p1;
83
84    let depth = depth(clip_b);
85
86    var clip_position = vec4(clip_b.w * ((2. * screen) / resolution - 1.), depth, clip_b.w);
87    return VertexOutput(clip_position, color);
88}
89
90@vertex
91fn vertex_miter(vertex: VertexInput) -> VertexOutput {
92    var positions = array<vec3<f32>, 6>(
93        vec3(0, 0, 0),
94        vec3(0.5, 0, 0),
95        vec3(0, 0.5, 0),
96        vec3(0, 0, 0),
97        vec3(0, 0.5, 0),
98        vec3(0, 0, 0.5),
99    );
100    var position = positions[vertex.index];
101
102    let world_from_local = affine3_to_square(joints_gizmo.world_from_local);
103
104    var clip_a = view.clip_from_world * world_from_local * vec4(vertex.position_a, 1.);
105    var clip_b = view.clip_from_world * world_from_local * vec4(vertex.position_b, 1.);
106    var clip_c = view.clip_from_world * world_from_local * vec4(vertex.position_c, 1.);
107
108    // Manual near plane clipping to avoid errors when doing the perspective divide inside this shader.
109    clip_a = clip_near_plane(clip_a, clip_c);
110    clip_b = clip_near_plane(clip_b, clip_a);
111    clip_c = clip_near_plane(clip_c, clip_b);
112    clip_a = clip_near_plane(clip_a, clip_c);
113
114    let resolution = view.viewport.zw;
115    let screen_a = resolution * (0.5 * clip_a.xy / clip_a.w + 0.5);
116    let screen_b = resolution * (0.5 * clip_b.xy / clip_b.w + 0.5);
117    let screen_c = resolution * (0.5 * clip_c.xy / clip_c.w + 0.5);
118
119    var color = vertex.color;
120    var line_width = joints_gizmo.line_width;
121
122    @if(PERSPECTIVE)
123    line_width /= clip_b.w;
124
125    // Line thinness fade from https://acegikmo.com/shapes/docs/#anti-aliasing
126    if line_width > 0.0 && line_width < 1. {
127        color.a *= line_width;
128        line_width = 1.;
129    }
130
131    let ab = normalize(screen_b - screen_a);
132    let cb = normalize(screen_b - screen_c);
133    let ab_norm = vec2(-ab.y, ab.x);
134    let cb_norm = vec2(cb.y, -cb.x);
135    let tangent = normalize(ab - cb);
136    let normal = vec2(-tangent.y, tangent.x);
137    let sigma = sign(dot(ab + cb, normal));
138
139    var p0 = line_width * sigma * ab_norm;
140    var p1 = line_width * sigma * normal / dot(normal, ab_norm);
141    var p2 = line_width * sigma * cb_norm;
142    
143    var screen = screen_b + position.x * p0 + position.y * p1 + position.z * p2;
144
145    var depth = depth(clip_b);
146
147    var clip_position = vec4(clip_b.w * ((2. * screen) / resolution - 1.), depth, clip_b.w);
148    return VertexOutput(clip_position, color);
149}
150
151@vertex
152fn vertex_round(vertex: VertexInput) -> VertexOutput {
153    let world_from_local = affine3_to_square(joints_gizmo.world_from_local);
154
155    var clip_a = view.clip_from_world * world_from_local * vec4(vertex.position_a, 1.);
156    var clip_b = view.clip_from_world * world_from_local * vec4(vertex.position_b, 1.);
157    var clip_c = view.clip_from_world * world_from_local * vec4(vertex.position_c, 1.);
158
159    // Manual near plane clipping to avoid errors when doing the perspective divide inside this shader.
160    clip_a = clip_near_plane(clip_a, clip_c);
161    clip_b = clip_near_plane(clip_b, clip_a);
162    clip_c = clip_near_plane(clip_c, clip_b);
163    clip_a = clip_near_plane(clip_a, clip_c);
164
165    let resolution = view.viewport.zw;
166    let screen_a = resolution * (0.5 * clip_a.xy / clip_a.w + 0.5);
167    let screen_b = resolution * (0.5 * clip_b.xy / clip_b.w + 0.5);
168    let screen_c = resolution * (0.5 * clip_c.xy / clip_c.w + 0.5);
169
170    var color = vertex.color;
171    var line_width = joints_gizmo.line_width;
172
173    @if(PERSPECTIVE)
174    line_width /= clip_b.w;
175
176    // Line thinness fade from https://acegikmo.com/shapes/docs/#anti-aliasing
177    if line_width > 0.0 && line_width < 1. {
178        color.a *= line_width;
179        line_width = 1.;
180    }
181
182    let ab = normalize(screen_b - screen_a);
183    let cb = normalize(screen_b - screen_c);
184    let ab_norm = vec2(-ab.y, ab.x);
185    let cb_norm = vec2(cb.y, -cb.x);
186
187    // We render `joints_gizmo.resolution`triangles. The vertices in each triangle are ordered as follows:
188    // - 0: The 'center' vertex at `screen_b`.
189    // - 1: The vertex closer to the ab line.
190    // - 2: The vertex closer to the cb line. 
191    var in_triangle_index = f32(vertex.index) % 3.0;
192    var tri_index = floor(f32(vertex.index) / 3.0);
193    var radius = sign(in_triangle_index) * 0.5 * line_width;
194    var theta = acos(dot(ab_norm, cb_norm));
195    let sigma = sign(dot(ab_norm, cb));
196    var angle = theta * (tri_index + in_triangle_index - 1) / f32(joints_gizmo.resolution);
197    var position_x = sigma * radius * cos(angle);
198    var position_y = radius * sin(angle);
199
200    var screen = screen_b + position_x * ab_norm + position_y * ab;
201
202    var depth = depth(clip_b);
203
204    var clip_position = vec4(clip_b.w * ((2. * screen) / resolution - 1.), depth, clip_b.w);
205    return VertexOutput(clip_position, color);
206}
207
208fn clip_near_plane(a: vec4<f32>, b: vec4<f32>) -> vec4<f32> {
209    // Move a if a is behind the near plane and b is in front. 
210    if a.z > a.w && b.z <= b.w {
211        // Interpolate a towards b until it's at the near plane.
212        let distance_a = a.z - a.w;
213        let distance_b = b.z - b.w;
214        // Add an epsilon to the interpolator to ensure that the point is
215        // not just behind the clip plane due to floating-point imprecision.
216        let t = distance_a / (distance_a - distance_b) + EPSILON;
217        return mix(a, b, t);
218    }
219    return a;
220}
221
222fn depth(clip: vec4<f32>) -> f32 {
223    var depth: f32;
224    if joints_gizmo.depth_bias >= 0. {
225        depth = clip.z * (1. - joints_gizmo.depth_bias);
226    } else {
227        // depth * (clip.w / depth)^-depth_bias. So that when -depth_bias is 1.0, this is equal to clip.w
228        // and when equal to 0.0, it is exactly equal to depth.
229        // the epsilon is here to prevent the depth from exceeding clip.w when -depth_bias = 1.0
230        // clip.w represents the near plane in homogeneous clip space in bevy, having a depth
231        // of this value means nothing can be in front of this
232        // The reason this uses an exponential function is that it makes it much easier for the
233        // user to chose a value that is convenient for them
234        depth = clip.z * exp2(-joints_gizmo.depth_bias * log2(clip.w / clip.z - EPSILON));
235    }
236    return depth;
237}
238
239struct FragmentInput {
240    @location(0) color: vec4<f32>,
241};
242
243struct FragmentOutput {
244    @location(0) color: vec4<f32>,
245};
246
247@fragment
248fn fragment(in: FragmentInput) -> FragmentOutput {
249    // return FragmentOutput(vec4(1, 1, 1, 1));
250    return FragmentOutput(in.color);
251}