3 files changed, 85 insertions, 8 deletions
diff --git a/src/shader/instance.wgsl b/src/shader/instance.wgsl
index fb1e0b1..a549801 100644
--- a/src/shader/instance.wgsl
+++ b/src/shader/instance.wgsl
@@ -17,8 +17,8 @@ struct Instance {
 @group(0) @binding(3) var<storage, read> cells: array<u32>;
 
 struct VertexOutput {
-    @builtin(position) clip_position: vec4<f32>,
-    @location(0) world: vec2<f32>,
+    @builtin(position) clip_position: vec4f,
+    @location(0) world: vec2f,
     @location(1) @interpolate(flat) instance: u32,
 };
 
@@ -46,7 +46,7 @@ fn vs_main(
 }
 
 @fragment
-fn fs_main(in: VertexOutput) -> @location(0) vec4<f32> {
+fn fs_main(in: VertexOutput) -> @location(0) vec4f {
     let instance = instances[in.instance];
 
     let d = in.world - instance.centre;
diff --git a/src/shader/particle.wgsl b/src/shader/particle.wgsl
index 3dd61a9..227468b 100644
--- a/src/shader/particle.wgsl
+++ b/src/shader/particle.wgsl
@@ -14,8 +14,8 @@ struct Particle {
 @group(0) @binding(2) var<storage, read> particles: array<Particle>;
 
 struct VertexOutput {
-    @builtin(position) clip_position: vec4<f32>,
-    @location(0) world: vec2<f32>,
+    @builtin(position) clip_position: vec4f,
+    @location(0) world: vec2f,
     @location(1) @interpolate(flat) instance: u32,
     @location(2) @interpolate(flat) material: u32,
     @location(3) @interpolate(flat) life: f32,
@@ -29,7 +29,7 @@ fn vs_main(
     let particle = particles[n];
 
     // (0,0),(1,0),(0,1),(1,1)
-    let corner = vec2<f32>(f32(i & 1u), f32((i >> 1u) & 1u));
+    let corner = vec2f(f32(i & 1u), f32((i >> 1u) & 1u));
     let world = particle.position + corner;
 
     var out: VertexOutput;
@@ -43,9 +43,10 @@ fn vs_main(
 }
 
 @fragment
-fn fs_main(in: VertexOutput) -> @location(0) vec4<f32> {
+fn fs_main(in: VertexOutput) -> @location(0) vec4f {
     let particle = particles[in.instance];
     // TODO can pack more in here and shift
     let c = palette[in.material];
-    return vec4<f32>(c.r, c.g, c.b, c.a * smoothstep(0.0, 1, in.life));
+    // if life is less than 1, smoothly reduce alpha to 0
+    return vec4f(c.r, c.g, c.b, c.a * smoothstep(0.0, 1, in.life));
 }
diff --git a/src/shader/vfx_line.wgsl b/src/shader/vfx_line.wgsl
new file mode 100644
index 0000000..bef7645
--- /dev/null
+++ b/src/shader/vfx_line.wgsl
@@ -0,0 +1,76 @@
+struct Camera {
+    scale: vec2f,
+    centre: vec2f,
+};
+
+struct MaterialDef {
+    color: vec4f,
+    // the length of the path segment for t
+    length: f32,
+};
+
+struct VfxLine {
+    a: vec2f,
+    b: vec2f,
+    width: f32,
+    material: u32,
+    alive_for: f32,
+    lifetime: f32,
+}
+
+@group(0) @binding(0) var<uniform> camera: Camera;
+@group(0) @binding(1) var<storage, read> materials: array<MaterialDef>;
+@group(0) @binding(2) var<storage, read> vfx_lines: array<VfxLine>;
+
+struct VertexOutput {
+    @builtin(position) clip_position: vec4f,
+    @location(0) @interpolate(flat) color: vec4f,
+    // the length of the path segment for t
+    @location(1) @interpolate(flat) length: f32,
+    @location(2) @interpolate(flat) cur_centre: f32,
+    @location(3) dist: f32,
+};
+
+@vertex
+fn vs_main(
+    @builtin(vertex_index) i: u32,
+    @builtin(instance_index) n: u32,
+) -> VertexOutput {
+    let vfx_line = vfx_lines[n];
+
+    let d = vfx_line.b - vfx_line.a;
+    // (-y, x) is a 90deg ccw rotation
+    let p = normalize(vec2f(-d.y, d.x)) * (vfx_line.width * 0.5);
+    // 0=a,1=b
+    let cv = f32(i & 1u);
+    // direction to offset the orthogonal width
+    let co = f32(i >> 1u) * 2.0 - 1.0;
+    // select a/b, add offset
+    let world = mix(vfx_line.a, vfx_line.b, cv) + p * co;
+    var out: VertexOutput;
+    out.clip_position = vec4f((world - camera.centre) * camera.scale, 0.0, 1.0);
+
+    // material
+    let material = materials[vfx_line.material];
+    out.color = material.color;
+    out.length = material.length;
+
+    // computed
+    let l = length(d);
+    out.cur_centre = (l + material.length) * (vfx_line.alive_for / vfx_line.lifetime) - (material.length / 2);
+
+    // interpolated
+    out.dist = cv * l;
+
+    return out;
+}
+
+@fragment
+fn fs_main(in: VertexOutput) -> @location(0) vec4f {
+    // distance on line of the centre of the current (w.r.t. time) line segment
+    // can do this in vertex
+    // our distance along the line vs the current centre
+    let dist_from_centre = abs(in.dist - in.cur_centre);
+    let c = in.color;
+    return vec4f(c.r, c.g, c.b, c.a * (1 - smoothstep(0.0, in.length / 2, dist_from_centre)));
+}