Trails shrinks over time

voxygen/src/render/pipelines/trail.rs

@@ -1,6 +1,9 @@
 use super::super::{AaMode, GlobalsLayouts, Vertex as VertexTrait};
 use bytemuck::{Pod, Zeroable};
-use std::mem;
+use std::{
+    mem,
+    ops::{Add, Mul},
+};
 
 #[repr(C)]
 #[derive(Copy, Clone, Debug, Zeroable, Pod, PartialEq)]
@@ -22,6 +25,26 @@ impl Vertex {
     pub fn zero() -> Self { Self { pos: [0.0; 3] } }
 }
 
+impl Mul<f32> for Vertex {
+    type Output = Self;
+
+    fn mul(self, val: f32) -> Self::Output {
+        Self {
+            pos: self.pos.map(|a| a * val),
+        }
+    }
+}
+
+impl Add<Vertex> for Vertex {
+    type Output = Self;
+
+    fn add(self, other: Self) -> Self::Output {
+        Self {
+            pos: self.pos.zip(other.pos).map(|(a, b)| a + b),
+        }
+    }
+}
+
 impl VertexTrait for Vertex {
     const QUADS_INDEX: Option<wgpu::IndexFormat> = Some(wgpu::IndexFormat::Uint16);
     const STRIDE: wgpu::BufferAddress = mem::size_of::<Self>() as wgpu::BufferAddress;

voxygen/src/scene/trail.rs

@@ -21,6 +21,7 @@ pub struct TrailMgr {
 }
 
 const TRAIL_DYNAMIC_MODEL_SIZE: usize = 15;
+const TRAIL_SHRINKAGE: f32 = 0.8;
 
 impl TrailMgr {
     pub fn new(renderer: &mut Renderer) -> Self {
@@ -39,8 +40,18 @@ impl TrailMgr {
             // Update offset
             self.offset = (self.offset + 1) % TRAIL_DYNAMIC_MODEL_SIZE;
 
-            // Reset quad for each entity mesh at new offset
             self.entity_meshes.values_mut().for_each(|mesh| {
+                // Shrink size of each quad over time
+                let vertices = mesh.vertices_mut_vec();
+                for i in 0..TRAIL_DYNAMIC_MODEL_SIZE {
+                    // Verts per quad are in b, c, a, d order
+                    vertices[i * 4 + 2] = vertices[i * 4 + 2] * TRAIL_SHRINKAGE
+                        + vertices[i * 4] * (1.0 - TRAIL_SHRINKAGE);
+                    vertices[i * 4 + 3] = vertices[i * 4 + 3] * TRAIL_SHRINKAGE
+                        + vertices[i * 4 + 1] * (1.0 - TRAIL_SHRINKAGE);
+                }
+
+                // Reset quad for each entity mesh at new offset
                 let zero = TrailVertex::zero();
                 mesh.replace_quad(self.offset * 4, Quad::new(zero, zero, zero, zero));
             });