cursor trail

src/Arts.cs

@@ -89,9 +89,30 @@ static class Arts
             );
 
             Mesh.Cube.Draw(
-                mat_mono,
-                Stretch.cursor.ToMatrix(3 * U.cm)
+                mat_justcolor,
+                Stretch.cursor.ToMatrix(V.XYZ(-1, 1, 1) * 1.2f * U.cm),
+                Color.Hex(0x000000FF).ToLinear()
             );
+            Mesh.Cube.Draw(
+                mat_mono,
+                Stretch.cursor.ToMatrix(1 * U.cm)
+            );
+
+            // particles
+            Particle[] particles = Stretch.particles;
+            for (int i = 0; i < particles.Length; i++)
+            {
+                Particle particle = particles[i];
+                Mesh.Sphere.Draw(
+                    mat_unlit,
+                    Matrix.TRS(
+                        particle.pos,
+                        particle.ori,
+                        particle.scl
+                    ),
+                    Color.Hex(0xFFFFFFFF).ToLinear()
+                );
+            }
         }
 
         // color_cube

src/Dofs.cs

@@ -12,10 +12,21 @@ static class Stretch
     public static float stretch = 0.0f;
     public static Pose cursor;
 
+    // vfx
+    public static Particle[] particles = new Particle[64];
+    static int index = 0;
+    static float trail_dist = 3 * U.cm;
+    static Vec3 last_particle_pos = Vec3.Zero;
+
     public static void Init()
     {
         to_grab = new(-0.3f, -0.25f, -0.5f, true);
         from_grab = new(-0.3f, -0.25f, -0.4f, true);
+
+        for (int i = 0; i < particles.Length; i++)
+        {
+            particles[i] = new();
+        }
     }
 
     public static void Frame()
@@ -25,6 +36,29 @@ static class Stretch
 
         Vec3 dir = delta.Normalized;
         cursor.position = to_grab.pose.position + dir * stretch * strength;
+
+        if (Vec3.Distance(cursor.position, last_particle_pos) > trail_dist)
+        {
+            index = (index + 1) % particles.Length;
+            Particle particle = particles[index];
+            particle.pos = last_particle_pos + Vec3.Direction(cursor.position, last_particle_pos) * trail_dist;
+            // particle.vel = Quat.FromAngles(Random.Shared.NextSingle() * 360, 0, 0) * Quat.FromAngles(0, Random.Shared.NextSingle() * 360, 0) * Vec3.Forward * 6.0f;
+            particle.ori = Quat.Identity;
+            particle.scl = 3 * U.mm;
+
+            last_particle_pos = particle.pos;
+        }
+
+        for (int i = 0; i < particles.Length; i++)
+        {
+            Particle particle = particles[i];
+            if (particle.vel.MagnitudeSq > float.Epsilon)
+            {
+                // particle.pos += particle.vel * Time.Stepf;
+                // particle.vel *= 1 - (3 * Time.Stepf);
+            }
+            particle.scl *= 1.0f - (3 * Time.Stepf);
+        }
     }
 
     // design