Added particle trail effect

src/renderer/cursor_renderer/cursor_vfx.rs

@@ -1,7 +1,7 @@
 use skulpin::skia_safe::{paint::Style, BlendMode, Canvas, Color, Paint, Point, Rect};
 
-use crate::editor::{Colors, Cursor};
 use super::animation_utils::*;
+use crate::editor::{Colors, Cursor};
 
 pub trait CursorVFX {
     fn update(&mut self, current_cursor_destination: Point, dt: f32) -> bool;
@@ -35,7 +35,7 @@ impl PointHighlight {
 impl CursorVFX for PointHighlight {
     fn update(&mut self, _current_cursor_destination: Point, dt: f32) -> bool {
         self.t = (self.t + dt * 5.0).min(1.0); // TODO - speed config
-        return self.t < 1.0;
+        self.t < 1.0
     }
 
     fn restart(&mut self, position: Point) {
@@ -82,3 +82,110 @@ impl CursorVFX for PointHighlight {
         }
     }
 }
+
+#[derive(Clone)]
+struct ParticleData {
+    pos: Point,
+    speed: Point,
+    lifetime: f32,
+}
+
+pub struct ParticleTrail {
+    particles: Vec<ParticleData>,
+    previous_cursor_dest: Point,
+}
+
+impl ParticleTrail {
+    pub fn new() -> ParticleTrail {
+        ParticleTrail {
+            particles: vec![],
+            previous_cursor_dest: Point::new(0.0, 0.0),
+        }
+    }
+
+    fn add_particle(&mut self, pos: Point, speed: Point, lifetime: f32) {
+        self.particles.push(ParticleData {
+            pos,
+            speed,
+            lifetime,
+        });
+    }
+
+    // Note this method doesn't keep particles in order
+    fn remove_particle(&mut self, idx: usize) {
+        self.particles[idx] = self.particles[self.particles.len() - 1].clone();
+        self.particles.pop();
+    }
+}
+
+const PARTICLE_DENSITY: f32 = 0.05; // TODO - density should be based on font size too
+const PARTICLE_LIFETIME: f32 = 1.0;
+
+impl CursorVFX for ParticleTrail {
+    fn update(&mut self, current_cursor_dest: Point, dt: f32) -> bool {
+        // Update lifetimes and remove dead particles
+        let mut i = 0;
+        while i < self.particles.len() {
+            let particle: &mut ParticleData = &mut self.particles[i];
+            particle.lifetime -= dt;
+            if particle.lifetime <= 0.0 {
+                self.remove_particle(i);
+            } else {
+                i += 1;
+            }
+        }
+
+        for i in 0..self.particles.len() {
+            let particle = &mut self.particles[i];
+            particle.pos += particle.speed * dt;
+        }
+
+        // Spawn new particles
+        if current_cursor_dest != self.previous_cursor_dest {
+            let travel = current_cursor_dest - self.previous_cursor_dest;
+            let travel_distance = travel.length();
+            let particle_count = (travel_distance * PARTICLE_DENSITY) as usize;
+
+            let prev_p = self.previous_cursor_dest;
+            for i in 0..particle_count {
+                let t = i as f32 / (particle_count as f32 - 1.0);
+                let rand_seed = t * std::f32::consts::E * 20.0;
+                let rand = Point::new(rand_seed.sin(), rand_seed.cos());
+
+                let pos = prev_p + travel * (t + 0.3 * rand.x / particle_count as f32);
+
+                self.add_particle(pos, rand * 10.0, t * PARTICLE_LIFETIME);
+            }
+
+            self.previous_cursor_dest = current_cursor_dest;
+        }
+
+        // Keep animating as long as there are particles alive
+        !self.particles.is_empty()
+    }
+
+    fn restart(&mut self, position: Point) {}
+
+    fn render(&self, canvas: &mut Canvas, cursor: &Cursor, colors: &Colors, font_size: (f32, f32)) {
+        let mut paint = Paint::new(skulpin::skia_safe::colors::WHITE, None);
+        paint.set_style(Style::Stroke);
+        paint.set_stroke_width(font_size.1 * 0.2);
+        let base_color: Color = cursor.background(&colors).to_color();
+
+        paint.set_blend_mode(BlendMode::SrcOver);
+
+        self.particles.iter().for_each(|particle| {
+            let l = particle.lifetime / PARTICLE_LIFETIME;
+            let alpha = (l * 255.0) as u8;
+            let color = Color::from_argb(alpha, base_color.r(), base_color.g(), base_color.b());
+            paint.set_color(color);
+
+            let radius = font_size.0 * 0.5 * l;
+            let hr = radius * 0.5;
+
+            let rect = Rect::from_xywh(particle.pos.x - hr, particle.pos.y - hr, radius, radius);
+            canvas.draw_oval(&rect, &paint);
+            //canvas.draw_rect(&rect, &paint);
+        });
+    }
+}

src/renderer/cursor_renderer/mod.rs

@@ -194,7 +194,8 @@ impl CursorRenderer {
             command_line_delay: 0,
             blink_status: BlinkStatus::new(),
             previous_cursor_shape: None,
-            cursor_vfx: Box::new(PointHighlight::new(Point{x:0.0, y:0.0}, HighlightMode::Ripple)),
+            //cursor_vfx: Box::new(PointHighlight::new(Point{x:0.0, y:0.0}, HighlightMode::Ripple)),
+            cursor_vfx: Box::new(ParticleTrail::new()),
         };
         renderer.set_cursor_shape(&CursorShape::Block, DEFAULT_CELL_PERCENTAGE);
         renderer