Rework arrows falling into water and lava

Hits no longer splash; glancing and spent arrows splash where they land,
drift burning on lava, and arrows on a removed bridge sink.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/render3d.rs

@@ -2257,7 +2257,7 @@ fn draw_projectile(f: &Fx, p: f32, t: f32) {
     let c = rgba(f.col);
     let sz = f.size;
     match f.style {
-        ST_ARROW | ST_ARROW_WALL => {
+        ST_ARROW | ST_ARROW_WALL | ST_ARROW_FALL => {
             let back = at((p - 0.08).max(0.0));
             let dir = (head - back).normalize_or_zero();
             line3(head - dir * 0.3, head, 0.03, Color::from_rgba(120, 84, 48, 255));
@@ -2504,6 +2504,23 @@ fn draw_parts_solid(g: &Game) {
             _ => {}
         }
     }
+    // arrows drifting on lava: the shaft glows and chars, then crumbles
+    for p in g.parts.iter().filter(|p| p.kind == BURNING_ARROW) {
+        let life = (p.t / p.max).clamp(0.0, 1.0);
+        let k = 1.0 - life * life;
+        let bob = (p.t * 3.0 + p.x * 2.0).sin() * 0.01;
+        let mid = vec3(p.x, -LIQ_D + 0.025 + bob, p.y);
+        let dir = vec3(p.vx, 0.0, p.vy).normalize_or_zero();
+        let half = dir * (0.17 * k);
+        let wood = vec3(0.45, 0.31, 0.18);
+        let glow = vec3(1.0, 0.45, 0.1);
+        let char_ = vec3(0.08, 0.05, 0.04);
+        let c = if life < 0.5 { wood.lerp(glow, life * 2.0) } else { glow.lerp(char_, (life - 0.5) * 2.0) };
+        line3(mid - half, mid + half, 0.03, Color::new(c.x, c.y, c.z, 1.0));
+        if life < 0.6 {
+            draw_cube(mid + half, Vec3::splat(0.035), None, Color::from_rgba(200, 200, 210, 255));
+        }
+    }
     for p in g.stuck.iter().filter(|p| p.kind == ARROW) {
         let left = p.max - p.t;
         let k = if left < 10.0 { left / 10.0 } else { 1.0 };