Verlet ropes :)

1 files changed, 80 insertions, 0 deletions

diff --git a/src/verlet.odin b/src/verlet.odin
new file mode 100644
index 0000000..1434109
--- /dev/null
+++ b/src/verlet.odin
@@ -0,0 +1,80 @@
+package demonchime
+
+import "core:math"
+import "core:math/linalg"
+
+import rl "vendor:raylib"
+
+import "phys"
+
+VERLET_STEPS :: 50
+VERLET_MIN_DIST_TO_PLAYER :: 8
+
+Verlet_Node :: struct {
+  pos: Vec2,
+  prev_pos: Vec2,
+  accel: Vec2,
+  is_static: bool,
+}
+
+Verlet_Rope :: struct {
+  nodes: []Verlet_Node,
+  node_length: f32,
+}
+
+create_verlet_node :: proc(pos: Vec2, is_static := false) -> Verlet_Node {
+  return Verlet_Node{
+    pos = pos,
+    prev_pos = pos,
+    is_static = is_static,
+  }
+}
+
+update_verlet_node :: proc(node: ^Verlet_Node) {
+  if node.is_static {
+    return
+  }
+
+  dt: f32 = FIXED_UPDATE_RATE
+
+  node.accel.y += GRAVITY
+
+  player_pos := phys.get_position(player.body)
+  player_dist := linalg.distance(node.pos, player_pos) 
+  if player_dist < VERLET_MIN_DIST_TO_PLAYER {
+    dir := linalg.normalize(node.pos - player_pos)
+    node.pos = player_pos + dir * VERLET_MIN_DIST_TO_PLAYER
+  }
+
+  prev_pos := node.pos
+  node.pos = (node.pos * 2 - node.prev_pos) + node.accel * (dt*dt)
+  node.prev_pos = prev_pos
+
+  node.accel = {}
+}
+
+update_verlet_rope :: proc(rope: ^Verlet_Rope) {
+  for &node in rope.nodes {
+    update_verlet_node(&node)
+  }
+
+  for _ in 0..<VERLET_STEPS {
+    for i in 0..<len(rope.nodes) - 1 {
+      cur := &rope.nodes[i]
+      nex := &rope.nodes[i + 1]
+
+      dist := linalg.distance(cur.pos, nex.pos)
+      err := dist - rope.node_length
+      dir := linalg.normalize(nex.pos - cur.pos)
+
+      if cur.is_static && !nex.is_static {
+        nex.pos -= dir * err
+      } else if !cur.is_static && nex.is_static {
+        cur.pos += dir * err
+      } else if !cur.is_static && !nex.is_static {
+        cur.pos += dir * err * 0.5
+        nex.pos -= dir * err * 0.5
+      }
+    }
+  }
+}