From 7a03b89b993db8598c8407688fdffb1952f74c3a Mon Sep 17 00:00:00 2001
From: Cameron Reikes <cameronreikes@gmail.com>
Date: Wed, 25 Jan 2023 07:37:53 -0800
Subject: [PATCH] Apply force at point

---
 physics.jai | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/physics.jai b/physics.jai
index 10823a4..c0b06b3 100644
--- a/physics.jai
+++ b/physics.jai
@@ -38,6 +38,12 @@ MASS :: 1.0;
 moment_of_inertia :: (using r: Rect) -> float {
     return MASS*(halfsize.y*halfsize.y + halfsize.x*halfsize.x)/12.0;
 }
+apply_force_at_point :: (r: *Rect, force: Vector2, point_world_space: Vector2) {
+    r.force += force;
+    offset_from_center_of_mass := point_world_space - r.pos;
+    r.torque += offset_from_center_of_mass.x * force.y - offset_from_center_of_mass.y * force.x;
+}
+
 draw_rect :: (using r: Rect) {
     facing_to_right := rotate(xy(halfsize.x,0.0), angle);
     facing_to_up    := rotate(xy(0.0,halfsize.y), angle);
@@ -93,7 +99,7 @@ main :: () {
 
     rects: [..]Rect;
     array_add(*rects, .{pos = #run xy(0.0,  0.0), halfsize = #run xy(0.3)});
-    array_add(*rects, .{pos = #run xy(1.5, 0.0), halfsize = #run xy(0.3)});
+    array_add(*rects, .{pos = #run xy(2.5, 0.0), halfsize = #run xy(0.3)});
 
 
     quit := false;
@@ -139,9 +145,19 @@ main :: () {
                 defer unprocessed_time -= TIMESTEP;
                 
 
-
-
-                rects[0].angle += TIMESTEP * 1.0;
+                if get_time() < 0.5
+                {
+                    apply_force_at_point(*rects[0], xy(3, 0), rects[0].pos + xy(-0.1, 0.03));
+                }
+                for * rects
+                {
+                    defer { it.force = .{}; it.torque = 0.0; };
+                    it.vel += (it.force/MASS) * TIMESTEP;
+                    it.pos += it.vel * TIMESTEP;
+
+                    it.angle_vel += (it.torque / moment_of_inertia(it)) * TIMESTEP;
+                    it.angle += it.angle_vel * TIMESTEP;
+                }
             }
         }