Physics for Games

+ +

Part 1: Linear Forces

+ The first - and perhaps easiest - part of implementing any rigid body physics system is getting the entities in your scene to move in response to linear forces. + With this implementation alone, you can achieve an interesting level of realism in your 2D (and even 3D) scene. +

+ Let's begin by recalling the relationships between acceleration, velocity, and position. +

+ Knowing all this, you should be able to understand the following source code fairly easily; +

+                        
+function update(dtSeconds) {
+    // Add up the forces acting on the circle
+    const GRAVITY = 9.8;
+    const lGravityForce = vec2(0, -1.0 * (lCircle.mass * GRAVITY));
+    lCircle.force = addVec2(lCircle.force, lGravityForce);
+
+    // Figure out acceleration (a = F / m)
+    const lCurrentAcceleration = scaleVec2(lCircle.force, 1.0 / lCircle.mass);
+
+    // Calculate the new velocity: v = v0 + a * t
+    lCircle.velocity = addVec2(lCircle.velocity, scaleVec2(lCurrentAcceleration, dtSeconds));
+
+    // Update the position based on velocity: x = x0 + v * t
+    lCircle.position = addVec2(lCircle.position, scaleVec2(lCircle.velocity, dtSeconds));
+
+    // Update the model matrix accordingly
+    lCircle.model = translateMatrix(mat4(), lCircle.position.x, lCircle.position.y, 0);
+
+    // Reset the force vector for the next update
+    lCircle.force = vec2()
+}
+                        
+

Linear Force:N/A
Linear Acceleration:N/A
Linear Velocity:N/A
Linear Position:N/A

+ +

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