You can build a stunning interactive web physics engine from scratch by combining mathematical modeling, an efficient update loop, and HTML5 Canvas rendering.
Building your own engine helps you understand how video games and interactive simulations calculate movement and collisions behind the scenes. Core Architecture
Every physics engine relies on a continuous loop that updates positions and renders the results to the screen.
The Game Loop: Uses requestAnimationFrame to sync updates with the screen refresh rate.
Delta Time: Measures the exact time passed between frames to ensure smooth movement.
The State: Stores object properties like position, velocity, mass, and acceleration. Vector Mathematics
Physics in a 2D or 3D space requires vector math to handle directions and forces.
Vector Class: Create a custom JavaScript class for 2D vectors (x, y).
Basic Operations: Implement methods for adding, subtracting, and multiplying vectors.
Magnitude: Calculate vector length using the Pythagorean theorem.
Normalization: Scale a vector to a length of 1 to isolate its direction. Equations of Motion
Objects move by applying forces that change their velocity and position over time.
Acceleration: Derived from force divided by mass (A = F / M).
Velocity: Updated by adding acceleration multiplied by delta time (V = V + A × dt).
Position: Updated by adding velocity multiplied by delta time (P = P + V × dt).
Gravity: A constant downward force applied to all moving objects every frame. Collision Detection
The engine must constantly check if shapes are overlapping or intersecting.
Circle-to-Circle: Check if the distance between two centers is less than their combined radii.
AABB (Boxes): Check for overlaps on the X and Y axes using Axis-Aligned Bounding Boxes.
Spatial Partitioning: Grid the screen into cells to check nearby objects and save CPU power. Collision Resolution
Once a collision is detected, objects must bounce or react realistically based on physics laws.
Penetration Resolution: Move overlapping objects apart along the collision normal so they stop sticking.
Impulse Resolution: Calculate the new velocities using the law of conservation of momentum.
Restitution: Apply a coefficient (0 to 1) to control how bouncy or elastic the collision is.
Friction: Apply tangential forces to slow down objects sliding against each other. Adding Interactivity
Stunning engines feel alive because users can touch, throw, and manipulate the environment.
Mouse Joints: Connect the user’s cursor to an object using a virtual spring force.
Dynamic Obstacles: Let users draw walls or obstacles directly onto the canvas in real-time.
Parameter Sliders: Add HTML inputs to alter gravity, friction, and time scales on the fly.
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