compute_physics_bounce

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Overview

• Sphere position, radius, velocity, restitution, friction, and color are stored in a storage buffer
• In the compute shader, one invocation is responsible for one sphere and calculates gravity integration, collisions with the floor and walls, and sphere-sphere collision response
• It uses ping-pong src / dst buffers so every invocation reads the same previous state and writes to a separate sphere entry
• The compute result is not read back to the CPU; the vertex shader reads the same storage buffer directly and renders the spheres as instances
• The original scene scale is reduced to 1/100, 1 unit is treated as 1 m, and gravity is set to about 1.634 m/s², which corresponds to roughly one-sixth of Earth gravity
• The container is 0.76 m wide and 0.50 m deep, and sphere radii are about 1.25 - 1.8 cm
• The default 96 spheres fall from about 0.22 - 0.25 m in height, near the upper edge of the wireframe frame
• The sample does not modify webg core classes such as PhysicsSpace or the rendering classes
• It enables computeFrame: true on WebgApp and issues its Compute and Render Passes from the onComputeFrame handler
• It manages source/destination indices with the sample-local PingPongBuffer and uses timestamp queries to measure GPU Compute time across all substeps plus Render Pass time

How to Run

• Open ./compute_physics_bounce.html
• Use a browser with WebGPU support, and check the help panel and HUD together with the sample when needed

Checkpoints

• This sample is meant as a compute-shader comparison target for the CPU rigid-body version in samples/physics_bounce
• Press P to pause, R to reset, and C to toggle sphere-sphere collisions on or off
• The touch buttons T / C / P / R can also control tilt, collisions, pause, and reset
• You can specify the sphere count with the URL parameter ?count=. The default is 96, and the maximum is 512
• Because it uses an all-pairs test, the computational cost is O(N^2). No accelerated broad phase such as a spatial grid is used
• The spheres do not have rotational degrees of freedom; they are simplified rigid bodies that solve only linear velocity
• The help panel's Compute load, Render load, GPU load, and JS load can be used to compare which stage grows as the sphere count increases