threejs-performance-and-packing

Pack vertex outputs and fragment inputs into a 16-row by 4-column register grid, flattening structures and ordering variables by type from mat4 down to float. Non-square matrices reserve space equal to the larger dimension, so reduce matrix sizes where possible.

Allocate variables in strict type order: mat4 arrays and instances, then mat2, vec4, mat3, vec3, vec2, and finally float. The allocator does not backtrack, so non-contiguous column saturation causes immediate layout failure.

Fragment shaders have no default floating-point precision in GLSL ES, so compilation fails without an explicit declaration. Add a statement like `precision mediump float;` at the top of the shader to satisfy multi-pass compilation checks.

highp is 32-bit with range near IEEE-754 single precision, mediump is minimum 16-bit with 2^-10 relative precision, and lowp is minimum 9-bit with 2^-8 absolute precision intended for 8-bit color values. Choose the lowest precision that preserves visual correctness on mobile.

No, lowp only covers the range (-2, 2) with 2^-8 absolute precision and is designed strictly for 8-bit color map representations. Positions, normals, and lighting calculations typically require mediump or highp to avoid visible artifacts.