thor85/glsl-float-to-rgba

WebGL shader function to encode a 32-bit float to the RGBA color channels of a texel

glsl-float-to-rgba

Installation

npm install --save glsl-float-to-rgba

Signature

vec4 floatToRgba(float texelFloat, bool littleEndian);

Usage

This package exports a GLSL function, floatToRgba, that encodes a 32-bit floating point values to the RGBA channels of a WebGL texture. This is a workaround for the lack of support in baseline WebGL 1.0 for floating-point textures. WebGL 2.0 allows floating-point textures, and WebGL 1.0 allows them when the extension OES_texture_float is available, but OES_texture_float only guarantees reading from floating-point textures, not writing to. This package seeks to fill that gap.

floatToRgba is designed to be used as a GLSLify module. To encode a texel in your shader code, pass the float to the function floatToRgba. Note that because the function has to encode the float to its constituent bits, it needs to know whether the machine on which it's running uses big-endian or little-endian representation.

// fragment shader

#pragma glslify: floatToRgba = require('glsl-float-to-rgba')

// does the machine use little-endian representation?
uniform bool littleEndian;

void main() {
  float floatValue = ...

  gl_FragColor = floatToRgba(floatValue, littleEndian);
}

var pixels = new Uint8Array(CANVAS.width * CANVAS.height * 4);
gl.readPixels(0, 0, CANVAS.width, CANVAS.height, gl.RGBA, gl.UNSIGNED_BYTE, pixels);
pixels = new Float32Array(pixels.buffer);

Here's a simple way to compute endianness in JavaScript. Pass the result as a uniform variable to your shader.

const littleEndian = (function machineIsLittleEndian() {
  const uint8Array = new Uint8Array([0xAA, 0xBB]);
  const uint16array = new Uint16Array(uint8Array.buffer);
  return uint16array[0] === 0xBBAA;
})();

Attribution

Based on routine described here.