A helper module for unit testing shaders and comparing the result of gl_FragColor from a 1x1 WebGL canvas. See glsl-hsl2rgb for a practical example.

Example:

var createShaderOutput = require('gl-shader-output');
// Fragment shader source, or a gl-shader instance
var fragShader = [
    'precision mediump float;',
    'uniform float green;',
    'void main() {',
        'gl_FragColor = vec4(0.0, green, 0.0, 1.0);',
    '}'
].join('\n');
// get a draw function for our test
var draw = createShaderOutput(fragShader);
// returns the frag color as [R, G, B, A]
var color = draw();
// we could also set uniforms before rendering
var color2 = draw({ green: 0.5 });
// due to precision loss, you may want to use a fuzzy equality check
var epsilon = 0.01;
var almostEqual = require('array-almost-equal');
almostEqual(color2, [0.0, 0.5, 0.0, 1.0], epsilon);

You can use this with tools like smokestack for test-driven GLSL development.

Takes a shader with optional opt settings and returns a draw function.

Where shader can be one of the following:

• A GLSL String, which is used as the fragment shader
• An instance of gl-shader
• A function with the signature fn(gl), which returns a new gl-shader instance

Options:

• gl the WebGL context – defaults to shader.gl if an instance is passed, otherwise constructs a new context
• width the width of gl context, by default 1
• height the height of gl context, by default 1
• float whether to use floating point values, default true (requires an extension)

Also supports webgl-context options such as alpha and premultipliedAlpha.

The returned function has the following signature:

Where uniforms is an optional map of uniform names to values (such as [x, y] array for vec2), applied before rendering.

The return value is the gl_FragColor RGBA of the canvas, in floats, such as [0.5, 1.0, 0.25, 1.0].

MIT, see LICENSE.md for details.