StackGenVis/frontend/node_modules/gl-util/readme.md

# gl-util [![unstable](http://badges.github.io/stability-badges/dist/unstable.svg)](http://github.com/badges/stability-badges)

Set of practical functions for webgl.

[![npm install gl-util](https://nodei.co/npm/gl-util.png?mini=true)](https://npmjs.org/package/gl-util/)

```js
const u = require('gl-util');

let gl = u.context(canvas)

let prog = u.program(gl, `
	precision mediump float;

	attribute vec2 position;

	void main() {
		gl_Position = vec4(position * 2. - 1., 0, 1);
	}
`, `
	precision mediump float;

	uniform vec4 color;

	void main () {
		gl_FragColor = color;
	}
`);
u.attribute(prog, 'position', [0,0, 1,0, 0,1]);
u.uniform(prog, 'color', [1, .2, 0, 1.]);

gl.drawArrays(gl.TRIANGLES, 0, 3);
```

## API

### `context(container|canvas|options?)`

Create and/or return WebGL context for the canvas element, possibly based on options. If `container` is not defined, `document.body` is used.

| Option | Meaning |
|---|---|
| `canvas` | A canvas element to obtain context for. |
| `container` | An element to create canvas in and return context for it. |
| `width` | If specified, will set the canvas width. |
| `height` | If specified, will set the canvas height. |
| `pixelRatio` | Multiplier for `width` and `height`. |
| `attributes` | Attributes object. Available attributes: `alpha`, `depth`, `stencil`, `antialias`, `premultipliedAlpha`, `preserveDrawingBuffer` and `failIfMajorPerformanceCaveat`. |

```js
const getContext = require('gl-util/context')

// create canvas element in the document.body and retrieve context for it
let gl = getContext({
	attributes: {
		antialias: true
	}
})
```

### `prog = program(gl, prog|vert?, frag?)`

Set active program or create a new program from vertex and fragment sources. Programs are cached for the context by source. The _WebGLProgram_ instance is returned.

```js
const program = require('gl-util/program')

// create and set program
let prog = program(gl, `
	precision mediump float;

	attribute vec2 position;

	void main() {
		gl_Position = vec4(position * 2. - 1., 0, 1);
	}
`, `
	precision mediump float;

	uniform sampler2D image;
	uniform vec2 shape;
	uniform float x;

	void main () {
		gl_FragColor = texture2D(image, gl_FragCoord.xy / shape);
	}
`)

// set active program
program(gl, prog)
```

### `unif = uniform(gl|program, {name: data, ...} | name?, data?)`

Get/set uniform or multiple uniforms. Returns an object with uniform parameters: `{name, location, data, type}`. Uniforms are stored per-program instance.

```js
const uniform = require('gl-util/uniform')

uniform(gl, 'color', [1, .2, 0, 1]);
```

### `txt = texture(gl, {name: params, ...} | name?, params?)`

Set texture[s] data or parameters:

| Name | Meaning |
|---|---|
| `data` | Data passed to texture. Can be array, typed array, image, canvas or string denoting the URL of image to load. |
| `index` | Texture unit number, if undefined - calculated automatically. |
| `filter` | Sets texture scaling for both min and mag. Can be defined as two separate properties `minFilter` and `magFilter`. By default `gl.LINEAR`. |
| `wrap` | Defines texture tiling vertically and horizontally. Can be defined precisely as `wrapS` and `wrapT`. By default `gl.CLAMP_TO_EDGE`, can be `gl.MIRRORED_REPEAT` or `gl.`. |
| `width` | In pixels |
| `height` | In pixels |
| `format` | `gl.ALPHA`, `gl.RGB`, `gl.RGBA` (default), `gl.LUMINANCE`, `gl.LUMINANCE_ALPHA`, `gl.DEPTH_COMPONENT`, `gl.DEPTH_STENCIL`, [etc](https://developer.mozilla.org/en-US/docs/Web/API/WebGLRenderingContext/texImage2D) |
| `type` | `gl.UNSIGNED_BYTE`, can be `gl.FLOAT` with proper extension enabled |
| `level` | `0`, mipmap level. |

Returns object with texture properties `{data, index, location, minFilter, magFilter, wrapS, wrapT, width, height, format, type, texture}`.

```js
const texture = require('gl-util/texture')

let {width, height} = texture(gl, 'image', './picture.gif');
```

### `attr = attribute(gl, {name: params, ...} | name?, params?)`

Set attribute[s] data or parameters:

| Name | Default | Meaning |
|---|---|---|
| `data` | `null` | Data for the attribute, can be array, typed array or array buffer |
| `size` | `2` | Number of data items per vertex |
| `stride` | `0` | Offset in bytes between the beginning of consecutive vertex attributes. |
| `offset` | `0` | Offset in bytes of the first component in the data. Must be a multiple of type. |
| `type` | `gl.FLOAT` | Data type of each component in the `data` array. Must be one of: `gl.BYTE`, `gl.UNSIGNED_BYTE`, `gl.SHORT`, `gl.UNSIGNED_SHORT`, `gl.FLOAT`. |
| `usage` | `gl.STATIC_DRAW` | Mode of draw: `gl.STATIC_DRAW` (rare changes), `gl.DYNAMIC_DRAW` (frequent changes) or `gl.STREAM_DRAW` (frequent updates) |
| `normalized` | `false` | If fixed-point data values should be normalized or are to converted to fixed point values when accessed. |
| `index` | `0` | Attribute unit number, detected automatically if omitted. |
| `target` | `gl.ARRAY_BUFFER` | |
| `buffer` | `null` | WebGLBuffer to use for attribute |

Returns attribute properties `{data, size, stride, offset, usage, type, normalized, index, target, buffer}`.

```js
const attribute = require('gl-util/attribute')

attribute(gl, 'position', [0,0,1,0,0,1]);
```

### `clear(gl, optsion?)`

Clear the viewport.

## Motivation

There are [regl](https://github.com/regl-project/regl), [stack.gl](https://github.com/stackgl/) and many other WegGL components or frameworks, so why gl-util?

* WebGL frameworks API is usually difficult to remember, not much better than pure WebGL, although _regl_ does a great job. _gl-util_ is like functions from any WebGL tutorial - tiny, handy and already familiar.
* _gl-util_ does not supersede WebGL API - that allows for debugging pure WebGL at any moment.
* _gl-util_ is tiny - if one needs minimalistic WebGL setup it may be better to opt for a couple of functions than massive stack.gl components or regl (70kb+).
* regl API may be cumbersome for organizing components


## License

(c) 2018 Dmitry Yv. MIT License


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