gl-pixel-stream


Streams chunks of gl.readPixels from the specified FrameBuffer Object. This is primarily useful for exporting WebGL scenes and textures to high resolution images (i.e. print-ready).

Before calling this method, ensure your FBO is populated with the content you wish to export. On each chunk, this will bind the given FBO, set the viewport, read the new pixels, and then unbind all FBOs.

The following image was generated with the demo.js in this module. This approach can render upwards of 10000x10000 images on a late 2013 MacBookPro.

!earth

(download full 3200x1800 image)

Install

``sh
npm install gl-pixel-stream --save
`

Example

A simple example with gl-fbo might look like this:

`js
var pixelStream = require('gl-pixel-stream')

// bind your FBO
fbo.bind()

// draw your scene to it
drawScene()

// get a pixel stream
var stream = pixelStream(gl, fbo.handle, fbo.shape)

// pipe it out somewhere
stream.pipe(output)
`

A more practical example involves streaming through png-stream/encoder to a write stream. See demo.js for an example of this, which uses Electron (through hihat) to merge the WebGL and Node.js APIs.

See Running From Source for details.

Usage

![NPM](https://www.npmjs.com/package/gl-pixel-stream)

#### stream = glPixelStream(gl, fboHandle, shape, [opts])

Creates a new stream which streams the data from gl.readPixels, reading from the given FrameBuffer. It is assumed to already be populated with your scene/texture.

The stream emits a Buffer containing the uint8 pixels, default RGBA.

- gl (required) the WebGL context
- fboHandle (required) the handle for the WebGLFramebuffer instance
- shape (required) an Array, the [width, height] of the output
- opts (optional) additional settings

The additional settings can be:

- chunkSize (Number) the number of rows to fetch from the GPU in a single call to gl.readPixels, defaults to 128
- flipY (Boolean) whether to flip the output image on the Y axis (default false)
- format a WebGL format like gl.RGBA or gl.RGB for reading, default gl.RGBA
- stride (Number) the number of channels in a pixel, guessed from the specified format, or defaults to 4
- onProgress (Function) a function that has an event parameter with current and total chunk count, as well as bounds array with [ x, y, width, height ] from readPixels

Running from Source

Clone and install:

`sh
git clone https://github.com/Jam3/gl-pixel-stream.git
cd gl-pixel-stream
npm install
`

To run the tests:

`sh
npm run test
`

To run the demo in "production" mode (no DevTools window). This will output an image.png in the current folder.

`sh
npm run start
`

To run the demo in "development" mode. This opens a DevTools window and reloads the bundle on demo.js file-save.

`sh
npm run dev
`

The output image.png should look like this, and be the size specified in the demo.js` file:

!earth

License

MIT, see LICENSE.md for details.