a-big-triangle/triangle.js

Draws a big triangle

'use strict'

var weakMap      = typeof WeakMap === 'undefined' ? require('weak-map') : WeakMap
var createBuffer = require('gl-buffer')
var createVAO    = require('gl-vao')

var TriangleCache = new weakMap()

function createABigTriangle(gl) {

  var triangleVAO = TriangleCache.get(gl)
  var handle = triangleVAO && (triangleVAO._triangleBuffer.handle || triangleVAO._triangleBuffer.buffer)
  if(!handle || !gl.isBuffer(handle)) {
    var buf = createBuffer(gl, new Float32Array([-1, -1, -1, 4, 4, -1]))
    triangleVAO = createVAO(gl, [
      { buffer: buf,
        type: gl.FLOAT,
        size: 2
      }
    ])
    triangleVAO._triangleBuffer = buf
    TriangleCache.set(gl, triangleVAO)
  }
  triangleVAO.bind()
  gl.drawArrays(gl.TRIANGLES, 0, 3)
  triangleVAO.unbind()
}

module.exports = createABigTriangle