texture.js
function( format, type, internal ){
    this.format   = format   || this.gl.RGB;
    this.internal = internal || this.format;
    this.type     = type     || this.gl.UNSIGNED_BYTE;
  }
function( format, type, internal ){
    this.format   = format   || this.gl.RGB;
    this.internal = internal || this.format;
    this.type     = type     || this.gl.UNSIGNED_BYTE;
  }
function ( format , type , internal ) { this . format = format || this . gl . RGB ; this . internal = internal || this . format ; this . type = type || this . gl . UNSIGNED_BYTE ; }
define underlying format, internal format and data type of texture
@param {GLenum} [format  =GL_RGB] the pixel format, default to gl.RGB (can be gl.RGB, gl.RGBA, gl.LUMINANCE...)
@param {GLenum} [type    =GL_UNSIGNED_BYTE] the pixel data type, default to gl.UNSIGNED_BYTE
@param {GLenum} [internal=format] the pixel internal format, default to the same value than 'format' parameter (which must be in webgl 1)
define underlying format internal format and data type of texture