gl-text/dist.js

'use strict'

var Font = require('css-font')
var pick = require('pick-by-alias')
var createRegl = require('regl')
var createGl = require('gl-util/context')
var WeakMap = require('es6-weak-map')
var rgba = require('color-normalize')
var fontAtlas = require('font-atlas')
var pool = require('typedarray-pool')
var parseRect = require('parse-rect')
var isObj = require('is-plain-obj')
var parseUnit = require('parse-unit')
var px = require('to-px')
var kerning = require('detect-kerning')
var extend = require('object-assign')
var metrics = require('font-measure')
var flatten = require('flatten-vertex-data')
var ref = require('bit-twiddle');
var nextPow2 = ref.nextPow2;

var shaderCache = new WeakMap


// Safari does not support font-stretch
var isStretchSupported = false
if (document.body) {
    var el = document.body.appendChild(document.createElement('div'))
    el.style.font = 'italic small-caps bold condensed 16px/2 cursive'
    if (getComputedStyle(el).fontStretch) {
        isStretchSupported = true
    }
    document.body.removeChild(el)
}

var GlText = function GlText (o) {
	if (isRegl(o)) {
		o = {regl: o}
		this.gl = o.regl._gl
	}
	else {
		this.gl = createGl(o)
	}

	this.shader = shaderCache.get(this.gl)

	if (!this.shader) {
		this.regl = o.regl || createRegl({ gl: this.gl })
	}
	else {
		this.regl = this.shader.regl
	}

	this.charBuffer = this.regl.buffer({ type: 'uint8', usage: 'stream' })
	this.sizeBuffer = this.regl.buffer({ type: 'float', usage: 'stream' })

	if (!this.shader) {
		this.shader = this.createShader()
		shaderCache.set(this.gl, this.shader)
	}

	this.batch = []

	// multiple options initial state
	this.fontSize = []
	this.font = []
	this.fontAtlas = []

	this.draw = this.shader.draw.bind(this)
	this.render = function () {
		// FIXME: add Safari regl report here:
		// charBuffer and width just do not trigger
		this.regl._refresh()
		this.draw(this.batch)
	}
	this.canvas = this.gl.canvas

	this.update(isObj(o) ? o : {})
};

GlText.prototype.createShader = function createShader () {
	var regl = this.regl

	// FIXME: store 2 shader versions: with normal viewport and without
	// draw texture method
	var draw = regl({
		blend: {
			enable: true,
			color: [0,0,0,1],

			func: {
				srcRGB: 'src alpha',
				dstRGB: 'one minus src alpha',
				srcAlpha: 'one minus dst alpha',
				dstAlpha: 'one'
			}
		},
		stencil: {enable: false},
		depth: {enable: false},

		count: regl.prop('count'),
		offset: regl.prop('offset'),
		attributes: {
			charOffset: {
				offset: 4,
				stride: 8,
				buffer: regl.this('sizeBuffer')
			},
			width: {
				offset: 0,
				stride: 8,
				buffer: regl.this('sizeBuffer')
			},
			char: regl.this('charBuffer'),
			position: regl.this('position')
		},
		uniforms: {
			atlasSize: function (c, p) { return [p.atlas.width, p.atlas.height]; },
			atlasDim: function (c, p) { return [p.atlas.cols, p.atlas.rows]; },
			atlas: function (c, p) { return p.atlas.texture; },
			charStep: function (c, p) { return p.atlas.step; },
			em: function (c, p) { return p.atlas.em; },
			color: regl.prop('color'),
			opacity: regl.prop('opacity'),
			viewport: regl.this('viewportArray'),
			scale: regl.this('scale'),
			align: regl.prop('align'),
			baseline: regl.prop('baseline'),
			translate: regl.this('translate'),
			positionOffset: regl.prop('positionOffset')
		},
		primitive: 'points',
		viewport: regl.this('viewport'),

		vert: ("\n\t\t\tprecision highp float;\n\t\t\tattribute float width, charOffset, char;\n\t\t\tattribute vec2 position;\n\t\t\tuniform float fontSize, charStep, em, align, baseline;\n\t\t\tuniform vec4 viewport;\n\t\t\tuniform vec4 color;\n\t\t\tuniform vec2 atlasSize, atlasDim, scale, translate, positionOffset;\n\t\t\tvarying vec2 charCoord, charId;\n\t\t\tvarying float charWidth;\n\t\t\tvarying vec4 fontColor;\n\t\t\tvoid main () {\n\t\t\t\t" + (!GlText.normalViewport ? 'vec2 positionOffset = vec2(positionOffset.x,- positionOffset.y);' : '') + "\n\n\t\t\t\tvec2 offset = floor(em * (vec2(align + charOffset, baseline)\n\t\t\t\t\t+ positionOffset))\n\t\t\t\t\t/ (viewport.zw * scale.xy);\n\n\t\t\t\tvec2 position = (position + translate) * scale;\n\t\t\t\tposition += offset * scale;\n\n\t\t\t\t" + (GlText.normalViewport ? 'position.y = 1. - position.y;' : '') + "\n\n\t\t\t\tcharCoord = position * viewport.zw + viewport.xy;\n\n\t\t\t\tgl_Position = vec4(position * 2. - 1., 0, 1);\n\n\t\t\t\tgl_PointSize = charStep;\n\n\t\t\t\tcharId.x = mod(char, atlasDim.x);\n\t\t\t\tcharId.y = floor(char / atlasDim.x);\n\n\t\t\t\tcharWidth = width * em;\n\n\t\t\t\tfontColor = color / 255.;\n\t\t\t}"),

		frag: "\n\t\t\tprecision highp float;\n\t\t\tuniform sampler2D atlas;\n\t\t\tuniform float fontSize, charStep, opacity;\n\t\t\tuniform vec2 atlasSize;\n\t\t\tuniform vec4 viewport;\n\t\t\tvarying vec4 fontColor;\n\t\t\tvarying vec2 charCoord, charId;\n\t\t\tvarying float charWidth;\n\n\t\t\tfloat lightness(vec4 color) {\n\t\t\t\treturn color.r * 0.299 + color.g * 0.587 + color.b * 0.114;\n\t\t\t}\n\n\t\t\tvoid main () {\n\t\t\t\tvec2 uv = gl_FragCoord.xy - charCoord + charStep * .5;\n\t\t\t\tfloat halfCharStep = floor(charStep * .5 + .5);\n\n\t\t\t\t// invert y and shift by 1px (FF expecially needs that)\n\t\t\t\tuv.y = charStep - uv.y;\n\n\t\t\t\t// ignore points outside of character bounding box\n\t\t\t\tfloat halfCharWidth = ceil(charWidth * .5);\n\t\t\t\tif (floor(uv.x) > halfCharStep + halfCharWidth ||\n\t\t\t\t\tfloor(uv.x) < halfCharStep - halfCharWidth) return;\n\n\t\t\t\tuv += charId * charStep;\n\t\t\t\tuv = uv / atlasSize;\n\n\t\t\t\tvec4 color = fontColor;\n\t\t\t\tvec4 mask = texture2D(atlas, uv);\n\n\t\t\t\tfloat maskY = lightness(mask);\n\t\t\t\t// float colorY = lightness(color);\n\t\t\t\tcolor.a *= maskY;\n\t\t\t\tcolor.a *= opacity;\n\n\t\t\t\t// color.a += .1;\n\n\t\t\t\t// antialiasing, see yiq color space y-channel formula\n\t\t\t\t// color.rgb += (1. - color.rgb) * (1. - mask.rgb);\n\n\t\t\t\tgl_FragColor = color;\n\t\t\t}"
	})

	// per font-size atlas
	var atlas = {}

	return { regl: regl, draw: draw, atlas: atlas }
};

GlText.prototype.update = function update (o) {
		var this$1 = this;

	if (typeof o === 'string') { o = { text: o } }
	else if (!o) { return }

	// FIXME: make this a static transform or more general approact
	o = pick(o, {
		position: 'position positions coord coords coordinates',
		font: 'font fontFace fontface typeface cssFont css-font family fontFamily',
		fontSize: 'fontSize fontsize size font-size',
		text: 'text texts chars characters value values symbols',
		align: 'align alignment textAlign textbaseline',
		baseline: 'baseline textBaseline textbaseline',
		direction: 'dir direction textDirection',
		color: 'color colour fill fill-color fillColor textColor textcolor',
		kerning: 'kerning kern',
		range: 'range dataBox',
		viewport: 'vp viewport viewBox viewbox viewPort',
		opacity: 'opacity alpha transparency visible visibility opaque',
		offset: 'offset positionOffset padding shift indent indentation'
	}, true)


	if (o.opacity != null) {
		if (Array.isArray(o.opacity)) {
			this.opacity = o.opacity.map(function (o) { return parseFloat(o); })
		}
		else {
			this.opacity = parseFloat(o.opacity)
		}
	}

	if (o.viewport != null) {
		this.viewport = parseRect(o.viewport)

		if (GlText.normalViewport) {
			this.viewport.y = this.canvas.height - this.viewport.y - this.viewport.height
		}

		this.viewportArray = [this.viewport.x, this.viewport.y, this.viewport.width, this.viewport.height]

	}
	if (this.viewport == null) {
		this.viewport = {
			x: 0, y: 0,
			width: this.gl.drawingBufferWidth,
			height: this.gl.drawingBufferHeight
		}
		this.viewportArray = [this.viewport.x, this.viewport.y, this.viewport.width, this.viewport.height]
	}

	if (o.kerning != null) { this.kerning = o.kerning }

	if (o.offset != null) {
		if (typeof o.offset === 'number') { o.offset = [o.offset, 0] }

		this.positionOffset = flatten(o.offset)
	}

	if (o.direction) { this.direction = o.direction }

	if (o.range) {
		this.range = o.range
		this.scale = [1 / (o.range[2] - o.range[0]), 1 / (o.range[3] - o.range[1])]
		this.translate = [-o.range[0], -o.range[1]]
	}
	if (o.scale) { this.scale = o.scale }
	if (o.translate) { this.translate = o.translate }

	// default scale corresponds to viewport
	if (!this.scale) { this.scale = [1 / this.viewport.width, 1 / this.viewport.height] }

	if (!this.translate) { this.translate = [0, 0] }

	if (!this.font.length && !o.font) { o.font = GlText.baseFontSize + 'px sans-serif' }

	// normalize font caching string
	var newFont = false, newFontSize = false

	// obtain new font data
	if (o.font) {
		(Array.isArray(o.font) ? o.font : [o.font]).forEach(function (font, i) {
			// normalize font
			if (typeof font === 'string') {
				try {
					font = Font.parse(font)
				} catch (e) {
					font = Font.parse(GlText.baseFontSize + 'px ' + font)
				}
			}
			else { font = Font.parse(Font.stringify(font)) }

			var baseString = Font.stringify({
				size: GlText.baseFontSize,
				family: font.family,
				stretch: isStretchSupported ? font.stretch : undefined,
				variant: font.variant,
				weight: font.weight,
				style: font.style
			})

			var unit = parseUnit(font.size)
			var fs = Math.round(unit[0] * px(unit[1]))
			if (fs !== this$1.fontSize[i]) {
				newFontSize = true
				this$1.fontSize[i] = fs
			}

			// calc new font metrics/atlas
			if (!this$1.font[i] || baseString != this$1.font[i].baseString) {
				newFont = true

				// obtain font cache or create one
				this$1.font[i] = GlText.fonts[baseString]
				if (!this$1.font[i]) {
					var family = font.family.join(', ')
					var style = [font.style]
					if (font.style != font.variant) { style.push(font.variant) }
					if (font.variant != font.weight) { style.push(font.weight) }
					if (isStretchSupported && font.weight != font.stretch) { style.push(font.stretch) }

					this$1.font[i] = {
						baseString: baseString,

						// typeface
						family: family,
						weight: font.weight,
						stretch: font.stretch,
						style: font.style,
						variant: font.variant,

						// widths of characters
						width: {},

						// kernin pairs offsets
						kerning: {},

						metrics: metrics(family, {
							origin: 'top',
							fontSize: GlText.baseFontSize,
							fontStyle: style.join(' ')
						})
					}

					GlText.fonts[baseString] = this$1.font[i]
				}
			}
		})
	}

	// FIXME: make independend font-size
	// if (o.fontSize) {
	// let unit = parseUnit(o.fontSize)
	// let fs = Math.round(unit[0] * px(unit[1]))

	// if (fs != this.fontSize) {
	// 	newFontSize = true
	// 	this.fontSize = fs
	// }
	// }

	if (newFont || newFontSize) {
		this.font.forEach(function (font, i) {
			var fontString = Font.stringify({
				size: this$1.fontSize[i],
				family: font.family,
				stretch: isStretchSupported ? font.stretch : undefined,
				variant: font.variant,
				weight: font.weight,
				style: font.style
			})

			// calc new font size atlas
			this$1.fontAtlas[i] = this$1.shader.atlas[fontString]

			if (!this$1.fontAtlas[i]) {
				var metrics = font.metrics

				this$1.shader.atlas[fontString] =
				this$1.fontAtlas[i] = {
					fontString: fontString,
					// even step is better for rendered characters
					step: Math.ceil(this$1.fontSize[i] * metrics.bottom * .5) * 2,
					em: this$1.fontSize[i],
					cols: 0,
					rows: 0,
					height: 0,
					width: 0,
					chars: [],
					ids: {},
					texture: this$1.regl.texture()
				}
			}

			// bump atlas characters
			if (o.text == null) { o.text = this$1.text }
		})
	}

	// if multiple positions - duplicate text arguments
	// FIXME: this possibly can be done better to avoid array spawn
	if (typeof o.text === 'string' && o.position && o.position.length > 2) {
		var textArray = Array(o.position.length * .5)
		for (var i = 0; i < textArray.length; i++) {
			textArray[i] = o.text
		}
		o.text = textArray
	}

	// calculate offsets for the new font/text
	var newAtlasChars
	if (o.text != null || newFont) {
		// FIXME: ignore spaces
		// text offsets within the text buffer
		this.textOffsets = [0]

		if (Array.isArray(o.text)) {
			this.count = o.text[0].length
			this.counts = [this.count]
			for (var i$1 = 1; i$1 < o.text.length; i$1++) {
				this.textOffsets[i$1] = this.textOffsets[i$1 - 1] + o.text[i$1 - 1].length
				this.count += o.text[i$1].length
				this.counts.push(o.text[i$1].length)
			}
			this.text = o.text.join('')
		}
		else {
			this.text = o.text
			this.count = this.text.length
			this.counts = [this.count]
		}

		newAtlasChars = []

		// detect & measure new characters
		this.font.forEach(function (font, idx) {
			GlText.atlasContext.font = font.baseString

			var atlas = this$1.fontAtlas[idx]

			for (var i = 0; i < this$1.text.length; i++) {
				var char = this$1.text.charAt(i)

				if (atlas.ids[char] == null) {
					atlas.ids[char] = atlas.chars.length
					atlas.chars.push(char)
					newAtlasChars.push(char)
				}

				if (font.width[char] == null) {
					font.width[char] = GlText.atlasContext.measureText(char).width / GlText.baseFontSize

					// measure kerning pairs for the new character
					if (this$1.kerning) {
						var pairs = []
						for (var baseChar in font.width) {
							pairs.push(baseChar + char, char + baseChar)
						}
						extend(font.kerning, kerning(font.family, {
							pairs: pairs
						}))
					}
				}
			}
		})
	}

	// create single position buffer (faster than batch or multiple separate instances)
	if (o.position) {
		if (o.position.length > 2) {
			var flat = !o.position[0].length
			var positionData = pool.mallocFloat(this.count * 2)
			for (var i$2 = 0, ptr = 0; i$2 < this.counts.length; i$2++) {
				var count = this.counts[i$2]
				if (flat) {
					for (var j = 0; j < count; j++) {
						positionData[ptr++] = o.position[i$2 * 2]
						positionData[ptr++] = o.position[i$2 * 2 + 1]
					}
				}
				else {
					for (var j$1 = 0; j$1 < count; j$1++) {
						positionData[ptr++] = o.position[i$2][0]
						positionData[ptr++] = o.position[i$2][1]
					}
				}
			}
			if (this.position.call) {
				this.position({
					type: 'float',
					data: positionData
				})
			} else {
				this.position = this.regl.buffer({
					type: 'float',
					data: positionData
				})
			}
			pool.freeFloat(positionData)
		}
		else {
			if (this.position.destroy) { this.position.destroy() }
			this.position = {
				constant: o.position
			}
		}
	}

	// populate text/offset buffers if font/text has changed
	// as [charWidth, offset, charWidth, offset...]
	// that is in em units since font-size can change often
	if (o.text || newFont) {
		var charIds = pool.mallocUint8(this.count)
		var sizeData = pool.mallocFloat(this.count * 2)
		this.textWidth = []

		for (var i$3 = 0, ptr$1 = 0; i$3 < this.counts.length; i$3++) {
			var count$1 = this.counts[i$3]
			var font = this.font[i$3] || this.font[0]
			var atlas = this.fontAtlas[i$3] || this.fontAtlas[0]

			for (var j$2 = 0; j$2 < count$1; j$2++) {
				var char = this.text.charAt(ptr$1)
				var prevChar = this.text.charAt(ptr$1 - 1)

				charIds[ptr$1] = atlas.ids[char]
				sizeData[ptr$1 * 2] = font.width[char]

				if (j$2) {
					var prevWidth = sizeData[ptr$1 * 2 - 2]
					var currWidth = sizeData[ptr$1 * 2]
					var prevOffset = sizeData[ptr$1 * 2 - 1]
					var offset = prevOffset + prevWidth * .5 + currWidth * .5;

					if (this.kerning) {
						var kerning$1 = font.kerning[prevChar + char]
						if (kerning$1) {
							offset += kerning$1 * 1e-3
						}
					}

					sizeData[ptr$1 * 2 + 1] = offset
				}
				else {
					sizeData[ptr$1 * 2 + 1] = sizeData[ptr$1 * 2] * .5
				}

				ptr$1++
			}
			this.textWidth.push(
				!sizeData.length ? 0 :
				// last offset + half last width
				sizeData[ptr$1 * 2 - 2] * .5 + sizeData[ptr$1 * 2 - 1]
			)
		}


		// bump recalc align offset
		if (!o.align) { o.align = this.align }
		this.charBuffer({data: charIds, type: 'uint8', usage: 'stream'})
		this.sizeBuffer({data: sizeData, type: 'float', usage: 'stream'})
		pool.freeUint8(charIds)
		pool.freeFloat(sizeData)

		// udpate font atlas and texture
		if (newAtlasChars.length) {
			this.font.forEach(function (font, i) {
				var atlas = this$1.fontAtlas[i]

				// FIXME: insert metrics-based ratio here
				var step = atlas.step

				var maxCols = Math.floor(GlText.maxAtlasSize / step)
				var cols = Math.min(maxCols, atlas.chars.length)
				var rows = Math.ceil(atlas.chars.length / cols)

				var atlasWidth = nextPow2( cols * step )
				// let atlasHeight = Math.min(rows * step + step * .5, GlText.maxAtlasSize);
				var atlasHeight = nextPow2( rows * step );

				atlas.width = atlasWidth
				atlas.height = atlasHeight;
				atlas.rows = rows
				atlas.cols = cols

				if (!atlas.em) { return }

				atlas.texture({
					data: fontAtlas({
						canvas: GlText.atlasCanvas,
						font: atlas.fontString,
						chars: atlas.chars,
						shape: [atlasWidth, atlasHeight],
						step: [step, step]
					})
				})

			})
		}
	}

	if (o.align) {
		this.align = o.align
		this.alignOffset = this.textWidth.map(function (textWidth, i) {
			var align = !Array.isArray(this$1.align) ? this$1.align : this$1.align.length > 1 ? this$1.align[i] : this$1.align[0]

			if (typeof align === 'number') { return align }
			switch (align) {
				case 'right':
				case 'end':
					return -textWidth
				case 'center':
				case 'centre':
				case 'middle':
					return -textWidth * .5
			}

			return 0
		})
	}

	if (this.baseline == null && o.baseline == null) {
		o.baseline = 0
	}
	if (o.baseline != null) {
		this.baseline = o.baseline
		if (!Array.isArray(this.baseline)) { this.baseline = [this.baseline] }
		this.baselineOffset = this.baseline.map(function (baseline, i) {
			var m = (this$1.font[i] || this$1.font[0]).metrics
			var base = 0

			base += m.bottom * .5

			if (typeof baseline === 'number') {
				base += (baseline - m.baseline)
			}
			else {
				base += -m[baseline]
			}

			if (!GlText.normalViewport) { base *= -1 }
			return base
		})
	}

	// flatten colors to a single uint8 array
	if (o.color != null) {
		if (!o.color) { o.color = 'transparent' }

		// single color
		if (typeof o.color === 'string' || !isNaN(o.color)) {
			this.color = rgba(o.color, 'uint8')
		}
		// array
		else {
			var colorData

			// flat array
			if (typeof o.color[0] === 'number' && o.color.length > this.counts.length) {
				var l = o.color.length
				colorData = pool.mallocUint8(l)
				var sub = (o.color.subarray || o.color.slice).bind(o.color)
				for (var i$4 = 0; i$4 < l; i$4 += 4) {
					colorData.set(rgba(sub(i$4, i$4 + 4), 'uint8'), i$4)
				}
			}
			// nested array
			else {
				var l$1 = o.color.length
				colorData = pool.mallocUint8(l$1 * 4)
				for (var i$5 = 0; i$5 < l$1; i$5++) {
					colorData.set(rgba(o.color[i$5] || 0, 'uint8'), i$5 * 4)
				}
			}

			this.color = colorData
		}
	}

	// update render batch
	if (o.position || o.text || o.color || o.baseline || o.align || o.font || o.offset || o.opacity) {
		var isBatch = (this.color.length > 4)
			|| (this.baselineOffset.length > 1)
			|| (this.align && this.align.length > 1)
			|| (this.fontAtlas.length > 1)
			|| (this.positionOffset.length > 2)
		if (isBatch) {
			var length = Math.max(
				this.position.length * .5 || 0,
				this.color.length * .25 || 0,
				this.baselineOffset.length || 0,
				this.alignOffset.length || 0,
				this.font.length || 0,
				this.opacity.length || 0,
				this.positionOffset.length * .5 || 0
			)
			this.batch = Array(length)
			for (var i$6 = 0; i$6 < this.batch.length; i$6++) {
				this.batch[i$6] = {
					count: this.counts.length > 1 ? this.counts[i$6] : this.counts[0],
					offset: this.textOffsets.length > 1 ? this.textOffsets[i$6] : this.textOffsets[0],
					color: !this.color ? [0,0,0,255] : this.color.length <= 4 ? this.color : this.color.subarray(i$6 * 4, i$6 * 4 + 4),
					opacity: Array.isArray(this.opacity) ? this.opacity[i$6] : this.opacity,
					baseline: this.baselineOffset[i$6] != null ? this.baselineOffset[i$6] : this.baselineOffset[0],
					align: !this.align ? 0 : this.alignOffset[i$6] != null ? this.alignOffset[i$6] : this.alignOffset[0],
					atlas: this.fontAtlas[i$6] || this.fontAtlas[0],
					positionOffset: this.positionOffset.length > 2 ? this.positionOffset.subarray(i$6 * 2, i$6 * 2 + 2) : this.positionOffset
				}
			}
		}
		// single-color, single-baseline, single-align batch is faster to render
		else {
			if (this.count) {
				this.batch = [{
					count: this.count,
					offset: 0,
					color: this.color || [0,0,0,255],
					opacity: Array.isArray(this.opacity) ? this.opacity[0] : this.opacity,
					baseline: this.baselineOffset[0],
					align: this.alignOffset ? this.alignOffset[0] : 0,
					atlas: this.fontAtlas[0],
					positionOffset: this.positionOffset
				}]
			}
			else {
				this.batch = []
			}
		}
	}
};

GlText.prototype.destroy = function destroy () {
	// TODO: count instances of atlases and destroy all on null
};


// defaults
GlText.prototype.kerning = true
GlText.prototype.position = { constant: new Float32Array(2) }
GlText.prototype.translate = null
GlText.prototype.scale = null
GlText.prototype.font = null
GlText.prototype.text = ''
GlText.prototype.positionOffset = [0, 0]
GlText.prototype.opacity = 1
GlText.prototype.color = new Uint8Array([0, 0, 0, 255])
GlText.prototype.alignOffset = [0, 0]


// whether viewport should be top↓bottom 2d one (true) or webgl one (false)
GlText.normalViewport = false

// size of an atlas
GlText.maxAtlasSize = 1024

// font atlas canvas is singleton
GlText.atlasCanvas = document.createElement('canvas')
GlText.atlasContext = GlText.atlasCanvas.getContext('2d', {alpha: false})

// font-size used for metrics, atlas step calculation
GlText.baseFontSize = 64

// fonts storage
GlText.fonts = {}

// max number of different font atlases/textures cached
// FIXME: enable atlas size limitation via LRU
// GlText.atlasCacheSize = 64

function isRegl (o) {
	return typeof o === 'function' &&
	o._gl &&
	o.prop &&
	o.texture &&
	o.buffer
}


module.exports = GlText