Source: src/pixi/textures/Texture.js

/**
 * @author Mat Groves http://matgroves.com/ @Doormat23
 */

/**
 * TextureSilentFail is a boolean that defaults to `false`.
 * If `true` then `PIXI.Texture.setFrame` will no longer throw an error if the texture dimensions are incorrect.
 * Instead `Texture.valid` will be set to `false` (#1556)
 *
 * @type {boolean}
 */
PIXI.TextureSilentFail = false;

/**
 * A texture stores the information that represents an image or part of an image. It cannot be added
 * to the display list directly. Instead use it as the texture for a PIXI.Sprite. If no frame is provided then the whole image is used.
 *
 * @class Texture
 * @constructor
 * @param baseTexture {BaseTexture} The base texture source to create the texture from
 * @param frame {Rectangle} The rectangle frame of the texture to show
 * @param [crop] {Rectangle} The area of original texture
 * @param [trim] {Rectangle} Trimmed texture rectangle
 */
PIXI.Texture = function(baseTexture, frame, crop, trim)
{
    /**
     * Does this Texture have any frame data assigned to it?
     *
     * @property noFrame
     * @type Boolean
     */
    this.noFrame = false;

    if (!frame)
    {
        this.noFrame = true;
        frame = new PIXI.Rectangle(0,0,1,1);
    }

    if (baseTexture instanceof PIXI.Texture)
    {
        baseTexture = baseTexture.baseTexture;
    }

    /**
     * The base texture that this texture uses.
     *
     * @property baseTexture
     * @type BaseTexture
     */
    this.baseTexture = baseTexture;

    /**
     * The frame specifies the region of the base texture that this texture uses
     *
     * @property frame
     * @type Rectangle
     */
    this.frame = frame;

    /**
     * The texture trim data.
     *
     * @property trim
     * @type Rectangle
     */
    this.trim = trim;

    /**
     * This will let the renderer know if the texture is valid. If it's not then it cannot be rendered.
     *
     * @property valid
     * @type Boolean
     */
    this.valid = false;

    /**
     * Is this a tiling texture? As used by the likes of a TilingSprite.
     *
     * @property isTiling
     * @type Boolean
     */
    this.isTiling = false;

    /**
     * This will let a renderer know that a texture has been updated (used mainly for webGL uv updates)
     *
     * @property requiresUpdate
     * @type Boolean
     */
    this.requiresUpdate = false;

    /**
     * This will let a renderer know that a tinted parent has updated its texture.
     *
     * @property requiresReTint
     * @type Boolean
     */
    this.requiresReTint = false;

    /**
     * The WebGL UV data cache.
     *
     * @property _uvs
     * @type Object
     * @private
     */
    this._uvs = null;

    /**
     * The width of the Texture in pixels.
     *
     * @property width
     * @type Number
     */
    this.width = 0;

    /**
     * The height of the Texture in pixels.
     *
     * @property height
     * @type Number
     */
    this.height = 0;

    /**
     * This is the area of the BaseTexture image to actually copy to the Canvas / WebGL when rendering,
     * irrespective of the actual frame size or placement (which can be influenced by trimmed texture atlases)
     *
     * @property crop
     * @type Rectangle
     */
    this.crop = crop || new PIXI.Rectangle(0, 0, 1, 1);

    /**
     * A flag that controls if this frame is rotated or not.
     * Rotation allows you to use rotated frames in texture atlas packing, it has nothing to do with
     * Sprite rotation.
     *
     * @property rotated
     * @type Boolean
     */
    this.rotated = false;

    if (baseTexture.hasLoaded)
    {
        if (this.noFrame) frame = new PIXI.Rectangle(0, 0, baseTexture.width, baseTexture.height);
        this.setFrame(frame);
    }

};

PIXI.Texture.prototype.constructor = PIXI.Texture;

/**
 * Called when the base texture is loaded
 *
 * @method onBaseTextureLoaded
 * @private
 */
PIXI.Texture.prototype.onBaseTextureLoaded = function()
{
    var baseTexture = this.baseTexture;

    if (this.noFrame)
    {
        this.frame = new PIXI.Rectangle(0, 0, baseTexture.width, baseTexture.height);
    }

    this.setFrame(this.frame);
};

/**
 * Destroys this texture
 *
 * @method destroy
 * @param destroyBase {Boolean} Whether to destroy the base texture as well
 */
PIXI.Texture.prototype.destroy = function(destroyBase)
{
    if (destroyBase) this.baseTexture.destroy();

    this.valid = false;
};

/**
 * Specifies the region of the baseTexture that this texture will use.
 *
 * @method setFrame
 * @param frame {Rectangle} The frame of the texture to set it to
 */
PIXI.Texture.prototype.setFrame = function(frame)
{
    this.noFrame = false;

    this.frame = frame;
    this.width = frame.width;
    this.height = frame.height;

    this.crop.x = frame.x;
    this.crop.y = frame.y;
    this.crop.width = frame.width;
    this.crop.height = frame.height;

    if (!this.trim && (frame.x + frame.width > this.baseTexture.width || frame.y + frame.height > this.baseTexture.height))
    {
        if (!PIXI.TextureSilentFail)
        {
            throw new Error('Texture Error: frame does not fit inside the base Texture dimensions ' + this);
        }

        this.valid = false;
        return;
    }

    this.valid = frame && frame.width && frame.height && this.baseTexture.source && this.baseTexture.hasLoaded;

    if (this.trim)
    {
        this.width = this.trim.width;
        this.height = this.trim.height;
        this.frame.width = this.trim.width;
        this.frame.height = this.trim.height;
    }

    if (this.valid) this._updateUvs();

};

/**
 * Updates the internal WebGL UV cache.
 *
 * @method _updateUvs
 * @private
 */
PIXI.Texture.prototype._updateUvs = function()
{
    if(!this._uvs)this._uvs = new PIXI.TextureUvs();

    var frame = this.crop;
    var tw = this.baseTexture.width;
    var th = this.baseTexture.height;

    this._uvs.x0 = frame.x / tw;
    this._uvs.y0 = frame.y / th;

    this._uvs.x1 = (frame.x + frame.width) / tw;
    this._uvs.y1 = frame.y / th;

    this._uvs.x2 = (frame.x + frame.width) / tw;
    this._uvs.y2 = (frame.y + frame.height) / th;

    this._uvs.x3 = frame.x / tw;
    this._uvs.y3 = (frame.y + frame.height) / th;
};

/**
 * Updates the internal WebGL UV cache.
 *
 * @method _updateUvsInverted
 * @private
 */
PIXI.Texture.prototype._updateUvsInverted = function () {

    if (!this._uvs) { this._uvs = new PIXI.TextureUvs(); }

    var frame = this.crop;
    var tw = this.baseTexture.width;
    var th = this.baseTexture.height;

    this._uvs.x0 = frame.x / tw;
    this._uvs.y0 = frame.y / th;

    this._uvs.x1 = (frame.x + frame.height) / tw;
    this._uvs.y1 = frame.y / th;

    this._uvs.x2 = (frame.x + frame.height) / tw;
    this._uvs.y2 = (frame.y + frame.width) / th;

    this._uvs.x3 = frame.x / tw;
    this._uvs.y3 = (frame.y + frame.width) / th;

};

/**
 * Helper function that creates a new a Texture based on the given canvas element.
 *
 * @static
 * @method fromCanvas
 * @param canvas {Canvas} The canvas element source of the texture
 * @param scaleMode {Number} See {}PIXI.scaleModes{{/crossLink}} for possible values
 * @return {Texture}
 */
PIXI.Texture.fromCanvas = function(canvas, scaleMode)
{
    var baseTexture = PIXI.BaseTexture.fromCanvas(canvas, scaleMode);

    return new PIXI.Texture(baseTexture);
};

PIXI.TextureUvs = function()
{
    this.x0 = 0;
    this.y0 = 0;

    this.x1 = 0;
    this.y1 = 0;

    this.x2 = 0;
    this.y2 = 0;

    this.x3 = 0;
    this.y3 = 0;
};