package {

	import flash.display.Bitmap;
	import flash.display.BitmapData;
	import flash.display.BitmapDataChannel;
	import flash.geom.Point;
	import flash.geom.Rectangle;

	[SWF(width=600, height=300, backgroundColor=0x000000)]

	/**
	* Demonstrates how BitmapData's histogram() method can be used to access brightness level data for each all
	* channels of each pixel, and how this may be visually displayed.
	*/
	public class graphic_flex_image_effects_04_Flex_HistogramTest extends graphic_flex_image_effects_04_Flex_AbstractImageLoader {

		/**
		* Constructor. Passes path of image to load to super class.
		*/
		public function graphic_flex_image_effects_04_Flex_HistogramTest() {
			super("graphic-flex-image-effects-04-assets-goat.jpg");
		}

		/**
		* Run after the image loads in super class. This gets the histrogram data and draws this in a colored
		* column chart in a new image that is displayed to the right of the loaded image.
		*/
		override protected function runPostImageLoad():void {
			var bitmapData:BitmapData = _loadedBitmap.bitmapData;
			addChild(_loadedBitmap);
			var histogram:Vector.<Vector.<Number>> = bitmapData.histogram();
			// retrieve the maximum number of pixels in a single brightness level;
			// this is used to set the top of the column chart
			var maxPixels:uint = getMaxPixels(histogram);
			// new image in which the histrogram data will be displayed
			var histogramData:BitmapData = new BitmapData(256, 256, false, 0xFF000000);
			// draws each individual color channel's histrogram data into the new image
			drawChannelData(maxPixels, histogramData, histogram[0], BitmapDataChannel.RED);
			drawChannelData(maxPixels, histogramData, histogram[1], BitmapDataChannel.GREEN);
			drawChannelData(maxPixels, histogramData, histogram[2], BitmapDataChannel.BLUE);
			// adds the bitmap data to a bitmap and the stage
			var histogramBitmap:Bitmap = new Bitmap(histogramData);
			histogramBitmap.x = bitmapData.width + (bitmapData.width-256)/2;
			histogramBitmap.y = (bitmapData.height-256)/2;
			addChild(histogramBitmap);
		}

		/**
		* Returns the maximum number of pixels in a single brightness level in all channels.
		*
		* @param histogram The histrogram data retrieved from an image.
		*
		* @return The maximum number of pixels in a single brightness level in all channels.
		*/
		private function getMaxPixels(histogram:Vector.<Vector.<Number>>):uint {
			var maxPixels:uint = 0;
			var x:uint;
			var channel:Vector.<Number>;
			// run through all three channels
			for (var i:uint = 0; i < 3; i++) {
				channel = histogram[i];
				// run through all 256 brightness levels
				for (x = 0; x < 256; x++) {
					maxPixels = Math.max(channel[x], maxPixels);
				}
			}
			return maxPixels;
		}

		/**
		* Draws a column chart of a channel's histogram data into the specified bitmap.
		*
		* @param maxPixels The maximum number of pixels that will be displayed on the y axis, defining chart size.
		* @param bitmapData The bitmap data in which to draw the channel data column chart.
		* @param channelData The histogram data for the channel to draw.
		* @param channel The channel of the image in which to draw the column chart.
		*/
		private function drawChannelData(
			maxPixels:uint,
			bitmapData:BitmapData,
			channelData:Vector.<Number>,
			channel:uint
		):void {
			// new bitmap data of exact same dimensions is used
			var channelBitmapData:BitmapData = bitmapData.clone();
			var y:Number;
			// run through all 256 brightness levels and draw column for each
			for (var x:uint = 0; x < 256; x++) {
				// scale of the column is dictated by the number of pixels of that brightness in that channel
				// and the maxPixels value, which defines the height of the y axis and the chart
				y = channelData[x]/maxPixels*256;
				// draw a column from the bottom of the image up (256-y)
				channelBitmapData.fillRect(new Rectangle(x, 256-y, 1, y), 0xFFFFFFFF);
			}
			// copy the single channel's data into the final bitmap data
			bitmapData.copyChannel(
				channelBitmapData,
				channelBitmapData.rect,
				new Point(),
				channel,
				channel
			);
		}

	}

}