#

API Documentation for: NEXT
Show: Inherited Protected Private Deprecated

# AlphaMapFilter Class

Extends Filter
Defined in: `AlphaMapFilter:38`
Module: EaselJS

Applies a greyscale alpha map image (or canvas) to the target, such that the alpha channel of the result will be copied from the red channel of the map, and the RGB channels will be copied from the target.

Generally, it is recommended that you use AlphaMaskFilter, because it has much better performance.

#### Example

This example draws a red->blue box, caches it, and then uses the cache canvas as an alpha map on a 100x100 image.

      var box = new createjs.Shape();
      box.graphics.beginLinearGradientFill(["#ff0000", "#0000ff"], [0, 1], 0, 0, 0, 100)
      box.graphics.drawRect(0, 0, 100, 100);
      box.cache(0, 0, 100, 100);

      var bmp = new createjs.Bitmap("path/to/image.jpg");
      bmp.filters = [
          new createjs.AlphaMapFilter(box.cacheCanvas)
      ];
      bmp.cache(0, 0, 100, 100);
      stage.addChild(bmp);

See Filter for more information on applying filters.

## Constructor

### `AlphaMapFilter`

(

- `alphaMap`

)

Defined in `AlphaMapFilter:38`

#### Parameters:

- `alphaMap` Image | HTMLCanvasElement

  The greyscale image (or canvas) to use as the alpha value for the result. This should be exactly the same dimensions as the target.

- Index
- Methods
- Properties

## Item Index

### Methods

- applyFilter
- clone
- getBounds
- initialize
- toString

### Properties

- alphaMap

## Methods

### `applyFilter`

(

- `ctx`
- `x`
- `y`
- `width`
- `height`
- `[targetCtx]`
- `[targetX]`
- `[targetY]`

)
Boolean

Inherited from Filter: `applyFilter:94`

Applies the filter to the specified context.

#### Parameters:

- `ctx` CanvasRenderingContext2D

  The 2D context to use as the source.

- `x` Number

  The x position to use for the source rect.

- `y` Number

  The y position to use for the source rect.

- `width` Number

  The width to use for the source rect.

- `height` Number

  The height to use for the source rect.

- `[targetCtx]` CanvasRenderingContext2D optional

  The 2D context to draw the result to. Defaults to the context passed to ctx.

- `[targetX]` Number optional

  The x position to draw the result to. Defaults to the value passed to x.

- `[targetY]` Number optional

  The y position to draw the result to. Defaults to the value passed to y.

#### Returns:

Boolean:

If the filter was applied successfully.

### `clone`

() AlphaMapFilter

Inherited from Filter but overwritten in `clone:125`

Returns a clone of this object.

#### Returns:

AlphaMapFilter:

A clone of the current AlphaMapFilter instance.

### `getBounds`

() Rectangle

Inherited from Filter: `getBounds:83`

Returns a rectangle with values indicating the margins required to draw the filter or null. For example, a filter that will extend the drawing area 4 pixels to the left, and 7 pixels to the right (but no pixels up or down) would return a rectangle with (x=-4, y=0, width=11, height=0).

#### Returns:

Rectangle:

a rectangle object indicating the margins required to draw the filter or null if the filter does not effect bounds.

### `initialize`

() protected

Inherited from Filter: `initialize:75`

Initialization method.

### `toString`

() String

Inherited from Filter: `toString:109`

Returns a string representation of this object.

#### Returns:

String:

a string representation of the instance.

## Properties

### `alphaMap`

Image | HTMLCanvasElement

Defined in `alphaMap:80`

The greyscale image (or canvas) to use as the alpha value for the result. This should be exactly the same dimensions as the target.