To modify the appearance of a bitmap, you can apply a noise effect
to it, using either the
noise()
method or the
perlinNoise()
methods.
A noise effect can be likened to the static that appears on an untuned
television screen.
To apply a noise effect to a a bitmap, use the
noise()
method.
This method applies a random color value to pixels within a specified
area of a bitmap image.
This method accepts five parameters:
-
randomSeed
(int): The random seed number
that determines the pattern. Despite its name, this number actually
creates the same results if the same number is passed. To get a
true random result, use the
Math.random()
method
to pass a random number for this parameter.
-
low
(uint): This parameter refers to the
lowest value to be generated for each pixel (0 to 255). The default
value is 0. Setting this value lower results in a darker noise pattern,
while setting it to a higher value results in a brighter pattern.
-
high
(uint): This parameter refers to the
highest value to be generated for each pixel (0 to 255). The default
value is 255. Setting this value lower results in a darker noise
pattern, while setting it to a higher value results in a brighter pattern.
-
channelOptions
(uint): This parameter specifies
to which color channel of the bitmap object the noise pattern will
be applied. The number can be a combination of any of the four color
channel ARGB values. The default value is 7.
-
grayScale
(Boolean): When set to
true
,
this parameter applies the
randomSeed
value to
the bitmap pixels, effectively washing all color out of the image.
The alpha channel is not affected by this parameter. The default value
is
false
.
The following example creates a bitmap image and applies a blue
noise pattern to it:
package
{
import flash.display.Sprite;
import flash.display.Bitmap;
import flash.display.BitmapData;
import flash.display.BitmapDataChannel;
public class BitmapNoise1 extends Sprite
{
public function BitmapNoise1()
{
var myBitmap:BitmapData = new BitmapData(250, 250,false, 0xff000000);
myBitmap.noise(500, 0, 255, BitmapDataChannel.BLUE,false);
var image:Bitmap = new Bitmap(myBitmap);
addChild(image);
}
}
}
If you want to create a more organic-looking texture, use the
perlinNoise()
method.
The
perlinNoise()
method produces realistic, organic
textures that are ideal for smoke, clouds, water, fire, or even
explosions.
Because it is generated by an algorithm, the
perlinNoise()
method
uses less memory than bitmap-based textures. However, it can still
have an impact on processor usage, slowing down your content and
causing the screen to be redrawn more slowly than the frame rate,
especially on older computers. This is mainly due to the floating-point
calculations that need to occur to process the perlin noise algorithms.
The method accepts nine parameters (the first six are required):
-
baseX
(Number): Determines the x (size)
value of patterns created.
-
baseY
(Number): Determines the y (size)
value of the patterns created.
-
numOctaves
(uint): Number of octaves or
individual noise functions to combine to create this noise. Larger
numbers of octaves create images with greater detail but also require
more processing time.
-
randomSeed
(int): The random seed number
works exactly the same way as it does in the
noise()
function.
To get a true random result, use the
Math.random()
method
to pass a random number for this parameter.
-
stitch
(Boolean): If set to
true
,
this method attempts to stitch (or smooth) the transition edges
of the image to create seamless textures for tiling as a bitmap
fill.
-
fractalNoise
(Boolean): This parameter relates
to the edges of the gradients being generated by the method. If
set to
true
, the method generates fractal noise
that smooths the edges of the effect. If set to
false
,
it generates turbulence. An image with turbulence has visible discontinuities
in the gradient that can make it better approximate sharper visual
effects, like flames and ocean waves.
-
channelOptions
(uint): The
channelOptions
parameter
works exactly the same way as it does in the
noise()
method.
It specifies to which color channel (of the bitmap) the noise pattern
is applied. The number can be a combination of any of the four color
channel ARGB values. The default value is 7.
-
grayScale
(Boolean): The
grayScale
parameter
works exactly the same way as it does in the
noise()
method.
If set to
true
, it applies the
randomSeed
value
to the bitmap pixels, effectively washing all color out of the image.
The default value is
false
.
-
offsets
(Array): An array of points that
correspond to x and y offsets for each octave. By manipulating the
offset values, you can smoothly scroll the layers of the image.
Each point in the offset array affects a specific octave noise function.
The default value is
null.
The following example creates a 150 x 150 pixel BitmapData object
that calls the
perlinNoise()
method to generate
a green and blue cloud effect:
package
{
import flash.display.Sprite;
import flash.display.Bitmap;
import flash.display.BitmapData;
import flash.display.BitmapDataChannel;
public class BitmapNoise2 extends Sprite
{
public function BitmapNoise2()
{
var myBitmapDataObject:BitmapData =
new BitmapData(150, 150, false, 0x00FF0000);
var seed:Number = Math.floor(Math.random() * 100);
var channels:uint = BitmapDataChannel.GREEN | BitmapDataChannel.BLUE
myBitmapDataObject.perlinNoise(100, 80, 6, seed, false, true, channels, false, null);
var myBitmap:Bitmap = new Bitmap(myBitmapDataObject);
addChild(myBitmap);
}
}
}
