uk.ac.starlink.ttools.plot2.paper

Class Compositor

java.lang.Object

uk.ac.starlink.ttools.plot2.paper.Compositor

Direct Known Subclasses:

Compositor.BoostCompositor

public abstract class Compositor
extends Object

Represents an algorithm for combining multiple RGBA values to produce a single RGBA value. The createBuffer(int) method produces a buffer containing a vector of pixels for which the compositing operation can be performed on each element.

In general RGB values are not pre-multiplied by alpha as used by this class.

Since:

12 Feb 2013

Author:

Mark Taylor

See Also:

RgbImage

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Compositor.BoostCompositor Compositor with boosted saturation.
static interface	Compositor.Buffer Buffer of pixels on which compositing operations can be performed.

Field Summary

Fields

Modifier and Type	Field and Description
static Compositor	SATURATION Implementation which adds colours until the alpha is saturated and then makes no further updates to colour.

Constructor Summary

Constructors

Constructor and Description
Compositor()

Method Summary

Modifier and Type	Method and Description
static float	byteToFloat(int i) Maps an integer in the range 0-255 to a float in the range 0-1.
abstract Compositor.Buffer	createBuffer(int count) Creates a buffer on which compositing operations can be performed.
static int	floatToByte(float f) Maps a float in the range 0-1 to an int in the range 0-255.
abstract float	scaleAlpha(float alpha) Adjusts an alpha value in accordance with this compositor's policy.
static int	srcOverOpaque(int sRgba, int dRgb) Returns the result of compositing a possibly transparent source pixel over an opaque destination pixel.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

SATURATION

public static final Compositor SATURATION

Implementation which adds colours until the alpha is saturated and then makes no further updates to colour.

Constructor Detail

Compositor

public Compositor()

Method Detail

scaleAlpha

public abstract float scaleAlpha(float alpha)

Adjusts an alpha value in accordance with this compositor's policy. It takes an alpha value in the range 0-1 and maps it into the range to be used for output from this compositor.

Parameters:

alpha - input alpha in range 0-1

Returns:

adjusted alpha, also in range 0-1

createBuffer

public abstract Compositor.Buffer createBuffer(int count)

Creates a buffer on which compositing operations can be performed.

Parameters:

count - number of pixel elements in buffer

Returns:

new buffer

byteToFloat

public static float byteToFloat(int i)

Maps an integer in the range 0-255 to a float in the range 0-1. Bits more significant than the first 8 are ignored.

Parameters:

i - integer value

Returns:

float in range 0-1

floatToByte

public static int floatToByte(float f)

Maps a float in the range 0-1 to an int in the range 0-255.

Parameters:

f - float in range 0-1

Returns:

int in range 0-255

srcOverOpaque

public static int srcOverOpaque(int sRgba,
                                int dRgb)

Returns the result of compositing a possibly transparent source pixel over an opaque destination pixel.

Parameters:

sRgba - RGBA for source pixel

dRgb - RGB for opaque destination pixel

Returns:

RGBA for composition result