Composition - Serabe/rinzelight GitHub Wiki

Composing two images is drawing the source image onto the destiny image.

The Porter-Duff rules define how the composition is made. There are 12 of them:

• clear.
• dst.
• dst-atop.
• dst-in
• dst-over
• src
• src-in
• src-out
• src-over
• xor

The Porter-Duff rules are functions in rinzelight. They can be used with no or one arguments. The argument is taken as a factor. Take a look at AlphaComposite javadoc for more info. The most important point about Porter-Duff rules being functions is that you must use them as (rule) not simply as rule. For example

(compose dst src (src-over)); Right!
(compose dst src src-over); Wrong!

The following examples shows the differences between the different methods.

clear

dst

dst-atop

dst-in

dst-out

dst-over

src

src-atop

src-in

src-out

src-over

xor

rinzelight.composition contains two with- macros. Both of them executes the code inside a doto whose object is the Graphics2D for the given image. Furthermore, they reset the composite to the original one.

These are lowlevel macros, so you cannot use rinzelight function inside them.

This method sets the XOR mode to the color passed as second argument.

This method sets the active composite to the one given as second parameter.

Compose function is heavily overloaded. It can take from two to five arguments. Each case will be discussed.

dst and src are the images for the composition, comp is the composite used for it (it may be one of the Porter-Duff rules or a custom Composite object). x and y are the coordinates of the pixel where the composition starts.

dst and src are the images for the composition, comp is the composite used for it (it may be one of the Porter-Duff rules or a custom Composite object). grav is the gravity used to get the coordinates of the pixel where the composition starts.

dst and src are the images for the composition. The third argument may be a composite or a gravity. The composite? predicate is applied to the third argument and, if it is not a Composite, then (src-over) is applied. If it is a composite, composition takes place starting on upper-left corner (pixel 0,0).

dst and src are the images for the composition. Default composite ((src-over)) is supplied, and the starting pixel is 0,0.

Since working with different parameters has been widely covered, the example will show the different predefined gravities in action.

Center

North

North-east

East

South-east

South

South-west

West

North-west

You may be wondering why composites need to be executed and geometries can be passed as a function. Here is the reasoning behind it:

A composite is an object, i.e. an instance of a class implementing Composite, while a geometry is defined as a function. Porter-Deff rules are defined as functions instead of composites since they can be multiplied by a factor. It certainly be more logical to use a macro, but by now I don’t know how to write a macro inside a macro, but it is certainly the way to follow.