[JAVA][Beginning Java 8 Games Development]

Chapter 5 ■ An Introduction to Game Design: Concepts, Multimedia, and Using Scene Builder
Representing Color and Alpha in Java 8 Game Code: Using Hexadecimal Notation
Now that you know what color depth and alpha channels are, and that color and transparency are represented by
using a combination of four different image channels (alpha, red, green, and blue [ARGB]) within any given digital
image, it is important to understand how, as programmers, you are supposed to represent these four ARGB image
color and transparency channel values in Java 8 and JavaFX.
In the Java programming language, color and alpha are used not only in 2D digital imagery (commonly referred
to as bitmap imagery), but also in 2D illustration (commonly referred to as vector imagery). Colors and transparency
values are also often used across a number of different color setting options. As you have already seen with the
Stage object and the Scene object, you can set a background color (or transparency value) for a stage, scene, layout
container (StackPane), or UI control, among other things.
In Java (and thus JavaFX) different levels of ARGB color intensity values are represented using hexadecimal
notation. Hexadecimal (or hex) is based on the original Base16 computer notation. This was used long ago to
represent 16 bits of data value. Unlike the more common Base10, which counts from 0 to 9, Base16 notation counts
from 0 to F, where F represents the Base10 value of 15 (0 to 15 yields 16 data values).
A hexadecimal value in Java always starts with a 0 and an x, like this: 0xFFFFFF. This hexadecimal color value
represents the Color.WHITE constant and uses no alpha channel. Each of the six slots in this 24-bit hexadecimal
representation stands for a single Base16 value, so to get the 256 values required for each RGB color will take two
slots, as 16 × 16 = 256. Therefore, to represent a 24-bit image using hexadecimal notation, you would need to have
six slots after the pound sign to hold each of the six hexadecimal data values (data pairs representing 256 levels of
value each). If you multiply 16 × 16 × 16 × 16 × 16 × 16 you will get the 16,777,216 colors that are possible using 24-bit,
truecolor image data.
The hexadecimal data slots represent RGB values in the following format: 0xRRGGBB. For the Java constant
Color.WHITE, all the red, green, and blue channels in the hexadecimal color data value representation are at the full
(maximum color value) luminosity setting. If you add all these colors together, you will get white light.
The color yellow would be represented by the red and green channels’ being on, and the blue channel’s being
off, so a hexadecimal representation for Color.YELLOW would therefore be 0xFFFF00, where both the red and green
channel slots are fully on (FF, or a 255 Base10 data value), and the blue channel slots are fully off (00, or a 0 value).
The eight hexadecimal data slots for an ARGB value will hold data using the following format: 0xAARRGGBB.
Thus, for the Color.WHITE, all alpha, red, green, and blue channels in the hexadecimal color data value
representation would be at their maximum luminosity (or opacity), and the alpha channel would be fully opaque, that
is, not transparent, as represented by an FF value. Therefore, the hexadecimal value for the Color.WHITE constant
would be 0xFFFFFFFF.
A 100 percent transparent alpha channel can be represented by setting an alpha slot to 0, as you observed when
you created a windowless Java 8 application (see Chapter 4). Therefore, you would represent transparent image pixel
values using any value between 0x00000000 and 0x00FFFFFF. It is important to note that if an alpha channel value
equates to full transparency, it would follow that the 16,777,216 color values that could be contained in the other six
(RGB) hexadecimal data value slots will not matter at all, because that pixel, being transparent, will be evaluated as
not being there and thus will not be composited in the final image or animation composite image.
Digital Image Masking: Using Alpha Channels to Create Game Sprites
One of the primary applications for alpha channels in game design is to mask out areas of an image or animation
(series of images) so that it can be used as a game sprite in a game play image-compositing scenario. Masking is the
process of cutting subject matter out of a digital image so that the subject matter can be placed on its own virtual layer,
using alpha channel transparency values. This is done using a digital imaging software package, such as GIMP.
Digital image–compositing software packages, such as Photoshop and GIMP, feature tools that are included for use
in masking and image compositing. You cannot do effective image compositing without doing effective masking, so this
is an important area to master for game designers who wish to integrate graphics elements, such as image sprites and
sprite animation, into their game designs. The art of digital image masking has been around for a very long time!
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