This program has been put together to help people who use, or want to use, ARM machine code to create graphical programs such as demos and games, and the aim of this program is to aid the creation of the raw sprite data needed in these situations.
The raw sprite data I speak of contains chunks of screen memory data, which can be written straight onto the screen memory to display a picture or sprite.Screen memory is the section of memory that is sent to, and so displayed on, the screen.
The Extractor application is needed because, when using machine code, the standard Acorn sprite file tends to be too complex to be of any use. So people who need to use sprites from machine code make small programs to extract the raw sprite data from the Acorn format sprite files. Unfortunately, these programs tend to be inflexible and rather idiosyncratic, making them unsuitable for distribution to the public. Extractor offers a flexible system for the creation of these simpler files and it also works on the desktop to make it more user friendly.
For those of you who are more experienced in this type of machine code programming, Extractor has been designed with you in mind as well as the beginner. During the production of Extractor I conferred with an experienced machine code programmer to find out what I needed to include, like the 14 different styles of sprite and mask interlace (chapter 3), the options for different raw data file formats (chapter 7) and the style used to extract the sprite data from the screen. The latter has two possibilities:
1 - "Move down after each line"
What this means is that the program extracts the top line of the sprite first and works it's way down the sprite. This default method has been used throughout this manual.
2 - "Move up after each line"
This contrasting option means that the program extracts the bottom line of the sprite first and works it's way up the sprite. This method has been included for those experienced programmers who would prefer to use it.
N.B. Every line of the sprite is extracted in the same way, from left to right in bytes.
This is how to get to these options on the Extractor menu structure.
This option can be set for each sprite individually.
Also, if you use machine code designed to work with one extraction method and have the raw sprite data extracted using the other method, the sprite will be upside-down when plotted. You may find this useful.
