Workshop:Amiga, Pascal, graphics.library and timer.device

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Respect the copyright

This workshop is based on the workshop titled "Retrocoding: Amiga, C, graphics.library und timer.device" which is written and copyrighted by Kai Scherrer.

The workshop you read here is a translation into English from the work done by Kai. The original workshop was aimed at the c-programmer and also this part has been rewritten here to address the Pascal programmer instead.

That means that the workshop here contains some changes in comparison to the original work done by Kai. The translation and changes respects and upholds original authors copyright.

Let's start with clarifying something first: Everything read in this lead section is written by me (the translator). That also means that text listed in and after the table of contents is based on the work written by original author.

This should hopefully clear things up with regards of the use of the words "I", "we" and "me".

This document is a translation (from German to English, changed programming language from c to Pascal) of a programming workshop for the Amiga, originally written by Kai Scherrer.

The original author wrote this tutorial for the c programming language as well as introduced the reader to different c-compilers for the Amiga as well as discussed their advantages/disadvantages and/or usage.

Because this document is targeting users that (want to) program using the Pascal language, there are many difference in comparison to the original documentation. As you perhaps might have noticed, these differences begin right from the start including this foreword.

notes with regards to Free Pascal

This documentation is aimed at those using the Free Pascal compiler. This compiler is able to run on a variety of operating systems including Amiga, AmigaOS, AROS and MorphOS (so you can use the compiler natively), but can also be used to cross-compile f.e. from Windows, Mac and/or Linux to target the aforementioned platforms.

Another wicked alternative for compiling single-file projects is using the online compiler. There is even a special version of the online compiler for old browsers that don't quite handle javascript

Note that the original author used vbcc for his workshop and that Free Pascal is able to use the same back-end (vasm/vlink) that is used by vbcc to create executables. In fact this is default when compiling natively on Amiga for example.

Free Pascal uses some defaults that might not always be obvious for most. For example, current API units automatically opens and closes libraries for you when you include such a unit in your project. The auto-opening and closing is something that usually isn't done for most programming languages targeting the Amiga platform.

Another note worth mentioning is the fact that Pascal does not has a dedicated program entry point by the name of main. As such, there is also no main header declaration. But, if you have your roots in c-programming and can't live without main() then this can easily be accommodated, for example:

// c main like entry-point.
function main(argc: Integer; argv: PPChar): integer;
  if EverthingElseWentOk() 
    then result := RETURN_OK 
      else result := RETURN_FAIL;

// This is the Pascal equivalent of main program entry point
  ExitCode := main(ArgC, ArgV);

Note that Pascal uses the identifier ExitCode to return a value to the shell but also realize that ArgC and ArgV can't be used to distinguish between program-startup from shell or WB (red: is that true ?)


As a typing exercise i wrote a simple and small Graphics-Engine. Actually "engine" is perhaps a bit exaggerated, but for the sake of simplicity and lack of a better word, my little baby has been written :-)

This gave me the idea to write a small workshop that handles the topic of Amiga Programming. In this workshop i describe the function and development progress of the engine, as well as explain some details about some of the components of AmigaOS.

The engine itself uses double-buffering to display the graphics: drawing operations are performed on a non-visible bitmap and only when a image is completely finished drawing, it is then copied to the visible bitmap of the window in one go. Later in the workshop, I would like to use this technique to display a full-screen image that does not copy the contents of the bitmaps, but uses the bitmaps themselves to display.

The desired frame rate is freely adjustable and is controlled by timer.device. In addition, we will control each animation based on the actual time that past, so that animations can be played at the correct speed even if the computer fails to keep up with the frame rate.

Our engine is designed to operate in a system-friendly and multitasking environment that runs on OS 1.2 and up (red: Free Pascal currently only provide headers that match OS3.x). As of OS 3.0, functionality is used which improves performance for graphics cards. However, in the current version there is no further support for such RTG-systems: Our renderer is therefor limited to 8-bit graphics. Nor is there any support for special features of the Amiga chipset: So there will be no hardware scrolling, sprites or copperlists.

For those there is another nice play-field where you can play and experiment with the functions of graphics.library and bitplanes - and in principle and without much changes, the obtained results can also be incorporated in 'real' demo's, games or programs.

To accomplish this I will introduce some basic functions from graphics.library to develop a simple 2d vector renderer that is even able to reach acceptable performance on stock 68000 systems.

In order to be able to follow this workshop you need a working Pascal compiler. Therefor i will start with a short explanation on the installation and use of Free Pascal.

In addition, you should have at least some rudimentary knowledge of the Pascal programming language. I will not provide too much background information otherwise. Although it would be nice to have everything explained all in one place, on the other hand we do not want to dwell too much into known details. So if you don't understand something from this workshop then don't hesitate to ask. At best you would have me revise he relevant posts or add some digression.

And now for some fun!

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