GFAgraphics

Introduction to graphics

Thanks to the VDI GFABASIC offers the coder a wealth of commands to draw something on screen. This part of the tutorial aims to help you getting started with graphics from GFABASIC.

First of all you have to understand how a nice picture works on the Atari ST. Everything you see on your screen is made up from tiny little dots. With the various graphics commands you can manipulate all of those dots to display anything on screen.

The amount of dots you can manipulate is dictated by the current screen resolution. The ST offers 3 different resolutions. By default GFABASIC starts your program in the current one so if you did boot GFA from a medium resolution desktop your program will use medium resolution too. (One can change that behaviour but that is not the goal of this part of the tutorial.)

The screen resoultions differ on their size and the amount of colors you can use to draw the picture. Without tricks the ST offers the following video modes:

• ST-LOW: 320x200 pixels, 16 colors
• ST-MED: 640x200 pixels, 4 colors
• ST-HIGH: 640x400 pixels, 2 colors

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