GTIA SKETCHPAD
Graphics utility for Modes 9, 10, and 11
GTIA Sketchpad is a drawing program for Graphics Modes 9, 10, and 11. With it you can create pictures of up to sixteen colors using simple commands and a joystick. You can save and retrieve your compositions on tape or disk and even make a printout if you have an Epson printer with Graftrax. I wrote this program because I wanted to take advantage of the GTIA capabilities but none of the drawing packages on the market were written for the new modes.
PROGRAM OPERATION
After a brief blanking of the screen you will be presented with a menu of the modes available. For purposes of experimentation, type "1" to set up Mode 9. You are now asked for a background color. This is a number from 0 to 15 corresponding to the Atari color set:
0 Black------------1 Gold
2 Orange----------3 Red
4 Pink-------------5 Violet
6 Indigo-----------7 Blue
8 Light Blue------9 Blue Green
10 Aqua-----------11 Green Blue
12 Green----------13 Yellow Green
14 Orange Green-15 Orange
Type 0 for a black background and you will see the basic screen setup. At the bottom there is a text window. Above this there is a color bar which ranges from black to white. Finally, there is a flashing dot in the center of the screen.
Look at the text window. You will see the following: "Point, Line, Doodle, Box, Circle, Fill, Whole screen, Save, Retrieve, Hardcopy, New, Quit."
To select any of the above, press the letter which is highlighted in inverse video and follow the instructions that appear. For example, press [B] and you will be asked to position the cursor to one corner and press the trigger, then move to the opposite corner and press the trigger again. If you did this and nothing happened, it is because you drew a black box on a black background. To choose a different color, press either of the arrow keys. The marker under the color bar will move correspondingly. All of the commands work in similar ways. When plotting points or drawing lines, or when you use the "doodle mode" you will stay in that command mode until you press [ESC]. You can exit any command by pressing [ESC] at any time, and you can change color at any time. When drawing circles, you will be prompted for a correction factor. This ranges from 1.0 to 0.270 and allows you to correct for the normally skewed shapes of the pixels. 1.0 will draw an ellipse, while 0.270 will draw a circle. "Fill" will fill with the fill-color any area that is completely bounded.
[W], for Whole Screen, will fill the drawing area with the current color. To erase your drawing, use [W] with the background color. To stop the whole-screen fill at any point, press [ESC].
To save a copy of your artwork, press [S] and answer the prompt with "C:" for cassette or "D:filename" for disk. When the file is saved, you will see the options menu appear in the text window. To retrieve the file, press [R] and follow the same procedure. Pressing [E] will cancel the command.
[H] will allow you to create a printout of your screen on an Epson MX-80 with Graftrax. You have a choice of two types of printout: a random dot pattern or a fixed pattern. While this is a matter of taste if you are in a hurry use the faster, patterned version.
Should you somehow crash the program, you can re-enter it without losing your picture by BASIC's direct mode.
All ofthe above commands are the same for all three modes (9, 10, and 11). The only difference among modes is seen in the setup. If you use Mode 10, you will be prompted for color, and for the luminance of each of nine colors. The color is a number from the previously-listed chart, and luminance is a number from 0 to 15, with 0 being the darkest. Mode 11 will prompt you for the luminance value at which all sixteen colors will be displayed, with 0 again being the darkest.
Listing: GTIAPAD.BAS Download