TRS-80 Graphics. For the Model I and the Model III by David A. Kater, Susan J. Thomas

By David A. Kater, Susan J. Thomas

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Take the case of moving a single graphic dot around the screen. 10 I I[JI] A. moving dot. The motion is due to the RES E T statement. Every time a new rectangle is lit, the one to its left is erased . The motion seems fairly continuous; it will certainly pass for a bouncing ball in a ping-pong game. But what would happen if we tried to move a larger object across the screen? Change the following lines: 30 FOR X=1 TO 40 FOR Y=1 50 NEXT Y : NEXT X TO 10 and RUN . Here we are trying to move a vertical bar sideways, but the motion appears jerky at best.

2'JOJIJ2J J. ~. ~O'I '2' 1 Title page layout. We strongly recommend that you carefully layout graphic displays on a video display worksheet before writing any program. Laying out a display by first using pencil and eraser could save you hours of using trial and error later to touch up poor displays on the screen . You may find it desirable to make a copy of the video display worksheet on a sheet of acetate similar to those used with overhead projectors . Try your local copy center. You can write on acetate with overhead pens and erase with a cloth.

Why, you can hardly see those little critters! We need to add a time delay before erasing each * . So change line 30 to 30 FOR 1=1 TO 30 19 20 Basic Graphics on the TRS-80 and add 70 FOR J=1 TO 100 : NEXT J Note that the colon allows us to have two statements on the same line . At this point, type LIS T to make sure your listing looks like this: 10 20 30 40 60 70 80 80 CLS S$="*" FOR 1=1 TO 30 R=RND(1023) PRINT@ R, S$i FOR J=1 TO 100 PRINT@ R, " " 1 NE}(T I . NE){T J RUN the program. Yes, that's much better.

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