Radio Shack TRS-80 Operation Manual page 37

Operation Manual
Computer Graphics
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Figure 14. Example of an a-by-a Pixel Grid
Strings allow numerous graphic variations because of the
many pixel combinations you can define.
Important Note: You cannot use more than two consecutive
rows of tiles which match the background or an Illegal
Function Call error will occur. For example:
PAINT
(1,I),CHR$(&HFF)+CHR$(&HFF)+CHR$(&H~~)+CHR$(&H~~)
+CHR$(&H~~)+CHR$(&H~~),l,CHR$(&H~~)
returns an Illegal Function Call error.
Using Tiling
You may want to use a sheet of graph paper to draw a style
pattern. This way, you'll be able to visualize the pattern
and calculate the binary and hexadecimal numbers needed.
Note: Tiling should only be done on either a totally black
or white background; otherwise, results are unpredictable.
To draw an example of a tile on paper:
1. Take a sheet of paper and draw a grid according to the
size you want (a x a, 24 x a, etc.). Each boxed area
on this grid, hypothetically, represents one pixel on
your screen.
2. Decide what type of pattern you want (zigzag, diagonal
lines, perpendicular lines, etc.).
3. Fill in each grid in each 8-pixel-wide row of the tile
if you want that pixel to be ON, according to your
pattern. If you want the pixel to be OFF, leave the
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