Difference between revisions of "Picture Encoding"
m (Protected "Picture Encoding" ([edit=autoconfirmed] (indefinite) [move=autoconfirmed] (indefinite))) |
|
(No difference)
|
Latest revision as of 09:05, 4 December 2010
This article describes how pictures are encoded in graphics memory. This applies to Graphics RAM and Graphics ROM.
Each card stores a single 8x8 picture in a sequence of 8 bytes. The first byte of the sequence holds the topmost row of pixels. The last byte holds the bottom row of pixels. Bit 7 in each byte holds the leftmost column of pixels, and bit 0 in each byte holds the rightmost column. Pictorally:
Bit # 7 6 5 4 3 2 1 0 +---------------+ 0 | | B 1 | | y 2 | | t 3 | | e 4 | | 5 | | # 6 | | 7 | | +---------------+
Suppose, for instance, we want to define a picture for the letter R. That picture might look like so: ('#' indicates pixels that are "on", and '.' indicates pixels that are "off")
Bit # 7 6 5 4 3 2 1 0 +---------------+ 0 |# # # # # # . .| B 1 |. # # . . # # .| y 2 |. # # . . # # .| t 3 |. # # # # # . .| e 4 |. # # . . # # .| 5 |. # # . . # # .| # 6 |. # # . . # # .| 7 |# # # . . # # #| +---------------+
All of the "on" pixels are represented with 1 bits, and all of the "off" pixels are represented with 0 bits. The binary pattern for this character would be:
DECLE %11111100 DECLE %01100110 DECLE %01100110 DECLE %01111100 DECLE %01100110 DECLE %01100110 DECLE %01100110 DECLE %11100111
You could copy this exact bit pattern into one of the card slots in GRAM, and voila! You have a stylized R.