/* * apple2.text.c * * This code sits as a kind of wrapper over the bitmap fonts that the * Apple II uses. Neither the system nor inverted fonts are exactly * composed in the type of character set that Apple expects; they * implement the glpyhs we need in order to make such. You can have * inversed characters in the primary character set, for one; in the * alternate character set, you can have MouseText glyphs, yet they are * implemented as part of both fonts. */ #include #include "apple2/text.h" /* * This table maps display buffer addresses for 40-column text to the * corresponding row on-screen (given a 40x24 grid). A negative column * indicates that the address is not displayable. */ static int buffer_rows[] = { // 0 1 2 3 4 5 6 7 8 9 A B C D E F 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // $400 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // $410 0, 0, 0, 0, 0, 0, 0, 0, 8, 8, 8, 8, 8, 8, 8, 8, // $420 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, // $430 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, // $440 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, // $450 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, // $460 16, 16, 16, 16, 16, 16, 16, 16, -1, -1, -1, -1, -1, -1, -1, -1, // $470 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // $480 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // $490 1, 1, 1, 1, 1, 1, 1, 1, 9, 9, 9, 9, 9, 9, 9, 9, // $4A0 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, // $4B0 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, // $4C0 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, // $4D0 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, // $4E0 17, 17, 17, 17, 17, 17, 17, 17, -1, -1, -1, -1, -1, -1, -1, -1, // $4F0 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, // $500 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, // $510 2, 2, 2, 2, 2, 2, 2, 2, 10, 10, 10, 10, 10, 10, 10, 10, // $520 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, // $530 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, // $540 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, // $550 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, // $560 18, 18, 18, 18, 18, 18, 18, 18, -1, -1, -1, -1, -1, -1, -1, -1, // $570 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, // $580 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, // $590 3, 3, 3, 3, 3, 3, 3, 3, 11, 11, 11, 11, 11, 11, 11, 11, // $5A0 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, // $5B0 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, // $5C0 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, // $5D0 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, // $5E0 19, 19, 19, 19, 19, 19, 19, 19, -1, -1, -1, -1, -1, -1, -1, -1, // $5F0 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, // $600 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, // $610 4, 4, 4, 4, 4, 4, 4, 4, 12, 12, 12, 12, 12, 12, 12, 12, // $620 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, // $630 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, // $640 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, // $650 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, // $660 20, 20, 20, 20, 20, 20, 20, 20, -1, -1, -1, -1, -1, -1, -1, -1, // $670 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, // $680 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, // $690 5, 5, 5, 5, 5, 5, 5, 5, 13, 13, 13, 13, 13, 13, 13, 13, // $6A0 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, // $6B0 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, // $6C0 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, // $6D0 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, // $6E0 21, 21, 21, 21, 21, 21, 21, 21, -1, -1, -1, -1, -1, -1, -1, -1, // $6F0 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, // $700 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, // $710 6, 6, 6, 6, 6, 6, 6, 6, 14, 14, 14, 14, 14, 14, 14, 14, // $720 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, // $730 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, // $740 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, // $750 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, // $760 22, 22, 22, 22, 22, 22, 22, 22, -1, -1, -1, -1, -1, -1, -1, -1, // $770 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, // $780 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, // $790 7, 7, 7, 7, 7, 7, 7, 7, 15, 15, 15, 15, 15, 15, 15, 15, // $7A0 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, // $7B0 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, // $7C0 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, // $7D0 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, // $7E0 23, 23, 23, 23, 23, 23, 23, 23, -1, -1, -1, -1, -1, -1, -1, -1, // $7F0 }; /* * Similar to buffer_rows, this table defines the column numbers for * buffer display addresses. */ static int buffer_cols[] = { // 0 1 2 3 4 5 6 7 8 9 A B C D E F 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, // $400 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, // $410 32, 33, 34, 35, 36, 37, 38, 39, 0, 1, 2, 3, 4, 5, 6, 7, // $420 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, // $430 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, // $440 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, // $450 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, // $460 32, 33, 34, 35, 36, 37, 38, 39, -1, -1, -1, -1, -1, -1, -1, -1, // $470 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, // $480 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, // $490 32, 33, 34, 35, 36, 37, 38, 39, 0, 1, 2, 3, 4, 5, 6, 7, // $4A0 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, // $4B0 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, // $4C0 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, // $4D0 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, // $4E0 32, 33, 34, 35, 36, 37, 38, 39, -1, -1, -1, -1, -1, -1, -1, -1, // $4F0 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, // $500 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, // $510 32, 33, 34, 35, 36, 37, 38, 39, 0, 1, 2, 3, 4, 5, 6, 7, // $520 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, // $530 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, // $540 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, // $550 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, // $560 32, 33, 34, 35, 36, 37, 38, 39, -1, -1, -1, -1, -1, -1, -1, -1, // $570 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, // $580 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, // $590 32, 33, 34, 35, 36, 37, 38, 39, 0, 1, 2, 3, 4, 5, 6, 7, // $5A0 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, // $5B0 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, // $5C0 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, // $5D0 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, // $5E0 32, 33, 34, 35, 36, 37, 38, 39, -1, -1, -1, -1, -1, -1, -1, -1, // $5F0 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, // $600 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, // $610 32, 33, 34, 35, 36, 37, 38, 39, 0, 1, 2, 3, 4, 5, 6, 7, // $620 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, // $630 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, // $640 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, // $650 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, // $660 32, 33, 34, 35, 36, 37, 38, 39, -1, -1, -1, -1, -1, -1, -1, -1, // $670 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, // $680 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, // $690 32, 33, 34, 35, 36, 37, 38, 39, 0, 1, 2, 3, 4, 5, 6, 7, // $6A0 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, // $6B0 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, // $6C0 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, // $6D0 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, // $6E0 32, 33, 34, 35, 36, 37, 38, 39, -1, -1, -1, -1, -1, -1, -1, -1, // $6F0 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, // $700 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, // $710 32, 33, 34, 35, 36, 37, 38, 39, 0, 1, 2, 3, 4, 5, 6, 7, // $720 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, // $730 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, // $740 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, // $750 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, // $760 32, 33, 34, 35, 36, 37, 38, 39, -1, -1, -1, -1, -1, -1, -1, -1, // $770 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, // $780 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, // $790 32, 33, 34, 35, 36, 37, 38, 39, 0, 1, 2, 3, 4, 5, 6, 7, // $7A0 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, // $7B0 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, // $7C0 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, // $7D0 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, // $7E0 32, 33, 34, 35, 36, 37, 38, 39, -1, -1, -1, -1, -1, -1, -1, -1, // $7F0 }; /* * This is the primary character set of display symbols. The order of * characters generally follows ASCII order, but doesn't map to ASCII * exactly. To begin with, you will note that lower-case characters are * not found until the last two rows; moreover, control characters have * letter-equivalents which may be displayed--for example, at boot time, * when the display buffer is filled with zero-bytes (and the effect is * that you see the screen is filled with at symbols). */ static char primary_display[] = { // $00 - $3F '@', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '[', '\\', ']', '^', '_', ' ', '!', '"', '#', '$', '%', '&', '\'', '(', ')', '*', '+', ',', '-', '.', '/', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', ':', ';', '<', '=', '>', '?', // $40 - $7F '@', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '[', '\\', ']', '^', '_', ' ', '!', '"', '#', '$', '%', '&', '\'', '(', ')', '*', '+', ',', '-', '.', '/', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', ':', ';', '<', '=', '>', '?', // $80 - $BF '@', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '[', '\\', ']', '^', '_', ' ', '!', '"', '#', '$', '%', '&', '\'', '(', ')', '*', '+', ',', '-', '.', '/', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', ':', ';', '<', '=', '>', '?', // $C0 - $FF '@', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '[', '\\', ']', '^', '_', '`', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '{', '|', '}', '~', ' ', }; /* * Following is the alternate character display set. It differs in some * fundamental ways, and particularly it contains "MouseText" symbols * (which are not yet implemented!); it also has lower-case symbols in * different positions than the primary set. */ static char alternate_display[] = { // $00 - $3F '@', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '[', '\\', ']', '^', '_', ' ', '!', '"', '#', '$', '%', '&', '\'', '(', ')', '*', '+', ',', '-', '.', '/', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', ':', ';', '<', '=', '>', '?', // $40 - $7F // Note that $40 - $5F are actually the MouseText symbols, which are // not yet implemented; note also that $60 - $7F are lower-case '@', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '[', '\\', ']', '^', '_', '`', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '{', '|', '}', '~', ' ', // $80 - $BF '@', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '[', '\\', ']', '^', '_', ' ', '!', '"', '#', '$', '%', '&', '\'', '(', ')', '*', '+', ',', '-', '.', '/', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', ':', ';', '<', '=', '>', '?', // $C0 - $FF // Note here that, even though lower-case symbols are represented in // $60 - $7F, they are repeated here in the same positions as they // are in the primary set. '@', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '[', '\\', ']', '^', '_', '`', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '{', '|', '}', '~', ' ', }; /* * Return the row where the given address will be displayed. */ int apple2_text_row(size_t addr) { return buffer_rows[addr - 0x400]; } /* * Return the column where the given address will be displayed. */ int apple2_text_col(size_t addr) { return buffer_cols[addr - 0x400]; } /* * Return the primary character set representation matching the given * character code. */ char apple2_text_primary(vm_8bit ch) { return primary_display[ch]; } /* * Return the alternate character set representation matching the given * character code. */ char apple2_text_alternate(vm_8bit ch) { return alternate_display[ch]; } /* * Draw a text character at the given address. */ void apple2_text_draw(apple2 *mach, size_t addr) { int err, row; bool inverse, flashing; vm_8bit ch; vm_area dest; vm_bitfont *font; // By default, use the primary display set char *charset = primary_display; // If we're updating a page 2 address and we're not in some kind of // double resolution mode, then we shouldn't actually render the // thing. if (addr > 0x07FF && !apple2_is_double_video(mach)) { return; } // Default font = mach->sysfont; // This is actually not a byte that is displayable, so let's get out row = buffer_rows[addr - 0x400]; if (row == -1) { return; } err = apple2_text_area(&dest, font, addr); if (err != OK) { return; } // What are we working with? ch = mos6502_get(mach->cpu, addr); // The ASCII code we will use is only that which is composed of the // first 6 bits. //ch = ch & 0x7f; if (mach->display_mode & DISPLAY_ALTCHAR) { if (ch < 0x40 || (ch >= 0x60 && ch < 0x7F)) { font = mach->invfont; } else if (ch >= 0x40 && ch <= 0x5F) { font = mach->sysfont; } charset = alternate_display; } else { if (ch < 0x40) { font = mach->invfont; } // Note: < 0x80 is flashing, but we don't have that implemented // yet } vm_bitfont_render(font, mach->screen, &dest, charset[ch]); } /* * This function will fill in the width, height, and x and y offsets for * a character at the given address using the given font. */ int apple2_text_area(vm_area *area, vm_bitfont *font, size_t addr) { // The text display buffers are located at "Page 1" and "Page 2", // which are at byte 1024-2047 (0x0400-0x07FF) and byte 2048-3071 // (0x0800-0x0BFF) respectively. If the given address is not in // those (contiguous) ranges, then let's bail. if (addr < 0x0400 || addr > 0x0BFF) { return ERR_INVALID; } // Certain addresses are not meant to be displayable, and are // actually used for system data if (buffer_rows[addr] == -1 || buffer_cols[addr] == -1) { return ERR_INVALID; } // In a given page for 40-column mode, you get 960 grid parts that // you may use. In 80-column mode, it's more like 1920 grid parts // (40x24 = 960, 80x24 = 1920). The way we look at this is the // address indicates the place on the grid where text should go. We // don't care how it got there. Let's figure out that position // on-screen. area->xoff = buffer_cols[addr - 0x400] * font->width; area->yoff = buffer_rows[addr - 0x400] * font->height; // Our width and height must be that of the font. area->width = font->width; area->height = font->height; return OK; }