libc: add Sprinter palette API (graphics + text planes)
palette.h/video/palette.c wrap BIOS $A4 PIC_SET_PAL/PIC_GET_PAL and $A6 SET_PAL_INIT for the 8 palette pages (0-3 graphics, 4-7 text planes). gfx_palette.c and conio/text_palette.c are thin per-domain wrappers; text_palette.c maps the text "plane" 0..3 (paper/ink/blink-paper/ blink-ink) onto BIOS pages 4..7. Covered by tests/text_palette. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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# Build text_palette.exe — uses lib/sprinter.lib in TINY memory mode.
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PROJ_ROOT := $(abspath $(CURDIR)/../..)
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EXAMPLE := text_palette
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include $(PROJ_ROOT)/app.mk
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/*
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* text_palette — interactive smoke test for the text-mode palette API.
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*
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* Walks through four palette states. Each stage clears the screen first
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* and then renders 16 lines, one per ink-colour index, each line showing:
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*
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* <RGB values read back from the INK plane>
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* < part 1: fg = N on bg = 0 — colour N text on the default black >
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* < part 2: fg = 15 on bg = N — bright-white text on a coloured bg >
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*
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* Stages:
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* 1) Initial CGA palette (boot default).
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* 2) Grayscale ramp installed via text_pal_load() in all four text
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* planes (4..7) so flash is fully suppressed; both ink (low nibble)
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* and paper (mid nibble) get 16 shades — bit 7 of the attribute
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* byte is folded into the paper index so we cover all 16 bg slots.
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* 3) CGA defaults restored via pal_reset_at(PAL_CGA, plane, 0) for
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* plane = 4..7 — explicit per-plane reset in case BIOS interprets
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* the A register narrowly.
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* 4) Sinclair palette via pal_reset_at(PAL_SINCLAIR, plane, 0) for
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* plane = 4..7.
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*
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* Memory: tiny (one bank). The 1 KB palette buffer for text_pal_load()
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* is static — keeps it out of the (small) stack frame.
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*/
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#include <stdio.h>
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#include <conio.h>
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#include <palette.h>
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#include <stdint.h>
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/* 256 entries × 4 bytes (B, G, R, 0). Static so it lives in DATA. */
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static uint8_t pal_buf[256 * 4];
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#define ATTR_DEFAULT COLOR(COLOR_LIGHTGRAY, COLOR_BLACK)
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/* For each colour index N=0..15 print:
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* - RGB triple read back from the INK plane
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* - sample text in fg=N on bg=0
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* - sample text in fg=15 on bg=N
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*
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* The bg=N attribute uses ALL FOUR bits of the mid nibble (including the
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* blink bit). In the CGA default this means N >= 8 will flash; with our
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* grayscale loader the four planes are identical, so it just selects one
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* of 16 paper colours. */
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static void show_palette_state(void)
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{
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for (uint8_t n = 0; n < 16; n++) {
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uint8_t r = 0, g = 0, b = 0;
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text_pal_get_color(TEXT_PAL_INK, n, &r, &g, &b);
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textattr(ATTR_DEFAULT);
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cprintf(" #%X R=%3u G=%3u B=%3u ", n, r, g, b);
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/* part 1: fg=N on bg=0 */
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textattr((uint8_t)(n & 0x0F));
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cprintf(" fg=%X on bg=0 ", n);
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/* part 2: fg=15 on bg=N (4-bit bg slot, may carry blink bit) */
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textattr((uint8_t)(((n & 0x0F) << 4) | 0x0F));
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cprintf(" white on bg=%X ", n);
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textattr(ATTR_DEFAULT);
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cputs("\r\n");
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}
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}
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/* Build a 16-step grayscale ramp and load it into ALL FOUR text planes
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* (paper, ink, blink-paper, blink-ink). Identical paper/blink-paper and
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* ink/blink-ink means there is nothing to alternate between → no flash.
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*
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* INK / BLINK_INK index by attr's low nibble: 16 fg grey levels
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* PAPER / BLINK_PAPER index by attr's mid nibble: 16 bg grey levels
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* (full 4 bits incl. bit 7) */
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static void load_grayscale_all_planes(void)
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{
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/* INK and BLINK_INK: shade taken from attr & 0x0F. */
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for (uint16_t a = 0; a < 256; a++) {
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uint8_t v = (uint8_t)((a & 0x0F) * 17u); /* 0,17,34,...,255 */
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pal_buf[a * 4 + 0] = v; /* B */
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pal_buf[a * 4 + 1] = v; /* G */
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pal_buf[a * 4 + 2] = v; /* R */
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pal_buf[a * 4 + 3] = 0;
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}
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text_pal_load(TEXT_PAL_INK, 0, 0, pal_buf);
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text_pal_load(TEXT_PAL_BLINK_INK, 0, 0, pal_buf);
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/* PAPER and BLINK_PAPER: shade taken from (attr >> 4) & 0x0F. */
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for (uint16_t a = 0; a < 256; a++) {
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uint8_t v = (uint8_t)(((a >> 4) & 0x0F) * 17u);
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pal_buf[a * 4 + 0] = v;
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pal_buf[a * 4 + 1] = v;
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pal_buf[a * 4 + 2] = v;
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pal_buf[a * 4 + 3] = 0;
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}
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text_pal_load(TEXT_PAL_PAPER, 0, 0, pal_buf);
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text_pal_load(TEXT_PAL_BLINK_PAPER, 0, 0, pal_buf);
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}
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/* Reset all four text-mode planes (BIOS palette pages 4..7) to a built-in
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* default. We loop over the pages explicitly because the BIOS doc isn't
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* crisp about whether one SET_PAL_INIT call covers all four pages or
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* just the one named in A. Looping is always safe. */
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static void reset_all_text_planes(uint8_t type)
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{
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for (uint8_t p = 4; p <= 7; p++) {
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pal_reset_at(type, p, 0);
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}
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}
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static void wait_key(const char *prompt)
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{
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cputs(prompt);
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(void)getch();
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}
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int main(void)
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{
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uint8_t prev_mode = get_videotextmode();
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set_videotextmode(TEXT_MODE_80x32);
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textattr(ATTR_DEFAULT);
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/* ----- (1) Initial CGA palette ---------------------------------- */
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clrscr();
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cputs("[1] Initial CGA palette (boot default)\r\n");
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cputs("---------------------------------------\r\n");
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show_palette_state();
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wait_key("\r\nPress any key to install grayscale...");
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/* ----- (2) Grayscale ramp in all four planes -------------------- */
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load_grayscale_all_planes();
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clrscr();
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cputs("[2] Grayscale ramp via text_pal_load() (planes 4..7)\r\n");
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cputs("-----------------------------------------------------\r\n");
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show_palette_state();
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wait_key("\r\nPress any key to restore CGA...");
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/* ----- (3) Restore CGA defaults --------------------------------- */
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reset_all_text_planes(PAL_CGA);
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clrscr();
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cputs("[3] CGA palette restored (planes 4..7)\r\n");
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cputs("---------------------------------------\r\n");
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show_palette_state();
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wait_key("\r\nPress any key to install Sinclair...");
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/* ----- (4) Sinclair palette ------------------------------------- */
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reset_all_text_planes(PAL_SINCLAIR);
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clrscr();
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cputs("[4] Sinclair/Spectrum palette (planes 4..7)\r\n");
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cputs("--------------------------------------------\r\n");
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show_palette_state();
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wait_key("\r\nPress any key to exit...");
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/* Leave the system in a sane state. */
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reset_all_text_planes(PAL_CGA);
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textattr(ATTR_DEFAULT);
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clrscr();
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set_videotextmode(prev_mode);
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return 0;
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}
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