Sprinter-SDCC/tests/text_palette/text_palette.c

/*
 * text_palette — interactive smoke test for the text-mode palette API.
 *
 * Walks through four palette states. Each stage clears the screen first
 * and then renders 16 lines, one per ink-colour index, each line showing:
 *
 *   <RGB values read back from the INK plane>
 *   < part 1: fg = N on bg = 0   — colour N text on the default black >
 *   < part 2: fg = 15 on bg = N  — bright-white text on a coloured bg >
 *
 * Stages:
 *   1) Initial CGA palette (boot default).
 *   2) Grayscale ramp installed via text_pal_load() in all four text
 *      planes (4..7) so flash is fully suppressed; both ink (low nibble)
 *      and paper (mid nibble) get 16 shades — bit 7 of the attribute
 *      byte is folded into the paper index so we cover all 16 bg slots.
 *   3) CGA defaults restored via pal_reset_at(PAL_CGA, plane, 0) for
 *      plane = 4..7 — explicit per-plane reset in case BIOS interprets
 *      the A register narrowly.
 *   4) Sinclair palette via pal_reset_at(PAL_SINCLAIR, plane, 0) for
 *      plane = 4..7.
 *
 * Memory: tiny (one bank). The 1 KB palette buffer for text_pal_load()
 * is static — keeps it out of the (small) stack frame.
 */

#include <stdio.h>
#include <conio.h>
#include <palette.h>
#include <stdint.h>

/* 256 entries × 4 bytes (B, G, R, 0). Static so it lives in DATA. */
static uint8_t pal_buf[256 * 4];

#define ATTR_DEFAULT  COLOR(COLOR_LIGHTGRAY, COLOR_BLACK)

/* For each colour index N=0..15 print:
 *   - RGB triple read back from the INK plane
 *   - sample text in fg=N on bg=0
 *   - sample text in fg=15 on bg=N
 *
 * The bg=N attribute uses ALL FOUR bits of the mid nibble (including the
 * blink bit). In the CGA default this means N >= 8 will flash; with our
 * grayscale loader the four planes are identical, so it just selects one
 * of 16 paper colours. */
static void show_palette_state(void)
{
    for (uint8_t n = 0; n < 16; n++) {
        uint8_t r = 0, g = 0, b = 0;
        text_pal_get_color(TEXT_PAL_INK, n, &r, &g, &b);

        textattr(ATTR_DEFAULT);
        cprintf(" #%X  R=%3u G=%3u B=%3u  ", n, r, g, b);

        /* part 1: fg=N on bg=0 */
        textattr((uint8_t)(n & 0x0F));
        cprintf(" fg=%X on bg=0 ", n);

        /* part 2: fg=15 on bg=N  (4-bit bg slot, may carry blink bit) */
        textattr((uint8_t)(((n & 0x0F) << 4) | 0x0F));
        cprintf(" white on bg=%X ", n);

        textattr(ATTR_DEFAULT);
        cputs("\r\n");
    }
}

/* Build a 16-step grayscale ramp and load it into ALL FOUR text planes
 * (paper, ink, blink-paper, blink-ink). Identical paper/blink-paper and
 * ink/blink-ink means there is nothing to alternate between → no flash.
 *
 * INK / BLINK_INK index by attr's low nibble:    16 fg grey levels
 * PAPER / BLINK_PAPER index by attr's mid nibble: 16 bg grey levels
 *                                                 (full 4 bits incl. bit 7) */
static void load_grayscale_all_planes(void)
{
    /* INK and BLINK_INK: shade taken from attr & 0x0F. */
    for (uint16_t a = 0; a < 256; a++) {
        uint8_t v = (uint8_t)((a & 0x0F) * 17u);   /* 0,17,34,...,255 */
        pal_buf[a * 4 + 0] = v;   /* B */
        pal_buf[a * 4 + 1] = v;   /* G */
        pal_buf[a * 4 + 2] = v;   /* R */
        pal_buf[a * 4 + 3] = 0;
    }
    text_pal_load(TEXT_PAL_INK,       0, 0, pal_buf);
    text_pal_load(TEXT_PAL_BLINK_INK, 0, 0, pal_buf);

    /* PAPER and BLINK_PAPER: shade taken from (attr >> 4) & 0x0F. */
    for (uint16_t a = 0; a < 256; a++) {
        uint8_t v = (uint8_t)(((a >> 4) & 0x0F) * 17u);
        pal_buf[a * 4 + 0] = v;
        pal_buf[a * 4 + 1] = v;
        pal_buf[a * 4 + 2] = v;
        pal_buf[a * 4 + 3] = 0;
    }
    text_pal_load(TEXT_PAL_PAPER,       0, 0, pal_buf);
    text_pal_load(TEXT_PAL_BLINK_PAPER, 0, 0, pal_buf);
}

/* Reset all four text-mode planes (BIOS palette pages 4..7) to a built-in
 * default. We loop over the pages explicitly because the BIOS doc isn't
 * crisp about whether one SET_PAL_INIT call covers all four pages or
 * just the one named in A. Looping is always safe. */
static void reset_all_text_planes(uint8_t type)
{
    for (uint8_t p = 4; p <= 7; p++) {
        pal_reset_at(type, p, 0);
    }
}

static void wait_key(const char *prompt)
{
    cputs(prompt);
    (void)getch();
}

int main(void)
{
    uint8_t prev_mode = gettextmode();
    settextmode(TEXT_MODE_80x32);
    textattr(ATTR_DEFAULT);

    /* ----- (1) Initial CGA palette ---------------------------------- */
    clrscr();
    cputs("[1] Initial CGA palette (boot default)\r\n");
    cputs("---------------------------------------\r\n");
    show_palette_state();
    wait_key("\r\nPress any key to install grayscale...");

    /* ----- (2) Grayscale ramp in all four planes -------------------- */
    load_grayscale_all_planes();
    clrscr();
    cputs("[2] Grayscale ramp via text_pal_load() (planes 4..7)\r\n");
    cputs("-----------------------------------------------------\r\n");
    show_palette_state();
    wait_key("\r\nPress any key to restore CGA...");

    /* ----- (3) Restore CGA defaults --------------------------------- */
    reset_all_text_planes(PAL_CGA);
    clrscr();
    cputs("[3] CGA palette restored (planes 4..7)\r\n");
    cputs("---------------------------------------\r\n");
    show_palette_state();
    wait_key("\r\nPress any key to install Sinclair...");

    /* ----- (4) Sinclair palette ------------------------------------- */
    reset_all_text_planes(PAL_SINCLAIR);
    clrscr();
    cputs("[4] Sinclair/Spectrum palette (planes 4..7)\r\n");
    cputs("--------------------------------------------\r\n");
    show_palette_state();
    wait_key("\r\nPress any key to exit...");

    /* Leave the system in a sane state. */
    reset_all_text_planes(PAL_CGA);
    textattr(ATTR_DEFAULT);
    clrscr();
    settextmode(prev_mode);
    return 0;
}