LithosAnanke/src/word_source/ttf_words.c

/*
  StarForth — Steady-State Virtual Machine Runtime

  Copyright (c) 2023–2025 Robert A. James
  All rights reserved.

  Licensed under the StarForth License, Version 1.0
*/

/* ttf_words.c — TrueType text entry point (FABRIC.md item 4.3.7e).
 * Kernel-only; no-op on hosted builds. */

#include "include/ttf_words.h"
#include "../../include/log.h"
#include "../../include/word_registry.h"

#ifdef __STARKERNEL__
#include "starkernel/framebuffer.h"
#include "starkernel/ttf.h"
#include "starkernel/capsule_generated.h"

#define TTF_WORDS_CACHE_SLOTS 32
#define TTF_WORDS_DEFAULT_FONT "fonts:JetBrainsMono-Regular.ttf"

static ttf_font_t g_ttf_font;
static int g_ttf_font_ready = 0;
static ttf_raster_cache_slot_t g_ttf_cache_slots[TTF_WORDS_CACHE_SLOTS];
static ttf_raster_cache_t g_ttf_cache;

static int ttf_words_ensure_font(void) {
    if (g_ttf_font_ready) return 1;
    if (ttf_load_from_capsule(
            capsule_get_directory(), capsule_get_descriptors(),
            capsule_get_names(), capsule_get_arena(),
            TTF_WORDS_DEFAULT_FONT, &g_ttf_font) != TTF_OK)
        return 0;
    ttf_raster_cache_init(&g_ttf_cache, g_ttf_cache_slots, TTF_WORDS_CACHE_SLOTS);
    g_ttf_font_ready = 1;
    return 1;
}

/* Decode one UTF-8 codepoint from VM memory at *a (VM-space address),
 * with *len bytes known remaining. Mirrors capsules/fabric.4th's
 * DECODE-UTF8 exactly: same lead-byte-length table, same U+FFFD
 * fallback (advancing exactly one byte) on an invalid or truncated
 * sequence. Advances *a and *len past the consumed bytes. */
static uint32_t ttf_words_decode_utf8(VM *vm, vaddr_t *a, cell_t *len) {
    uint8_t lead, b[4];
    uint32_t seqlen, i, cp;

    if (*len <= 0 || !vm_addr_ok(vm, *a, 1)) {
        *len = 0;
        return 0xFFFD;
    }
    lead = vm_load_u8(vm, *a);

    if (lead < 0x80) seqlen = 1;
    else if ((lead & 0xE0) == 0xC0) seqlen = 2;
    else if ((lead & 0xF0) == 0xE0) seqlen = 3;
    else if ((lead & 0xF8) == 0xF0) seqlen = 4;
    else seqlen = 0;

    if (seqlen == 0 || (cell_t) seqlen > *len || !vm_addr_ok(vm, *a, seqlen)) {
        *a += 1;
        *len -= 1;
        return 0xFFFD;
    }

    for (i = 0; i < seqlen; i++) b[i] = vm_load_u8(vm, *a + i);

    switch (seqlen) {
        case 1:
            cp = b[0];
            break;
        case 2:
            cp = ((uint32_t) (b[0] & 0x1F) << 6) | (b[1] & 0x3F);
            break;
        case 3:
            cp = ((uint32_t) (b[0] & 0x0F) << 12) | ((uint32_t) (b[1] & 0x3F) << 6) | (b[2] & 0x3F);
            break;
        default:
            cp = ((uint32_t) (b[0] & 0x07) << 18) | ((uint32_t) (b[1] & 0x3F) << 12)
               | ((uint32_t) (b[2] & 0x3F) << 6) | (b[3] & 0x3F);
            break;
    }

    *a += seqlen;
    *len -= (cell_t) seqlen;
    return cp;
}

/* TTF-TEXT ( c-addr u x y size color -- ) */
static void ttf_word_text(VM *vm) {
    cell_t color, size, y, x, u, addr_cell;
    vaddr_t a;
    cell_t remaining;
    uint32_t pen_x, baseline_y;
    q48_16_t scale;

    if (vm->dsp < 5) {
        log_message(LOG_ERROR, "TTF-TEXT: Stack underflow");
        vm->error = 1;
        return;
    }
    color = vm_pop(vm);
    size = vm_pop(vm);
    y = vm_pop(vm);
    x = vm_pop(vm);
    u = vm_pop(vm);
    addr_cell = vm_pop(vm);

    if (!ttf_words_ensure_font()) {
        log_message(LOG_ERROR, "TTF-TEXT: font capsule load failed");
        vm->error = 1;
        return;
    }
    if (size <= 0 || size > TTF_CACHE_MAX_SIZE_PX) {
        log_message(LOG_ERROR, "TTF-TEXT: size out of range");
        vm->error = 1;
        return;
    }

    a = VM_ADDR(addr_cell);
    remaining = u;
    pen_x = (uint32_t) x;
    /* Caller-facing (x,y) is Cartesian: origin at the bottom-left of the physical
     * framebuffer, y increasing upward. fb_put_pixel() takes framebuffer coordinates
     * (origin top-left, y increasing downward), so flip once here per-call rather
     * than at every blit site. */
    baseline_y = fb_height() - (uint32_t) y;
    scale = q48_div(q48_from_u64((uint32_t) size), q48_from_u64(g_ttf_font.units_per_em));

    while (remaining > 0) {
        uint32_t cp = ttf_words_decode_utf8(vm, &a, &remaining);
        ttf_bitmap_t bmp;
        int rc, was_hit;
        uint32_t gid, adv_units, px, py;
        q48_16_t adv_q;

        rc = ttf_raster_cache_get(&g_ttf_cache, &g_ttf_font, cp, (uint32_t) size, &bmp, &was_hit);
        if (rc == TTF_OK) {
            for (py = 0; py < bmp.height; py++) {
                for (px = 0; px < bmp.width; px++) {
                    if (bmp.pixels[py * bmp.width + px]) {
                        fb_put_pixel(pen_x + px - TTF_CACHE_MARGIN,
                                     baseline_y + py - (uint32_t) size - TTF_CACHE_MARGIN,
                                     (uint32_t) color);
                    }
                }
            }
        }

        gid = ttf_codepoint_to_glyph(&g_ttf_font, cp);
        adv_units = ttf_glyph_advance_width(&g_ttf_font, gid);
        adv_q = q48_mul(q48_from_u64(adv_units), scale);
        pen_x += (uint32_t) q48_to_u64(adv_q);
    }
}
#endif /* __STARKERNEL__ */

void register_ttf_words(VM *vm)
{
#ifdef __STARKERNEL__
    register_word(vm, "TTF-TEXT", ttf_word_text);
#else
    (void) vm;
#endif
}