ex_gui_text_shorten.c

shortening text to a width, at the end, at the start, or a path

shortening text to a width, at the end, at the start, or a path

Author

Castagnier Mickael

Version

1.0

Date

24/09/2026

A label too narrow for its text cut it at the end, which is right for a sentence and wrong for a path: it kept the leading directories every file in the folder shares and threw away the file name. n_gui_label_set_truncate() chooses the cut, and n_gui_text_shorten() is the same shortening for a caller that draws its own text.

Headless: the builtin font is monospaced, so widths are counted in characters.

 
#define ALLEGRO_UNSTABLE 1
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
 
#include "nilorea/n_common.h"
#include "nilorea/n_log.h"
#include "nilorea/n_gui.h"
 
static int log_level = LOG_ERR;
static int failures = 0;

static void expect_true(const char* what, int ok) {
    if (!ok) {
        n_log(LOG_ERR, "FAIL: %s", what);
        failures++;
    } else {
        n_log(LOG_INFO, "ok: %s", what);
    }
}

static int process_args(int argc, char** argv) {
    int opt = 0;
 
    while ((opt = getopt(argc, argv, "V:")) != -1) {
        if (opt == 'V') {
            log_level = atoi(optarg);
        } else {
            return -1;
        }
    }
    return 0;
}

static int utf8_whole(const char* s) {
    const unsigned char* p = (const unsigned char*)s;
 
    while (*p) {
        int n = (*p & 0x80) == 0 ? 1 : (*p & 0xE0) == 0xC0 ? 2
                                   : (*p & 0xF0) == 0xE0   ? 3
                                   : (*p & 0xF8) == 0xF0   ? 4
                                                           : 0;
        int k = 0;
        if (n == 0) return 0;
        for (k = 1; k < n; k++)
            if ((p[k] & 0xC0) != 0x80) return 0;
        p += n;
    }
    return 1;
}
 
int main(int argc, char** argv) {
    char out[256];
    float cw = 0.0f;
 
    set_log_level(LOG_ERR);
    if (process_args(argc, argv) != 0) {
        fprintf(stderr, "Usage: %s [-V LOG_LEVEL]\n", argv[0]);
        return 2;
    }
    set_log_level(log_level);
    if (!al_init() || !al_init_font_addon()) {
        n_log(LOG_ERR, "allegro init failed");
        return 1;
    }
    ALLEGRO_FONT* font = al_create_builtin_font();
    if (!font) return 1;
    cw = (float)al_get_text_width(font, "a");
    expect_true("the builtin font is monospaced", al_get_text_width(font, "abcdefghij") == (int)(cw * 10.0f));
 
    expect_true("text that fits is left alone",
                n_gui_text_shorten(font, "short", cw * 10.0f, N_GUI_TRUNCATE_END, out, sizeof(out)) == 0 &&
                    strcmp(out, "short") == 0);
 
    n_gui_text_shorten(font, "abcdefghij", cw * 6.0f, N_GUI_TRUNCATE_END, out, sizeof(out));
    expect_true("the end is cut: abc...", strcmp(out, "abc...") == 0);
    n_gui_text_shorten(font, "abcdefghij", cw * 6.0f, N_GUI_TRUNCATE_START, out, sizeof(out));
    expect_true("the start is cut: ...hij", strcmp(out, "...hij") == 0);
 
    n_gui_text_shorten(font, "/home/user/photos/IMG_0001.CR3", cw * 22.0f, N_GUI_TRUNCATE_PATH, out,
                       sizeof(out));
    expect_true("a path loses whole leading components and keeps its file name",
                strcmp(out, ".../IMG_0001.CR3") == 0);
    n_gui_text_shorten(font, "C:\\Users\\me\\Pictures\\IMG_0001.CR3", cw * 26.0f, N_GUI_TRUNCATE_PATH, out,
                       sizeof(out));
    expect_true("either separator counts", strcmp(out, ".../Pictures\\IMG_0001.CR3") == 0);
    n_gui_text_shorten(font, "dir/averyveryverylongname.CR3", cw * 10.0f, N_GUI_TRUNCATE_PATH, out,
                       sizeof(out));
    expect_true("a file name wider than the box alone keeps its end",
                strcmp(out, "...ame.CR3") == 0);
 
    n_gui_text_shorten(font, "caf\xc3\xa9 cr\xc3\xa8me br\xc3\xbbl\xc3\xa9\x65", cw * 7.0f, N_GUI_TRUNCATE_START,
                       out, sizeof(out));
    expect_true("a cut at the start never splits a UTF-8 sequence", utf8_whole(out));
    n_gui_text_shorten(font, "caf\xc3\xa9 cr\xc3\xa8me br\xc3\xbbl\xc3\xa9\x65", cw * 7.0f, N_GUI_TRUNCATE_END,
                       out, sizeof(out));
    expect_true("nor does a cut at the end", utf8_whole(out));
 
    expect_true("NULL is refused", n_gui_text_shorten(NULL, "x", 10.0f, 0, out, sizeof(out)) == -1 &&
                                       n_gui_text_shorten(font, "x", 10.0f, 0, NULL, 10) == -1);
 
    /* The label's own setting. */
    N_GUI_CTX* gui = n_gui_new_ctx(font);
    if (!gui) {
        al_destroy_font(font);
        return 1;
    }
    n_gui_set_display_size(gui, 800.0f, 600.0f);
    int win = n_gui_add_window(gui, "W", 0.0f, 0.0f, 300.0f, 200.0f);
    int label = n_gui_add_label(gui, win, "/a/b/c.txt", 10.0f, 10.0f, 80.0f, 20.0f, N_GUI_ALIGN_LEFT);
    int button = n_gui_add_button(gui, win, "B", 10.0f, 40.0f, 40.0f, 20.0f, N_GUI_SHAPE_ROUNDED, NULL, NULL);
    expect_true("a label cuts at the end until told otherwise",
                n_gui_label_get_truncate(gui, label) == N_GUI_TRUNCATE_END);
    n_gui_label_set_truncate(gui, label, N_GUI_TRUNCATE_PATH);
    expect_true("and cuts a path when told to", n_gui_label_get_truncate(gui, label) == N_GUI_TRUNCATE_PATH);
    n_gui_label_set_truncate(gui, label, 42);
    expect_true("an unknown mode is the end", n_gui_label_get_truncate(gui, label) == N_GUI_TRUNCATE_END);
    n_gui_label_set_truncate(gui, button, N_GUI_TRUNCATE_START);
    expect_true("a button has no truncate mode", n_gui_label_get_truncate(gui, button) == N_GUI_TRUNCATE_END);
 
    n_gui_destroy_ctx(&gui);
    al_destroy_font(font);
    if (failures) {
        fprintf(stderr, "ex_gui_text_shorten: %d failure(s)\n", failures);
        return 1;
    }
    printf("ex_gui_text_shorten: ok\n");
    return 0;
}