ex_gui_slider_default.c

A slider's default, put back by a double click (headless).

A slider's default, put back by a double click (headless). "Double click a slider to reset it" is a convention every editor has, and every host implemented it again for each slider it remembered, from n_gui_double_clicked_widget(), and forgot a few. n_gui_slider_set_default() gives the slider its default once; the double click then sets it, calls on_change as a drag would, and ends the drag the second press began, so a pointer that moves before the release does not drag the handle away again.

Author

Castagnier Mickael

Version

1.0

Date

25/09/2026

/*
 * Nilorea Library
 * Copyright (C) 2005-2026 Castagnier Mickael
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * permissions and limitations under the License.
 *
 * SPDX-License-Identifier: Apache-2.0
 */

 
#define ALLEGRO_UNSTABLE 1
 
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
#include "nilorea/n_common.h"
#include "nilorea/n_gui.h"
#include "nilorea/n_log.h"

static int failures = 0;

static int changes = 0;
static double last_value = -1.0;

static void expect_true(const char* label, int cond) {
    if (!cond) {
        n_log(LOG_ERR, "%s: FAILED", label);
        failures++;
    } else {
        n_log(LOG_INFO, "%s: OK", label);
    }
}

static void on_change(int widget_id, double value, void* user_data) {
    (void)widget_id;
    (void)user_data;
    changes++;
    last_value = value;
}

static ALLEGRO_EVENT mouse_event(int type, int x, int y) {
    ALLEGRO_EVENT ev;
    memset(&ev, 0, sizeof(ev));
    ev.type = (unsigned int)type;
    ev.mouse.x = x;
    ev.mouse.y = y;
    ev.mouse.button = 1;
    return ev;
}

static void press_at(N_GUI_CTX* gui, int x, int y, int release) {
    n_gui_process_event(gui, mouse_event(ALLEGRO_EVENT_MOUSE_AXES, x, y));
    n_gui_process_event(gui, mouse_event(ALLEGRO_EVENT_MOUSE_BUTTON_DOWN, x, y));
    if (release) n_gui_process_event(gui, mouse_event(ALLEGRO_EVENT_MOUSE_BUTTON_UP, x, y));
}
 
int main(void) {
    ALLEGRO_FONT* font;
    N_GUI_CTX* gui;
    int win, with, without;
    double def = 0.0, at_click = 0.0;
 
    set_log_level(LOG_ERR);
    if (!al_init() || !al_init_font_addon()) {
        n_log(LOG_ERR, "allegro init failed");
        return 1;
    }
    font = al_create_builtin_font(); /* no display needed */
    if (!font) {
        n_log(LOG_ERR, "al_create_builtin_font failed");
        return 1;
    }
    gui = n_gui_new_ctx(font);
    if (!gui) {
        n_log(LOG_ERR, "n_gui_new_ctx failed");
        al_destroy_font(font);
        return 1;
    }
    n_gui_set_display_size(gui, 800.0f, 600.0f);
    win = n_gui_add_window(gui, "W", 0.0f, 0.0f, 400.0f, 300.0f);
    n_gui_window_set_flags(gui, win, N_GUI_WIN_FRAMELESS);
    with = n_gui_add_slider(gui, win, 0.0f, 0.0f, 300.0f, 30.0f, 0.0, 100.0, 50.0, N_GUI_SLIDER_VALUE, on_change, NULL);
    without = n_gui_add_slider(gui, win, 0.0f, 60.0f, 300.0f, 30.0f, 0.0, 100.0, 50.0, N_GUI_SLIDER_VALUE, on_change, NULL);
    n_gui_open_window(gui, win);
 
    expect_true("a slider has no default until given one", !n_gui_slider_get_default(gui, with, NULL));
    n_gui_slider_set_default(gui, with, 50.0);
    expect_true("and has the one it is given",
                n_gui_slider_get_default(gui, with, &def) && fabs(def - 50.0) < 1e-9);
 
    /* One click near the left end moves the handle there, as always. */
    press_at(gui, 30, 15, 1);
    at_click = n_gui_slider_get_value(gui, with);
    expect_true("a click moves the handle to the pointer", at_click < 25.0 && changes == 1);
 
    /* The second press of a double click: it too moves the handle to the
       pointer, then the default is put back and on_change told. */
    press_at(gui, 30, 15, 0);
    expect_true("a double click puts the default back", fabs(n_gui_slider_get_value(gui, with) - 50.0) < 1e-9);
    expect_true("and on_change hears it", fabs(last_value - 50.0) < 1e-9);
    /* The button is still down. Moving the pointer must not drag it away. */
    n_gui_process_event(gui, mouse_event(ALLEGRO_EVENT_MOUSE_AXES, 250, 15));
    expect_true("the drag the second press began is over",
                fabs(n_gui_slider_get_value(gui, with) - 50.0) < 1e-9);
    n_gui_process_event(gui, mouse_event(ALLEGRO_EVENT_MOUSE_BUTTON_UP, 250, 15));
 
    /* A slider with no default is left where the clicks put it. */
    press_at(gui, 30, 75, 1);
    press_at(gui, 30, 75, 1);
    expect_true("a slider with no default ignores the gesture", n_gui_slider_get_value(gui, without) < 25.0);
 
    n_gui_destroy_ctx(&gui);
    al_destroy_font(font);
    if (failures) {
        n_log(LOG_ERR, "ex_gui_slider_default: %d failure(s)", failures);
        return 1;
    }
    n_log(LOG_NOTICE, "ex_gui_slider_default: all checks passed");
    return 0;
}