ex_gui_combobox_wheel.c

The mouse wheel scrolls an open combobox list (headless).

The mouse wheel scrolls an open combobox list (headless). An open combobox with more items than it shows has a scrollbar, and the wheel over its items has to move the list, as it does in every desktop toolkit. It used to step the highlight instead, one item a notch, and the list only moved once the highlight reached its edge; a pointer resting on an item put the highlight back under it, so the wheel ran over the visible items and the rest stayed out of reach. Reported from AfterAPro's plugin list: "working fine for what's visible but does not scroll".

Each check opens the list, turns the wheel with the pointer on one row and then clicks that same row: the item that click selects is the one the row shows, which says how far the list scrolled.

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 <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;

#define CB_X 10
#define CB_Y 10
#define CB_W 200
#define CB_H 30

#define ITEMS 9

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

static void click_at(N_GUI_CTX* gui, int x, int y) {
    n_gui_process_event(gui, mouse_event(ALLEGRO_EVENT_MOUSE_AXES, x, y, 0));
    n_gui_process_event(gui, mouse_event(ALLEGRO_EVENT_MOUSE_BUTTON_DOWN, x, y, 0));
    n_gui_process_event(gui, mouse_event(ALLEGRO_EVENT_MOUSE_BUTTON_UP, x, y, 0));
}

static int row_y(int row) {
    return CB_Y + CB_H + row * CB_H + CB_H / 2;
}

static int wheel_then_click(N_GUI_CTX* gui, int cb, int row, int notches) {
    int i = 0;
    int x = CB_X + CB_W / 3;
 
    click_at(gui, x, CB_Y + CB_H / 2); /* open it */
    n_gui_process_event(gui, mouse_event(ALLEGRO_EVENT_MOUSE_AXES, x, row_y(row), 0));
    for (i = 0; i < abs(notches); i++)
        n_gui_process_event(gui, mouse_event(ALLEGRO_EVENT_MOUSE_AXES, x, row_y(row), notches > 0 ? -1 : 1));
    click_at(gui, x, row_y(row));
    return n_gui_combobox_get_selected(gui, cb);
}
 
int main(void) {
    ALLEGRO_FONT* font;
    N_GUI_CTX* gui;
    int win, cb, i;
    char name[16];
 
    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, 500.0f);
    n_gui_window_set_flags(gui, win, N_GUI_WIN_FRAMELESS);
    cb = n_gui_add_combobox(gui, win, (float)CB_X, (float)CB_Y, (float)CB_W, (float)CB_H, NULL, NULL);
    for (i = 0; i < ITEMS; i++) {
        snprintf(name, sizeof(name), "item %d", i);
        n_gui_combobox_add_item(gui, cb, name);
    }
    n_gui_open_window(gui, win);
 
    expect_true("with no wheel, a row selects the item it shows", wheel_then_click(gui, cb, 1, 0) == 1);
    n_gui_combobox_set_selected(gui, cb, 0);
    expect_true("three notches down scroll the list by three items", wheel_then_click(gui, cb, 1, 3) == 4);
    n_gui_combobox_set_selected(gui, cb, 0);
    expect_true("the wheel reaches the last item and stops there", wheel_then_click(gui, cb, 5, 20) == ITEMS - 1);
    n_gui_combobox_set_selected(gui, cb, ITEMS - 1);
    expect_true("and comes back up to the first", wheel_then_click(gui, cb, 0, -20) == 0);
 
    n_gui_destroy_ctx(&gui);
    al_destroy_font(font);
    if (failures) {
        n_log(LOG_ERR, "ex_gui_combobox_wheel: %d failure(s)", failures);
        return 1;
    }
    n_log(LOG_NOTICE, "ex_gui_combobox_wheel: all checks passed");
    return 0;
}