boredos_mirror/docs/appdev/ui_api.md

UI API (libui.h)

For an application to be visible on the screen, it must interact with the BoredOS Window Manager (WM). The tools required for this are located in src/userland/libc/libui.h and libui.c.

Core Concepts

The UI library sends requests (via SYS_GUI) to the kernel to reserve an area on the screen (a Window) and then issues commands to color specific pixels within that area. The kernel is responsible for compositing this area over other windows.

Example: Creating a Window

First, include the library and define an event structure:

#include <libui.h>
#include <stdlib.h>

int main(void) {
    // 1. Create the window
    // Arguments: Title, Width, Height, Flags (e.g. 0 for bordered window)
    int window_id = ui_create_window("Hello World App", 400, 300, 0);

    if (window_id < 0) {
        printf("Failed to create window!\n");
        return 1;
    }

    // ... Event loop will go here ...
    return 0;
}

Drawing Primitives

The library offers functions to mutate the window's internal buffer. After issuing drawing commands, you must instruct the kernel to push the changes onto the screen.

// Fill the entire window with a solid blue background
// Arguments: Window ID, X, Y, Width, Height, ARGB Color value
ui_fill_rect(window_id, 0, 0, 400, 300, 0xFF0000FF);

// Tell the kernel to commit the drawing commands to the screen
ui_swap_buffers(window_id);

Available rendering methods:

• ui_fill_rect(id, x, y, w, h, color): Draw a solid rectangle.
• ui_draw_rect(id, x, y, w, h, color): Draw an outline of a rectangle.
• ui_draw_line(id, x0, y0, x1, y1, color): Bresenham line algorithm.
• ui_draw_string(id, string, x, y, color): Render text using the kernel's built-in font.
• ui_update_region(id, x, y, w, h): A targeted version of ui_swap_buffers that only updates a specific area, saving performance.

Handling the Event Loop

Graphical applications are event-driven. They stay alive inside a while (1) loop, periodically asking the kernel if the user clicked the mouse or pressed a key inside their window.

    ui_event_t event;

    // Main UI Loop
    while (1) {
        // ui_poll_event is non-blocking. It returns 1 if an event occurred, 0 otherwise.
        if (ui_poll_event(&event)) {
            
            // The WM dispatch sets event.window_id 
            // We only care about events meant for our specific window
            if (event.window_id == window_id) {

                if (event.type == UI_EVENT_MOUSE_DOWN) {
                    printf("User clicked at X:%d Y:%d\n", event.mouse_x, event.mouse_y);
                    
                    // Respond visually to the click
                    ui_fill_rect(window_id, event.mouse_x, event.mouse_y, 10, 10, 0xFFFF0000); // Red dot
                    ui_swap_buffers(window_id);
                } 
                else if (event.type == UI_EVENT_WINDOW_CLOSE) {
                    // Start tearing down the application safely
                    break;
                }
            }
        }
        
        // Prevent 100% CPU usage by yielding execution time back to the OS scheduler
        syscall1(SYSTEM_CMD_YIELD, 0);
    }