Example 02: Basic Window

An introduction to libui and creating graphical apps.

--- This example demonstrates how to create an empty window that stays active on the screen until the user explicitly closes it by clicking the 'X' button. ## 📝 Concepts Introduced * Including `libui.h` and the event structure. * Creating a `ui_window_t` handle. * Creating an infinite event loop using `ui_get_event()`. * Yielding CPU time to the kernel via `sys_yield()`. --- ## 💻 The Code (`src/userland/gui/basic_window.c`) ```c #include #include #include int main(void) { // 1. Ask the Window Manager to create a new window // Arguments are: Title, X Position, Y Position, Width, Height ui_window_t wid = ui_window_create("My First GUI", 100, 100, 400, 300); if (wid < 0) { printf("Failed to create the window!\n"); return 1; } // 2. Define our event object gui_event_t event; // 3. Enter the main event loop while (1) { // ui_get_event is non-blocking. It returns true if an event was waiting. if (ui_get_event(wid, &event)) { // Check what type of event occurred if (event.type == GUI_EVENT_CLOSE) { // The user clicked the 'X' button in the titlebar! printf("Window closed cleanly by user.\n"); break; // Break the infinite loop } } // 4. CRITICAL: Yield the remainder of our timeslice // If we don't do this, the while(1) loop will consume 100% of the CPU // and starve the rest of the OS! sys_yield(); } // Returning from main will automatically destroy the window and exit the process. return 0; } ``` ## 🛠️ How it Works 1. **Window Handle (`wid`)**: `ui_window_create` sends a request to the kernel. The kernel allocates the memory for the window and returns a numerical ID (the handle) that we use for all future interactions with that specific window. 2. **The Event Loop**: Graphical programs run forever until closed. The `while (1)` loop serves this purpose. 3. **Polling**: `ui_get_event` asks the kernel, "Hey, did the user click my window or press a key since the last time I asked?". It is non-blocking, so it immediately returns `false` if nothing happened. 4. **CPU Yielding**: Since we are constantly polling in a tight loop, we call `sys_yield()` at the end of the loop frame. This politely tells the OS scheduler, "I'm done checking for events, go ahead and let another program run for a bit." ## 🚀 Running It Launch the Terminal and type `basic_window`. You'll see an empty window appear that you can move around the screen!