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72 lines
2.7 KiB
Markdown
72 lines
2.7 KiB
Markdown
<div align="center">
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<h1>Example 02: Basic Window</h1>
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<p><em>An introduction to libui and creating graphical apps.</em></p>
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</div>
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---
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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.
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## 📝 Concepts Introduced
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* Including `libui.h` and the event structure.
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* Creating a `ui_window_t` handle.
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* Creating an infinite event loop using `ui_get_event()`.
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* Yielding CPU time to the kernel via `sys_yield()`.
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---
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## 💻 The Code (`src/userland/gui/basic_window.c`)
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```c
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#include <stdlib.h>
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#include <libui.h>
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#include <syscall.h>
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int main(void) {
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// 1. Ask the Window Manager to create a new window
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// Arguments are: Title, X Position, Y Position, Width, Height
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ui_window_t wid = ui_window_create("My First GUI", 100, 100, 400, 300);
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if (wid < 0) {
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printf("Failed to create the window!\n");
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return 1;
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}
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// 2. Define our event object
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gui_event_t event;
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// 3. Enter the main event loop
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while (1) {
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// ui_get_event is non-blocking. It returns true if an event was waiting.
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if (ui_get_event(wid, &event)) {
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// Check what type of event occurred
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if (event.type == GUI_EVENT_CLOSE) {
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// The user clicked the 'X' button in the titlebar!
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printf("Window closed cleanly by user.\n");
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break; // Break the infinite loop
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}
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}
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// 4. CRITICAL: Yield the remainder of our timeslice
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// If we don't do this, the while(1) loop will consume 100% of the CPU
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// and starve the rest of the OS!
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sys_yield();
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}
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// Returning from main will automatically destroy the window and exit the process.
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return 0;
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}
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```
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## 🛠️ How it Works
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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.
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2. **The Event Loop**: Graphical programs run forever until closed. The `while (1)` loop serves this purpose.
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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.
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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."
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## 🚀 Running It
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Launch the Terminal and type `basic_window`. You'll see an empty window appear that you can move around the screen!
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