Graphical User Interface (GUI) APIs
This section covers the core Application Programming Interfaces (APIs) for developing graphical user interfaces on the Windows platform. These APIs allow applications to create windows, display text and graphics, respond to user input, and manage the visual elements of the user experience.
Core Concepts
The Windows GUI is built around a message-driven architecture. Applications receive messages from the operating system (e.g., mouse clicks, keyboard input, window resizing) and must process these messages to update the interface and respond to user actions.
- Windows: Top-level elements of the GUI. Every visual element, from a simple button to a complex document window, is a window.
- Device Context (DC): An information structure that describes the drawing attributes of a device such as a display or printer.
- GDI (Graphics Device Interface): The subsystem responsible for drawing text, shapes, and bitmaps on the screen.
Key API Categories
Window Management
APIs for creating, managing, and destroying windows.
CreateWindowExCreates an overlapping, pop-up, or child window with a specified extended style; otherwise, this function creates a basic, overlapping, pop-up, or child window.
Syntax:
HWND CreateWindowEx(DWORD dwExStyle, LPCTSTR lpClassName, LPCTSTR lpWindowName, DWORD dwStyle, int x, int y, int nWidth, int nHeight, HWND hWndParent, HMENU hMenu, HINSTANCE hInstance, LPVOID lpParam);
DefWindowProcCalls the default window procedure to provide default processing for any window messages that an application does not process.
Syntax:
LRESULT DefWindowProc(HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam);
User Input Handling
APIs for processing keyboard and mouse events.
GetMessage: Retrieves messages from the application's message queue.TranslateMessage: Translates virtual-key messages into character messages.DispatchMessage: Dispatches a message to the appropriate window procedure.
Graphics and Drawing (GDI)
APIs for rendering graphics and text.
CreateCompatibleDC: Creates a memory device context (DC) that is compatible with the specified device.SelectObject: Selects an object into a specified device context.Rectangle: Draws a rectangle.TextOut: Writes a string of characters at the specified position.