gdi

GDI, or Graphics Device Interface, is a core Windows API for representing graphical objects and transmitting them to output devices such as monitors and printers. It provides a device-independent framework in which drawing commands are issued against a device context (DC), an abstract surface that describes the target display or printer and its coordinate system. The actual rendering is performed by the Windows graphics subsystem and the underlying device drivers.

GDI offers a set of graphic primitives and resources, including lines, curves, shapes, text, and bitmaps. It uses objects such as pens, brushes, fonts, and palettes to define how drawing should appear. Clipping regions, mapping modes, and transformations allow developers to control where and how drawing occurs, enabling operations like scaling, rotation, and coordinate translation across different devices.

Programming with GDI follows a typical flow: obtain a device context (for example, via GetDC or BeginPaint), create or select GDI objects (Pen, Brush, Font) with functions like CreatePen or CreateFont, perform drawing operations (MoveToEx, LineTo, Rectangle, Ellipse, TextOut), and finally release resources with DeleteObject and ReleaseDC. For printing, the same API is used against a printer DC. Proper management of GDI objects is important to avoid resource leaks and ensure stable rendering.

GDI has been supplemented and, in modern practice, largely superseded by more modern APIs such as Direct2D and DirectWrite for hardware-accelerated rendering and advanced text shaping. A higher-level wrapper, GDI+, exists for easier development in some Windows environments, and GDI remains in use primarily for legacy applications and compatibility.