Windows Graphics Device Interface (GDI)

Introduction to GDI

The Graphics Device Interface (GDI) is a core component of the Microsoft Windows operating system that provides a standardized way for applications to draw graphics and text on the screen and printers. It handles operations such as drawing lines, curves, shapes, text, and bitmaps.

Core GDI Components

• Device Context (DC): An abstract representation of a drawing surface, such as a screen, printer, or memory bitmap.
• Pens: Used for drawing lines and borders.
• Brushes: Used for filling shapes and areas.
• Fonts: Used for rendering text.
• Bitmaps: Raster graphics images.
• Palettes: Used for managing colors in 256-color environments.

Common GDI Functions

Drawing Shapes

• Rectangle(): Draws a rectangle.
• Ellipse(): Draws an ellipse.
• LineTo(): Draws a line.
• Polygon(): Draws a polygon.
• RoundRect(): Draws a rectangle with rounded corners.

Text Rendering

• TextOut(): Writes a string of text at the specified coordinates.
• DrawText(): Formats and displays text within a rectangular block.
• CreateFont(): Creates a logical font.

Managing Graphics Objects

• CreatePen(): Creates a new pen.
• CreateSolidBrush(): Creates a solid-colored brush.
• SelectObject(): Selects a GDI object into a device context.
• DeleteObject(): Deletes a GDI object.

Color and Brushes

GDI supports various ways to define colors and brushes:

• Using predefined color values (e.g., RGB(255, 0, 0) for red).
• Creating solid color brushes using CreateSolidBrush.
• Using stock brushes (e.g., GetStockObject(WHITE_BRUSH)).

GDI vs. GDI+

While GDI is a foundational API, Microsoft also developed GDI+. GDI+ offers a more modern, object-oriented approach to graphics, supporting features like anti-aliasing, gradients, and advanced image manipulation. For new development, GDI+ is often recommended, but understanding GDI remains crucial for legacy applications and lower-level graphics control.

Example Snippet

Here's a conceptual example of drawing a red rectangle using GDI:

#include <windows.h>

// Assume hdc is a valid Device Context
HDC hdc;
RECT rect = { 10, 10, 100, 100 }; // Coordinates for the rectangle
HBRUSH hBrush = CreateSolidBrush(RGB(255, 0, 0)); // Red brush

// Select the brush and draw the rectangle
HBRUSH hOldBrush = (HBRUSH)SelectObject(hdc, hBrush);
Rectangle(hdc, rect.left, rect.top, rect.right, rect.bottom);

// Restore the old brush and clean up
SelectObject(hdc, hOldBrush);
DeleteObject(hBrush);