BMP Circle Generator

A C++ program that generates a BMP image file from scratch — no external libraries required. It manually constructs BMP file headers and pixel data to render a red circle on a white background.

How It Works

The program builds a valid 24-bit BMP file by:

1. Constructing BMP headers — Writes the 14-byte file header and 40-byte info header using packed structs to ensure correct binary layout.
2. Generating pixel data — Iterates over a 100×100 pixel grid, using the circle equation (x - cx)² + (y - cy)² ≤ r² to determine whether each pixel falls inside the circle (red) or outside (white).
3. Handling row padding — Each row is padded to a 4-byte boundary, as required by the BMP specification.
4. Writing to file — Outputs the raw binary data to circle.bmp.

Output

A 100×100 pixel BMP image with a red circle (radius 30) centered at (50, 50) on a white background.

Build & Run

g++ -o circle "circlcle bmp.cpp"
./circle

This creates circle.bmp in the current directory.

Concepts Demonstrated

• Low-level binary file I/O in C++
• BMP file format specification (headers, pixel layout, row padding)
• Memory layout control with #pragma pack
• Pointer arithmetic and reinterpret_cast