Mandelbrot - CS361 Homework 5

A C++ program that renders the Mandelbrot set to 24-bit BMP files. The implementation is multithreaded by a single "manager" thread enqueues row work items and multiple worker threads render rows in parallel into an in-memory BGR buffer which is then written to disk as a BMP.

Author

• By: Samii Shabuse
• Class: CS361: Concurrent Programming

Project layout

• Makefile — build targets and example BMP targets (e0.bmp .. e4.bmp).
• bin/mandelbrot — build output (created by the Makefile).
• src/mandelbrot.cpp — main program: argument parsing, tiling/dispatching, iteration, coloring, multithreading.
• src/bitmap.h / src/bitmap.cpp — BMP writer (public function write_bmp_24).
• src/multithread.cpp — small JobQueue implementation used by the manager/worker threads.

Requirements

• A C++17-capable compiler (g++ recommended).
• POSIX threads support (the Makefile uses -pthread).

Build

From the repository root run:

make

This will create bin/mandelbrot.

Usage

The program prints a short usage message when called with the wrong number of arguments. The expected arguments are:

mandelbrot x_min x_max y_min y_max out_file

• x_min, x_max, y_min, y_max — rectangle in the complex plane to render (long double precision parsed with stold).
• out_file — path to write a 24-bit BMP image.

Example (also provided as Makefile targets):

./bin/mandelbrot -2 1 -1.5 1.5 e0.bmp
./bin/mandelbrot -0.5 0 0.3 1.2 e1.bmp

Or use the Makefile targets:

make e0.bmp
make e1.bmp

Implementation details

• Image width is defined by WIDTH in src/mandelbrot.cpp (default 1500). The program computes the height to preserve aspect ratio:

  HEIGHT = round(WIDTH * (y_range / x_range)).

• Iterations: MAX_ITERATIONS (default 100 because of homework instructions) is used as the escape threshold. The iteration function returns the number of iterations before |z|^2 > 4 or MAX_ITERATIONS if the point appears to be in the set.

• Coloring: a function mandelbrot_colorize(int it) maps an iteration count to a simple RGB palette. Points inside the set (no escape) are colored black.

• Multithreading: JobQueue holds integer row indices. A manager thread enqueues every row index and calls close(); worker threads pop indices and render each row into the shared bgr buffer. Each worker writes to distinct row ranges, so no synchronization is required for pixel writes.

• BMP writer: write_bmp_24 writes a 24-bit BMP file with rows padded to a multiple of 4 bytes and writes rows bottom-to-top as the BMP format requires.