SDL2 PPM Image Viewer

A simple C program that displays PPM (Portable Pixmap) images using SDL2. This image viewer supports binary PPM (P6 format) files and renders them pixel by pixel.

Features

• Loads and displays PPM (P6 format) image files
• Supports images with various maximum color values (not just 255)
• Simple keyboard controls (press 'Q' to quit)
• Cross-platform compatibility (Windows, Linux, macOS)
• Clean CPU-based rendering workflow

Requirements

• SDL2 library
• C compiler (GCC, Clang, MSVC, etc.)
• PPM image files (P6 binary format)

Installation

Linux (Ubuntu/Debian)

sudo apt-get install libsdl2-dev

macOS (using Homebrew)

brew install sdl2

Windows

Download SDL2 development libraries from libsdl.org and set up your build environment accordingly.

Building

Compile the program using:

gcc -o ppm_viewer iv.c `sdl2-config --cflags --libs`

Or with more detailed options:

gcc -Wall -Wextra -o ppm_viewer iv.c `sdl2-config --cflags --libs`

Usage

Run the program with a PPM file as argument:

./ppm_viewer image.ppm

Controls

• Q - Quit the application
• Window Close Button - Quit the application

Supported File Format

Currently only supports P6 format PPM files (binary format). This is indicated by the "P6" magic number at the beginning of the file.

PPM File Format Details

• Magic number: P6
• Binary color data (RGB triplets)
• Header format: P6\nwidth height\nmaxval\n
• Color values scaled automatically if maxval is not 255

Program Structure

1. Command-line Argument Processing

   • Validates input filename
   • Extracts and checks file extension (.ppm)

2. PPM File Parsing

   • Reads P6 header information
   • Handles comments and whitespace
   • Extracts width, height, and maximum color value

3. SDL2 Initialization

   • Creates window with dimensions matching the image
   • Sets up surface for pixel manipulation

4. Image Rendering

   • Reads RGB values from PPM file
   • Scales colors if maxval is not 255
   • Draws each pixel individually using SDL_FillRect

5. Event Loop

   • Handles keyboard input ('Q' to quit)
   • Manages window events
   • ivtains display until user exits

Limitations

• Only supports P6 (binary) PPM format
• No image scaling or resizing
• Basic rendering (no hardware acceleration)
• No support for other image formats (PNG, JPEG, etc.)
• Single image viewing at a time

Code Notes

• The program uses CPU-based rendering which is simple but may be slow for large images
• For hardware-accelerated rendering, see the commented GPU workflow section
• Memory is properly cleaned up on exit
• Event polling is required for proper window management on Wayland and X11

License

This code is provided as-is for educational purposes. Modify and distribute as needed.

Troubleshooting

1. "Only supports .ppm for now" - Ensure you're using a PPM file with .ppm extension
2. "Only P6 format PPM files are supported" - Convert your PPM file to binary (P6) format
3. SDL2 errors - Verify SDL2 is properly installed and linked
4. Black screen - Check that the PPM file is not empty and has valid RGB data

Example

To view a sample PPM image:

./ppm_viewer test.ppm

The program will display a 100x100 pixel gradient from red to blue.