EasyGifReader

EasyGifReader is a single-class C++ library that aims to simplify reading an animated GIF file. It is built on top of and depends on giflib. While giflib does decode the binary format of the GIF file and converts it to structured data, there is still a lot left to do to make sense of this data before the animation can be presented, such as:

• Dealing with indexed color bitmaps and color maps.
• Compositing partial frames - ones that do not cover the entire area of the GIF.
• Correctly handling frame disposal modes - an optimization that allows each frame to use prior frames as its basis in multiple ways.
• Resolving transparency.
• Parsing loop count information from extension blocks.

Some of the data in a GIF file is ambiguous or interpreted inconsistently across software. In these cases, the library replicates the behavior of Google Chrome, which can be considered as the industry standard due to its status as the largest web browser. If you find a GIF file that behaves differently in Chrome, please report it as a bug.

Installation

To use this library in your project, first make sure that giflib is available in the include path and is being linked. Then, simply add the files EasyGifReader.h and EasyGifReader.cpp to your C++ project.

Usage

Using the EasyGifReader class is very straightforward and intuitive. The following example demonstrates how a GIF file can be loaded, and each of its frames inspected.

try {
    EasyGifReader gif = EasyGifReader::openFile("animation.gif");
    int frameCount = gif.frameCount();
    int width = gif.width();
    int height = gif.height();
    bool loop = gif.repeatsInfinitely();
    for (const EasyGifReader::Frame &frame : gif) {
        const EasyGifReader::PixelComponent *framePixels = frame.pixels();
        double frameDuration = frame.duration().seconds();
        // TODO display framePixels for frameDuration seconds
    }
} catch (EasyGifReader::Error gifError) {
    logError("Reading GIF file failed");
}

To clarify, framePixels is an array of width*height 32-bit pixels in the RGBA byte order. Due to limitations of the GIF format, the alpha component will always be either 0xFF or 0x00.