Compositor is an open-source, full-featured image editing application developed for macOS, designed as a free, familiar alternative to Adobe Photoshop for users prioritizing a professional compositing and post-processing workflow. Built with an emphasis on non-destructive editing and performance, the application leverages GPU-accelerated rendering and a memory-conscious architecture to handle large-scale image projects.

Core Methodology and Technical Implementation

The software is architected as an Xcode project, utilizing a native macOS development stack. Its technical foundation is centered on several key areas:

• Non-Destructive Layering and GPU Processing: The engine supports complex layer hierarchies, including folders with independent opacity and the full suite of Photoshop-compatible blend modes. Layer effects—such as drop shadows, glows, and strokes—are processed via the GPU to maintain interactivity and live preview capabilities. All transformations, including move, scale, rotate, and free distort, are rendered non-destructively, preserving original pixel resolution regardless of transformation magnitude.
• Advanced Masking and Selection Logic: The application employs sophisticated selection algorithms, including object-based tracing and content-aware tools. Its masking system supports linking/unlinking masks for independent transformation, as well as complex operations such as feathering, inverting, and blurring. Content-Aware Fill functionality is implemented to allow for image extension beyond original canvas boundaries.
• Imaging Pipeline and Filter Architecture: Compositor features a "Camera Raw" filtering panel, which processes light, color, curves, and color grading parameters in a side panel. Adjustments and filters—such as Gaussian Blur, Motion Blur, and Noise—are designed to operate beyond layer edges to prevent artifacts. The application also includes an automated background removal tool and a comprehensive suite of image adjustments like Levels, Curves, and Gradient Maps.
• Interoperability and Memory Management: A significant portion of the logic is dedicated to parsing and exporting PSD and PSB file formats. The importer handles complex structures—such as folders, masks, and editable shapes—while performing a conversion report to inform the user when specific proprietary vectors or vertical text styles must be rasterized. To maintain stability, the application uses a dynamic memory budget that scales according to the available system resources on the host machine.
• Workflow and User Experience: The interface emphasizes familiar Photoshop-style keyboard shortcuts, which are remappable, and includes specialized developer-focused tools such as scripting for automated release builds. The build process utilizes $xcrun$ and $notarytool$ to ensure that the final artifacts are signed, notarized, and stapled, meeting macOS security standards.

Compositor maintains an MIT license, allowing for modular modification of the source code to suit specific user workflows.