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FMX.ShadowVolume

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README

FMX.ShadowVolume

A FireMonkey (FMX) demonstration of stencil‑based Shadow Volumes for TCube

This repository contains a Delphi / FMX unit that implements real‑time Shadow Volume rendering on simple 3D objects (TCube).
The goal is to provide a clean and understandable demonstration of how to generate and render geometric shadow volumes using the stencil buffer, a classic technique used in OpenGL and DirectX.

The project is intentionally simple and focuses on clarity rather than completeness, making it a good starting point for anyone exploring low‑level 3D shadow techniques in FMX.

🎯 Purpose

FMX does not provide built‑in shadow volumes, so this project shows how to:

  • detect lit and shadowed faces of a cube
  • compute silhouette edges relative to a point light
  • extrude these edges to build a closed shadow volume
  • render the volume using the stencil buffer
  • support both shadow‑volume rendering modes:
    • Z‑PASS
    • Z‑FAIL (Carmack’s Reverse)

The implementation is self‑contained and designed for experimentation, learning, and extension.

📦 Contents

Main Unit

Execute.FMX.ShadowVolume.pas

This unit includes:

  • TShadowVolume
  • silhouette detection
  • volume extrusion
  • stencil setup and rendering
  • optional debug rendering (rays, volume outlines)
  • full support for Z‑PASS and Z‑FAIL modes via conditional compilation

Demo Project

A small FMX application demonstrating:

  • a cube illuminated by a point light
  • the generated shadow volume
  • the final shadow mask rendered via stencil operations
  • optional visualization of rays and extruded geometry

🔍 How It Works

  1. Face classification
    Each cube face is tested against the light direction to determine whether it is lit or shadowed.
  2. Silhouette extraction
    Edges between lit and shadowed faces form the silhouette.
  3. Volume construction
    Silhouette edges are extruded away from the light to form quads.
    Shadowed faces are used as near caps, and extruded faces form far caps.
  4. Stencil rendering
    The volume is rendered twice (front faces and back faces) with increment/decrement operations.
    The final shadowed region is where the stencil value is non‑zero.

Both Z‑PASS and Z‑FAIL are implemented, allowing the demo to illustrate the differences between the two techniques and the situations where each mode is appropriate.

🖼 Screenshots

The repository includes several images showing:

  • the cube
  • the extruded shadow volume
  • the stencil mask
  • the final shadow overlay

screen

⚠️ Limitations

This is a demonstration, not a full shadow system:

  • only TCube is supported
  • no soft shadows
  • no caps for arbitrary open geometry
  • no support for concave or complex meshes
  • no optimization for large scenes

Still, it provides a solid foundation for extending shadow volumes to other FMX 3D objects.

📄 License

This project is released under the MIT License.
You are free to use, modify, and integrate it into your own applications.

🤝 Contributions

Contributions, improvements, and extensions are welcome.
Feel free to open issues or submit pull requests.