XeGTAO Documentation

DirectXTex is a shared source library for texture content processing. It is primarily used for reading and writing DDS files and performing operations such as:

• Resizing and mip-map generation
• Format conversion
• Block compression (BC) for Direct3D runtime texture resources
• Height-map to normal-map conversion

The library utilizes the Windows Image Component (WIC) APIs and includes built-in readers/writers for .TGA and .HDR formats. It also supports WIC-based bitmap formats including BMP, JPEG, PNG, TIFF, and HD Photo.

XeGTAO is a DirectX/HLSL implementation of the GTAO algorithm, providing a radiometrically-correct ambient occlusion term.

Key Features

• Directional GTAO: Supports computing a directional component (bent normals / cones). Adding this component increases the cost by approximately 25%.
• Denoising: Includes an integrated spatial denoising filter.
• Temporal Accumulation: Designed to leverage TAA (Temporal Anti-Aliasing) for higher detail and better radiometric correctness.

Performance Benchmarks (Approximate)

• High Quality (Full Resolution):
  • 3840x2160 on RTX 3070: ~1.4ms
  • 1920x1080 on RTX 2060: ~0.56ms
  • 1920x1080 on 11th Gen Intel Core i7-1195G7 (Integrated): ~2.39ms
• Low Quality: A faster, lower-quality preset is also available.

Requirements

• API: DirectX 12 (Shader Model 6_3).
• Platform: Windows 10+.

Assimp includes several post-processing tools to optimize or repair mesh data during the import process. These include:

• Normals and tangent space generation
• Triangulation
• Vertex cache locality optimization
• Removal of degenerate primitives and duplicate vertices
• Sorting by primitive type
• Merging of redundant materials

Assimp is licensed under a modified 3-clause BSD License.

Key points:

• You may link to Assimp statically (unlike LGPL).
• You must include the Assimp license text with your product.
• The license provides no warranty (use at your own risk).

The imgui_scoped header provides experimental RAII-style (Resource Acquisition Is Initialization) wrappers for common Dear ImGui functions. These wrappers are intended to manage the lifecycle of ImGui state (like pushing/popping styles or IDs) automatically using C++ scope rules.

Note: This is an experimental feature and is not currently in the main Dear ImGui repository. It is based on pull request #2197 and discussed in issue #2096 of the official repository.

XeGTAO attenuates the effect from distant samples based on two primary settings:

• Effect radius: The near-field occlusion radius.
• Falloff range: The range over which the effect is attenuated.

Unlike the original GTAO paper, XeGTAO interpolates the sample horizon angle towards the hemisphere horizon (computed as $\text{cos}(\text{normal_angle} \pm \pi/2)$) rather than towards -1. This makes the attenuation function independent of the projected normal vector, preventing haloing or detail loss under certain view angles.

FreeType assumes blending occurs in linear space rather than gamma space. To achieve correct visual results when using imgui_freetype:

• Use sRGB.
• Convert to linear space in your pixel shader output.

Note: Using FreeType will impact default Dear ImGui styles; you may need to tweak alpha values to compensate.

When optimizing a mesh, the order of operations is critical for achieving the best results. You should feed your mesh through the following pipeline in this specific order:

1. Indexing (Remove redundant vertices and generate an index buffer)
2. Vertex cache optimization (Reorder triangles for GPU cache efficiency)
3. Overdraw optimization (Reorder triangles to minimize pixel shader overdraw)
4. Vertex fetch optimization (Reorder vertex buffer for memory locality)
5. Vertex quantization (Reduce attribute precision to save bandwidth)
6. Vertex/index buffer compression (Optional final step)

XeGTAO uses a 5x5 depth-aware spatial denoising filter. It does not implement its own temporal reprojection; instead, it relies on the host engine's Temporal Anti-Aliasing (TAA) for the temporal component.

To leverage temporal stability, you should enable temporal noise in your pipeline. This allows TAA to smooth the AO, but you must ensure temporal variance remains low enough so TAA does not mischaracterize the noise as scene features. If TAA is unavailable, the effect relies solely on the 5x5 spatial denoiser.

To use icons in ImGui, merge an icon font into your existing font stack using ImFontConfig::MergeMode = true. This allows you to refer to icons directly in your strings.

Note: The character ranges array must remain in scope for the duration of font usage because AddFont* functions use it lazily and do not copy it.

// Load a first font
io.Fonts->AddFontDefault();

// Define ranges (must stay in scope)
static const ImWchar icons_ranges[] = { 0xf000, 0xf3ff, 0 };

ImFontConfig config;
config.MergeMode = true;

// Merge DroidSans
io.Fonts->AddFontFromFileTTF("DroidSans.ttf", 18.0f, &config, io.Fonts->GetGlyphRangesJapanese());

// Merge FontAwesome icons
io.Fonts->AddFontFromFileTTF("fontawesome-webfont.ttf", 18.0f, &config, icons_ranges);

All strings in ImGui must use UTF-8 encoding.

• C++11: Use the u8"string" syntax for UTF-8 literals.
• Legacy C++: Convert strings to UTF-8 manually or load text from files already saved in UTF-8.
• Remapping: You can use font->AddRemapChar() to map local codepage characters to Unicode codepoints, though this can cause issues for international users editing source code.