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README
Apache-2.0

glTF 2.0 Sample Viewer

This is the official Khronos glTF 2.0 sample viewer using WebGL: glTF 2.0 Sample Viewer

Table of Contents

Version

Pre-release

Credits

Developed by UX3D and based on the former glTF-WebGL-PBR project. Supported by the Khronos Group and Facebook for animations, skinning and morphing.

Features

Experimental

Viewer

Link to the live glTF 2.0 Sample Viewer.

Usage

Controls

click + drag : Rotate model

scroll : Zoom camera

GUI : Use to change models and settings

Change glTF model

  • Choose one of the glTF models in the selction list

or

  • Drag and drop glTF files into viewer

Setup

For local usage and debugging, please follow these instructions:

(1) Checkout the master branch

(2) Install dependencies with npm install

(3) Pull the submodules for the required glTF sample models and environments git submodule update --init --recursive

(4a) Start a demo in the browser with npm run dev, and open http://localhost:8000.

(4b) Start a demo in Electron with npm run dev:electron.

When making changes, the project is automatically rebuilt and the dist/ folder is updated. Files in the dist/ folder should not be included in pull requests — they will be updated by project maintainers with each new release.

Offline / Headless Rendering

NOTE: The dimensions of the rendered image are limited by the (virtual) desktop size.

Requirements

Configure environment

  • npm install (also installs Electron)
  • npm run build (“compile” the code)

Run

  • npm run start-offscreen -- -- -h for a list of available options

Example

  • npm run start-offscreen -- -- assets/models/2.0/FlightHelmet/glTF/FlightHelmet.gltf

After execution, the screenshot is stored as output.png on the file system.

Debugging

  • Requirements
  • Install the Debugger for Firefox extension for Visual Studio Code
  • Open the project folder in Visual Studio Code and select Debug->Add Configuration->Firefox so the .vscode/launch.json file is created.
  • Debug->Start Debugging should now launch a Firefox window with the sample viewer and VS Code breakpoints should be hit.

Physically-Based Materials in glTF 2.0

With the change from glTF 1.0 to glTF 2.0, one of the largest changes included core support for materials that could be used for physically-based shading. Part of this process involved chosing technically accurate, yet user-friendly, parameters for which developers and artists could use intuitively. This resulted in the introduction of the Metallic-Roughness Material to glTF. If you would like to read more about glTF, you can find the content at its GitHub page.

A good reference about Physically-Based Materials and its workflow can be found on the THE PBR GUIDE - PART 1 and THE PBR GUIDE - PART 2 from allegorithmic.

For implementation details and further theory, please find more information in the Real Shading in Unreal Engine 4 presentation from the SIGGRAPH 2013 course.

Appendix A: Metallic-Roughness Material

For further reference, please read the glTF 2.0: Appendix B: BRDF Implementation The following sections do summarize the important shader code.

vec3 F_specular = D * Vis * F;
vec3 F_diffuse = (1.0 - F) * diffuse;
vec3 F = F_specular + F_diffuse;

Please note: Vis = G / (4 * NdotL * NdotV)

Specular Term (F_specular)

Microfacet metallic-roughness BRDF

vec3 metallicBRDF (vec3 f0, vec3 f90, float alphaRoughness, float VdotH, float NdotL, float NdotV, float NdotH)
{
    vec3 F = fresnel(f0, f90, VdotH);
    float Vis = V_GGX(NdotL, NdotV, alphaRoughness);
    float D = D_GGX(NdotH, alphaRoughness);

    return F * Vis * D;
}

Surface Reflection Ratio (F)

Fresnel Schlick

vec3 fresnel(vec3 f0, vec3 f90, float VdotH)
{
    return f0 + (f90 - f0) * pow(clamp(1.0 - VdotH, 0.0, 1.0), 5.0);
}

Please note, that the above shader code includes the optimization for "turning off" the Fresnel edge brightening (see "Real-Time Rendering" Fourth Edition on page 325).

Geometric Occlusion / Visiblity (V)

Smith Joint GGX

float V_GGX(float NdotL, float NdotV, float alphaRoughness)
{
    float alphaRoughnessSq = alphaRoughness * alphaRoughness;

    float GGXV = NdotL * sqrt(NdotV * NdotV * (1.0 - alphaRoughnessSq) + alphaRoughnessSq);
    float GGXL = NdotV * sqrt(NdotL * NdotL * (1.0 - alphaRoughnessSq) + alphaRoughnessSq);

    float GGX = GGXV + GGXL;
    if (GGX > 0.0)
    {
        return 0.5 / GGX;
    }
    return 0.0;
}

Normal Distribution (D)

Trowbridge-Reitz GGX

float D_GGX(float NdotH, float alphaRoughness)
{
    float alphaRoughnessSq = alphaRoughness * alphaRoughness;
    float f = (NdotH * NdotH) * (alphaRoughnessSq - 1.0) + 1.0;
    return alphaRoughnessSq / (M_PI * f * f);
}

Diffuse Term (F_diffuse)

Lambertian

vec3 lambertian(vec3 f0, vec3 f90, vec3 diffuseColor, float VdotH)
{
    return (1.0 - fresnel(f0, f90, VdotH)) * (diffuseColor / M_PI);
}

Appendix B: FAQ

Q: Why do I not see environment lighting here https://github.khronos.org/glTF-Sample-Viewer/?
A: The glTF Sample Viewer is using KTX2 for the pre-filtered environments. However, the mime type is not yet registered here.

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