Development Blog

This shot shows why HDR environment maps are important. The reflective surface is very dark, but the bright sun is still shining in the reflection. This would not be possible with an LDR image.

This project is relevant to the topic:

https://github.com/KhronosGroup/glTF-IBL-Sampler

What I ended up doing is running an HDR file through the IBL sampler above, then loading the KTX2, converting the mipmaps to BC6H, and saving as a DDS:

    auto plg = LoadPlugin("Plugins/KTX2TextureLoader");
    auto plg2 = LoadPlugin("Plugins/ISPCTexComp");

    auto skybox = LoadTexture("Materials/Environments/Cloudy Blue/specular.ktx2", LOAD_MIPCHAIN);
    std::vector<shared_ptr<Pixmap> > mipmaps;
    for (int layer = 0; layer < skybox->mipchain.size(); ++layer)
    {
        for (int miplevel = 0; miplevel < skybox->CountMipmaps(); ++miplevel)
        {
            auto mipmap = skybox->mipchain[layer][miplevel];
            mipmaps.push_back(mipmap->Convert(TEXTURE_BC6H));
        }
    }
    SaveTexture("Materials/Environments/Cloudy Blue/specular.dds", TEXTURE_CUBE, mipmaps, 6);

 

Updated code for generating cubemap:

#include "UltraEngine.h"

using namespace UltraEngine;

// https://www.ultraengine.com/community/blogs/entry/2780-building-a-single-file-4k-hdr-skybox-with-bc6-compression/
int main(int argc, const char* argv[])
{
    //Settings
    const bool compression = true;

    // Load required plugin
    auto fiplugin = LoadPlugin("Plugins/FITextureLoader");
    auto cplugin = LoadPlugin("Plugins/ISPCTexComp");

    // Load cube faces output from https://matheowis.github.io/HDRI-to-CubeMap/
    std::vector<std::shared_ptr<Pixmap> > mipchain;
    WString files[6] = { "px.hdr", "nx.hdr", "py.hdr", "ny.hdr", "pz.hdr", "nz.hdr" };
    for (int n = 0; n < 6; ++n)
    {
        auto pixmap = LoadPixmap(files[n]);
        Assert(pixmap);
        if (pixmap->format != VK_FORMAT_R16G16B16A16_SFLOAT)
        {
            pixmap = pixmap->Convert(TextureFormat(VK_FORMAT_R16G16B16A16_SFLOAT));// this step is required for BC6H conversion
        }
        while (true)
        {
            auto mipmap = pixmap;

            if (compression) mipmap = mipmap->Convert(TEXTURE_BC6H);
            Assert(mipmap);
            mipchain.push_back(mipmap);
            auto size = pixmap->size;
            if (size.x == mipmap->blocksize and size.y == mipmap->blocksize) break;

            size /= 2;
            pixmap = pixmap->Resize(size.x, size.y);
            Assert(pixmap);            
        }
    }
    
    // Save cubemap
    SaveTexture("skybox.dds", TEXTURE_CUBE, mipchain, 6);

    return 0;
}