OS_Thumbnail.cpp

#include <Urho3D/Resource/Image.h>

#include <vector>
#include <set>

#include <windows.h>
#include <shlobj.h>

#include <Urho3D/DebugNew.h>

std::set<std::string> os_ThumbnailTried;

std::vector<unsigned char> HBitmapToPixels(HBITMAP bitmapHandle, int& width, int& height)
{
    BITMAP bmp = { 0 };
    BITMAPINFO bmpInfo = { 0 };

    HDC dc = CreateCompatibleDC(NULL);
    std::memset(&bmpInfo, 0, sizeof(BITMAPINFO)); //not necessary really..
    HBITMAP oldBitmap = (HBITMAP)SelectObject(dc, bitmapHandle);
    GetObject(bitmapHandle, sizeof(BITMAP), &bmp);

    bmpInfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    bmpInfo.bmiHeader.biWidth = width = bmp.bmWidth;
    bmpInfo.bmiHeader.biHeight = height = bmp.bmHeight;
    bmpInfo.bmiHeader.biPlanes = 1;
    bmpInfo.bmiHeader.biBitCount = 32;
    bmpInfo.bmiHeader.biCompression = BI_RGB;
    bmpInfo.bmiHeader.biSizeImage = ((width * bmp.bmBitsPixel + 31) / 32) * 4 * height;

    std::vector<unsigned char> pixelData = std::vector<unsigned char>();
    pixelData.resize(bmpInfo.bmiHeader.biSizeImage);
    GetDIBits(dc, bitmapHandle, 0, height, pixelData.data(), &bmpInfo, DIB_RGB_COLORS);
    SelectObject(dc, oldBitmap);

    height = std::abs(height);
    DeleteDC(dc);

    for (size_t i = 0; i < pixelData.size(); i += 4)
        std::swap(pixelData[i], pixelData[i + 2]);
    return pixelData;
}

std::wstring MultiByteToWideString(const std::string &str)
{
    if (str.empty()) return std::wstring();
    int size_needed = MultiByteToWideChar(CP_UTF8, 0, &str[0], (int)str.size(), NULL, 0);
    std::wstring wstrTo(size_needed, 0);
    MultiByteToWideChar(CP_UTF8, 0, &str[0], (int)str.size(), &wstrTo[0], size_needed);
    return wstrTo;
}

Urho3D::SharedPtr<Urho3D::Texture2D> CreateThumbnail(Urho3D::Context* ctx, const Urho3D::String& path, unsigned size)
{
    Urho3D::SharedPtr<Urho3D::Texture2D> ret;

    // Check if this thumbnail has been attempted, if so then early ut
    //  issue: previews that invalidate with file changes
    //  issue: cache outside of here, not just in resource cache (GetResource is slow for constant calling)
    //  issue: do any recognition of 'singular' icon outside of here (ie. *.xml files all using the same icon)
    if (os_ThumbnailTried.find(path.CString()) != os_ThumbnailTried.end())
        return ret;
    os_ThumbnailTried.insert(path.CString());

    IShellItem *shellItem;
    WCHAR wideStr[MAX_PATH];
    memset(wideStr, 0, sizeof(WCHAR) * MAX_PATH);
    MultiByteToWideChar(CP_UTF8, MB_COMPOSITE, path.CString(), path.Length(), wideStr, MAX_PATH);

    auto wStr = MultiByteToWideString(path.CString());

    HRESULT hr = SHCreateItemFromParsingName(wStr.c_str(), NULL, IID_PPV_ARGS(&shellItem));
    if (SUCCEEDED(hr))
    {
        IShellItemImageFactory* imageFactory;
        hr = SHCreateItemFromParsingName(wStr.c_str(), NULL, IID_PPV_ARGS(&imageFactory));
        if (SUCCEEDED(hr))
        {
            SIZE iconSize = { size, size };
            HBITMAP thumbnail;
            hr = imageFactory->GetImage(iconSize, SIIGBF_BIGGERSIZEOK, &thumbnail);
            if (SUCCEEDED(hr))
            {
                int w = size, h = size;
                auto pixelData = HBitmapToPixels(thumbnail, w, h);
                if (w > 0 && h > 0)
                {
                    Urho3D::UniquePtr<Urho3D::Image> img(new Urho3D::Image(ctx));
                    img->SetSize(w, h, 4);
                    memcpy(img->GetData(), pixelData.data(), pixelData.size());
                    ret = new Urho3D::Texture2D(ctx);
                    ret->SetData(img.Get(), true);
                }
                DeleteObject(thumbnail);
            }
            imageFactory->Release();
        }
    }
    return ret;
}

Code snippet for loading windows thumbnails into an Urho3D texture/image.