{

std::vector<MipLevelData> mip_maps{start_level};

// each subsequent mipmap is half the size of the preceding one

static constexpr auto scale = 2u;

// next mip level dimensions

auto width = start_level.width / scale;

auto height = start_level.height / scale;

while ((width > 0u) && (height > 0u))

{

const auto scale_x = static_cast<float>(mip_maps.back().width) / static_cast<float>(width);

const auto scale_y = static_cast<float>(mip_maps.back().height) / static_cast<float>(height);

// we work on RGBA images

static constexpr auto stride = 4u;

DataBuffer mip_data(width * height * stride);

auto *dst = mip_data.data();

const auto *src = reinterpret_cast<const std::uint8_t *>(mip_maps.back().data.data());

// simple downsize algorithm by skipping pixels, will produce aliasing

for (auto y = 0u; y < height; ++y)

{

const auto y_nearest = static_cast<int>(std::floor(y * scale_y));

for (auto x = 0u; x < width; ++x)

{

const auto x_nearest = static_cast<int>(std::floor(x * scale_x));

std::memcpy(dst, src + ((y_nearest * mip_maps.back().width) + x_nearest) * stride, stride);

dst += stride;

}

}

mip_maps.push_back({.data = std::move(mip_data), .width = width, .height = height});

width /= scale;

height /= scale;

}

return mip_maps;