Use mipmaps from .dds file if present (#198)

* Use mipmaps from .dds file if present

* Don't load mips from disk if they're present in the base file

* Keep mipmap count >= 1

* Remove unintended formatting changes

* Validate DDS mipmap handling

---------

Co-authored-by: Luke Street <luke@street.dev>

lib/gfx/dds_io.cpp

@@ -1,5 +1,6 @@
 #include "dds_io.hpp"
 
+#include <algorithm>
 #include <cstring>
 #include <filesystem>
 #include <fstream>
@@ -52,6 +53,11 @@ struct DDSHeaderDX10 {
 static_assert(sizeof(DDSHeaderDX10) == 20);
 
 constexpr uint32_t kDDSMagic = 0x20534444; // "DDS"
+constexpr uint32_t kDDSDMipmapCount = 0x00020000;
+constexpr uint32_t kDDSCapsComplex = 0x00000008;
+constexpr uint32_t kDDSCapsMipmap = 0x00400000;
+constexpr uint32_t kDDSCaps2Cubemap = 0x00000200;
+constexpr uint32_t kDDSCaps2Volume = 0x00200000;
 
 bool ensure_directory(const std::filesystem::path& dir) noexcept {
   std::error_code ec;
@@ -101,12 +107,36 @@ bool validate_dds_header(const DDSHeader& header) noexcept {
   if (header.width == 0 || header.height == 0) {
     return false;
   }
-  if ((header.caps2 & (0x00000200 | 0x00200000)) != 0) { // Unsupported
+  if ((header.caps2 & (kDDSCaps2Cubemap | kDDSCaps2Volume)) != 0) { // Unsupported
     return false;
   }
   return true;
 }
 
+uint32_t max_mip_count(uint32_t width, uint32_t height) noexcept {
+  uint32_t count = 1;
+  while (width > 1 || height > 1) {
+    width = std::max(width >> 1, 1u);
+    height = std::max(height >> 1, 1u);
+    ++count;
+  }
+  return count;
+}
+
+std::optional<uint32_t> resolve_mip_count(const DDSHeader& header) noexcept {
+  if (header.mipMapCount <= 1) {
+    return 1;
+  }
+
+  const bool hasMipFlags = (header.flags & kDDSDMipmapCount) != 0 && (header.caps & kDDSCapsComplex) != 0 &&
+                           (header.caps & kDDSCapsMipmap) != 0;
+  if (!hasMipFlags || header.mipMapCount > max_mip_count(header.width, header.height)) {
+    return std::nullopt;
+  }
+
+  return header.mipMapCount;
+}
+
 std::optional<wgpu::TextureFormat> resolve_dx10_format(uint32_t dxgiFormat) noexcept {
   switch (dxgiFormat) {
   case 28:
@@ -253,8 +283,12 @@ std::optional<ConvertedTexture> parse_dds_bytes(ArrayRef<uint8_t> bytes) noexcep
     return std::nullopt;
   }
 
-  const uint32_t mipCount = 1u;
-  const auto expectedSize = calc_texture_size(parsedLayout->format, header->width, header->height, mipCount);
+  const auto mipCount = resolve_mip_count(*header);
+  if (!mipCount.has_value()) {
+    return std::nullopt;
+  }
+
+  const auto expectedSize = calc_texture_size(parsedLayout->format, header->width, header->height, *mipCount);
   if (expectedSize == 0 || parsedLayout->dataOffset + expectedSize > bytes.size()) {
     return std::nullopt;
   }
@@ -265,7 +299,7 @@ std::optional<ConvertedTexture> parse_dds_bytes(ArrayRef<uint8_t> bytes) noexcep
       .format = parsedLayout->format,
       .width = header->width,
       .height = header->height,
-      .mips = mipCount,
+      .mips = *mipCount,
       .data = std::move(data),
   };
 }

lib/gfx/texture_replacement.cpp

@@ -401,6 +401,23 @@ std::optional<aurora::gfx::ConvertedTexture> load_texture_file(const std::filesy
   return aurora::gfx::dds::load_dds_file(path);
 }
 
+bool remove_mipmaps(aurora::gfx::ConvertedTexture& texture) noexcept {
+  if (texture.mips <= 1) {
+    return true;
+  }
+
+  const uint64_t size = aurora::gfx::calc_texture_size(texture.format, texture.width, texture.height, 1);
+  if (size == 0 || size > texture.data.size()) {
+    return false;
+  }
+
+  aurora::ByteBuffer data{static_cast<size_t>(size)};
+  std::memcpy(data.data(), texture.data.data(), static_cast<size_t>(size));
+  texture.mips = 1;
+  texture.data = std::move(data);
+  return true;
+}
+
 constexpr bool is_unsupported_texture_format(wgpu::TextureFormat format) {
   switch (format) {
   case wgpu::TextureFormat::BC1RGBAUnorm:
@@ -464,6 +481,10 @@ std::optional<aurora::gfx::ConvertedTexture> load_file_replacement(const Replace
     return std::nullopt;
   }
 
+  if (base->mips > 1) {
+    return base;
+  }
+
   std::vector<aurora::gfx::ConvertedTexture> more;
   std::error_code ec;
   for (uint32_t mipLevel = 1;; ++mipLevel) {
@@ -487,6 +508,11 @@ std::optional<aurora::gfx::ConvertedTexture> load_file_replacement(const Replace
 
       break;
     }
+    // If a sidecar mip file contains mipmaps, keep only the top level mip.
+    if (!remove_mipmaps(*lvl)) {
+      Log.warn("texture_replacement: could not slice first mip {}", fs_path_to_string(mipPath));
+      break;
+    }
     more.push_back(std::move(*lvl));
   }