QueueFamilyIndices struct: fn definitions in .cpp

Instead of defining struct functions in header file, only declare them
in the header file and define them in the source file.

src/blue_noise.cpp

@@ -33,6 +33,12 @@ static VKAPI_ATTR VkBool32 VKAPI_CALL fn_VULKAN_DEBUG_CALLBACK(
 }
 #endif  // VULKAN_VALIDATION == 1
 
+dither::internal::QueueFamilyIndices::QueueFamilyIndices() : computeFamily() {}
+
+bool dither::internal::QueueFamilyIndices::isComplete() {
+  return computeFamily.has_value();
+}
+
 dither::internal::QueueFamilyIndices
 dither::internal::vulkan_find_queue_families(VkPhysicalDevice device) {
   QueueFamilyIndices indices;

src/blue_noise.hpp

@@ -39,11 +39,11 @@ std::vector<unsigned int> blue_noise_impl(int width, int height,
 
 #if DITHERING_VULKAN_ENABLED == 1
 struct QueueFamilyIndices {
-  QueueFamilyIndices() : computeFamily() {}
+  QueueFamilyIndices();
 
   std::optional<uint32_t> computeFamily;
 
-  bool isComplete() { return computeFamily.has_value(); }
+  bool isComplete();
 };
 
 QueueFamilyIndices vulkan_find_queue_families(VkPhysicalDevice device);