GL,Vk: clarify behavior with implementation-specific type/format values.

It may soon start happening that those will have an
implementation-specific value that is neither a GL or a Vulkan
identifier, so people should not just pass them around without checking.

src/Magnum/GL/Mesh.h

@@ -511,7 +511,14 @@ class MAGNUM_GL_EXPORT Mesh: public AbstractObject {
          */
         explicit Mesh(MeshPrimitive primitive = MeshPrimitive::Triangles);
 
-        /** @overload */
+        /** @overload
+         * @brief Construct with a generic primitive type
+         *
+         * Note that implementation-specific values are passed as-is with
+         * @ref meshPrimitiveUnwrap(). It's the user responsibility to ensure
+         * an implementation-specific value actually represents a valid OpenGL
+         * primitive type.
+         */
         explicit Mesh(Magnum::MeshPrimitive primitive): Mesh{meshPrimitive(primitive)} {}
 
         /**
@@ -654,7 +661,14 @@ class MAGNUM_GL_EXPORT Mesh: public AbstractObject {
             return *this;
         }
 
-        /** @overload */
+        /** @overload
+         * @brief Set a generic primitive type
+         *
+         * Note that implementation-specific values are passed as-is with
+         * @ref meshPrimitiveUnwrap(). It's the user responsibility to ensure
+         * an implementation-specific value actually represents a valid OpenGL
+         * primitive type.
+         */
         Mesh& setPrimitive(Magnum::MeshPrimitive primitive) {
             return setPrimitive(meshPrimitive(primitive));
         }

src/Magnum/Vk/ImageCreateInfo.h

@@ -226,9 +226,25 @@ class MAGNUM_VK_EXPORT ImageCreateInfo {
          * this constructor.
          */
         explicit ImageCreateInfo(VkImageType type, ImageUsages usages, PixelFormat format, const Vector3i& size, Int layers, Int levels, Int samples = 1, ImageLayout initialLayout = ImageLayout::Undefined, Flags flags = {});
-        /** @overload */
+
+        /** @overload
+         * @brief Construct with a generic pixel format
+         *
+         * Note that implementation-specific values are passed as-is with
+         * @ref pixelFormatUnwrap(). It's the user responsibility to ensure
+         * an implementation-specific value actually represents a valid Vulkan
+         * pixel format.
+         */
         explicit ImageCreateInfo(VkImageType type, ImageUsages usages, Magnum::PixelFormat format, const Vector3i& size, Int layers, Int levels, Int samples = 1, ImageLayout initialLayout = ImageLayout::Undefined, Flags flags = {});
-        /** @overload */
+
+        /** @overload
+         * @brief Constructor with a generic compressed pixel format
+         *
+         * Note that implementation-specific values are passed as-is with
+         * @ref compressedPixelFormatUnwrap(). It's the user responsibility to
+         * ensure an implementation-specific actually represents a valid Vulkan
+         * pixel format.
+         */
         explicit ImageCreateInfo(VkImageType type, ImageUsages usages, Magnum::CompressedPixelFormat format, const Vector3i& size, Int layers, Int levels, Int samples = 1, ImageLayout initialLayout = ImageLayout::Undefined, Flags flags = {});
 
         /* No overload w/o initialLayout here as the general public is expected

src/Magnum/Vk/MeshLayout.h

@@ -227,7 +227,15 @@ class MAGNUM_VK_EXPORT MeshLayout {
          *      @ref vkPipelineInputAssemblyStateCreateInfo()
          */
         explicit MeshLayout(MeshPrimitive primitive);
-        /** @overload */
+
+        /** @overload
+         * @brief Construct with a generic primitive type
+         *
+         * Note that implementation-specific values are passed as-is with
+         * @ref meshPrimitiveUnwrap(). It's the user responsibility to ensure
+         * an implementation-specific value actually represents a valid Vulkan
+         * primitive type.
+         */
         explicit MeshLayout(Magnum::MeshPrimitive primitive);
 
         /**
@@ -376,7 +384,15 @@ class MAGNUM_VK_EXPORT MeshLayout {
         MeshLayout& addAttribute(UnsignedInt location, UnsignedInt binding, VertexFormat format, UnsignedInt offset) &;
         /** @overload */
         MeshLayout&& addAttribute(UnsignedInt location, UnsignedInt binding, VertexFormat format, UnsignedInt offset) &&;
-        /** @overload */
+
+        /** @overload
+         * @brief Add an attribute with a generic primitive type
+         *
+         * Note that implementation-specific values are passed as-is with
+         * @ref vertexFormatUnwrap(). It's the user responsibility to ensure an
+         * implementation-specific value actually represents a valid Vulkan
+         * vertex format.
+         */
         MeshLayout& addAttribute(UnsignedInt location, UnsignedInt binding, Magnum::VertexFormat format, UnsignedInt offset) &;
         /** @overload */
         MeshLayout&& addAttribute(UnsignedInt location, UnsignedInt binding, Magnum::VertexFormat format, UnsignedInt offset) &&;