feat(texture): add TextureBuilder class

include/zenkit/Texture.hh

@@ -1,6 +1,7 @@
 // Copyright © 2021-2023 GothicKit Contributors.
 // SPDX-License-Identifier: MIT
 #pragma once
+#include "zenkit/Error.hh"
 #include "zenkit/Library.hh"
 
 #include <array>
@@ -37,6 +38,18 @@ namespace zenkit {
 		DXT5 = 0xE,   ///< \brief DXT5 compression texture format
 	};
 
+	class InvalidMipmapSize final : public Error {
+	public:
+		explicit InvalidMipmapSize(uint32_t expect, size_t got)
+		    : Error("Invalid texture mipmap size. Expected " + std::to_string(expect) + ", got " +
+		            std::to_string(got)) {}
+	};
+
+	class UnsupportedFormatError final : public Error {
+	public:
+		explicit UnsupportedFormatError(std::string msg) : Error("Format not supported: " + msg) {}
+	};
+
 	/// \brief Simple ARGB quad.
 	struct ColorARGB {
 		std::uint8_t a, r, g, b;
@@ -134,5 +147,21 @@ namespace zenkit {
 
 		// Quirk: largest mipmap (level 0) stored at the end of the vector
 		std::vector<std::vector<std::uint8_t>> _m_textures;
+
+		friend class TextureBuilder;
+	};
+
+	class TextureBuilder {
+	public:
+		TextureBuilder(uint32_t width, uint32_t height);
+
+		TextureBuilder& add_mipmap(std::vector<uint8_t> bytes, TextureFormat format);
+
+		Texture build(TextureFormat format);
+
+	private:
+		std::uint32_t _m_width;
+		std::uint32_t _m_height;
+		std::vector<std::pair<std::vector<uint8_t>, TextureFormat>> _m_mipmaps;
 	};
 } // namespace zenkit

src/Texture.cc

@@ -352,4 +352,38 @@ namespace zenkit {
 			w->write(m.data(), m.size());
 		}
 	}
+
+	TextureBuilder::TextureBuilder(uint32_t width, uint32_t height) : _m_width(width), _m_height(height) {}
+
+	TextureBuilder& TextureBuilder::add_mipmap(std::vector<uint8_t> bytes, TextureFormat format) {
+		auto expected_size = _ztex_mipmap_size(format, _m_width, _m_height, _m_mipmaps.size());
+		if (bytes.size() != expected_size) {
+			throw InvalidMipmapSize {expected_size, bytes.size()};
+		}
+
+		_m_mipmaps.emplace_back(std::move(bytes), format);
+		return *this;
+	}
+
+	Texture TextureBuilder::build(TextureFormat format) {
+		if (format == TextureFormat::P8) {
+			throw UnsupportedFormatError {"P8"};
+		}
+
+		Texture tex;
+		tex._m_format = format;
+		tex._m_width = _m_width;
+		tex._m_height = _m_height;
+		tex._m_reference_width = _m_width;
+		tex._m_reference_height = _m_height;
+		tex._m_mipmap_count = _m_mipmaps.size();
+		tex._m_average_color = {}; // FIXME(lmichaelis): Calculate the average color
+
+		for (auto i = 0u; i < _m_mipmaps.size(); ++i) {
+			auto& [data, fmt] = _m_mipmaps[i];
+			tex._m_textures.push_back(_ztex_convert_format(data.data(), _m_width >> i, _m_height >> i, fmt, format));
+		}
+
+		return tex;
+	}
 } // namespace zenkit