feat(Texture): add support for A4R4G4B4 texture format

Intended to fix Try/OpenGothic#668

src/Texture.cc

@@ -18,6 +18,20 @@ namespace zenkit {
 		std::uint16_t g : 6;
 		std::uint16_t r : 5;
 	};
+
+	struct a4r4g4b4 {
+		std::uint16_t b : 4;
+		std::uint16_t g : 4;
+		std::uint16_t r : 4;
+		std::uint16_t a : 4;
+	};
+
+	struct a1r5g5b5 {
+		std::uint16_t b : 5;
+		std::uint16_t g : 5;
+		std::uint16_t r : 5;
+		std::uint16_t a : 1;
+	};
 #pragma pack(pop)
 
 	/// \brief Calculates the size in bytes of a texture at the given mipmap level.
@@ -149,6 +163,16 @@ namespace zenkit {
 
 			break;
 		}
+		case TextureFormat::A4R4G4B4: {
+			for (auto i = 0u; i < width * height; ++i) {
+				conv[i * 4 + 2] = ((bytes[i * 2 + 0] >> 0) & 0x0F) * 17;
+				conv[i * 4 + 1] = ((bytes[i * 2 + 0] >> 4) & 0x0F) * 17;
+				conv[i * 4 + 0] = ((bytes[i * 2 + 1] >> 0) & 0x0F) * 17;
+				conv[i * 4 + 3] = ((bytes[i * 2 + 1] >> 4) & 0x0F) * 17;
+			}
+
+			break;
+		}
 		default:
 			throw ParserError {"texture",
 			                   "cannot convert format to rgba: " + std::to_string(static_cast<int32_t>(src))};