godot/servers/rendering/storage/variant_converters.h

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/*  variant_converters.h                                                  */
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#ifndef VARIANT_CONVERTERS_H
#define VARIANT_CONVERTERS_H

#include "core/error/error_macros.h"
#include "core/variant/array.h"
#include "core/variant/variant.h"

#include <initializer_list>
#include <type_traits>

template <typename T>
struct VariantConverterStd140 {
	// Generic base template for all Vector2/3/4(i) classes.
	static constexpr int Elements = T::AXIS_COUNT;

	template <typename P>
	static void convert(const T &p_v, P *p_write, bool p_compact) {
		for (int i = 0; i < Elements; i++) {
			p_write[i] = p_v[i];
		}
	}
};

template <>
struct VariantConverterStd140<float> {
	static constexpr int Elements = 1;

	template <typename P>
	static void convert(float p_v, P *p_write, bool p_compact) {
		p_write[0] = p_v;
	}
};

template <>
struct VariantConverterStd140<int32_t> {
	static constexpr int Elements = 1;

	template <typename P>
	static void convert(int32_t p_v, P *p_write, bool p_compact) {
		p_write[0] = p_v;
	}
};

template <>
struct VariantConverterStd140<uint32_t> {
	static constexpr int Elements = 1;

	template <typename P>
	static void convert(uint32_t p_v, P *p_write, bool p_compact) {
		p_write[0] = p_v;
	}
};

template <>
struct VariantConverterStd140<Basis> {
	static constexpr int Elements = 9;

	template <typename P>
	static void convert(const Basis &p_v, P *p_write, bool p_compact) {
		// Basis can have compact 9 floats or std140 layout 12 floats.
		int i = 0;

		p_write[i++] = p_v.rows[0][0];
		p_write[i++] = p_v.rows[1][0];
		p_write[i++] = p_v.rows[2][0];
		if (!p_compact) {
			p_write[i++] = 0;
		}

		p_write[i++] = p_v.rows[0][1];
		p_write[i++] = p_v.rows[1][1];
		p_write[i++] = p_v.rows[2][1];
		if (!p_compact) {
			p_write[i++] = 0;
		}

		p_write[i++] = p_v.rows[0][2];
		p_write[i++] = p_v.rows[1][2];
		p_write[i++] = p_v.rows[2][2];
		if (!p_compact) {
			p_write[i++] = 0;
		}
	}
};

template <>
struct VariantConverterStd140<Transform2D> {
	static constexpr int Elements = 12;

	template <typename P>
	static void convert(const Transform2D &p_v, P *p_write, bool p_compact) {
		p_write[0] = p_v.columns[0][0];
		p_write[1] = p_v.columns[0][1];
		p_write[2] = 0;
		p_write[3] = 0;

		p_write[4] = p_v.columns[1][0];
		p_write[5] = p_v.columns[1][1];
		p_write[6] = 0;
		p_write[7] = 0;

		p_write[8] = p_v.columns[2][0];
		p_write[9] = p_v.columns[2][1];
		p_write[10] = 1;
		p_write[11] = 0;
	}
};

template <>
struct VariantConverterStd140<Transform3D> {
	static constexpr int Elements = 16;

	template <typename P>
	static void convert(const Transform3D &p_v, P *p_write, bool p_compact) {
		p_write[0] = p_v.basis.rows[0][0];
		p_write[1] = p_v.basis.rows[1][0];
		p_write[2] = p_v.basis.rows[2][0];
		p_write[3] = 0;

		p_write[4] = p_v.basis.rows[0][1];
		p_write[5] = p_v.basis.rows[1][1];
		p_write[6] = p_v.basis.rows[2][1];
		p_write[7] = 0;

		p_write[8] = p_v.basis.rows[0][2];
		p_write[9] = p_v.basis.rows[1][2];
		p_write[10] = p_v.basis.rows[2][2];
		p_write[11] = 0;

		p_write[12] = p_v.origin.x;
		p_write[13] = p_v.origin.y;
		p_write[14] = p_v.origin.z;
		p_write[15] = 1;
	}
};

template <>
struct VariantConverterStd140<Projection> {
	static constexpr int Elements = 16;

	template <typename P>
	static void convert(const Projection &p_v, P *p_write, bool p_compact) {
		for (int i = 0; i < 4; i++) {
			for (int j = 0; j < 4; j++) {
				p_write[i * 4 + j] = p_v.columns[i][j];
			}
		}
	}
};

template <typename T, typename P>
T construct_vector(const std::initializer_list<P> &values) {
	T vector{};
	int index = 0;
	for (P v : values) {
		vector[index++] = v;
		if (index >= T::AXIS_COUNT) {
			break;
		}
	}
	return vector;
}

// Compatibility converter, tries to convert certain Variant types into a Vector2/3/4(i).

template <typename T>
T convert_to_vector(const Variant &p_variant, bool p_linear_color = false) {
	const Variant::Type type = p_variant.get_type();

	if (type == Variant::QUATERNION) {
		Quaternion quat = p_variant;
		return construct_vector<T>({ quat.x, quat.y, quat.z, quat.w });
	} else if (type == Variant::PLANE) {
		Plane p = p_variant;
		return construct_vector<T>({ p.normal.x, p.normal.y, p.normal.z, p.d });
	} else if (type == Variant::RECT2 || type == Variant::RECT2I) {
		Rect2 r = p_variant;
		return construct_vector<T>({ r.position.x, r.position.y, r.size.x, r.size.y });
	} else if (type == Variant::COLOR) {
		Color c = p_variant;
		if (p_linear_color) {
			c = c.srgb_to_linear();
		}
		return construct_vector<T>({ c.r, c.g, c.b, c.a });
	} else if (p_variant.is_array()) {
		const Array &array = p_variant;
		const int size = MIN(array.size(), T::AXIS_COUNT);
		T vector{};
		for (int i = 0; i < size; i++) {
			vector[i] = array.get(i);
		}
		return vector;
	}

	return p_variant; // Default Variant conversion, covers all Vector2/3/4(i) types.
}

inline bool is_number_array(const Array &p_array) {
	const int size = p_array.size();
	for (int i = 0; i < size; i++) {
		if (!p_array.get(i).is_num()) {
			return false;
		}
	}
	return true;
}

inline bool is_convertible_array(Variant::Type type) {
	return type == Variant::ARRAY ||
			type == Variant::PACKED_VECTOR2_ARRAY ||
			type == Variant::PACKED_VECTOR3_ARRAY ||
			type == Variant::PACKED_COLOR_ARRAY;
}

template <class, class = void>
struct is_vector_type : std::false_type {};

template <class T>
struct is_vector_type<T, std::void_t<decltype(T::AXIS_COUNT)>> : std::true_type {};

template <typename T, typename P>
void convert_item_std140(const T &p_item, P *p_write, bool p_compact = false) {
	VariantConverterStd140<T>::template convert<P>(p_item, p_write, p_compact);
}

template <typename T, typename P>
Vector<P> convert_array_std140(const Variant &p_variant, [[maybe_unused]] bool p_linear_color = false) {
	if (is_convertible_array(p_variant.get_type())) {
		// Slow path, convert Variant arrays and some packed arrays manually into primitive types.
		const Array &array = p_variant;
		if (is_number_array(array)) {
			// Already flattened and converted (or empty) array, usually coming from saved resources.
			return p_variant;
		}

		const int items = array.size();
		constexpr int elements = VariantConverterStd140<T>::Elements;

		Vector<P> result;
		result.resize(items * elements);
		P *write = result.ptrw();

		for (int i = 0; i < items; i++) {
			const Variant &item = array.get(i);
			P *offset = write + (i * elements);

			if constexpr (is_vector_type<T>::value) {
				const T &vec = convert_to_vector<T>(item, p_linear_color);
				convert_item_std140<T, P>(vec, offset, true);
			} else {
				convert_item_std140<T, P>(item.operator T(), offset, true);
			}
		}
		return result;

	} else if (p_variant.is_array()) {
		// Fast path, return the packed array directly.
		return p_variant;
	}

	// Not an array type. Usually happens with uninitialized null shader resource parameters.
	// Just return an empty array, uniforms will be default initialized later.

	return Vector<P>();
}

template <typename T, typename From, typename To>
void write_array_std140(const Vector<From> &p_values, To *p_write, int p_array_size, int p_stride) {
	constexpr int elements = VariantConverterStd140<T>::Elements;
	const int src_count = p_values.size();
	const int dst_count = elements * p_array_size;
	const int stride_count = p_stride * p_array_size;
	const From *read = p_values.ptr();
	const T default_value{};

	memset(p_write, 0, sizeof(To) * stride_count);

	for (int i = 0, j = 0; i < dst_count; i += elements, j += p_stride) {
		if (i + elements - 1 < src_count) {
			// Only copy full items with all elements, no partial or missing data.
			for (int e = 0; e < elements; e++) {
				DEV_ASSERT(j + e < stride_count && i + e < src_count);
				p_write[j + e] = read[i + e];
			}
		} else {
			// If not enough source data was passed in, write default values.
			convert_item_std140(default_value, p_write + j);
		}
	}
}

#endif // VARIANT_CONVERTERS_H