devilutionX/Source/engine/cel_header.hpp

#pragma once

#include <cstdint>
#include <cstring>

#include <SDL_endian.h>

#include "utils/endian.hpp"
#include "utils/stdcompat/cstddef.hpp"

namespace devilution {

/**
 * Returns the pointer to the start of the frame data (often a header).
 */
inline byte *CelGetFrame(byte *data, int frame)
{
	const std::uint32_t begin = LoadLE32(&data[frame * sizeof(std::uint32_t)]);
	return &data[begin];
}

/**
 * Returns the pointer to the start of the frame data (often a header) and sets `frameSize` to the size of the data in bytes.
 */
inline byte *CelGetFrame(byte *data, int frame, int *frameSize)
{
	const std::uint32_t begin = LoadLE32(&data[frame * sizeof(std::uint32_t)]);
	*frameSize = static_cast<int>(LoadLE32(&data[(frame + 1) * sizeof(std::uint32_t)]) - begin);
	return &data[begin];
}

/**
 * Returns the pointer to the start of the frame data (often a header) and sets `frameSize` to the size of the data in bytes.
 */
inline const byte *CelGetFrame(const byte *data, int frame, int *frameSize)
{
	const std::uint32_t begin = LoadLE32(&data[frame * sizeof(std::uint32_t)]);
	*frameSize = static_cast<int>(LoadLE32(&data[(frame + 1) * sizeof(std::uint32_t)]) - begin);
	return &data[begin];
}

/**
 * Returns the pointer to the start of the frame's pixel data and sets `frameSize` to the size of the data in bytes.
 */
inline const byte *CelGetFrameClipped(const byte *data, int frame, int *frameSize)
{
	const byte *frameData = CelGetFrame(data, frame, frameSize);

	// The frame begins with a header that consists of 5 little-endian 16-bit integers
	// pointing to the start of the pixel data for rows 0, 32, 64, 96, and 128.
	const std::uint16_t begin = LoadLE16(frameData);

	*frameSize -= begin;
	return &frameData[begin];
}

} // namespace devilution