godot/thirdparty/libktx/lib/dfdutils/interpretdfd.c

/* -*- tab-width: 4; -*- */
/* vi: set sw=2 ts=4 expandtab: */

/* Copyright 2019-2020 The Khronos Group Inc.
 * SPDX-License-Identifier: Apache-2.0
 */

/**
 * @file
 * @~English
 * @brief Utility for interpreting a data format descriptor.
 * @author Andrew Garrard
 */

#include <stdint.h>
#include <stdio.h>
#include <KHR/khr_df.h>
#include "dfd.h"

static uint32_t bit_ceil(uint32_t x) { … }

/**
 * @~English
 * @brief Interpret a Data Format Descriptor for a simple format.
 *
 * Handles "simple" cases that can be translated to things a GPU can access.
 * For simplicity, it ignores the compressed formats, which are generally a
 * single sample (and I believe are all defined to be little-endian in their
 * in-memory layout, even if some documentation confuses this).  Focuses on
 * the layout and ignores sRGB except for reporting if that is the transfer
 * function by way of a bit in the returned value.
 *
 * @param[in] DFD Pointer to a Data Format Descriptor to interpret,
 *            described as 32-bit words in native endianness.
 *            Note that this is the whole descriptor, not just
 *            the basic descriptor block.
 * @param R[in,out] Pointer to struct to receive information about the decoded
 *                  red channel, the Y channel, if YUV, or the depth channel,
 *                  if any.
 * @param G[in,out] Pointer to struct to receive information about the decoded
 *                  green channel, the U (Cb) channel, if YUV, or the stencil
 *                  channel, if any.
 * @param B[in,out] Pointer to struct to receive information about the decoded
 *                  blue channel, if any or the V (Cr) channel, if YUV.
 * @param A[in,out] Pointer to struct to receive information about the decoded
 *                  alpha channel, if any or the second Y channel, if YUV and
 *                  any.
 * @param wordBytes[in,out] Pointer to a uint32_t to receive the byte size of
 *                          the channels (unpacked) or total size (packed).
 *
 * @return An enumerant describing the decoded value,
 *         or an error code in case of failure.
 *
 * The mapping of YUV channels to the parameter names used here is based on
 * the channel ids in @c khr_df.h and is different from the convention used
 * in format names in the Vulkan specification where G == Y, R = Cr and B = Cb.
 **/
enum InterpretDFDResult interpretDFD(const uint32_t *DFD,
                                     InterpretedDFDChannel *R,
                                     InterpretedDFDChannel *G,
                                     InterpretedDFDChannel *B,
                                     InterpretedDFDChannel *A,
                                     uint32_t *wordBytes)
{ … }