Jungfraujoch/preview/JFJochJPEG.cpp

// SPDX-FileCopyrightText: 2024 Filip Leonarski, Paul Scherrer Institute <filip.leonarski@psi.ch>
// SPDX-License-Identifier: GPL-3.0-only

#include <algorithm>
#include <climits>
#include <cstdint>
#include <string>
#include <vector>

#include "../common/JFJochException.h"
#include "../common/CompressedImage.h"
#include "JFJochJPEG.h"

// The encoder is the vendored stb_image_write, compiled into this file only and with static linkage,
// so no JPEG symbol or header leaves it. File output is compiled out - the image goes to memory.
#define STB_IMAGE_WRITE_IMPLEMENTATION
#define STB_IMAGE_WRITE_STATIC
#define STBI_WRITE_NO_STDIO
#if defined(_MSC_VER)
#pragma warning(push)
#pragma warning(disable: 4244 4505)
#elif defined(__GNUC__)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-function"
#pragma GCC diagnostic ignored "-Wmissing-field-initializers"
#endif
#include "stb/stb_image_write.h"
#if defined(_MSC_VER)
#pragma warning(pop)
#elif defined(__GNUC__)
#pragma GCC diagnostic pop
#endif

static void AppendToString(void *context, void *data, int size) {
    static_cast<std::string *>(context)->append(static_cast<const char *>(data), size);
}

std::string WriteJPEGToMem(const CompressedImage& image, int quality) {
    if (image.GetMode() != CompressedImageMode::RGB)
        throw JFJochException(JFJochExceptionCategory::InputParameterInvalid,
                              "Only RGB images allowed for JPEG saving");

    // 65535 is the JPEG format's limit; stb also indexes the pixels with an int.
    const int64_t width = image.GetWidth();
    const int64_t height = image.GetHeight();
    if (width <= 0 || height <= 0 || width > 65535 || height > 65535 || width * height * 3 > INT_MAX)
        throw JFJochException(JFJochExceptionCategory::InputParameterInvalid,
                              "Image size not supported by JPEG encoder");

    std::vector<uint8_t> buffer;
    image.GetUncompressed(buffer);

    std::string ret;
    if (stbi_write_jpg_to_func(AppendToString, &ret, static_cast<int>(width), static_cast<int>(height), 3,
                               buffer.data(), std::clamp(quality, 1, 100)) == 0)
        throw JFJochException(JFJochExceptionCategory::InputParameterInvalid, "JPEG encoding failed");
    return ret;
}