image_codec_jpeg.hpp File Reference

JPEG read/write backend using libjpeg. More...

#include <iostream>
#include <stdio.h>
#include "jpeglib.h"
#include <setjmp.h>
#include "image_data.hpp"

Go to the source code of this file.

Classes
struct	codec_error_mgr

Typedefs
typedef struct codec_error_mgr *	codec_error_mgr_ptr

Functions
static void	SaveTextureFileJpeg (rendering_engine::ImageData const &imageData, char const *filename)
	Saves image data to a JPEG file.
	codec_error_exit (j_common_ptr cinfo)
static bool	DoReadJpegFile (struct jpeg_decompress_struct *cinfo, char const *filename, unsigned int &width, unsigned int &height, std::vector< unsigned int > &rgbImageDataVector)
static bool	ReadJpegFile (char const *filename, unsigned int &width, unsigned int &height, std::vector< unsigned int > &rgbImageDataVector)
	Reads a JPEG file into an RGB image buffer.
static bool	ReadJpegFromMemory (const unsigned char *memory, size_t memorySize, unsigned int &width, unsigned int &height, std::vector< unsigned int > &rgbImageDataVector)
	Decode a JPEG image directly from a memory buffer.

Detailed Description

JPEG read/write backend using libjpeg.

Provides low-level I/O routines bridging ImageData and the libjpeg API. Supports 8-bit RGB images for loading and saving.

The implementation follows the official libjpeg API workflow:

• https://libjpeg.sourceforge.io/
• Steps: setup error handler -> create compressor/decompressor -> set parameters -> read/write scanlines -> clean up.

Custom error handling is implemented via codec_error_mgr to safely recover from libjpeg�s internal longjmp behavior.

Note

This file is an internal backend of the Rendering Engine and is not part of the public API.

See also

rendering_engine::ImageData

Definition in file image_codec_jpeg.hpp.

Typedef Documentation

codec_error_mgr_ptr

typedef struct codec_error_mgr* codec_error_mgr_ptr

Definition at line 98 of file image_codec_jpeg.hpp.

Function Documentation

codec_error_exit()

codec_error_exit

(

j_common_ptr

cinfo

)

Definition at line 105 of file image_codec_jpeg.hpp.

{
    /* cinfo->err really points to a codec_error_mgr struct, so coerce pointer */
    codec_error_mgr_ptr codecErr = (codec_error_mgr_ptr)cinfo->err;
 
    /* Always display the message. */
    /* We could postpone this until after returning, if we chose. */
    (*cinfo->err->output_message) (cinfo);
 
    /* Return control to the setjmp point */
    longjmp(codecErr->setjmp_buffer, 1);
}

DoReadJpegFile()

bool DoReadJpegFile ( struct jpeg_decompress_struct * cinfo, char const * filename, unsigned int & width, unsigned int & height, std::vector< unsigned int > & rgbImageDataVector )

static

Definition at line 154 of file image_codec_jpeg.hpp.

{
    /* We use our private extension JPEG error handler.
     * Note that this struct must live as long as the main JPEG parameter
     * struct, to avoid dangling-pointer problems.
     */
    struct codec_error_mgr jerr;
 
    FILE* infile;                 /* source file */
    JSAMPARRAY buffer;            /* Output row buffer */
    int row_stride;               /* physical row width in output buffer */
 
    if( (infile = fopen(filename, "rb")) == NULL )
    {
        std::cout << "File can not be open." << std::endl;
        return false;
    }
 
    /* Step 1: allocate and initialize JPEG decompression object */
 
    /* We set up the normal JPEG error routines, then override error_exit. */
    cinfo->err = jpeg_std_error(&jerr.pub);
    jerr.pub.error_exit = codec_error_exit;
    /* Establish the setjmp return context for my_error_exit to use. */
    if( setjmp(jerr.setjmp_buffer) ) {
        /* If we get here, the JPEG code has signaled an error.
         * We need to clean up the JPEG object, close the input file, and return.
         */
        jpeg_destroy_decompress(cinfo);
        fclose(infile);
        return false;
    }
    /* Now we can initialize the JPEG decompression object. */
    jpeg_create_decompress(cinfo);
 
    /* Step 2: specify data source (eg, a file) */
 
    jpeg_stdio_src(cinfo, infile);
 
    /* Step 3: read file parameters with jpeg_read_header() */
    
    (void)jpeg_read_header(cinfo, TRUE);
    /* We can ignore the return value from jpeg_read_header since
     *   (a) suspension is not possible with the stdio data source, and
     *   (b) we passed TRUE to reject a tables-only JPEG file as an error.
     * See libjpeg.txt for more info.
     */
 
     /* Step 4: set parameters for decompression */
 
     /* In this example, we don't need to change any of the defaults set by
      * jpeg_read_header(), so we do nothing here.
      */
 
    /* Step 5: Start decompressor and fulfill the output data */
    width = cinfo->image_width;
    height = cinfo->image_height;
 
    rgbImageDataVector.clear();
 
    (void)jpeg_start_decompress(cinfo);
    /* We can ignore the return value since suspension is not possible
     * with the stdio data source.
     */
 
     /* We may need to do some setup of our own at this point before reading
      * the data.  After jpeg_start_decompress() we have the correct scaled
      * output image dimensions available, as well as the output colormap
      * if we asked for color quantization.
      * In this example, we need to make an output work buffer of the right size.
      */
      /* JSAMPLEs per row in output buffer */
    row_stride = cinfo->output_width * cinfo->output_components;
    /* Make a one-row-high sample array that will go away when done with image */
    buffer = (*cinfo->mem->alloc_sarray)
        ((j_common_ptr)cinfo, JPOOL_IMAGE, row_stride, 1);
 
    /* Step 6: while (scan lines remain to be read) */
    /*           jpeg_read_scanlines(...); */
 
    /* Here we use the library's state variable cinfo->output_scanline as the
     * loop counter, so that we don't have to keep track ourselves.
     */
    ;
    while( cinfo->output_scanline < cinfo->output_height ) {
        /* jpeg_read_scanlines expects an array of pointers to scanlines.
         * Here the array is only one element long, but you could ask for
         * more than one scanline at a time if that's more convenient.
         */
        (void)jpeg_read_scanlines(cinfo, buffer, 1);
        /* Assume put_scanline_someplace wants a pointer and sample count. */
        for( int i = 0; i < row_stride; ++i )
        {
            rgbImageDataVector.push_back(*(buffer[0] + i));
        }
    }
 
    /* Step 7: Finish decompression */
 
    (void)jpeg_finish_decompress(cinfo);
    /* We can ignore the return value since suspension is not possible
     * with the stdio data source.
     */
 
     /* Step 8: Release JPEG decompression object */
 
     /* This is an important step since it will release a good deal of memory. */
    jpeg_destroy_decompress(cinfo);
 
    /* After finish_decompress, we can close the input file.
     * Here we postpone it until after no more JPEG errors are possible,
     * so as to simplify the setjmp error logic above.  (Actually, I don't
     * think that jpeg_destroy can do an error exit, but why assume anything...)
     */
    fclose(infile);
 
    /* At this point you may want to check to see whether any corrupt-data
     * warnings occurred (test whether jerr.pub.num_warnings is nonzero).
     */
 
     /* And we're done! */
    return true;
}

ReadJpegFile()

bool ReadJpegFile ( char const * filename, unsigned int & width, unsigned int & height, std::vector< unsigned int > & rgbImageDataVector )

static

Reads a JPEG file into an RGB image buffer.

Parameters

filename	Path to input JPEG file.
width	[out] Image width in pixels.
height	[out] Image height in pixels.
rgbImageDataVector	[out] Output vector of RGB pixel data (3 bytes per pixel).

Returns

true on success, false on failure.

Definition at line 135 of file image_codec_jpeg.hpp.

{
    /* This struct contains the JPEG decompression parameters and pointers to
     * working space (which is allocated as needed by the JPEG library).
     */
    struct jpeg_decompress_struct cinfo;
 
    return DoReadJpegFile(&cinfo, filename, width, height, rgbImageDataVector);
}

ReadJpegFromMemory()

bool ReadJpegFromMemory ( const unsigned char * memory, size_t memorySize, unsigned int & width, unsigned int & height, std::vector< unsigned int > & rgbImageDataVector )

static

Decode a JPEG image directly from a memory buffer.

This function behaves similarly to ReadJpegFile(), but instead of reading from disk, it reads raw JPEG bytes already loaded in memory.

Useful when assets are stored in:

• packed archives (Pack.bin)
• networked streams
• compressed inline resources

The function expects the buffer to contain valid JPEG-formatted data.

Parameters

memory	Pointer to the start of the JPEG byte stream.
memorySize	Total size of the memory buffer in bytes.
width	[out] Decoded image width in pixels.
height	[out] Decoded image height in pixels.
rgbImageDataVector	[out] Output RGB pixel buffer (3 bytes per pixel).

Returns

• true → Successful decode.
• false → Memory buffer was not a valid JPEG stream or decode failed.

Warning

The function does not attempt format detection beyond JPEG signature. Callers must ensure the memory buffer contains JPEG data.

Definition at line 314 of file image_codec_jpeg.hpp.

{
    struct jpeg_decompress_struct cinfo;
    struct codec_error_mgr jerr;
 
    cinfo.err = jpeg_std_error(&jerr.pub);
    jerr.pub.error_exit = codec_error_exit;
 
    if (setjmp(jerr.setjmp_buffer)) {
        jpeg_destroy_decompress(&cinfo);
        return false;
    }
 
    jpeg_create_decompress(&cinfo);
 
    jpeg_mem_src(&cinfo, memory, memorySize);
 
    jpeg_read_header(&cinfo, TRUE);
    jpeg_start_decompress(&cinfo);
 
    width = cinfo.output_width;
    height = cinfo.output_height;
    unsigned int components = cinfo.output_components; // should = 3
 
    size_t row_stride = width * components;
    rgbImageDataVector.resize(width * height * components);
 
    while (cinfo.output_scanline < cinfo.output_height)
    {
        unsigned char* row = (unsigned char*)(
            rgbImageDataVector.data() +
            cinfo.output_scanline * row_stride
            );
        jpeg_read_scanlines(&cinfo, &row, 1);
    }
 
    jpeg_finish_decompress(&cinfo);
    jpeg_destroy_decompress(&cinfo);
 
    return true;
}

SaveTextureFileJpeg()

void SaveTextureFileJpeg ( rendering_engine::ImageData const & imageData, char const * filename )

static

Saves image data to a JPEG file.

Parameters

imageData	Source image in RGB format.
filename	Path to the output file.

Definition at line 38 of file image_codec_jpeg.hpp.

{
    auto const imageDataVector = imageData.GetImageDataRGB();
    JSAMPLE* imageBuffer = new JSAMPLE[imageDataVector.size()];
    std::copy(imageDataVector.begin(), imageDataVector.end(), imageBuffer);
    int quality = 100;
 
    struct jpeg_compress_struct cinfo;
    struct jpeg_error_mgr jerr;
 
    FILE* outfile;                /* target file */
    JSAMPROW row_pointer[1];      /* pointer to JSAMPLE row[s] */
    int row_stride;               /* physical row width in image buffer */
 
    cinfo.err = jpeg_std_error(&jerr);
    jpeg_create_compress(&cinfo);
 
    if( (outfile = fopen(filename, "wb")) == NULL ) {
        fprintf(stderr, "can't open %s\n", filename);
        exit(1);
    }
    jpeg_stdio_dest(&cinfo, outfile);
 
    cinfo.image_width = imageData.GetWidth();   /* image width and height, in pixels */
    cinfo.image_height = imageData.GetHeight();
    cinfo.input_components = 3;                 /* # of color components per pixel */
    cinfo.in_color_space = JCS_RGB;             /* colorspace of input image */
 
    jpeg_set_defaults(&cinfo);
 
    jpeg_set_quality(&cinfo, quality, TRUE /* limit to baseline-JPEG values */);
 
    jpeg_start_compress(&cinfo, TRUE);
 
    row_stride = imageData.GetWidth() * 3; /* JSAMPLEs per row in image_buffer */
 
    while( cinfo.next_scanline < cinfo.image_height )
    {
        /* jpeg_write_scanlines expects an array of pointers to scanlines.
         * Here the array is only one element long, but you could pass
         * more than one scanline at a time if that's more convenient.
         */
        row_pointer[0] = &imageBuffer[cinfo.next_scanline * row_stride];
        (void)jpeg_write_scanlines(&cinfo, row_pointer, 1);
    }
 
    jpeg_finish_compress(&cinfo);
    /* After finish_compress, we can close the output file. */
    fclose(outfile);
 
    jpeg_destroy_compress(&cinfo);
    delete[] imageBuffer;
}