ExportImagePixelArea

Adam Morissun <[email protected]> Tue, 5 Jun 2018 22:08:40 -0700

Newsgroups	gmane.comp.video.graphicsmagick.help
Message-ID	<[email protected]>

Hi. Would someone explain how to use ExportImagePixelArea() ? I cannot 
make it work for the life of me.

I've attached the smallest C code I could devise to demonstrate my 
problem. I'm using Gimp to examine the '/tmp/pixels_**.data' files.

Thanks!

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rot_test.c (text/x-csrc, 2.4 KB)

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <assert.h>
#include <magick/api.h>

// write pixel data to a file
ssize_t write_pixels(const unsigned char *data, unsigned int len, const char *filename)
{
    int desc = open(filename, O_RDWR | O_CREAT, S_IRUSR | S_IWUSR);
    assert(desc > -1);
    ssize_t bytes = write(desc, data, len);
    if(bytes < 0)
        perror(0);
    close(desc);
    return bytes;
}

int main(int argc, char **argv) {
    const char filename[] = "pogo.jpg";
    InitializeMagick(NULL);

    ExceptionInfo exception;
    GetExceptionInfo(&exception);
    ImageInfo *image_info = CloneImageInfo(NULL);
    strcpy(image_info->filename, filename);
    Image *org = ReadImage(image_info, &exception);
    if(exception.severity != UndefinedException) {
        CatchException(&exception);
        return 1;
    }
    DescribeImage(org, stdout, 0);
    printf("matte? %i, depth %i\n", org->matte, org->depth);

    unsigned int size = org->rows * org->columns * org->depth;
    unsigned char* data = (unsigned char*)malloc(size);
    assert(data);
    ExportPixelAreaOptions opts;
    ExportPixelAreaOptionsInit(&opts);
    opts.endian = NativeEndian; // match OpenGL implementation on this machine
    ExportPixelAreaInfo ex_info;
    // update the default cache view? so ExportImagePixelArea() actually works
    // (do not free() pxls!)
    //PixelPacket *pxls = GetImagePixels(org, 0, 0, org->columns, org->rows);
    // now we export pixels
    int result = ExportImagePixelArea(org,
        org->matte ? RGBAQuantum : RGBQuantum,
        org->depth, data, &opts, &ex_info);
    assert(result != MagickFail);

    ssize_t bytes = write_pixels(data, size, "/tmp/pixels_before.data");
    free(data);

    Image *rot = RotateImage(org, 90, &exception);
    if(exception.severity != UndefinedException)
        CatchException(&exception);
    size = rot->rows * rot->columns * rot->depth;
    data = (unsigned char*)malloc(size);
    assert(data);
    ExportPixelAreaOptionsInit(&opts);
    opts.endian = NativeEndian;
    //pxls = GetImagePixels(rot, 0, 0, rot->columns, rot->rows);
    result = ExportImagePixelArea(rot,
        rot->matte ? RGBAQuantum : RGBQuantum,
        rot->depth, data, &opts, &ex_info);
    assert(result != MagickFail);
    bytes = write_pixels(data, size, "/tmp/pixels_after.data");
    free(data);

    DestroyImage(org);
    DestroyImage(rot);
    DestroyMagick();
    return 0;
}