Re: Using GdkPixbuf buffers with GraphicsMagick

[Luka Napotnik <luka napotnik gmail com>]

Here's a sample code that fails:

--------------------------------------------
#include <gtk/gtk.h>
#include <string.h>
#include <wand/magick_wand.h>

guchar *
pixels_pack(guchar *data,
                  int width,
                  int height)
{
    /* Allocate an array of dimensions width*height for
     * RGBA with 16 bits per channel. */
    guchar *pixels = g_malloc0(width*height*8);
    guchar *pixel_old, *pixel_new;
    int rowstride_old = width * 4;
    int rowstride_new = width * 8;
    int x, y;
    guint16 value;

    for (y = 0; y < height; y++) {
        for (x = 0; x < width; x++) {
            pixel_old = data + y * rowstride_old + x;
            pixel_new = pixels + y * rowstride_new + x;
            value = pixel_old[0];
            memcpy(pixel_new, &value, sizeof(gint16));
            pixel_new += 2;
            value = pixel_old[1];
            memcpy(pixel_new, &value, sizeof(gint16));
            pixel_new += 2;
            value = pixel_old[2];
            memcpy(pixel_new, &value, sizeof(gint16));
            pixel_new += 2;
            value = pixel_old[3];
            memcpy(pixel_new, &value, sizeof(gint16));
        }
    }

    return pixels;
}

void
image_grayscale(guchar *image_data,
                              gint32 width,
                              gint32 height,
                              int n_channels)
{
    MagickWand *magick_wand;
    magick_wand = NewMagickWand();
    MagickSetSize(magick_wand,800,600);
    if (MagickReadImageBlob(magick_wand, image_data, width*height*8) ==
FALSE)
        g_warning("Failed.");
}

int main(int argc, char **argv)
{
    GtkWidget *window, *image, *image1;
    GdkPixbuf *pixbuf, *pixbuf1;
    guchar *data, *pixels;
    gtk_init(&argc, &argv);
    int width, height, rowstride;

    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    image = gtk_image_new_from_file("/home/napsy/back2.png");

    pixbuf = gtk_image_get_pixbuf(image);

    if (!pixbuf)
        g_warning("pixbuf == NULL\n");

    width = gdk_pixbuf_get_width(pixbuf);
    height = gdk_pixbuf_get_height(pixbuf);
    rowstride = gdk_pixbuf_get_rowstride(pixbuf);
    data = gdk_pixbuf_get_pixels(pixbuf);

    pixels = pixels_pack(data, width, height);
    image_grayscale(pixels, width, height, 4);
    g_free(pixels);

    gtk_container_add(window, image);
    gtk_widget_show_all(window);
    gtk_main();
    return 0;
}

--------------------------------------------

Hope this helps.

Greets,
Luka

Dne 07.01.2009 (sre) ob 09:23 +0000 je jcupitt gmail com zapisal(a):
> 2009/1/7 Luka Napotnik <luka napotnik gmail com>:
> > I've converted the buffer to an RGBA array with 16-bits per channel. But
> > loading the blob still fails. Any other ideas?
>
> We can't tell you what's wrong if you don't show any code. You need to
> post a tiny (but complete) test program. It'll only take you 30
> minutes to write something to load a Pixbuf, unpack to libMagick
> format, filter, repack to Pixbuf and save again.
>
> John
-- 
lp,
Luka