Hi
I'm looking to manipulate a GdkPixbuf at the pixel level and have found
that the actual pixel data is not stored in the way I expected.
In order to get the pixel data I have used the following code (where
image is a static GtkWidget declared in the header file):
void pixel_data(GtkWidget *widget, GdkEvent *event, gpointer data)
{
int i, array_size;
GdkPixbuf *image_data;
i = 0;
image_data = gtk_image_get_pixbuf(GTK_IMAGE(image));
array_size = 3 * (gdk_pixbuf_get_width(image_data) *
gdk_pixbuf_get_height(image_data));
for(i=0; i < array_size; i++)
g_print("%d, ", (int) gdk_pixbuf_get_pixels(image_data)[i]);
}
My assumption was that the guchar pointer returned by
gdk_pixbuf_get_pixels() would store the pixel data as an 8 bit int for
the R, G and B channels for each pixel. ie. a 2*2 pixel image with 24bit
colour would print out the following (assuming the image was white):
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
However the following was output:
255, 255, 255, 255, 255, 255, 80, 64, 255, 255, 255, 255,
I then output the rowstride for the image which was 8 (bytes per row)
which prompted me to hack the code to loop 16 times and got:
255, 255, 255, 255, 255, 255, 80, 64, 255, 255, 255, 255, 255, 255, 0, 0,
rowstride: 8
My Question is simply why are there two extra bytes per image row, what do
they represent and what is a rowstride? - the documentation assumes this
knowledge!
I'm using GTK2.0 and redhat 7.3
Cheers
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