Re: Drawing a point in a pixbuf.

[Magnus Myrefors <myrefors magnus telia com>]

måndagen den 12 februari 2007 01.01 skrev Magnus Myrefors:
Hi again,
  I think I did try to change a value outside the pixbuf-data area due
  to negative y-values.
magnus m

> Hi,
>
> I have a function that tries to draw a point at (x,y) in a GdkPixbuf
> and I am using the formula:
>
>                  guchar *p;
>                  p = pixels + y * rowstride + x * n_channels;
>
> to locate the point in the pixbuf. I have used gdk_functions to get the
> 'pixels' value which is start of the pixbuf-values and the rowstride,
> n_channels and has_alpha. I checked the value of 'rowstride' and it was
> 2800 for my pixbuf and 'n_channels' was 4.
> However when I try to set the rgb-values for the pixel (x,y) I get a
> segmentation fault...? The code I have used is:
>
>                ->  *p++ = 0xff;
>                      *p++ = 0;
>                      *p++ = 0xfc;
>                      *p      =  has_alpha;
>
> The segmentation fault occurs at the arrow. I guess you can use
> gdk_draw_point() instead but I want to make the code a bit faster
> and use a function that can draw many pixels at once in a single function.
>
> magnus m
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