Re: pixmap/pixbuf confusion

[Owen Taylor <otaylor redhat com>]

On Sat, 2003-07-12 at 12:58, Michael Koppelman wrote:
> Sorry, I'm confused.
>
> I'm creating a pixmap:
>
> GdkPixmap *pixmap = gdk_pixmap_new( draw->window, width, height, -1);
> draw_plot( GDK_DRAWABLE(pixmap) );
> pixbuf = gdk_pixbuf_get_from_drawable( NULL, pixmap,\
>       gdk_colormap_get_system(), 0, 0, 0, 0, -1, -1);
>   
>
> The idea is that draw_plot is used to draw to a drawingarea for normal
> use, but in the above it is used to draw to my pixmap so I can save it
> out as a JPEG. This works just fine provided I don't mess with the width
> and height. However, my goal is to allow them to choose the dimensions
> of the JPEG. In draw_plot I get the size of the passed-in drawable, so
> my theory was that it doesn't matter if they enter a size for the JPEG
> that is bigger or smaller than the drawingarea.
>
> The problem is, if the width and height they entered is bigger or
> smaller than the drawingarea my pixbuf ends up with all sorts of data
> from the screen in it. It if is the size of the drawing area it behaves
> correctly.
>
> If I comment out the draw_plot line, I would have thought my pixmap
> would be empty, but it's not. It's got screen stuff in it.Clearly I
> don't understand. I want a blank pixmap of arbitrary size. I want to
> pass it into a routine that draws in it. Then I want to copy it into a
> pixbuf so I can save it as a JPEG. Where do you think I am messing this
> up?

Pixmaps are created with uninitialized contents.

What color do you think "empty" is? Draw a rectangle of that color
over the whole pixmap before drawing the contents.

(draw->style->bg[GTK_STATE_NORMAL] draw->style->bg_gc[GTK_STATE_NORMAL]
will be the color draw->window gets set to on expose unless you've
changed it)

Regards,
                                                Owen