Block-transfering PixBufs

EricHopkins · **Joined:** Tue Jan 01, 2013 4:57 pm **Posts:** 4

Is there a way to blit pixbufs onto Images or DrawingAreas? I'm using GTK+3 with VisualRuby.

saunderson · **Joined:** Thu Aug 27, 2009 9:44 pm **Posts:** 8

My answer is limited for the case that you want to blit a pixbuf onto a DrawingArea.

In the case you want to blit a pixbuf onto a drawingarea you are mainly concerned with cairo as the main drawing backend of gtk3.

The gdk3 api provides a function

Code:

void                gdk_cairo_set_source_pixbuf         (cairo_t *cr,
                                                         const GdkPixbuf *pixbuf,
                                                         gdouble pixbuf_x,
                                                         gdouble pixbuf_y);

that makes a pixbuf the source for the next paint operation onto a cairo context. It seems that the ruby wrapper provides this function as a method of Cairo::Context [1]

Since you convert the pixbuf to the source of the following cairo-paint operation you can perform any operation that cairo provides onto the "pixbuf" before your call the above function (like scale, translate etc.)

[1] http://ruby-gnome2.sourceforge.jp/hiki. ... %3AContext

EricHopkins · **Joined:** Tue Jan 01, 2013 4:57 pm **Posts:** 4

Ok great, it seems to be working. The relevant code in Ruby comes up as this:

Code:

da = @builder["frame_view"]
    # Get the dimensions of the frame
    dims = da.allocation
    d_width, d_height = dims.width, dims.height
    # Create the context
    c = da.window.create_cairo_context
    # Clear the pixbuf to a neutral colour
    c.set_operator(Cairo::Operator::SOURCE)
    c.set_source_rgb( RGB_NEUTRAL )
    c.paint
    # Find the center point
    center_x = (d_width / 2).round
    center_y = (d_height / 2).round
    # Paint the cell
    c.set_operator(Cairo::Operator::OVER)
    c.set_source_pixbuf(@cell.cell, center_x, center_y)
    c.paint

where @cell.cell returns a rectangular partition of the source pixbuf, like this:

Code:

Gdk::Pixbuf.new(source, rect.x, rect.y, rect.w, rect.h)

My last concern is, is there a way to apply just a partition of the source pixbuf to the cairo context, without having to create a new Pixbuf object?

Paul Childs · **Posted:** Wed Jan 16, 2013 8:25 am

Cairo is actually very flexible. It maps arbitrary sources to destinations via masks. A destination can be recycled again as a source for further work (see the layering description at http://www.cairographics.org/tutorial/#L2nouns). E.g. you can load up your pixbuf as source, draw a path as a mask and then do a clip in order to use just a portion of your original. Incidentally, loading a pixbuf is as simple as e.g. calling cairo_image_surface_create_from_png(). No need to get your hands dirty with gdk (a lot of functions got depreciated with gtk2->3) and you might not even need pixbuf for that matter either. You can then render to a variety of forms (DrawingArea and other widgets; svg/png files, etc.)

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