On 24/11/13 07:50, creak ml wrote:
Hi!
I'm using a Gtk::DrawingArea to do some a special profiling drawing tool.
At some point, I want to draw a box, fill it with a color, stroke it
in black and write a text on it (and not drawing out of the box). I
succeeded in a way, but I'm not sure it's the perfect way of doing it.
Since the drawings in this DrawingArea will be pretty intensive, I'd
like to have some advice from you because I'm a bit lost with what
save, restore and *_preserve methods do...
Here the (simplified) code of the drawing:
// In the on_draw() method.
// cr is a Cairo::RefPtr<Cairo::Context> const&.
// For each box I've got to draw.
// Set the rectangle bounds.
cr->rectangle(rectX, rectY, rectWidth, rectHeight);
// Save it, fill, preserve and restore.
cr->save();
cr->set_source_rgb(1.0, 0.8, 0.5);
cr->fill_preserve();
cr->restore();
// Save it again, stroke, preserve and restore.
cr->save();
cr->set_source_rgb(0.0, 0.0, 0.0);
cr->set_line_width(1.0);
cr->stroke_preserve();
cr->restore();
// Initialize pango font.
Pango::FontDescription font;
font.set_family("DejaVu Sans");
font.set_size(12 * PANGO_SCALE);
font.set_stretch(Pango::STRETCH_CONDENSED);
// Initialize pango layout.
Glib::RefPtr<Pango::Layout> layout = create_pango_layout(text);
layout->set_font_description(font);
// Get the text dimensions.
int textWidth;
int textHeight;
layout->get_pixel_size(textWidth, textHeight);
// Position the text in the middle.
// Save, clip, set color, move to the middle, draw text, reset
clip, restore.
cr->save();
cr->clip();
cr->set_source_rgb(0.0, 0.0, 0.0);
cr->move_to(rectX + (rectWidth - textWidth) / 2, rectY +
(rectHeight - textHeight) / 2);
layout->show_in_cairo_context(cr);
cr->reset_clip();
cr->restore();
Trust me, if I remove one save/restore or one preserve, the draw is
becoming pretty f*cked up.
Maybe a first thing would be to cache the font.
Do you have other ideas, GTKMM gurus? ;)
Cheers,
Creak
Hi Creak,
I assume you found the manual-
https://developer.gnome.org/gtkmm-tutorial/unstable/index.html and have
read the chapter on drawing? It should answer your questions. The
online (or offline, if you've got the docs ) reference
manualhttps://developer.gnome.org/gtkmm/unstable/
<https://developer.gnome.org/gtkmm/unstable/> lists all the functions
including the ones you're asking about; generally the *mm documentation
is of a high standard. Make sure you're using references for the
version you're using; there's been a number of changes between version 2
and 3 of gtkmm.
tldr: a Cairo::context has a set of attributes at any point in time,
including clip regions, colour for background and foreground, line size,
etc. By encasing all writes to the Context in save and restore, you
prevent your code from modifying the base context. With that
understanding, you may want to encase your code slightly differently;
for instance, saving before clipping, then saving/ restoring around each
paint (the save / restore functions push the context onto a stack, so
you can have effectively unlimited depth).
The *_preserve functions write to the context but preserve the path they
write on, which is lost with the other (stroke and fill) methods.
Useful if you want to e..g. stroke in one colour and fill in another.
Have a look at the examples in the manual for ideas.
HTH,
Ian.
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