gtk_plot_canvas_paint

Nyquist · **Joined:** Thu May 26, 2011 11:11 am **Posts:** 11

Hi,
Does someone know what exactly the function from gtkextra gtk_plot_canvas_paint does in order to repaint the canvas?

Since I must work with huge canvasses it costs a lot (in terms of time) to paint it entirely. So I'm searching for a surrogate group of functions that can paint only a restricted area of it.

Thanks in advance.

zerohour · **Posted:** Tue Dec 20, 2011 7:16 pm

I assume this is for your picdsp project.
What versions and revisions of Gtk and GtkExtra are you using ?
Can you give the hardware specs of the computer your testing this on.
From what I've read, GtkExtra2 uses Gdk for drawing and GtkExtra3 uses Cairo.
For GtkExtra+3.0.1, gtk_plot_canvas_paint() is in gtkplotcanvas.c

Code:

/**
 * gtk_plot_canvas_paint:
 * @canvas: a #GtkPlotCanvas.
 *
 *
 */
void
gtk_plot_canvas_paint (GtkPlotCanvas *canvas)
{
  GtkWidget *widget;
  GList *childs;

  widget = GTK_WIDGET(canvas);

  if(gtk_widget_get_realized(widget) && !canvas->pixmap) return;
  if(canvas->freeze_count > 0) return;

  if(!gtk_plot_pc_init(canvas->pc)) return;

  gtk_plot_pc_gsave(canvas->pc);

  if(!GTK_IS_PLOT_PS(canvas->pc) || !canvas->transparent){
    if(canvas->transparent){
      GdkColor white;
      gdk_color_white(gtk_widget_get_colormap(GTK_WIDGET(canvas)), &white);
      gtk_plot_pc_set_color(canvas->pc, &white);
    } else
      gtk_plot_pc_set_color(canvas->pc, &canvas->background);
    gtk_plot_pc_draw_rectangle(canvas->pc,
                              TRUE,
                              0,0,canvas->pixmap_width, canvas->pixmap_height);
  }

  gtk_plot_canvas_draw_grid(canvas);

  childs = canvas->childs;
  while(childs)
   {
     GtkPlotCanvasChild *child;

     child = GTK_PLOT_CANVAS_CHILD(childs->data);
     gtk_plot_canvas_child_draw(canvas, child);
     childs = childs->next;
   }

  gtk_plot_pc_grestore(canvas->pc);
  gtk_plot_pc_leave(canvas->pc);
}

gtk_plot_pc_draw_rectangle is in gtkplotpc.c

Code:

void gtk_plot_pc_draw_rectangle                          (GtkPlotPC *pc,
                                                         gint filled,
                                                         gdouble x, gdouble y,
                                                         gdouble width,
                                                         gdouble height) 
{
  GTK_PLOT_PC_CLASS(GTK_OBJECT_GET_CLASS(GTK_OBJECT(pc)))->draw_rectangle(pc, filled, x, y, width, height);
}

And draw_rectangle is on line 216 of: gtkplotcairo.c

Code:

pc_class->draw_rectangle = gtk_plot_cairo_draw_rectangle;

And finally gtk_plot_cairo_draw_rectangle is in gtkplotcairo.c:

Code:

static void 
gtk_plot_cairo_draw_rectangle                          (GtkPlotPC *pc,
                                                        gint filled,
                                                        gdouble x, gdouble y,
                                                        gdouble width, gdouble height)
{
  cairo_t *cairo = GTK_PLOT_CAIRO(pc)->cairo;
  if(!cairo)
    return;

  cairo_move_to(cairo, x, y);
  cairo_line_to(cairo, x+width, y);
  cairo_line_to(cairo, x+width, y+height);
  cairo_line_to(cairo, x, y+height);
  cairo_close_path(cairo);
  if (filled)
    cairo_fill(cairo);
  else
    cairo_stroke(cairo);
}

So it seams gtk_plot_canvas_paint uses Cairo and it's basic drawing routines like: cairo_move_to and cairo_line_to. So if your not already using it, switching to GtkExtra3 might speed things up a bit. Or cut out the middle man entirely and use Cairo directly like Tadeboro gave here:
http://www.gtkforums.com/viewtopic.php?f=16&t=3301&hilit=humidity

Nyquist · **Joined:** Thu May 26, 2011 11:11 am **Posts:** 11

Hi,
thanks for your reply.

Yes, of course, it's for my dspic project. I'm using GtkExtra+3.0.1 on Ubuntu 10.10.
My hardware configuration is.. mmh.. a 2 GB RAM - intel atom N450 netbook.

I have traced the origins of gtk_plot_canvas as you did but I think that the actual drawing function lies in gtk_plot_canvas_child_draw(canvas, child);
Maybe gtk_plot_pc_draw_rectangle is the which one that paints the canvas background while childs are painted with the aforementioned one.
However, I really can't get where gtk_plot_canvas_child_draw(canvas, child) leads to.
It uses a not well specified draw(canvas,child) function whose pointer is setted to NULL inside the gtk_plot_canvas class.

Besides, there is a similar function called draw_selection(canvas, child, area) which (I think) is supposed to draw only a restricted area of a child.
It uses gdk_draw_rectangle and other stuff like this. I tried to adapt its code to my needs but that did't leads me to any way (maybe because I'm missing something).
(all these functions belong to gtkplotcanvas.c and gtkplotcanvas.h)

I can't understand the difference between painting a canvas towards invalidating his area (also called refresh)!

Lets take an example: suppose I'm going to draw a plot using two separate arrays, one for x and the other for y.
To do this I will simply link these arrays to my dataset and than I will call an invalidate function for the interested area.
But if I want the data (already painted) to change, why I can't simply modify its arrays values and invalidate that area again so that to be updated with the new ones?
I hope I have been clear enough.

However, I'm definitely going to have a look to Tadeboro's code and to cairo's libraries in order to better focus where the problem could lie.

zerohour · **Posted:** Wed Dec 21, 2011 3:42 am

Those Atom's have particularly poor graphics performance. I have a second computer, an Asus nettop with an Atom N450 and built in Nvidia ion graphics. I bought it for streaming NetFlix. It works pretty well for that but web browsing is terrible and I have fast cable Internet access. Perhaps at least a portion of your speed issue is the hardware. Can you test it on something like a Intel Corei3 or Corei5 ?

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