Scrolling text in Gtk

[Tuvok <tuvok jasmine eu org>]

Hi,

What I need to do, is to make a bar with scrolling text inside it (like
the bars with stock prices on tv).

I've tried two methods, both of which are very slow. I've done it with
Canvas and with Cairo. Below follows code.

Did I do something wrong? Is there a way to make this code run faster?
Should I use some different libraries for it?


Rendering 4 such windows (1680x50) takes up 40-50% on both cores (AMD
X2, 2.4GHz).



Method I: Canvas

The rendering part of code:

   GtkWidget *canvasWdg;
   GnomeCanvasItem *text;
   GnomeCanvasGroup *rootGroup;

   ifstream in(filename);
   string textLine;
   getline(in, textLine);

   canvasWdg = gnome_canvas_new();

   gtk_container_add(GTK_CONTAINER(window), canvasWdg);

   gnome_canvas_set_scroll_region(GNOME_CANVAS(canvasWdg), 0.0, 0.0,
width*1.0,
                                  height*1.0);
   rootGroup = gnome_canvas_root(GNOME_CANVAS(canvasWdg));

   text = gnome_canvas_item_new(rootGroup, GNOME_TYPE_CANVAS_TEXT, "x",
                                0.0, "y", 0.0, "text", textLine.c_str(),
                                "anchor", GTK_ANCHOR_NW,
                                "fill_color", "white", "size",
                                (int)((height*0.7)*1000),
                                "size-set", TRUE, NULL);

   double x1, x2, y1, y2;
   gnome_canvas_item_get_bounds(GNOME_CANVAS_ITEM(text), &x1, &y1, &x2,
&y2);
// align the text in window:
   gnome_canvas_item_move(GNOME_CANVAS_ITEM(text), 1.0*width,
                          ((height*1.0)/2-(y2-y1)/2));

   g_timeout_add(40, moveText, text);

   gtk_widget_show_all(window);

and the timeout function:

gboolean moveText(void *text)
{

   gnome_canvas_item_move(GNOME_CANVAS_ITEM((GnomeCanvasItem*)text),
-2.0, 0.0);

   return TRUE;
}



Method II: Cairo

I've made a Gtk widget, which draws with cairo on expose event; I'll put
here only the expose function:

static gboolean mdk_text_scroller_expose(GtkWidget *textScroller,
GdkEventExpose *event)
{

   MdkTextScroller *ts = MDK_TEXT_SCROLLER(textScroller);


   cairo_t *cr;

   cr = gdk_cairo_create(textScroller->window);
                                                                                                              
                 

    gdk_cairo_region(cr,
event->region);                                                                                               
                               

cairo_clip(cr);                                                                                               
                                                    


   cairo_select_font_face(cr, "Sans", CAIRO_FONT_SLANT_NORMAL,
CAIRO_FONT_WEIGHT_NORMAL);

   cairo_set_font_size(cr, ts->size);
   cairo_move_to(cr, ts->x+ts->xOffset, ts->y+ts->yOffset);
   cairo_set_source_rgb(cr, 1.0, 1.0, 1.0);
   cairo_show_text(cr, ts->text);

   if (ts->width == 0 || ts->height == 0)
   {
      cairo_text_extents_t ext;
      cairo_text_extents(cr, ts->text, &ext);
      ts->width = ext.width;
      ts->height = ext.height;
   }

   if (ts->width+ts->xOffset+100 < 0)
   {
      cairo_move_to(cr, ts->x+ts->xOffset+ts->width+100, ts->y
+ts->yOffset);
      cairo_show_text(cr, ts->text);
   }

   if (ts->x+ts->xOffset+ts->width < 0)
   {
      ts->xOffset=ts->xOffset+ts->width+100;
   }


   cairo_stroke(cr);

   cairo_destroy(cr);
}

it's then redrawn with the same timeout call:

gboolean moveText(void *text)
{
   mdk_change_text_position((GtkWidget*)text, -1, 0);
   gtk_widget_queue_draw((GtkWidget*)text);

   return TRUE;
}


-- 
thanks
Tuvok