Re: Scrolling text in Gtk

[Micah Carrick <email micahcarrick com>]

In the book "Foundations of GTK+ Development", there is a chapter on 
creating custom widgets in which a marquee widget is created (which 
scrolls text across the widget).

You could take a look at the source code from the book available at 
www.gtkbook.com

- Micah Carrick

 Developer - http://www.micahcarrick.com
 GTK+ Forums - http://www.gtkforums.com



Tuvok wrote:
> 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;
> }
>
>
>