how to handle rgb pixels before draw to drawingarea using cairo

[thexin chan <thexin1985 gmail com>]

Hello,
i am write a application like a tv watch soft,using em28xx capture video
as yuyv format,and converted to rgb24 when recived.

here ,some code to draw video frame to drawingarea.

gdk_threads_enter();    

gdk_draw_rgb_image(wbus->drawingarea->window,
        wbus->drawingarea->style->fg_gc[GTK_STATE_NORMAL],
        0,0,vidin->width,
        vidin->height,
        GDK_RGB_DITHER_NORMAL,
        frame->data,
        vidin->width * 3);

gdk_display_flush(gdk_display_get_default());   gdk_threads_leave();

i want to draw some string ,image on the drawingare,i call below
function after drawing frame,but there will blinking.

static void show_text_on_video(void)
{
        cairo_t *cr;
        PangoLayout *layout;
        PangoFontDescription *desc;
        
        cr = gdk_cairo_create(wbus->drawingarea->window);
        layout = pango_cairo_create_layout(cr);

        pango_layout_set_text(layout, "wbuscanner\néåå", -1);
        //desc = pango_font_description_from_string("SimSun Bold 60");
        //pango_layout_set_font_description(layout, desc);
        //pango_font_description_free(desc);

        cairo_select_font_face (cr, "Sans",
CAIRO_FONT_SLANT_NORMAL,CAIRO_FONT_WEIGHT_BOLD);
        cairo_set_font_size (cr, 70.0);
        cairo_move_to (cr, 70.0, 165.0);
        cairo_set_source_rgb(cr, 0.5, 0.5, 1);
        cairo_text_path(cr,"wbuscanner");
        //cairo_show_text(cr,"éæå");

        pango_cairo_update_layout(cr, layout);
        pango_cairo_show_layout(cr, layout);
        cairo_stroke(cr);

        cairo_destroy(cr);
}

then i used gdkpixmap create from rgb data and draw something on it ,and
draw to drawingarea,but this method was slower.(data is
frame->data,720*576,PAL)


        gdk_threads_enter();

        gdk_draw_rgb_image(wbus->pixmap,
                        wbus->drawingarea->style->bg_gc[GTK_STATE_NORMAL],
                        0,0,vidin->width,vidin->height,
                        GDK_RGB_DITHER_NONE,
                        frame->data,
                        vidin->width *3);

        cr = wbus->cr;
        //cairo_select_font_face (cr, "Sans",
CAIRO_FONT_SLANT_NORMAL,CAIRO_FONT_WEIGHT_BOLD);
        //cairo_set_font_size (cr, 70.0);
        cairo_move_to (cr, 70.0, 165.0);
        cairo_set_source_rgb(cr, 0.5, 0.5, 1);
        cairo_text_path(cr,"wbuscanner");
        cairo_stroke(cr);


        gdk_draw_pixmap(wbus->drawingarea->window,
                        wbus->drawingarea->style->fg_gc[GTK_STATE_NORMAL],
                        wbus->pixmap,0,0,0,0,vidin->width,vidin->height);

        gdk_display_flush(gdk_display_get_default());           
        gdk_threads_leave();


how can i draw strings ,image on the raw rgb24 ,and draw to drawingarea?


thanks.