Re: Problem wil GdkGC (colourful scrible using GdkRGB)

[Colin Thomas <colin designresources co uk>]

Hello Deekshit,

I have modified the scribble code to rotate through 4 colours (red/green/blue/yellow)
using GdkRGB (which does not require colour allocation, as mentioned by Havoc in 
another thread).

The code is below:

Note the three following points:

1. Attach a GdkRGC to the drawing area

   In main,
   
>    drawing_area = gtk_drawing_area_new ();

   becomes....   
   
>   gtk_widget_push_visual (gdk_rgb_get_visual ());
>   gtk_widget_push_colormap (gdk_rgb_get_cmap ());
>    drawing_area = gtk_drawing_area_new ();
>   gtk_widget_pop_visual ();
>   gtk_widget_pop_colormap ();

2. Set a counter to rotate through the colours

>   int Count = 0 ;

   and in draw_brush
 
>     if (Count == 3 ) {
>      Count =  0 ;
>     } else {
>      Count++;
>     }

3. Draw in different colours

   In draw_brush
   
   Create a graphics context from the pixmap
   
>      thisGraphicsContext = gdk_gc_new(pixmap);
      
   remebering to delete the graphics context after usage
   
>     gdk_gc_unref(thisGraphicsContext);
   
   Set the Pixel value on the GdkColor , and set the foreground colour to be it.
   
>    if (Count == 0 ) {
>     printf("Set Red\n");
>     ThisColour.pixel = gdk_rgb_xpixel_from_rgb (0xff0000);
>     gdk_gc_set_foreground( thisGraphicsContext, &ThisColour);
>    }
>    if (Count == 1 ) {
>     printf("Set Blue\n");
>     ThisColour.pixel = gdk_rgb_xpixel_from_rgb (0x0000ff);
>     gdk_gc_set_foreground( thisGraphicsContext, &ThisColour);
>    }
>    if (Count == 2 ) {
>     printf("Set Yellow\n");
>     ThisColour.pixel = gdk_rgb_xpixel_from_rgb (0xffff00);
>     gdk_gc_set_foreground( thisGraphicsContext, &ThisColour);
>    }
>    if (Count == 3 ) {
>     printf("Set Green\n");
>     ThisColour.pixel = gdk_rgb_xpixel_from_rgb (0x00ff00);
>     gdk_gc_set_foreground( thisGraphicsContext, &ThisColour);
>    }

   As Havoc points out:
      /* 0xff442e means 0xff red, 0x44 green, 0x2e blue */
      color.pixel = gdk_rgb_xpixel_from_rgb (0xff442e);
    
   Draw rectangle in this colour..
   
   Replace
   
>     gdk_draw_rectangle (pixmap,
>                     widget->style->black_gc,
>                     TRUE,
>                     update_rect.x, update_rect.y,
>                     update_rect.width, update_rect.height);

   with..
   
>    gdk_draw_rectangle (pixmap,
>                      thisGraphicsContext,
>                     TRUE,
>                     update_rect.x, update_rect.y,
>                     update_rect.width, update_rect.height);

Hope this both helps with the coloured scribble, and gives an example for using GdkRGB

Best regards

/colin.

########################################################################
/* example-start scribble-simple scribble-simple.c */

/* GTK - The GIMP Toolkit
 * Copyright (C) 1995-1997 Peter Mattis, Spencer Kimball and Josh MacDonald
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

#include <gtk/gtk.h>
int Count = 0 ;

/* Backing pixmap for drawing area */
static GdkPixmap *pixmap = NULL;

/* Create a new backing pixmap of the appropriate size */
static gint configure_event( GtkWidget         *widget,
                             GdkEventConfigure *event )
{
  if (pixmap)
    gdk_pixmap_unref(pixmap);

  pixmap = gdk_pixmap_new(widget->window,
                          widget->allocation.width,
                          widget->allocation.height,
                          -1);
  gdk_draw_rectangle (pixmap,
                      widget->style->white_gc,
                      TRUE,
                      0, 0,
                      widget->allocation.width,
                      widget->allocation.height);

  return TRUE;
}

/* Redraw the screen from the backing pixmap */
static gint expose_event( GtkWidget      *widget,
                          GdkEventExpose *event )
{
  gdk_draw_pixmap(widget->window,
                  widget->style->fg_gc[GTK_WIDGET_STATE (widget)],
                  pixmap,
                  event->area.x, event->area.y,
                  event->area.x, event->area.y,
                  event->area.width, event->area.height);

  return FALSE;
}

/* Draw a rectangle on the screen */
static void draw_brush( GtkWidget *widget,
                        gdouble    x,
                        gdouble    y)
{
  GdkRectangle update_rect;
  GdkColor ThisColour;
  GdkGC     * thisGraphicsContext;

 thisGraphicsContext = gdk_gc_new(pixmap);
 if (Count == 0 ) {
  printf("Set Red\n");
  ThisColour.pixel = gdk_rgb_xpixel_from_rgb (0xff0000);
  gdk_gc_set_foreground( thisGraphicsContext, &ThisColour);
 }
 if (Count == 1 ) {
  printf("Set Blue\n");
  ThisColour.pixel = gdk_rgb_xpixel_from_rgb (0x0000ff);
  gdk_gc_set_foreground( thisGraphicsContext, &ThisColour);
 }
 if (Count == 2 ) {
  printf("Set Yellow\n");
  ThisColour.pixel = gdk_rgb_xpixel_from_rgb (0xffff00);
  gdk_gc_set_foreground( thisGraphicsContext, &ThisColour);
 }
 if (Count == 3 ) {
  printf("Set Green\n");
  ThisColour.pixel = gdk_rgb_xpixel_from_rgb (0x00ff00);
  gdk_gc_set_foreground( thisGraphicsContext, &ThisColour);
 }

  update_rect.x = x - 5;
  update_rect.y = y - 5;
  update_rect.width = 10;
  update_rect.height = 10;
  gdk_draw_rectangle (pixmap,
                      thisGraphicsContext,
                      TRUE,
                      update_rect.x, update_rect.y,
                      update_rect.width, update_rect.height);
  gtk_widget_draw (widget, &update_rect);

  if (Count == 3 ) {
   Count =  0 ;
  } else {
   Count++;
  }
   gdk_gc_unref(thisGraphicsContext);
}

static gint button_press_event( GtkWidget      *widget,
                                GdkEventButton *event )
{
  if (event->button == 1 && pixmap != NULL)
    draw_brush (widget, event->x, event->y);

  return TRUE;
}

static gint motion_notify_event( GtkWidget *widget,
                                 GdkEventMotion *event )
{
  int x, y;
  GdkModifierType state;

  if (event->is_hint)
    gdk_window_get_pointer (event->window, &x, &y, &state);
  else
    {
      x = event->x;
      y = event->y;
      state = event->state;
    }
    
  if (state & GDK_BUTTON1_MASK && pixmap != NULL)
    draw_brush (widget, x, y);
  
  return TRUE;
}

void quit ()
{
  gtk_exit (0);
}

int main( int   argc, 
          char *argv[] )
{
  GtkWidget *window;
  GtkWidget *drawing_area;
  GtkWidget *vbox;

  GtkWidget *button;

  gtk_init (&argc, &argv);

  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  gtk_widget_set_name (window, "Test Input");

  vbox = gtk_vbox_new (FALSE, 0);
  gtk_container_add (GTK_CONTAINER (window), vbox);
  gtk_widget_show (vbox);

  gtk_signal_connect (GTK_OBJECT (window), "destroy",
                      GTK_SIGNAL_FUNC (quit), NULL);

  /* Create the drawing area */

 gtk_widget_push_visual (gdk_rgb_get_visual ());
 gtk_widget_push_colormap (gdk_rgb_get_cmap ());
  drawing_area = gtk_drawing_area_new ();
 gtk_widget_pop_visual ();
 gtk_widget_pop_colormap ();



  gtk_drawing_area_size (GTK_DRAWING_AREA (drawing_area), 200, 200);
  gtk_box_pack_start (GTK_BOX (vbox), drawing_area, TRUE, TRUE, 0);

  gtk_widget_show (drawing_area);

  /* Signals used to handle backing pixmap */

  gtk_signal_connect (GTK_OBJECT (drawing_area), "expose_event",
                      (GtkSignalFunc) expose_event, NULL);
  gtk_signal_connect (GTK_OBJECT(drawing_area),"configure_event",
                      (GtkSignalFunc) configure_event, NULL);

  /* Event signals */

  gtk_signal_connect (GTK_OBJECT (drawing_area), "motion_notify_event",
                      (GtkSignalFunc) motion_notify_event, NULL);
  gtk_signal_connect (GTK_OBJECT (drawing_area), "button_press_event",
                      (GtkSignalFunc) button_press_event, NULL);

  gtk_widget_set_events (drawing_area, GDK_EXPOSURE_MASK
                         | GDK_LEAVE_NOTIFY_MASK
                         | GDK_BUTTON_PRESS_MASK
                         | GDK_POINTER_MOTION_MASK
                         | GDK_POINTER_MOTION_HINT_MASK);

  /* .. And a quit button */
  button = gtk_button_new_with_label ("Quit");
  gtk_box_pack_start (GTK_BOX (vbox), button, FALSE, FALSE, 0);

  gtk_signal_connect_object (GTK_OBJECT (button), "clicked",
                             GTK_SIGNAL_FUNC (gtk_widget_destroy),
                             GTK_OBJECT (window));
  gtk_widget_show (button);

  gtk_widget_show (window);

  gtk_main ();

  return 0;
}
/* example-end */

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| Colin Thomas. 
| Design Consultant.                             
|                                           
| Email   : colin designresources co uk     
| Tele    : (44) 1234 240562 
| Fax     : (44) 1234 241262               
|                                           
| Address : Design Resources,
|           Old Cock Inn,    
|           Silver End,         
|           Olney,                           
|           Buckinghamshire,                
|           United Kingdom.                 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~