a simple colorpicker in GTK

colorpicker.c

//=====================================================================
// 拾取颜色并输出
// 返回值：
//   0 正常
//   1 被取消
//   2 语法错
//---------------------------------------------------------------------
#include<gtk/gtk.h>
#include<ctype.h>
//---------------------------------------------------------------------
/* 程序名称 */
char* self = NULL;

void usage(){
  printf("Colorpicker --- Pick color and print it\n\n"
      "Usage: %s [init_color]\n\n"
      "`init_color' should be in the form of #xxxxxx or rgba(r, g, b, a)\n"
      "If alpha is not 255, a `rgba' notation of the color is printed "
      "instead.\n"
      "If cancelled, nothing is printed and 1 is returned.\n\n"
      "by [email protected], 2010-08-16, ver 0.2\n"
      , self);
}
gint main(gint argc, gchar * argv[]){
  GtkWidget *colorseldlg;
  GdkColor color;
  GtkColorSelection *colorsel;
  gint response;
  gint r, g, b;
  guint16 alpha=65535;
  float f;

  self = argv[0];
  gtk_init(&argc, &argv);

  if(argc == 2){
    g = 0;
    b = 0;
    if(argv[1][0] == 'r'){
      if(argv[1][3] == 'a'){
	//rgba(...)
	sscanf(argv[1], "rgba(%d, %d, %d, %f)", &r, &g, &b, &f);
	color.red = r * 256;
	color.green = g * 256;
	color.blue = b * 256;
	alpha = f * 65535;
      }else if(argv[1][3] == '('){
	//rgb(...)
	sscanf(argv[1], "rgb(%d, %d, %d)", &r, &g, &b);
	color.red = r * 256;
	color.green = g * 256;
	color.blue = b * 256;
      }else{
	usage();
	return 2;
      }
      goto option_ok;
    }
    if(argv[1][0] == '#'){
      b = 1;
    }
    for(r=b; r<b+6; r++){
      if(!isxdigit(argv[1][r])){
	usage();
	return 2;
      }
    }
    if(b){
      /* # 开头 */
      argv[1]++;
    }
    sscanf(argv[1], "%2x%2x%2x", &r, &g, &b);
    color.red = r * 256;
    color.green = g * 256;
    color.blue = b * 256;
  }else if(argc == 1){
    color.red = 0xffff;
    color.green = 0xffff;
    color.blue = 0xffff;
  }else{
    usage();
    return 2;
  }

option_ok:
  colorseldlg = gtk_color_selection_dialog_new("Select color");
  colorsel = GTK_COLOR_SELECTION(
      gtk_color_selection_dialog_get_color_selection(
	GTK_COLOR_SELECTION_DIALOG(colorseldlg)));
  gtk_color_selection_set_current_color(colorsel, &color);
  gtk_color_selection_set_has_palette(colorsel, TRUE);
  gtk_color_selection_set_has_opacity_control(colorsel, TRUE);
  gtk_color_selection_set_current_alpha(colorsel, alpha);
  gtk_window_set_position(GTK_WINDOW(colorseldlg), GTK_WIN_POS_MOUSE);
  gtk_window_set_keep_above(GTK_WINDOW(colorseldlg), TRUE);

  response = gtk_dialog_run(GTK_DIALOG(colorseldlg));
  if(response == GTK_RESPONSE_OK){
    gtk_color_selection_get_current_color(colorsel, &color);
    r = color.red / 256;
    g = color.green / 256;
    b = color.blue / 256;
    alpha = gtk_color_selection_get_current_alpha(colorsel);
    alpha /= 256;
    if(alpha == 255)
      printf("#%02x%02x%02x\n", r, g, b);
    else
      printf("rgba(%d, %d, %d, %.2f)\n", r, g, b, (float)alpha/256);
  }else 
    /* 取消了 */
    return 1;

  return 0;
}
//=====================================================================

line 96, add:
gtk_window_set_position(GTK_WINDOW (colorseldlg), GTK_WIN_POS_CENTER);
set window to screen center