Coordinate from device to user space without a context

//valac --pkg gee-1.0 --pkg gtk+-3.0 -X -lm -X -w "$1" -o test
using Gtk;
using Cairo;

public void grid(Cairo.Context cr, bool white=false) {
    cr.move_to(0,0);
    double m=0f;
    double w=0f;
    double x=0f;
    //for (x=10f; x <= 210f; x+=10f) {
    for (x=0f; x <= 500f; x+=10f) {
      m++;
      w = 10 + ( Math.fmod(m,2) * 10); //fluctuating height
      //w = (x==100) ? 80 : w; //major stroke
      cr.rectangle (x,-w/2,1,w); //right arm
      cr.rectangle (-x,-w/2,1,w); //left arm
      cr.rectangle (-w/2,-x,w,1); //down arm
      cr.rectangle (-w/2,x,w,1); //up arm
    }
    if (white) {
      cr.set_source_rgb(1,1,1);
    } else {
      cr.set_source_rgba(0,0,0,0.2);
    }
    cr.fill();
}

public double c(int col) { return (double)col / 256.0; }

public class Dot: Object {
  public double x = 0;
  public double y = 0;
  public double sx = 1;
  public double sy = 1;
  public double rot = 0;
  public double radius = 8;
  public double r=0;
  public double g=0;
  public double b=0;
  public string name;
  public double device_x=0; 
  public double device_y=0; 
  
  //Device-space bounding box coords
  public double dbbx1;
  public double dbbx2;
  public double dbby1;
  public double dbby2;

  public bool is_hit = false;

  private Cairo.Matrix? mymatrix;


  public Dot(string n) {
    name = n;
  }
  
  public void move(double mx, double my) {
    //MESSY MYSTERY STUFF> My math brain is dribbly goo.

    double px = mx; double py=my;
    stdout.printf("BEFORE mx my: %G | %G\n", px, py);
    mymatrix.transform_point(ref px, ref py);
    stdout.printf("AFTER mx my: %G | %G\n", px, py);

    //Set my obj vars for a later draw()
    x=px; y=py;
  }

  public bool bbox_hit( double mx, double my) {
    /*Crude box test.
    Turns-out, I can just cmp the mouse x,y to my pre-saved
    device bounding box coords!
    */

    is_hit = (
      (mx > dbbx1) && 
      (mx < dbbx2) && 
      (my > dbby1) && 
      (my < dbby2)
    );
    return is_hit;
  }

  public void set_matrix(Cairo.Context cr) {

    //Super NB that we store the u2d coords BEFORE the matrix stuff
    device_x = x; 
    device_y = y; //prep in-vars
    cr.user_to_device(ref device_x, ref device_y); //stores into refs
    //stdout.printf("%s stored %G,%G\n", name, device_x, device_y);


    //NOTE - goes after the above code.
    cr.translate(x,y);
    cr.scale(sx,sy);
    cr.rotate((Math.PI/180.0)*rot);

        cr.save();
          //cr.identity_matrix();
          mymatrix = cr.get_matrix();
        cr.restore();

  }

  private void _record_bbox(Cairo.Context cr) {
    cr.save();
    //Oookay... getting weird:
    //I want a bounding box that fits me.
    //Step 1: According to random gmane list: set identity matrix
    //Step 2: use path_extents func and store into obj vars.
    //        these coords are now in DEVICE space, due to that
    //        matrix voodoo. (Even tho docs say user space.)
    //Oh, PS, do this all BEFORE a fill() - i.e. there must
    //be a current path.
    cr.identity_matrix();
    cr.path_extents (out dbbx1, out dbby1, out dbbx2, out dbby2);
    //stdout.printf("%G,%G,%G,%G\n",x1,y1,x2,y2);
    cr.restore();
  }

  public void draw_geom(Cairo.Context cr) {
      cr.arc (20 ,20, radius, 0, 2 * Math.PI);
      if (is_hit) {
        cr.set_source_rgb (1, 0, 0);
      } else {
        cr.set_source_rgb (r, g, b);
      }
      cr.rectangle(-radius+20,-radius+20,radius,radius);

      //Get myy bbox:
      //Have to do this here, before any commands that 
      //end the current path.
      _record_bbox(cr);
  }

  public void draw(Cairo.Context cr) {

      //random grid
      _grid(cr);

      draw_geom(cr);
      cr.fill ();

      //random label.
      cr.move_to(radius+5,0);
      cr.save(); //isolate the text from the current rotation and scale?
        cr.identity_matrix();
        cr.select_font_face ("Adventure", Cairo.FontSlant.NORMAL, Cairo.FontWeight.BOLD);
        cr.show_text(@"d$(this.name) u($x,$y) d($device_x,$device_y)");
      cr.restore();

  }

  public void draw_dbb(Cairo.Context cr) {
    //To draw the bb - the identity matrix must be applied again.
    //I dunno why. I tried drawing it in the main draw() event (of the
    //GraphicsArea) under that default matrix, but the rects get drawn 
    //way down the screen. I dunno and I know that I dunno. :(
    /*
"Resets the current transformation matrix (CTM) by setting it equal to the identity matrix. That is, the user-space and device-space axes will be aligned and one user-space unit will transform to one device-space unit."

    */
    cr.save();
    cr.identity_matrix();

    //stdout.printf("BB of %s: %g | %G | %G | %G\n",name, dbbx1,dbby1,dbbx2,dbby2);
    cr.rectangle(dbbx1,dbby1,(dbbx2-dbbx1),(dbby2-dbby1));
    cr.set_line_width(2);
    cr.set_source_rgb(1,1,1);
    cr.stroke();
    cr.restore();
  }


  private void _grid(Cairo.Context cr) {
    grid(cr);
  }

}

/*-------------------------------------------------*/
public class SceneGraphWidget : Gtk.DrawingArea {

  public Dot d1;
  public Dot d2;
  public Dot d3;
  public List<Dot> dlist;


  public const uint flag_button_press = 1<<0;
  public const uint flag_button_release = 1<<1;
  public const uint flag_motion_notify = 1<<2;
  public const uint flag_in_drag = 1<<3;
  
  public const uint pattern_click = flag_button_press | flag_button_release;
  public const uint pattern_drag_start = flag_button_press | flag_motion_notify;
  public const uint pattern_in_drag = pattern_drag_start | flag_in_drag;
  public const uint pattern_drop = flag_button_press | flag_in_drag | flag_button_release;


  private uint bitstate;

  private Dot? dotBeingDragged;
  private Dot? overDot;

  construct {


    d1 = new Dot("1");
    d2 = new Dot("2");
    d3 = new Dot("3");

    d1.r=0.02; d1.g=0.5; d1.b=0.02; d1.x=55; d1.y=55;

    d2.r=0; d2.g=0; d2.b=0; d2.x=17; d2.y=-112; d2.rot=0; 
    d2.radius = 40; d2.sx=0.5; d2.sy=0.5;

    d3.r=0; d3.g=0.7; d3.b=0.7; d3.radius=20;
    d3.x=-50; d3.y=0;
    
    dlist = new List<Dot>();
    dlist.append(d1);
    dlist.append(d2);
    dlist.append(d3);

    this.set_double_buffered (true);

    this.set_size_request (500,500);
    this.can_focus = true; //In order to receive keybd signals

    this.add_events (
    Gdk.EventMask.BUTTON_PRESS_MASK |
    Gdk.EventMask.BUTTON_RELEASE_MASK |
    /*Gdk.EventMask.KEY_PRESS_MASK */
    Gdk.EventMask.POINTER_MOTION_MASK
    /*Gdk.EventMask.POINTER_MOTION_HINT_MASK */
    );

    //"event" here is a SIGNAL available in a Gtk.Widget!
    //So, I can finally have a single handler for many event types!
    event.connect(handle_events); //!!! Check it out!
  }

  private void initmatrix ( Cairo.Context cr ) {
	/*
     Scale to window's size and shift the origin of the page to the center.
		  -y | -y
		  -x | +x
		 ----0------
		  -x | +x
		  +y | +y


    TODO: Figure out how to keep the window proportional...
		*/

    int w,h;
    double pw, ph;

    h = get_allocated_height ();
    w = get_allocated_width ();

    pw = (float) w / 500f; 
    ph = (float) h / 500f;

		var matrix = Cairo.Matrix (1, 0, 0, 1, w/2,h/2 ); //translate to middle.
		
    matrix.scale (pw, ph); //Scale to the window's size.
		cr.transform(matrix);
  }

  /* Override of the draw() callback, GTK3 requires this. */
  public override bool draw ( Cairo.Context cr ) {
    initmatrix(cr);
    //We are in Matrix A
     
     //Just draw some guides for sanity
    cr.set_source_rgb (1,1,1);
    cr.paint ();

    cr.rectangle(0,0,-250,-250);
    cr.set_source_rgb(c(255), c(204), c(102));
    cr.fill();

    cr.rectangle(0,0,250,-250);
    cr.set_source_rgb(c(153), c(204), c(255));
    cr.fill();
    
    cr.rectangle(0,0,250,250);
    cr.set_source_rgb(c(204), c(244), c(255));
    cr.fill();
    
    cr.rectangle(0,0,-250,250);
    cr.set_source_rgb(c(51), c(255), c(153));
    cr.fill();
    

    grid(cr, true);


      //Begin the pain
      cr.save();

      cr.save();
        d1.set_matrix(cr);
        d1.draw(cr);
        d1.draw_dbb(cr);


            cr.save();
              d2.set_matrix(cr);
              d2.draw(cr);
              d2.draw_dbb(cr);

            cr.restore();
      
      cr.restore();  

      d3.set_matrix(cr);
      d3.draw(cr);
      d3.draw_dbb(cr);


  
    cr.restore(); 
    //back in device space



    return true;
  }

 

  private bool handle_events(Gdk.Event event) {
    //stdout.printf("%s\n", event.type.to_string());

    if (event.type == Gdk.EventType.MOTION_NOTIFY) {

      bitstate |= flag_motion_notify;

          double mx = event.motion.x;
          double my = event.motion.y;
          //stdout.printf("Mouse at:(%G | %G)\n",mx,my);

          var some_hit = false;

          foreach(Dot d in dlist) {
            //If we are dragging AND
            //the dotBeingDragged is the one in the loop, then
            //skip the hit_test.
            //i.e. we don't need to hittest the object we are already dragging.
            if ( (bitstate == pattern_in_drag) && (dotBeingDragged == d) ) continue;
              if (d.bbox_hit(mx,my)) {
                some_hit = true;
                overDot = d;
              }
            }
          

          d2.rot += 1;d2.sx+=0.001;d2.sy+=0.001;

          //if we did not get some kind of hit, nullify the overDot - cos
          //there's no Dot we are over right now.
          if (!some_hit) overDot = null;

          //if ((!some_hit) && (bitstate != pattern_in_drag)) dotBeingDragged = null;
    }


    if (event.type == Gdk.EventType.BUTTON_PRESS) {
      //Set our flag:
      bitstate = bitstate | flag_button_press;

      //stdout.printf("  state : %d \n", event.key.state);

      Gdk.ModifierType modifiers;
      modifiers = Gtk.accelerator_get_default_mod_mask ();
      //stdout.printf ("  Gdk.ModifierType.CONTROL_MASK : %d \n", Gdk.ModifierType.CONTROL_MASK);
      //stdout.printf ("  state & modifiers %d\n", (event.button.state & modifiers) );

      if ( (event.button.state & modifiers) == Gdk.ModifierType.CONTROL_MASK ) {
        stdout.printf (" Control Key\n");
        }
    }

    if (event.type == Gdk.EventType.BUTTON_RELEASE) {
      //Set our flag:
      bitstate = bitstate | flag_button_release;
    }

    //Use our flags!

    if (bitstate == pattern_click) {
      stdout.printf("CLICK!\n");
    }

    if (bitstate == pattern_drag_start) {
      //stdout.printf("DRAG START\n");
      bitstate |= flag_in_drag; //signal we are dragging flag
      if (overDot != null ) dotBeingDragged = overDot;
      if (dotBeingDragged != null) stdout.printf("DRAGSTART %s\n", dotBeingDragged.name);
    }
    if (bitstate == pattern_in_drag) {
      //stdout.printf("IN DRAG\n");
      if (dotBeingDragged != null) { 
        stdout.printf("DRAGGING %s\n", dotBeingDragged.name);
        dotBeingDragged.move(event.motion.x, event.motion.y);
      //d2.x = mx; d2.y = my;
      }
    }

    if (bitstate == pattern_drop) {
      //stdout.printf("DROP!!!!!!!!!!!\n");
      if (dotBeingDragged != null) {
        stdout.printf("DROPPED %s\n", dotBeingDragged.name);
        dotBeingDragged = null;
      }
    }


    //switch off flags after we've used them.
    if (event.type == Gdk.EventType.MOTION_NOTIFY) {
      bitstate &= ~flag_motion_notify;
    }

    if (event.type == Gdk.EventType.BUTTON_PRESS) {
      //self.ui_state = self.ui_state & ~Mouserizer.__FLAG_RELEASING # clear bit
      bitstate = bitstate & ~flag_button_release; //clear release flag
    }
    if (event.type == Gdk.EventType.BUTTON_RELEASE) {
      bitstate &= ~flag_button_press; //clear press state
      bitstate &= ~flag_in_drag; //no drag either.
    }


    queue_draw ();

    return true; //True - stops the event here. False propogates it up.
  }


}

int main(string[] args) {

  Gtk.init ( ref args ); //ok = Gtk.init ... 

  var sgw = new SceneGraphWidget ();

  var w = new Gtk.Window();


  w.add( sgw );
  w.show_all ();
  w.destroy.connect (Gtk.main_quit);
  w.key_press_event.connect( (e) => { 
    if (e.keyval == Gdk.Key.Escape) {
      Gtk.main_quit(); 
      return true; 
    }
    return false;
  } );

  Gtk.main ();

  return 0;
}