1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
# Filename: A09b_2D_vector_sandbox.py
# Author: James D. Miller; Gustavus Adolphus College.

import sys, os
import pygame

# PyGame Constants
from pygame.locals import *
from pygame.color import THECOLORS

# PyGame gui
from pgu import gui

# Import the vector class from a local module (in this same directory)
from vec2d_jdm import Vec2D

#=====================================================================
# Classes
#=====================================================================

class Vectors_Add():
    def __init__(self, vectors_2d_m=None, theColor=THECOLORS["green"]):
        self.color = theColor
        self.selectable = False
        self.radius_m = 0.10
        self.radius_px = int(round(env.px_from_m( self.radius_m)))
        
        if vectors_2d_m == None:
            self.vectors_2d_m = v_sb.vectors
        else:
            self.vectors_2d_m = vectors_2d_m
        
        self.total_2d_m = Vec2D(0,0)
        self.total_history_2d_m = []
        self.total_history_tuples_px = []
        
        self.needing_reset = False
        
    def update(self, mode="reset"):
        self.total_2d_m = Vec2D(0,0)
        for eachvector_2d_m in self.vectors_2d_m:
            if mode == "add":
                # Change the base vector to the running total.
                eachvector_2d_m.base_2d_m = self.total_2d_m
                self.total_2d_m += eachvector_2d_m
            else:
                eachvector_2d_m.base_2d_m = Vec2D(0,0)
        
        # Put the current total vector into a FIFO.
        if (v_sb.tail_time_s > v_sb.tail_timelimit_s) and v_sb.enable_tails:
            self.total_history_2d_m.append( self.total_2d_m)
            # Displace the oldest part of the FIFO; pop it off.
            if len(self.total_history_2d_m) > 700:
                self.total_history_2d_m.pop(0)
            v_sb.tail_time_s = 0

    def draw_circle_vector(self, vec_A_2d_m, vec_B_2d_m, color=None, small_circle=False):
            if color==None:
                color = self.color
            
            # Draw line segment
            line_points = [env.ConvertWorldToScreen(vec_A_2d_m), env.ConvertWorldToScreen(vec_B_2d_m)]
            pygame.draw.aaline(game_window.surface, color, line_points[0], line_points[1], True)
            
            # Draw circle.
            self.radius_px = int(round(env.px_from_m( self.radius_m)))
            if small_circle:
                radius_px = int(round(self.radius_px/2.0))
            else:    
                radius_px = self.radius_px
            if radius_px < 1:
                radius_px = 1
            pygame.draw.circle(game_window.surface, color, env.ConvertWorldToScreen(vec_B_2d_m), radius_px, 1)
    
    def draw(self):
        if v_sb.display_total:
            self.update("add")
            # Draw the total vector.
            Visual_Vec2D( self.total_2d_m, theColor=self.color).draw()
            self.needing_reset = True
            
            # Draw the total vector's history.
            if v_sb.enable_tails:
                if v_sb.lines_not_points:
                    if len(self.total_history_2d_m) >= 2:
                        self.total_history_tuples_px = []
                        for point_2d_m in self.total_history_2d_m:
                            self.total_history_tuples_px.append( env.ConvertWorldToScreen( point_2d_m))
                        #pygame.draw.lines(game_window.surface, self.color, False, self.total_history_tuples_px, 1)
                        pygame.draw.aalines(game_window.surface, self.color, False, self.total_history_tuples_px, True)
                else:
                    for point_2d_m in self.total_history_2d_m:
                        pygame.draw.circle(game_window.surface, self.color, env.ConvertWorldToScreen( point_2d_m), 1, 1)
                    
        else:
            if self.needing_reset:
                # Reset these so all are drawn from the origin.
                self.update("reset")
                self.needing_reset = False

            
class Visual_Vec2D( Vec2D):
    def __init__(self, x_m_or_Vec2D, y_m=None, theColor=THECOLORS["yellow"], rotation_rate_dps=0):
        
        if isinstance( x_m_or_Vec2D, Vec2D):
            x_m = x_m_or_Vec2D.x
            y_m = x_m_or_Vec2D.y
        else:
            x_m = x_m_or_Vec2D
            y_m = y_m
        
        Vec2D.__init__(self, x_m, y_m)
        
        self.rotation_rate_dps = rotation_rate_dps
        
        self.radius_m = 0.10
        self.color = theColor
        self.selectable = True
        self.selected = False
        
        # Projection target
        self.projection_target_2d_m = None
        
        # Base vector (to displace the drawing of the vector from the origin)
        self.base_2d_m = Vec2D(0.0,0.0)
        
        # Arrowhead definition.
        self.sf_x = 0.3
        self.sf_y = 0.1
        self.arrowhead_vertices_2d_m =[Vec2D( -1.00 * self.sf_x, -0.50 * self.sf_y), 
                                       Vec2D( -1.00 * self.sf_x,  0.50 * self.sf_y), 
                                       Vec2D(  0.00 * self.sf_x,  0.00 * self.sf_y)]
        
        self.rt_vertices_2d_px  = []                       
        self.update()
        
    def update(self):
        # Rotate this vector a wee bit during each time step.
        if (not env.freeze) and (not self.selected):
            self.rotated(self.rotation_rate_dps * env.dt_s, sameVector=True)
        
        self.angle_deg = self.get_angle()
        
        # Rotate and translate the arrow head and convert for screen display.
        self.rotate_and_translate_vertices( self.arrowhead_vertices_2d_m, self.angle_deg)
        
    def rotate_and_translate_vertices(self, vertices_2d_m, angle_deg):
        # Put modified vectors in a new list.
        self.rt_vertices_2d_px = []
        for vertex_2d_m in vertices_2d_m:
            # Rotated and translated (add to the shaft).
            rt_vertex_2d_m = vertex_2d_m.rotated( angle_deg) + self + self.base_2d_m
            
            # Convert for screen display.
            rt_vertex_2d_px = env.ConvertWorldToScreen( rt_vertex_2d_m)
            
            self.rt_vertices_2d_px.append( rt_vertex_2d_px)
    
    def draw_selection_circle(self):
        # Draw circle.
        radius_px = int(round(env.px_from_m( self.radius_m)))
        if radius_px < 1:
            radius_px = 1
        
        pygame.draw.circle(game_window.surface, self.color, env.ConvertWorldToScreen(self), radius_px, 1)
        
    def draw_vector(self):
        
        # Draw main body of the arrow: line from base point to end point.
        line_points = [env.ConvertWorldToScreen(self.base_2d_m), env.ConvertWorldToScreen(self + self.base_2d_m)]
        pygame.draw.aaline(game_window.surface, self.color, line_points[0], line_points[1], True)
        #pygame.draw.line(game_window.surface, self.color, line_points[0], line_points[1], 2)
        
        # Draw the arrowhead
        if self.length_squared() > 0:
            if self.base_2d_m.equal(Vec2D(0.0,0.0)):
                arrow_head_line_thickness = 0
            else:
                arrow_head_line_thickness = 1
            pygame.draw.polygon(game_window.surface, self.color, self.rt_vertices_2d_px, arrow_head_line_thickness)
        
        # Draw a selection circle if there is a non-zero base vector.
        if self.base_2d_m.not_equal( Vec2D(0,0)):
            self.draw_selection_circle()          
    
    def draw(self):
        self.update()
        # Main vector
        self.draw_vector()
        
        if (self.selected and v_sb.enable_components):
            # Its two components
            Visual_Vec2D( self.x,      0, self.color).draw_vector()
            Visual_Vec2D(      0, self.y, self.color).draw_vector()
            # The normal
            if self.length_squared() > 0:
                normal_2d_m = self.normal()  # This returns a Vec2D object.
                Visual_Vec2D( normal_2d_m, theColor=THECOLORS["red"]).draw_vector()
                Visual_Vec2D( normal_2d_m.rotate90(), theColor=THECOLORS["red"]).draw_vector()
                
            Visual_Vec2D( self.projection_onto( self.projection_target_2d_m), theColor=self.color).draw_vector()
        
class VectorSandbox:
    def __init__(self, walls_dic):
        self.vectors = []
        self.walls = walls_dic
        self.selected_vector = None
        self.total_vector_2d_m = None
        
        self.display_total = False
        self.enable_components = True
        self.enable_tails = False
        self.lines_not_points = False
        
        self.tail_time_s = 0
        self.tail_timelimit_s = 1/30.0
        
    def draw(self):
        #{"L_m":0.0, "R_m":10.0, "B_m":0.0, "T_m":10.0}
        # Define endpoints for each axis.
        x_pos_2d_px =  env.ConvertWorldToScreen( Vec2D(  self.walls['R_m'],  0.0              ))
        x_neg_2d_px =  env.ConvertWorldToScreen( Vec2D( -self.walls['R_m'],  0.0              ))
        y_pos_2d_px =  env.ConvertWorldToScreen( Vec2D(                0.0,  self.walls['T_m']))
        y_neg_2d_px =  env.ConvertWorldToScreen( Vec2D(                0.0, -self.walls['T_m']))
        
        # Draw the two axes.
        pygame.draw.line(game_window.surface, THECOLORS["orangered1"], x_pos_2d_px,  x_neg_2d_px, 1)
        pygame.draw.line(game_window.surface, THECOLORS["orangered1"], y_pos_2d_px,  y_neg_2d_px, 1)
    
    def checkForVectorAtCursorPosition(self, x_px_or_tuple, y_px = None):
        if y_px == None:
            x_px = x_px_or_tuple[0]
            y_px = x_px_or_tuple[1]
        else:
            x_px = x_px_or_tuple
            y_px = y_px
        
        test_position_2d_m = env.ConvertScreenToWorld(Vec2D(x_px, y_px))
        for vector in self.vectors:
            if vector.selectable:
                vector_difference_2d_m = test_position_2d_m - vector
                # Use squared lengths for speed (avoid square root)
                mag_of_difference_m2 = vector_difference_2d_m.length_squared()
                if mag_of_difference_m2 < vector.radius_m**2:
                    vector.selected = True
                    return vector
        return None
        
    def updateSelectedVector(self):
        if (self.selected_vector == None):
            if env.buttonIsStillDown:
                self.selected_vector = self.checkForVectorAtCursorPosition(env.cursor_location_px)        
        else:
            if not env.buttonIsStillDown:
                # Deselect the vector and bomb out of here.
                self.selected_vector.selected = False
                self.selected_vector = None
                return None
            else:
                # Drag the vector to follow the cursor.
                cursor_pos_2d_m = env.ConvertScreenToWorld(Vec2D(env.cursor_location_px))
                self.selected_vector.x, self.selected_vector.y = cursor_pos_2d_m.x, cursor_pos_2d_m.y

                
class Environment:
    def __init__(self, screenSize_px, length_x_m):
        self.screenSize_px = Vec2D(screenSize_px)
        self.viewOffset_px = Vec2D(-self.screenSize_px.x/2,-self.screenSize_px.y/2)
        self.viewCenter_px = Vec2D(0,0)
        self.viewZoom = 1
        self.viewZoom_rate = 0.01
    
        self.key_b = 'U'
        self.key_n = 'U'
        self.key_m = 'U'
        self.key_h = 'U'
    
        self.px_to_m = length_x_m/float(self.screenSize_px.x)
        self.m_to_px = (float(self.screenSize_px.x)/length_x_m)
        
        self.inhibit_screen_clears = False
        
        # Keyboard/mouse state
        
        self.cursor_location_px = (0,0)   # x_px, y_px
        self.mouse_button = 1             # 1, 2, or 3
        self.buttonIsStillDown = False        
                
        self.selected_vector = None
        
        self.dt_s = 0
        self.freeze = False
    
    # Convert from meters to pixels 
    def px_from_m(self, dx_m):
        return dx_m * self.m_to_px * self.viewZoom
    
    # Convert from pixels to meters
    # Note: still floating values here)
    def m_from_px(self, dx_px):
        return float(dx_px) * self.px_to_m / self.viewZoom
    
    def control_zoom_and_view(self):
        if self.key_h == "D":
            self.viewZoom += self.viewZoom_rate * self.viewZoom
        if self.key_n == "D":
            self.viewZoom -= self.viewZoom_rate * self.viewZoom
    
    def ConvertScreenToWorld(self, point_2d_px):
        #self.viewOffset_px = self.viewCenter_px
        x_m = (                       point_2d_px.x + self.viewOffset_px.x) / (self.m_to_px * self.viewZoom)
        y_m = (self.screenSize_px.y - point_2d_px.y + self.viewOffset_px.y) / (self.m_to_px * self.viewZoom)
        return Vec2D( x_m, y_m)

    def ConvertWorldToScreen(self, point_2d_m):
        """
        Convert from world to screen coordinates (pixels).
        In the class instance, we store a zoom factor, an offset indicating where
        the view extents start at, and the screen size (in pixels).
        """

        # self.viewOffset = self.viewCenter - self.screenSize_px/2
        #self.viewOffset = self.viewCenter_px
        x_px = (point_2d_m.x * self.m_to_px * self.viewZoom) - self.viewOffset_px.x
        y_px = (point_2d_m.y * self.m_to_px * self.viewZoom) - self.viewOffset_px.y
        y_px = self.screenSize_px.y - y_px

        # Return a tuple of integers.
        return Vec2D(x_px, y_px, "int").tuple()

    def get_user_input(self):
        
        # Get all the events since the last call to get().
        for event in pygame.event.get():
            if (event.type == pygame.QUIT): 
                sys.exit()
            elif (event.type == pygame.KEYDOWN):
                if (event.key == K_ESCAPE):
                    sys.exit()
                elif (event.key==K_KP1):            
                    return "1p"
                elif (event.key==K_KP2):            
                    return "2p"
                elif (event.key==K_KP3):            
                    return "3p"
                elif (event.key==K_1):            
                    return 1           
                elif (event.key==K_2):                          
                    return 2
                elif (event.key==K_3):
                    return 3           
                elif (event.key==K_4):
                    return 4           
                elif (event.key==K_5):
                    return 5
                elif (event.key==K_6):
                    return 6
                elif (event.key==K_7):
                    return 7
                elif (event.key==K_8):
                    return 8
                elif (event.key==K_9):
                    return 9
                elif (event.key==K_0):
                    return 0
                
                # Sandbox control toggles.
                elif (event.key==K_c):
                    v_sb.enable_components = not v_sb.enable_components
                elif (event.key==K_t):
                    v_sb.enable_tails = not v_sb.enable_tails
                elif (event.key==K_f):
                    env.freeze = not env.freeze
                elif (event.key==K_a):
                    v_sb.display_total = not v_sb.display_total
                elif (event.key==K_l):
                    v_sb.lines_not_points = not v_sb.lines_not_points
                
                # Zoom keys.
                elif (event.key==K_b):
                    self.key_b = 'D'
                elif (event.key==K_n):
                    self.key_n = 'D'
                elif (event.key==K_m):
                    self.key_m = 'D'
                elif (event.key==K_h):
                    self.key_h = 'D'
                
                else:
                    return "nothing set up for this key"
            
            elif (event.type == pygame.KEYUP):
                    
                # Zoom keys
                if (event.key==K_b):
                    self.key_b = 'U'
                elif (event.key==K_n):
                    self.key_n = 'U'
                elif (event.key==K_m):
                    self.key_m = 'U'
                elif (event.key==K_h):
                    self.key_h = 'U'
            
            elif event.type == pygame.MOUSEBUTTONDOWN:
                self.buttonIsStillDown = True
            
                (button1, button2, button3) = pygame.mouse.get_pressed()
                if button1:
                    self.mouse_button = 1
                elif button2:
                    self.mouse_button = 2
                elif button3:
                    self.mouse_button = 3
                else:
                    self.mouse_button = 0
            
            elif event.type == pygame.MOUSEBUTTONUP:
                self.buttonIsStillDown = False
                self.mouse_button = 0
            
        if self.buttonIsStillDown:
            self.cursor_location_px = (mouseX, mouseY) = pygame.mouse.get_pos()

        
class GameWindow:
    def __init__(self, screen_tuple_px, title):
        self.width_px = screen_tuple_px[0]
        self.height_px = screen_tuple_px[1]
        
        # The initial World position vector of the Upper Right corner of the screen.
        # Yes, that's right y_px = 0 for UR.
        self.UR_2d_m = env.ConvertScreenToWorld(Vec2D(self.width_px, 0))
        
        # Create a reference to the display surface object. This is a pygame "surface".
        # Screen dimensions in pixels (tuple)
        self.surface = pygame.display.set_mode(screen_tuple_px)

        self.update_caption(title)
        
        self.surface.fill(THECOLORS["black"])
        pygame.display.update()
        
    def update_caption(self, title):
        pygame.display.set_caption( title)
        self.caption = title
    
    def update(self):
        pygame.display.update()
        
    def clear(self):
        # Useful for shifting between the various demos.
        self.surface.fill(THECOLORS["black"])
        pygame.display.update()

#===========================================================
# Functions
#===========================================================

def make_some_vectors(resetmode):
    game_window.update_caption("Vector Sandbox V.1: Demo #" + str(resetmode)) 
    env.inhibit_screen_clears = False
    
    env.always_render = False
    
    if resetmode == 1:
        v_1 = Visual_Vec2D( 0.0,  4.0, THECOLORS["white"],  rotation_rate_dps=-20)
        v_sb.vectors.append( v_1)
        
        v_2 = Visual_Vec2D( 0.0,  1.0, THECOLORS["yellow"], rotation_rate_dps=180)
        v_sb.vectors.append( v_2)
        
        v_1.projection_target_2d_m = v_2
        v_2.projection_target_2d_m = v_1
    
        v_sb.total_vector_2d_m = Vectors_Add()
    
    elif resetmode == 2:
        v_1 = Visual_Vec2D( 0.0,  3.0, THECOLORS["white"],  rotation_rate_dps=-20)
        v_sb.vectors.append( v_1)
        
        v_2 = Visual_Vec2D( 0.0,  2.0, THECOLORS["yellow"], rotation_rate_dps=-40)
        v_sb.vectors.append( v_2)
        
        v_1.projection_target_2d_m = v_2
        v_2.projection_target_2d_m = v_1
    
        v_3 = Visual_Vec2D( 0.0,  1.0, THECOLORS["tan"],   rotation_rate_dps=-60)
        v_sb.vectors.append( v_3)
        v_3.projection_target_2d_m = v_1
        
        v_sb.total_vector_2d_m = Vectors_Add()
    
    elif resetmode == 3:    
        for j in range(1,11):
            temp = Visual_Vec2D( 0.0, 3, THECOLORS["white"],  rotation_rate_dps=-(10*j))
            v_sb.vectors.append( temp)
            v_sb.vectors[j-1].projection_target_2d_m = v_sb.vectors[0]
            
        v_sb.total_vector_2d_m = Vectors_Add()
        
    elif resetmode == 4:
        for j in range(1,11):
            temp = Visual_Vec2D( 0.0, 0.4*j, THECOLORS["white"],  rotation_rate_dps=-(10*j))
            v_sb.vectors.append( temp)
            v_sb.vectors[j-1].projection_target_2d_m = v_sb.vectors[0]
            
        v_sb.total_vector_2d_m = Vectors_Add()
        
    elif resetmode == 5:
        for j in range(1,11):
            temp = Visual_Vec2D( 0.0, 3-0.2*j, THECOLORS["white"],  rotation_rate_dps=-(10*j))
            v_sb.vectors.append( temp)
            v_sb.vectors[j-1].projection_target_2d_m = v_sb.vectors[0]
            
        v_sb.total_vector_2d_m = Vectors_Add()

    elif resetmode == 6:
        for j in range(1,41):
            temp = Visual_Vec2D( 0.0, 0.4*j, THECOLORS["white"],  rotation_rate_dps=-(10*j))
            v_sb.vectors.append( temp)
            v_sb.vectors[j-1].projection_target_2d_m = v_sb.vectors[0]
            
        v_sb.total_vector_2d_m = Vectors_Add()        
        
    elif resetmode == 7:
        for j in range(1,141):
            temp = Visual_Vec2D( 0.0, 0.4*j, THECOLORS["white"],  rotation_rate_dps=-(10*j))
            v_sb.vectors.append( temp)
            v_sb.vectors[j-1].projection_target_2d_m = v_sb.vectors[0]
            
        v_sb.total_vector_2d_m = Vectors_Add()        
        
    else:
        print "Nothing set up for this key."

def display_number(numeric_value, font_object,  mode='FPS'):
    if mode=='FPS':
        # Small background rectangle for FPS text
        pygame.draw.rect(game_window.surface, THECOLORS["white"], pygame.Rect(10, 10, 35, 20))
        # The text
        fps_string = "%.0f" % numeric_value
        txt_surface = font_object.render(fps_string, True, THECOLORS["black"])
        game_window.surface.blit(txt_surface, [18, 11])
    elif mode=='gameTimer':
        # The text
        fps_string = "%.2f" % numeric_value
        txt_surface = font_object.render(fps_string, True, THECOLORS["white"])
        game_window.surface.blit(txt_surface, [600, 11])
    
#============================================================
# Main procedural script.
#============================================================

def main():

    # A few globals.
    global env, game_window, v_sb
    
    pygame.init()

    myclock = pygame.time.Clock()

    window_dimensions_px = (800, 700)   #window_width_px, window_height_px

    # Create the first user/client and the methods for moving between the screen and the world.
    env = Environment(window_dimensions_px, 10.0) # 10m in along the x axis.

    game_window = GameWindow(window_dimensions_px, 'Vector Sandbox V.1')

    # Define the Left, Right, Bottom, and Top boundaries of the game window.
    v_sb = VectorSandbox({"L_m":0.0, "R_m":game_window.UR_2d_m.x, "B_m":0.0, "T_m":game_window.UR_2d_m.y})

    # Add some vectors to the table.
    demo_mode = 1
    make_some_vectors( demo_mode)

    # Font object for rendering text onto display surface.
    fnt_FPS = pygame.font.SysFont("Arial", 14)
    fnt_gameTimer = pygame.font.SysFont("Arial", 60)
    
    # Limit the framerate, but let it float below this limit.
    framerate_limit = 480.0   # 480

    while True:
        env.dt_s = float(myclock.tick( framerate_limit) * 1e-3)
        
        # Listen to the user: establish the state of the keyboard and mouse and determine if a new demo is called for.
        resetmode = env.get_user_input()
            
        # Reset the game based on local user control.
        if resetmode in ["1p","2p","3p",1,2,3,4,5,6,7,8,9,0]:
            demo_mode = resetmode
            print resetmode
            # Delete all the objects in the sandbox. Cleaning out these list reference to these objects effectively
            # deletes the objects.
            v_sb.total_vector_2d_m = None
            v_sb.vectors = []
            
            # Now just black out the screen.
            game_window.clear()
            
            # Reinitialize the demo.
            make_some_vectors( demo_mode)               
                    
        # Control vector selection and mouse related movement.
        v_sb.updateSelectedVector()
            
        # Control the zoom
        env.control_zoom_and_view()
        
        # Erase the blackboard.
        if not env.inhibit_screen_clears:
            game_window.surface.fill((0,0,0))

        # Display FPS text.
        display_number(1/env.dt_s, fnt_FPS, mode='FPS')
        
        # Draw axis for the vector sandbox.
        v_sb.draw()
        
        # Draw vectors.
        if v_sb.total_vector_2d_m != None:
            v_sb.total_vector_2d_m.draw()    
        for eachvector in v_sb.vectors: 
            eachvector.draw()
        
        pygame.display.flip()

        v_sb.tail_time_s += env.dt_s
        
#============================================================
# Run the main program.    
#============================================================
        
main()