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
|
<html>
<head>
<title>Untitled Document</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<LINK REL="STYLESHEET" HREF="VisualRef.css" CHARSET="ISO-8859-1" TYPE="text/css">
</head>
<body bgcolor="#FFFFFF">
<p class="Normal"><font color="#0000A0">Drag example</font></p>
<p class="Normal">Here is the sequence of mouse events involved in dragging something:</p>
<p class="Normal">1) m1.press is True when you depress the mouse button (it is
'left' if left button; nonzero is True in Python).</p>
<p class="Normal"><br>
2) m1.drag is True when the mouse coordinates change from what they were at
the time of m1.press.<br>
At the time of the drag event, the mouse position is reported to be what it
was at the time of the press event, so that the dragging can start at the place
where the user first clicked. If the mouse is in motion at the time of the press
event, it is quite possible that the next position seen by the computer, at
the time of the drag event, could be quite far from the click position. This
is why the position of the drag event is reported as though it occurred at the
press location.</p>
<p class="Normal"><br>
3) No events occur while dragging; you continually use scene.mouse.pos to update
what you're dragging.</p>
<p class="Normal"><br>
4) m1.drop is True when you release the mouse button.</p>
<p class="Normal">You can program dragging with the mouse simply by continually
reading the current value of <span class="attribute">scene.mouse.pos</span>.
Here is a complete routine for dragging a sphere with the left button down.
Note the statements for making the cursor invisible during the drag.</p>
<h2 class="program0">scene.range = 10 # fixed size, no autoscaling</h2>
<p class="program"> </p>
<p class="program">ball = sphere(pos=(-5,0,0), radius=1., color=color.cyan)</p>
<p class="program">cube = box(pos=(+5,0,0), size=(2,2,2), color=color.red)</p>
<p class="program">pick = None # no object picked out of the scene yet</p>
<p class="program">while 1: </p>
<p class="program"> if scene.mouse.events: </p>
<p class="program"> m1 = scene.mouse.getevent()
# obtain drag or drop event</p>
<p class="program"> if m1.drag
and m1.pick == ball: # if clicked on the ball</p>
<p class="program"> drag_pos
= m1.pickpos # where on the ball the mouse was</p>
<p class="program"> pick
= m1.pick # pick is now True (nonzero)</p>
<p class="program"> scene.cursor.visible
= 0 # make cursor invisible </p>
<p class="program"> elif m1.drop:
# released the mouse button at end of drag</p>
<p class="program"> pick
= None # end dragging (None is False)</p>
<p class="program"> scene.cursor.visible
= 1 # cursor visible again</p>
<p class="program"> if pick: </p>
<p class="program"> new_pos = scene.mouse.project(normal=(0,1,0))
# project onto xz plane</p>
<p class="program"> if new_pos
!= drag_pos: # if the mouse has moved since last position</p>
<p class="program"> pick.pos
+= new_pos - drag_pos # offset for where the ball was clicked</p>
<p class="program"> drag_pos
= new_pos # update drag position</p>
<p class="Normal">If you do a lot of processing of each mouse movement, or you
are leaving a trail behind the moving object, you may need to check whether
the "new" mouse position is in fact different from the previous position
before processing the "move", as is done in the example above. For
example, a trail drawn with a curve object that contains a huge number of points
all at the same location may not display properly.</p>
<p class="Normal">Only some of the VPython objects can be "picked" by
clicking them, including sphere, box, and cylinder. Here is a more general routine
which lets you drag either the tail or the tip of an arrow:</p>
<h2 class="program0">scene.range = 10 # fixed size, no autoscaling</h2>
<p class="program"> </p>
<p class="program"><span class="program">pointer = arrow(pos=(0,4,0), axis=(3,2,0),
color=color.yellow)</span>)</p>
<p class="program"><span class="program">tolerance = 0.3 # must click within this
distance of tail or tip</span></p>
<p class="program"><span class="program">drag = None # have not selected tail
or tip of arrow</span></p>
<p class="program">while 1: </p>
<p class="program"> if scene.mouse.events: </p>
<p class="program"> m1 = scene.mouse.getevent()
# obtain press or drag or drop event</p>
<p class="program"> if m1.press:</p>
<p class="program"> <span class="program">if
mag(pointer.pos-m1.pos) <= tolerance:</span></p>
<p class="program"> <span class="program">drag
= 'tail' # pressed near tail of arrow</span></p>
<p class="program"> <span class="program">elif
mag((pointer.pos+pointer.axis)-m1.pos) <= tolerance:</span></p>
<p class="program"> <span class="program">drag
= 'tip' # pressed near tip of arrow</span></p>
<p class="program"> <span class="program">drag_pos
= m1.pos</span> # save press location</p>
<p class="program"> <span class="program">elif
m1.drag and drag: # if drag event and something to drag</span></p>
<p class="program"> scene.cursor.visible
= 0 # make cursor invisible </p>
<p class="program"> elif m1.drop:
# released the mouse button at end of drag</p>
<p class="program"> drag
= None # end dragging (None is False)</p>
<p class="program"> scene.cursor.visible
= 1 # cursor visible again</p>
<p class="program"> if drag: </p>
<p class="program"> new_pos = scene.mouse.pos</p>
<p class="program"> if new_pos
!= drag_pos: # if the mouse has moved since last position</p>
<p class="program"> displace
= new_pos - drag_pos # how much the mouse moved</p>
<p class="program"> drag_pos
= new_pos # update drag position</p>
<p class="program"> if
drag == 'tail':<span class="program"></span></p>
<p class="program"> <span class="program">pointer.pos
+= displace # displace the tail</span></p>
<p class="program"> else:<span class="program"></span></p>
<p class="program"> <span class="program">pointer.axis
+= displace # displace the tip</span></p>
<p class="program"> </p>
<div>
<div>
<p class="Normal">Choose Back, or <a href="mouse.html">Go to top of mouse
documentation</a></p>
<div>
<h2 class="program0"> </h2>
</div>
<h2 class="program0"> </h2>
<div>
<h2 class="program0"> </h2>
</div>
<h2 class="program0"> </h2>
</div>
</div>
</body>
</html>
|
