Flash/Flex学习笔记(47):反向运动学(上)
先回顾上篇所说的"正向运动学":以人行走的例子来说,基本上可以理解为大腿驱动小腿,小腿驱动脚,从而引发的一系列姿态调整和运动。再举一个例子,我们用着拿一根软鞭或链条的一端挥舞,被手挥舞的这一端会把"能量"向另一端传递(即固定端驱动紧接的部分,而紧接的部分又驱动下一段紧接的部分),从而使整个系统也随之运动.
而"反向运动学"正好相反,举个不恰当的例子,小时候估计很多人玩过“死”青蛙(之所以要说是死的,是为了排除活体的自主运动),用手去拖死青蛙的脚(即自由端),会发现拉脚的同时,也带动青蛙的大腿在拖动,进而拖动了整体青蛙“尸体”;如果换成链条的例子,则相当于反过来,我们拿起链条的另一端拖动,会带动与它紧密关联的部分一起运动,从而带动整个链条一起被拖动。
单关节拖动:
01
package
{
02
import
flash.display.Sprite;
03
import
flash.events.Event;
04
05
public
class
OneSegmentDrag
extends
Sprite {
06
private
var
segment0:Segment;
07
public
function
OneSegmentDrag() {
08
init();
09
}
10
11
private
function
init():
void
{
12
segment0=
new
Segment(
100
,
20
);
13
addChild(segment0);
14
segment0.x=stage.stageWidth/
2
;
15
segment0.y=stage.stageHeight/
2
;
16
addEventListener(Event.ENTER_FRAME,EnterFrameHandler);
17
}
18
19
private
function
EnterFrameHandler(event:Event):
void
{
20
var
dx:
Number
=mouseX-segment0.x;
21
var
dy:
Number
=mouseY-segment0.y;
22
var
angle:
Number
=Math.atan2(dy,dx);
23
segment0.rotation=angle*
180
/Math.PI;
24
var
w:
Number
=segment0.getPin().x-segment0.x;
25
var
h:
Number
=segment0.getPin().y-segment0.y;
26
segment0.x=mouseX-w;
27
segment0.y=mouseY-h;
28
}
29
30
}
31
}
示意图:
双关节的拖动:
01
var
seg1:Segment =
new
Segment(
100
,
20
);
02
seg1.x =
100
;
03
seg1.y =
50
;
04
addChild(seg1);
05
06
var
seg2:Segment =
new
Segment(
100
,
10
);
07
seg2.x = seg1.getPin().x;
08
seg2.y = seg1.getPin().y;
09
addChild(seg2);
10
11
addEventListener(Event.ENTER_FRAME,EnterFrameHandler);
12
13
function
EnterFrameHandler(e:Event):
void
{
14
//seg2跟着鼠标动
15
var
dx1:
Number
= mouseX - seg2.x;
16
var
dy1:
Number
= mouseY - seg2.y;
17
var
angle1:
Number
= Math.atan2(dy1,dx1);
18
seg2.rotation = angle1*
180
/Math.PI;
19
var
w1:
Number
= seg2.getPin().x - seg2.x;
20
var
h1:
Number
= seg2.getPin().y - seg2.y;
21
seg2.x = mouseX-w1;
22
seg2.y = mouseY-h1;
23
24
//seg1跟着seg2动
25
var
dx2:
Number
= seg2.x - seg1.x;
26
var
dy2:
Number
= seg2.y - seg1.y;
27
var
angle2:
Number
= Math.atan2(dy2,dx2);
28
seg1.rotation = angle2*
180
/Math.PI;
29
var
w2:
Number
= seg1.getPin().x - seg1.x;
30
var
h2:
Number
= seg1.getPin().y - seg1.y;
31
seg1.x = seg2.x -w2;
32
seg1.y = seg2.y -h2;
33
}
多关节的拖动:
01
var
segNum:
Number
=
10
;
02
var
segs:
Array
=
new
Array
(segNum);
03
04
function
init():
void
{
05
for
(
var
i:
int
=
0
; i<segNum; i++) {
06
segs[i]=
new
Segment(
40
,
12
);
07
segs[i].x=stage.stageWidth/
2
;
08
segs[i].y=stage.stageHeight/
2
;
09
addChild(segs[i]);
10
}
11
addEventListener(Event.ENTER_FRAME,EnterFrameHandler);
12
}
13
14
function
EnterFrameHandler(e:Event):
void
{
15
drag(segs[segNum-
1
],mouseX,mouseY);
16
for
(
var
i:
int
=segNum-
2
; i>=
0
; i--) {
17
drag(segs[i],segs[i+
1
].x,segs[i+
1
].y);
18
}
19
}
20
21
//拖动的封装
22
function
drag(seg:Segment,targetX:
Number
,targetY:
Number
):
void
{
23
var
dx:
Number
=targetX-seg.x;
24
var
dy:
Number
=targetY-seg.y;
25
var
angle:
Number
=Math.atan2(dy,dx);
26
seg.rotation=angle*
180
/Math.PI;
27
var
w:
Number
=seg.getPin().x-seg.x;
28
var
h:
Number
=seg.getPin().y-seg.y;
29
seg.x=targetX-w;
30
seg.y=targetY-h;
31
}
32
33
init();
如果说反向运动学的拖动,是用外力拖“死青蛙”的脚,则反向运动学中的伸展则正好相反,它相当于把青蛙的身体固定住,而青蛙的脚主动伸出去够某一物体(好吧,死青蛙是不会主动去抓物体的,人死不能复生,青蛙也一样,也许换成另一种说法更容易理解:我们坐在位子上不动,想伸手去拿桌子远处的东西,其实就是这个意思)
ok,如果感觉还不是太晕的话,再来小结下“正向运动”与“反向运动”的区别:
人行走时“下肢”系统的运动之所以被称做正向运动,主要特征是大腿先动,从而驱动小腿,而小腿又驱动脚,更准确的讲可以理解为“固定端驱动自由端”,能量的传递是自上而下,从固定端传递到自由端,也就是所谓的“正向”。
而人伸手去拿东西,可以看作 “手带动上臂”,而“上臂又带动胳膊”,即“自由端带动固定端”,能量的传递是自下而上,从自由端传递到固定端,即所谓的“反向”。
双关节的伸展:
上面的示例中,粗的关节当做胳膊,细的关节当做手臂,用鼠标在上面移动时,会发现手臂始终试图伸展到鼠标所在位置,但由于胳膊被固定点限制了,所以形成了这种效果。
下面是处理的示意图:
处理步骤:
1.手臂seg1,先绕着自己的固定点(x,y),朝鼠标所在点(mousex,mousey)旋转
2.得到一个新的点(tx,ty)--红色的实线三角形,然后胳膊seg2以(tx,ty)为目标旋转
3.重新将seg1挂到seg2的自由端
4.重复以上处理,直到二个关节的姿态不再有任何变化为止
01
var
seg1:Segment=
new
Segment(
80
,
10
);
02
seg1.x=
130
;
03
seg1.y=
160
;
04
addChild(seg1);
05
06
var
seg2:Segment=
new
Segment(
60
,
20
);
07
seg2.x=seg1.getPin().x;
08
seg2.y=seg1.getPin().y;
09
addChild(seg2);
10
11
function
init():
void
{
12
addEventListener(Event.ENTER_FRAME,EnterFrameHandler);
13
}
14
15
function
EnterFrameHandler(e:Event):
void
{
16
var
dx:
Number
=mouseX-seg1.x;
17
var
dy:
Number
=mouseY-seg1.y;
18
var
angle:
Number
=Math.atan2(dy,dx);
19
seg1.rotation=angle*
180
/Math.PI;
20
var
w:
Number
=seg1.getPin().x-seg1.x;
21
var
h:
Number
=seg1.getPin().y-seg1.y;
22
var
tx:
Number
=mouseX-w;
23
var
ty:
Number
=mouseY-h;
24
25
dx=tx-seg2.x;
26
dy=ty-seg2.y;
27
28
angle=Math.atan2(dy,dx);
29
seg2.rotation=angle*
180
/Math.PI;
30
seg1.x=seg2.getPin().x;
31
seg1.y=seg2.getPin().y;
32
}
33
34
init();
注意一个细节:反向运动伸展时,关节是倒着挂的,即最后一个addChild的Segment做为系统固定端,第一个Segment实例为做系统的伸展自由端。可以把上面的动画放慢到每秒一帧,上述处理步骤也许更容易看清楚
01
function
EnterFrameHandler(e:Event):
void
{
02
var
dx:
Number
=mouseX-seg1.x;
03
var
dy:
Number
=mouseY-seg1.y;
04
var
angle:
Number
=Math.atan2(dy,dx);
05
seg1.rotation=angle*
180
/Math.PI;
06
var
w:
Number
=seg1.getPin().x-seg1.x;
07
var
h:
Number
=seg1.getPin().y-seg1.y;
08
var
tx:
Number
=mouseX-w;
09
var
ty:
Number
=mouseY-h;
10
11
dx=tx-seg2.x;
12
dy=ty-seg2.y;
13
14
angle=Math.atan2(dy,dx);
15
seg2.rotation=angle*
180
/Math.PI;
16
seg1.x=seg2.getPin().x;
17
seg1.y=seg2.getPin().y;
18
19
//新增的画线部分,以方便观察
20
graphics.clear();
21
graphics.lineStyle(
1
,
0xff0000
,
0.5
);
22
graphics.moveTo(mouseX,mouseY);
23
graphics.lineTo(seg1.getPin().x,seg1.getPin().y);
24
25
graphics.lineStyle(
1
,
0x0000ff
,
0.5
);
26
graphics.moveTo(mouseX,mouseY);
27
graphics.lineTo(seg2.getPin().x,seg2.getPin().y);
28
29
}
多关节的伸展:
01
var
segNum:
uint
=
10
;
02
var
segs:
Array
=
new
Array
(segNum);
03
var
i:
int
=
0
;
04
05
function
init():
void
{
06
for
(i=
0
; i<segNum; i++) {
07
segs[i]=
new
Segment(
50
,
10
+
2
*i);
08
segs[i].x=
30
;
09
segs[i].y=
30
;
10
addChild(segs[i]);
11
}
12
addEventListener(Event.ENTER_FRAME,EnterFrameHandler);
13
}
14
15
function
EnterFrameHandler(e:Event):
void
{
16
var
target:Point=expand(segs[
0
],mouseX,mouseY);
17
18
//记住:第一个为伸展末端,最后一个为固定端
19
for
(i=
1
; i<segNum; i++) {
20
target=expand(segs[i],target.x,target.y);
21
}
22
23
//倒挂所有Segment
24
for
(i = segNum -
1
; i >
0
; i--) {
25
hang(segs[i-
1
],segs[i]);
26
}
27
28
}
29
30
function
expand(seg:Segment,targetX:
Number
,targetY:
Number
):Point {
31
var
dx:
Number
=targetX-seg.x;
32
var
dy:
Number
=targetY-seg.y;
33
var
angle:
Number
=Math.atan2(dy,dx);
34
seg.rotation=angle*
180
/Math.PI;
35
var
w:
Number
=seg.getPin().x-seg.x;
36
var
h:
Number
=seg.getPin().y-seg.y;
37
var
tx:
Number
=targetX-w;
38
var
ty:
Number
=targetY-h;
39
return
new
Point(tx,ty);
40
}
41
42
function
hang(segA:Segment,segB:Segment) {
43
segA.x=segB.getPin().x;
44
segA.y=segB.getPin().y;
45
}
46
47
init();
如果把目标点从鼠标位置换成某一个运动物体的坐标,效果会更好玩:
01
var
segNum:
uint
=
9
;
02
var
segs:
Array
=
new
Array
(segNum);
03
var
i:
int
=
0
;
04
var
ball:Ball;
05
var
gravity:
Number
=
0.3
;
06
var
bounce:
Number
=-
0.95
;
07
08
function
init():
void
{
09
ball =
new
Ball(
15
);
10
ball.vx=
10
;
11
addChild(ball);
//加入一个小球
12
13
for
(i=
0
; i<segNum; i++) {
14
segs[i]=
new
Segment(
45
,
10
+
1
*i);
15
segs[i].x=
30
;
16
segs[i].y=
30
;
17
addChild(segs[i]);
18
}
19
20
addEventListener(Event.ENTER_FRAME,EnterFrameHandler);
21
}
22
23
function
EnterFrameHandler(e:Event):
void
{
24
moveBall();
//让小球动起来
25
26
var
target:Point=expand(segs[
0
],ball.x,ball.y);
//最后一个跟着小球跑
27
28
for
(i=
1
; i<segNum; i++) {
29
target=expand(segs[i],target.x,target.y);
30
}
31
32
33
for
(i = segNum -
1
; i >
0
; i--) {
34
hang(segs[i-
1
],segs[i]);
35
}
36
}
37
38
function
expand(seg:Segment,targetX:
Number
,targetY:
Number
):Point {
39
var
dx:
Number
=targetX-seg.x;
40
var
dy:
Number
=targetY-seg.y;
41
var
angle:
Number
=Math.atan2(dy,dx);
42
seg.rotation=angle*
180
/Math.PI;
43
var
w:
Number
=seg.getPin().x-seg.x;
44
var
h:
Number
=seg.getPin().y-seg.y;
45
var
tx:
Number
=targetX-w;
46
var
ty:
Number
=targetY-h;
47
return
new
Point(tx,ty);
48
}
49
50
function
hang(segA:Segment,segB:Segment) {
51
segA.x=segB.getPin().x;
52
segA.y=segB.getPin().y;
53
}
54
55
function
moveBall():
void
{
56
ball.vy+=gravity;
57
ball.x+=ball.vx;
58
ball.y+=ball.vy;
59
if
(ball.x+ball.radius>stage.stageWidth) {
60
ball.x=stage.stageWidth-ball.radius;
61
ball.vx*=bounce;
62
}
else
if
(ball.x - ball.radius <
0
) {
63
ball.x=ball.radius;
64
ball.vx*=bounce;
65
}
66
if
(ball.y+ball.radius>stage.stageHeight) {
67
ball.y=stage.stageHeight-ball.radius;
68
ball.vy*=bounce;
69
}
else
if
(ball.y - ball.radius <
0
) {
70
ball.y=ball.radius;
71
ball.vy*=bounce;
72
}
73
}
74
75
init();
结合以前学到的碰撞检测,能做出更出色的交互效果:
01
var
segNum:
uint
=
4
;
02
var
segs:
Array
=
new
Array
(segNum);
03
var
i:
int
=
0
;
04
var
ball:Ball;
05
var
gravity:
Number
=
0.2
;
06
var
bounce:
Number
=-
0.95
;
07
08
function
init():
void
{
09
ball=
new
Ball(
15
);
10
ball.vx=
10
;
11
addChild(ball);
//加入一个小球
12
13
for
(i=
0
; i<segNum; i++) {
14
segs[i]=
new
Segment(
45
,
10
+
1
*i);
15
segs[i].x=
300
;
16
segs[i].y=
385
;
17
addChild(segs[i]);
18
}
19
20
addEventListener(Event.ENTER_FRAME,EnterFrameHandler);
21
}
22
23
function
EnterFrameHandler(e:Event):
void
{
24
moveBall();
25
26
var
target:Point=expand(segs[
0
],ball.x,ball.y);
27
28
for
(i=
1
; i<segNum; i++) {
29
target=expand(segs[i],target.x,target.y);
30
}
31
32
for
(i = segNum -
1
; i >
0
; i--) {
33
hang(segs[i-
1
],segs[i]);
34
}
35
36
checkHit();
//碰撞检测
37
}
38
39
function
expand(seg:Segment,targetX:
Number
,targetY:
Number
):Point {
40
var
dx:
Number
=targetX-seg.x;
41
var
dy:
Number
=targetY-seg.y;
42
var
angle:
Number
=Math.atan2(dy,dx);
43
seg.rotation=angle*
180
/Math.PI;
44
var
w:
Number
=seg.getPin().x-seg.x;
45
var
h:
Number
=seg.getPin().y-seg.y;
46
var
tx:
Number
=targetX-w;
47
var
ty:
Number
=targetY-h;
48
return
new
Point(tx,ty);
49
}
50
51
function
hang(segA:Segment,segB:Segment) {
52
segA.x=segB.getPin().x;
53
segA.y=segB.getPin().y;
54
}
55
56
function
moveBall():
void
{
57
ball.vy+=gravity;
58
ball.x+=ball.vx;
59
ball.y+=ball.vy;
60
if
(ball.x+ball.radius>stage.stageWidth) {
61
ball.x=stage.stageWidth-ball.radius;
62
ball.vx*=bounce;
63
}
else
if
(ball.x - ball.radius <
0
) {
64
ball.x=ball.radius;
65
ball.vx*=bounce;
66
}
67
if
(ball.y+ball.radius>stage.stageHeight) {
68
ball.y=stage.stageHeight-ball.radius;
69
ball.vy*=bounce;
70
}
else
if
(ball.y - ball.radius <
0
) {
71
ball.y=ball.radius;
72
ball.vy*=bounce;
73
}
74
}
75
76
77
function
checkHit():
void
{
78
var
segment:Segment=segs[
0
];
79
var
dx:
Number
=segment.getPin().x-ball.x;
80
var
dy:
Number
=segment.getPin().y-ball.y;
81
var
dist:
Number
=Math.sqrt(dx*dx+dy*dy);
82
if
(dist<ball.radius) {
83
ball.vx+=Math.random()*
2
-
1
;
//给小球一个很小的随机x轴向速度(这样看起来小球会在x轴上突然慢下来)
84
ball.vy-=
1.001
;
//y轴速度反向(这样看上去,会被反扔出去了)
85
}
86
}
87
88
init();