请教关于自定义操作器限制翻转角度的问题？

zmajun

本人目前在做一个使用OSG的项目，需要使用自定义的操作器，准备基于源码中的的TerrainManipulator做一定修改，查看源码后，操作器之间继承关系为TerrainManipulator->OrbitManipulator->StandardManipulator->CameraManipulator。现在遇到的问题是要控制操作器上下翻转的角度，大致在0~30度
之间，现在的TerrainManipulator操作器可以控制翻转角度在-90~90度之间。涉及到的代码主要如下：

1. /** Update rotation by yaw and pitch.
   
2. *
   
3. *  localUp parameter defines either camera's "UP" vector
   
4. *  that will be preserved during rotation, or it can be zero (0,0,0) to specify
   
5. *  that camera's "UP" vector will be not preserved and free rotation will be made.*/
   
6. void StandardManipulator::rotateYawPitch( Quat& rotation, const double yaw, const double pitch,
   
7.                                            const Vec3d& localUp )
   
8. {
   
9.     bool verticalAxisFixed = (localUp != Vec3d( 0.,0.,0. ));
   
10. 
    
11.     // fix current rotation
    
12.     if( verticalAxisFixed )
    
13.         fixVerticalAxis( rotation, localUp, true );
    
14. 
    
15.     // rotations
    
16.     Quat rotateYaw( -yaw, verticalAxisFixed ? localUp : rotation * Vec3d( 0.,1.,0. ) );
    
17.     Quat rotatePitch;
    
18.     Quat newRotation;
    
19.     Vec3d cameraRight( rotation * Vec3d( 1.,0.,0. ) );
    
20. 
    
21.     double my_dy = pitch;
    
22.     int i = 0;
    
23. 
    
24.     do {
    
25. 
    
26.         // rotations
    
27.         rotatePitch.makeRotate( my_dy, cameraRight );
    
28.         newRotation = rotation * rotateYaw * rotatePitch;
    
29. 
    
30.         // update vertical axis
    
31.         if( verticalAxisFixed )
    
32.             fixVerticalAxis( newRotation, localUp, false );
    
33. 
    
34.         // check for viewer's up vector to be more than 90 degrees from "up" axis
    
35.         Vec3d newCameraUp = newRotation * Vec3d( 0.,1.,0. );
    
36.         if( newCameraUp * localUp >0.)
    
37.         {
    
38. 
    
39.             // apply new rotation
    
40.             rotation = newRotation;
    
41.             return;
    
42. 
    
43.         }
    
44. 
    
45.         my_dy /= 2.;
    
46.         if( ++i == 20 )
    
47.         {
    
48.             rotation = rotation * rotateYaw;
    
49.             return;
    
50.         }
    
51. 
    
52.     } while( true );
    
53. }
    
54. 
    
55. 
    
56. /** The method corrects the rotation to make impression of fixed up direction.
    
57. *  Technically said, it makes the roll component of the rotation equal to zero.
    
58. *
    
59. *  Up vector is given by CoordinateFrame and it is +z by default.
    
60. *  It can be changed by osgGA::CameraManipulator::setCoordinateFrameCallback().
    
61. *
    
62. *  Eye parameter is user position, rotation is the rotation to be fixed, and
    
63. *  disallowFlipOver, when set on true, avoids pitch rotation component to grow
    
64. *  over +/- 90 degrees. If this happens and disallowFlipOver is true,
    
65. *  manipulator is rotated by 180 degrees. More precisely, roll rotation component is changed by 180 degrees,
    
66. *  making pitch once again between -90..+90 degrees limits.
    
67. */
    
68. void StandardManipulator::fixVerticalAxis( Vec3d& eye, Quat& rotation, bool disallowFlipOver )
    
69. {
    
70.    CoordinateFrame coordinateFrame = getCoordinateFrame( eye );
    
71.    Vec3d localUp = getUpVector( coordinateFrame );
    
72. 
    
73.    fixVerticalAxis( rotation, localUp, disallowFlipOver );
    
74. }
    
75. 
    
76. 
    
77. /** The method corrects the rotation to make impression of fixed up direction.
    
78. *  Technically said, it makes the roll component of the rotation equal to zero.
    
79. *
    
80. *  rotation parameter is the rotation to be fixed.
    
81. *  localUp is UP vector and must not be zero length.
    
82. *  disallowFlipOver, when set on true, avoids pitch rotation component to grow
    
83. *  over +/- 90 degrees. If this happens and disallowFlipOver is true,
    
84. *  manipulator is rotated by 180 degrees. More precisely, roll rotation component is changed by 180 degrees,
    
85. *  making pitch once again between -90..+90 degrees limits.*/
    
86. void StandardManipulator::fixVerticalAxis( Quat& rotation, const Vec3d& localUp, bool disallowFlipOver )
    
87. {
    
88.     // camera direction vectors
    
89.     Vec3d cameraUp = rotation * Vec3d( 0.,1.,0. );
    
90.     Vec3d cameraRight = rotation * Vec3d( 1.,0.,0. );
    
91.     Vec3d cameraForward = rotation * Vec3d( 0.,0.,-1. );
    
92. 
    
93.     // computed directions
    
94.     Vec3d newCameraRight1 = cameraForward ^ localUp;
    
95.     Vec3d newCameraRight2 = cameraUp ^ localUp;
    
96.     Vec3d newCameraRight = (newCameraRight1.length2() > newCameraRight2.length2()) ?
    
97.                             newCameraRight1 : newCameraRight2;
    
98.     if( newCameraRight * cameraRight < 0. )
    
99.         newCameraRight = -newCameraRight;
    
100. 
     
101.     // vertical axis correction
     
102.     Quat rotationVerticalAxisCorrection;
     
103.     rotationVerticalAxisCorrection.makeRotate( cameraRight, newCameraRight );
     
104. 
     
105.     // rotate camera
     
106.     rotation *= rotationVerticalAxisCorrection;
     
107. 
     
108.     if( disallowFlipOver )
     
109.     {
     
110. 
     
111.         // make viewer's up vector to be always less than 90 degrees from "up" axis
     
112.         Vec3d newCameraUp = newCameraRight ^ cameraForward;
     
113.         if( newCameraUp * localUp < 0. )
     
114.             rotation = Quat( PI, Vec3d( 0.,0.,1. ) ) * rotation;
     
115. 
     
116.     }
     
117. }

复制代码

上面的代码是在StandardManipulator操作器其中实现，我发现修改代码中if( newCameraUp * localUp > 0. )这句话将0.改为0.87(cos(30)的近似值)后可以将翻转角度限制在-30~30度之间，但是现在不知道如何将其控制在0~30度之间，请大神指点一下。

fenma3422

你可以来个&来判断