如何像CAD程序一样控制3D应用程序的视点

文章建议将鼠标位置投影到观看体内的一个半球上，然后应用一个等于先前投影位置、原点和当前投影位置形成的角度的旋转。

通常被称为圆球控制，来自Ken Shoemake在Graphics Gems IV中的文章

这是一个旧的帖子，但我有代码，做你所要求的。我很久以前就想明白了。我刚刚用c++为一个新项目重写了它。它有助于在XZ平面上绘制网格来测试此代码。

基本上，你需要添加一些代码到keyDown和Keyup事件，这样你就可以从圆弧围绕中心(鼠标L键)和缩放(鼠标R键)和移动(Shift键)切换，你可以改变这是任何你想要的键代码。您还需要为鼠标事件Down、Move和UP添加代码。在这些事件中，您可以设置例程使用的bool值。我使用旧的gluLookAt来设置视图矩阵。如果你不想用它，你需要写一个。下面是设置视图矩阵的代码:

    void set_Eyes(void)
    {
        float sin_x, sin_y, cos_x, cos_y;
        sin_x = sin(z_rotation + angle_offset); // angle_offset is not needed...
        cos_x = cos(z_rotation + angle_offset); // It's a special use variable.
        cos_y = cos(x_rotation);
        sin_y = sin(x_rotation);
        cam_y = sin(x_rotation) * view_radius; // view_radius is always a negitive number.
        cam_x = (sin_x - (1.0f - cos_y) * sin_x) * view_radius;
        cam_z = (cos_x - (1.0f - cos_y) * cos_x) * view_radius;
        gluLookAt(
            cam_x + u_look_point_X, //eye positions
            cam_y + u_look_point_Y,
            cam_z + u_look_point_Z,
            u_look_point_X, // where we are looking
            u_look_point_Y,
            u_look_point_Z,
            0.0F, 1.0F, 0.0F); // up vector... Y is up
        eyeX = cam_x + u_look_point_X; // where the eye is in 3D space...
        eyeY = cam_y + u_look_point_Y; // needed for some shaders
        eyeZ = cam_z + u_look_point_Z; // u_look_points is the point we are looking at.
    }

下面是做数学运算的代码。为了能够在移动鼠标的方向上移动观看点，无论你在Y轴上观看的角度是什么，你都必须对移动值进行一些2D旋转计算。数学并不复杂，但理解我的代码可能很复杂。

//=================================================
// Mouse Movement Control
// "ArcBall" Style of viewing and movement.
//
//
//=================================================

#include "stdafx.h"
#include "mouse_control.h"
using namespace std;
// external variables
extern float PI;// 3.141592654
extern bool Right_Mouse_Down;
extern bool Left_Mouse_Down;
//==================================================
float m_speed = 2.0; // control mouse movement speed
float m_speed_global = 2.0; // Move to external setting
//==================================================
// Keep z_rotaion in -PI*2 to PI*2 range
float check_overflow(float v)
{
    if (v > 0.0f) if (v > (PI * 2)) v -= (PI * 2);
    if (v < 0.0f) if (v < (-PI * 2)) v += (PI * 2);
    return v;
}
// Keep x_rotaion in 0.0 to -PI/2.0 range
float check_overflow_x(float v)
{
    const float Half_PI = PI / 2.0f;
    if (v < 0.0f)
        if (v < -Half_PI+0.001f) // need the +0.001f to avoide fail at set_eyes function
            v = -Half_PI+0.001f;
    if (v > 0.0f) v = 0.0f;
    return v;
}
// handle mouse rotation
void handle_mouse_eye_rotaion(CPoint point)
{
    CPoint delta = mouse_p - point;
    int deadzone = 0;
    m_speed = m_speed_global * -view_radius * 0.1f;
    if (xz_translation_flag || Left_Mouse_Down)
    {
        // about z
        if (delta.x < deadzone)
        {
            rotate_left(delta.x);
        }
        if (delta.x > deadzone)
        {
            rotate_right(delta.x);
        }
        // about x
        if (delta.y < deadzone)
        {
            rotate_down(delta.y);
        }
        if (delta.y > deadzone)
        {
            rotate_up(delta.y);
        }
        mouse_p = point;
    }
    else
    {
        if (Right_Mouse_Down && !y_move_flag)
        {
            zoom_radius(delta); // change zoom
            mouse_p = point;
        }
    }
}
// rotate view clockwise
void rotate_left(int x)
{
    if (x > 100) x = 100;
    if (x < -100) x = -100;
    float t = (float(x) / (100.0f * PI));
    if (!xz_translation_flag)
    {
        z_rotation += t * m_speed_global;
        z_rotation = check_overflow(z_rotation);
        return;
    }
    u_look_point_X -= (t * cosf(z_rotation)*2.0f * m_speed);
    u_look_point_Z += (t * sinf(z_rotation)*2.0f * m_speed);
}
// rotate view counter clockwise
void rotate_right(int x)
{
    if (x > 100) x = 100;
    if (x < -100) x = -100;
    float t = (float(x) / (100.0f * PI));
    if (!xz_translation_flag)
    {
        z_rotation += t * m_speed_global;
        z_rotation = check_overflow(z_rotation);
        return;
    }
    u_look_point_X -= (t * cosf(z_rotation)*2.0f * m_speed);
    u_look_point_Z += (t * sinf(z_rotation)*2.0f * m_speed);
}
//======================== Y
// rotate view up
void rotate_up(int x)
{
    if (x > 100) x = 100;
    if (x < -100) x = -100;
    float t = (float(x) / (100.0f * PI));
    if (!xz_translation_flag)
    {
        x_rotation += t * m_speed_global;
        x_rotation = check_overflow_x(x_rotation);
        return;
    }
    u_look_point_Z -= (t * cosf(z_rotation)*2.0f * m_speed);
    u_look_point_X -= (t * sinf(z_rotation)*2.0f * m_speed);
}
// rotate view down
void rotate_down(int x)
{
    if (x > 100) x = 100;
    if (x < -100) x = -100;
    float t = (float(x) / (100.0f * PI ));
    if (!xz_translation_flag)
    {
        x_rotation += t * m_speed_global;
        x_rotation = check_overflow_x(x_rotation);
        return;
    }
    u_look_point_Z -= (t * cosf(z_rotation)*2.0f * m_speed);
    u_look_point_X -= (t * sinf(z_rotation)*2.0f * m_speed);
}
// used to change zoom
void zoom_radius(CPoint delta)
{
    if (delta.y > 0)
    {
        if (delta.y > 100) delta.y = 100;
    }
    if (delta.y < 0)
    {
        if (delta.x < -100) delta.x = -100;
    }
    float y = float(delta.y) / 100.0f;
    view_radius += y* 2.0f * m_speed;
    // Adjust these to change max zoom in and out values.
    // view_radius MOST STAY A NEGATIVE NUMBER!
    // OpenGL ALWAYS LOOKS IN THE NEGATIVE Z SCREEN DIRECTION!
    if (view_radius > -0.5f) view_radius = -0.5f;
    if (view_radius < -1000.0f) view_radius = -1000.0f;
}
// debug junk
//string s;
//s = "mouse_p";
//outStr1(s, mouse_p.x, mouse_p.y);
//s = "delta";
//outStr1(s, delta.x, delta.y);
// debug code
void outStr1(string s, int a, int b)
{
    char buf[100];
    sprintf_s(buf, "%s : A= %i : B= %in", s.c_str(), a, b);
    OutputDebugStringA(buf);
    return;
}

注:"mouse_p"需要在按下鼠标左键或右键时设置。它用来获取鼠标所在位置到鼠标所在位置的增量距离。

"point"是鼠标移动事件中的鼠标位置。mouse_p在计算完成后被设置为匹配"point"。否则移动会开始失去控制!

按键弹起…将bool设置为false (xz_translation_flag和y_move_flag)。KEYDOWN…当按下shift键时设置xz_translation_flag = TRUE。Y_move_flag还没有直接绑定的函数。它将被用来移动u_look_point_Y变量来改变注视点的高度