Question

Creating a 3d camera with c++ and directx

Asked by: E_G_M

Hi,
Im trying to create a camera in direct x like the ones that are in major role playing games like world of warcraft. at the moment all i really want is when you drag the mouse across the screen the camera swings around the object at a set distance away from it. iv been having a look around the net but i cant find anything that i understand enough to develop my own. so any pointer would be much appreciated

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Asked On
2009-03-28 at 18:12:33ID24274498
Tags

directx

,

c++

,

camera

Topic

DirectX Graphics & Game Programming

Participating Experts
1
Points
125
Comments
6

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Answers

 

by: ikeworkPosted on 2009-03-29 at 07:11:08ID: 24012771

hi E_G_M,

here is a class, calculating the camera matrix for given moiuse-input with opengl & glut.. you can use that camera-matrix and pass it to directx

ike

#ifndef DEMOCAMERA_INCLUDED
#define DEMOCAMERA_INCLUDED
 
#include "geo.h"
 
class DemoCamera
{
public:
    DemoCamera( bool blnPerspectiveView, const vector &pos, float angle_x, float angle_y );
    ~DemoCamera();
 
    // apply camera to opengl
    void                applyCamera();
 
    const matrix&       getWorld2CameraMatrix() const   { return m_CameraMatrix; }
 
    // glut - callbacks
    // glut glutMouseFunc - callback
    // button:
    //  GLUT_LEFT_BUTTON, GLUT_MIDDLE_BUTTON, GLUT_RIGHT_BUTTON
    // state:
    //  GLUT_UP 1, GLUT_DOWN 0
    static void         callback_mouse(int button, int state, int x, int y);
    // glut glutMotionFunc - callback
    static void         callback_mouse_motion(int x, int y);
    // glut glutReshapeFunc - callback
    static void         callback_resize(int width, int height);
 
private:
    void                mouse(int button, int state, int x, int y);
    void                mouse_motion(int x, int y);
    void                resize(int width, int height);
 
    // calculate matrix if needed
    void                update();
 
private:
    bool        m_blnPerspectiveView;
    int         m_screen_width;
    int         m_screen_height;
    vector      m_pos;
    float       m_angle_x;
    float       m_angle_y;
    bool        m_blnMatrixDirty;
    matrix      m_CameraMatrix;
 
    struct MouseMoveCache
    {
        int mouse_button;
        int x_start, y_start;
        float angle_x_start, angle_y_start, distance_start;
    };
 
    MouseMoveCache  m_MouseMoveCache;
 
    static DemoCamera   *ms_pSingleton;
};
 
DemoCamera*   DemoCamera::ms_pSingleton = NULL;
 
inline
DemoCamera::DemoCamera( bool blnPerspectiveView, const vector &pos, float angle_x, float angle_y )
: 
  m_blnPerspectiveView( blnPerspectiveView ),
  m_screen_width( 0 ),
  m_screen_height( 0 ),
  m_pos( pos ),
  m_angle_x( angle_x ),
  m_angle_y( angle_y ),
  m_blnMatrixDirty( true ),
  m_CameraMatrix(),
  m_MouseMoveCache()
{
    assert( !ms_pSingleton );
    ms_pSingleton = this;
}
 
inline
DemoCamera::~DemoCamera()
{
    ms_pSingleton = NULL;
}
 
inline
void               
DemoCamera::applyCamera()
{
    update();
    glLoadIdentity();
    glMultMatrixf( (const GLfloat*)getWorld2CameraMatrix().data_ptr() );
}
 
inline
void        
DemoCamera::update()
{
    if( m_blnMatrixDirty )
    {
        m_CameraMatrix = matrix::translate( -m_pos ) * 
                         matrix::rotate_y( gdeg2rad( m_angle_y ) ) * 
                         matrix::rotate_x( gdeg2rad( m_angle_x ) );
        m_blnMatrixDirty = false;
    }
}
 
inline
void        
DemoCamera::mouse(int button, int state, int x, int y)
{
    printf( "button: %d  state: %d  x: %d  y: %d\n", button, state, x, y );
 
    if( state == 0 )
    {
        m_MouseMoveCache.mouse_button = button;
        m_MouseMoveCache.x_start = x;
        m_MouseMoveCache.y_start = y;
        m_MouseMoveCache.angle_x_start = m_angle_x;
        m_MouseMoveCache.angle_y_start = m_angle_y;
        m_MouseMoveCache.distance_start = m_pos[2];
    }
}
 
// glut glutMotionFunc - callback
inline
void 
DemoCamera::mouse_motion(int x, int y)
{
    const float DISTANCE_SCALE = m_blnPerspectiveView ? 0.25f : 0.025f;
 
    switch( m_MouseMoveCache.mouse_button )
    {
    case 0:
        m_angle_y = m_MouseMoveCache.angle_y_start + x-m_MouseMoveCache.x_start;
        m_angle_x = m_MouseMoveCache.angle_x_start + y-m_MouseMoveCache.y_start;
        m_blnMatrixDirty = true;
        break;
    case 2:
        m_pos[2] = m_MouseMoveCache.distance_start + (y-m_MouseMoveCache.y_start)*DISTANCE_SCALE;
        if( !m_blnPerspectiveView ) resize( m_screen_width, m_screen_height );
        m_blnMatrixDirty = true;
        break;
    }
    
}
 
inline
void 
DemoCamera::callback_mouse(int button, int state, int x, int y)
{
    if( ms_pSingleton ) ms_pSingleton->mouse( button, state, x, y );
}
 
inline
void 
DemoCamera::callback_mouse_motion(int x, int y)
{
    if( ms_pSingleton ) ms_pSingleton->mouse_motion( x, y );
}
 
inline
void 
DemoCamera::callback_resize(int width, int height)
{
    if( ms_pSingleton ) ms_pSingleton->resize( width, height );
}
 
inline
void 
DemoCamera::resize(int width, int height)
{
	if( height == 0 ) height = 1;
 
    m_screen_width = width;
    m_screen_height = height;
 
	glViewport( 0, 0, m_screen_width, m_screen_height );
 
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
 
    if( m_blnPerspectiveView )
    {
    	gluPerspective(45.0f,(GLfloat)width/(GLfloat)height,0.1f,100.0f);
    }
    else
    {
        float left, right, bottom, top;
        float aspect = (GLfloat)width/(GLfloat)height;
        if( m_screen_width > m_screen_height )
        {
            left =   -m_pos[2] * aspect;
            right =   m_pos[2] * aspect;
            top =     m_pos[2];
            bottom = -m_pos[2];
        }
        else
        {
            left =   -m_pos[2];
            right =   m_pos[2];
            top =     m_pos[2] * aspect;
            bottom = -m_pos[2] * aspect;    
        }
        glOrtho( left, right, bottom, top, -100.0f, +100.0f );
    }
 
	glMatrixMode(GL_MODELVIEW);							// Select The Modelview Matrix
	glLoadIdentity();
}
 
 
 
 
 
 
 
 
 
 
#endif // #ifndef DEMOCAMERA_INCLUDED
                                              
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by: E_G_MPosted on 2009-03-30 at 16:47:00ID: 24024567

hi ikework
thanks for posting that i understand most of it i think. but i'm just wondering whats happening in the DemoCamera::mouse_motion function. also i'm a bit confused as to what the m_pos variable is representing and how it is being used in the matrix.

E_G_M

 

by: ikeworkPosted on 2009-03-31 at 02:00:32ID: 24026897

hey E_G_M,

>> but i'm just wondering whats happening in the DemoCamera::mouse_motion function

its the callback-function, which is called by the framework, whenever the mouse is moving. it checks if a button is pressed and modifies its data accordingly..


>> i'm a bit confused as to what the m_pos variable is representing and how it is being used in the matrix

its the position of the camera and it is applied here

m_CameraMatrix = matrix::translate( -m_pos ) *
                         matrix::rotate_y( gdeg2rad( m_angle_y ) ) *
                         matrix::rotate_x( gdeg2rad( m_angle_x ) );

this matrix is passed to the graphics engine, before anything is rendered..



feel free to ask more ..

ike

 

by: E_G_MPosted on 2009-04-01 at 00:14:09ID: 24036599

hi ikework,
thanks for helping me out here iv just got a couple more questions if u don't mind. firstly when your creating the camera matrix in the update function why do u use negative sign in front of the camera position vector.

what exactly are m_angle_y and m_angle_x representing and what is the relation ship between them and m_MouseMoveCache.angle_y_start and m_MouseMoveCache.angle_x_start. i notice that in the class constructor it ask for values that get used to initialize m_angle_y and m_angle_x what angles should be given here?

in the mouse motion function i'm guessing that in the switch statment case 0 is left click and case 2 is  right click. why when modifying data for left click are the m_angle_y and m_angle_x modified and with right click the m_pos[2] value modified.

thanks again for your help
E_G_M

 

by: ikeworkPosted on 2009-04-01 at 01:10:30ID: 24036830

hey E_G_M,

>> when your creating the camera matrix in the update function why do u use negative sign in front of the camera position vector.

because there is actually no such thing as a camera with a position. all that happens is, that the scene is moved in the opposite direction. if the *camera* is at {10, 0, 0} the scene is moved -10 units towards the x-axis. that is why the position is negated. hope that makes sense to you..

>> what exactly are m_angle_y and m_angle_x representing

m_angle_y is the rotation of the camera around the y-axis. m_angle_x around the x-axis

>> what is the relation ship between them and m_MouseMoveCache.angle_y_start

when a mouse button-press occurs, we have to save the current rotation of the camera. so
m_MouseMoveCache.angle_y_start = m_angle_y when the mouse button is pressed.

>> why when modifying data for left click are the m_angle_y and m_angle_x modified and with right click the m_pos[2] value modified.

because the left mouse button is for rotationg the camera, changing its orientation
the right mouse-button is for zooming-in and -out, changing camera's z-position (m_pos[2] is the z-component of the position vector)


ike

 

by: E_G_MPosted on 2009-04-01 at 05:14:24ID: 24038268

thanks very much I've got it now.

E_G_M

20120131-EE-VQP-002

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