Compute objects moving with arrows and mouse - c++

Question

I am doing a maya simulator application with openGL, everything is progressing pretty well. Just have only one trouble, i can not calculate 100% accuracy of moving object by mouse.
I'm using the scaling of arrows in 3D coordinates and arrows in the screen coordinates and multiplying it with some scaling to calculate the degree of motion in the x and y direction of the screen coordinates. .
But these calculations do not give high accuracy, the mouse is deviated from the arrow. I need it always on the moving arrows, meaning that the accuracy is almost 100%
Anyone who has ideas or comments on this issue will always be appreciated
This is some code i try:
gluProject((GLdouble)x3DVertex, (GLdouble)y3DVertex, (GLdouble)z3DVertex, modelMatrix, projectMatrix, viewport, &xScreenVertex, &yScreenVertex, &zScreenVertex);
if (axis == 0)
{
gluProject((GLdouble)x3DVertex + 1, (GLdouble)y3DVertex, (GLdouble)z3DVertex, modelMatrix, projectMatrix, viewport, &xScreenArrow, &yScreenArrow, &zScreenArrow);
}
else if (axis == 1)
{
gluProject((GLdouble)x3DVertex, (GLdouble)y3DVertex + 1, (GLdouble)z3DVertex, modelMatrix, projectMatrix, viewport, &xScreenArrow, &yScreenArrow, &zScreenArrow);
}
else
{
gluProject((GLdouble)x3DVertex, (GLdouble)y3DVertex, (GLdouble)z3DVertex + 1, modelMatrix, projectMatrix, viewport, &xScreenArrow, &yScreenArrow, &zScreenArrow);
}
float totalScaleXY = abs(xScreenArrow - xScreenVertex) + abs(yScreenArrow - yScreenVertex);
scaleX = abs(xScreenArrow - xScreenVertex) / totalScaleXY;
scaleY = abs(yScreenArrow - yScreenVertex) / totalScaleXY;
float lengthArrowOnScreen = sqrt(pow((xScreenArrow - xScreenVertex), 2) + pow((yScreenArrow - yScreenVertex), 2));
scale3dAndScreen = 1 / lengthArrowOnScreen;
This is the code I'm testing, it's not very accurate

Answer 1

Here small ugly but very simple C++ example of what I had in mind for this:
//---------------------------------------------------------------------------
#include <vcl.h>
#include <math.h>
#pragma hdrstop
#include "Unit1.h"
#include "gl_simple.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
double mview[16],mmodel[16],mproj[16]; // OpenGL matrices
//---------------------------------------------------------------------------
// vector/matrix math
//---------------------------------------------------------------------------
double vector_len(double *a) { return sqrt((a[0]*a[0])+(a[1]*a[1])+(a[2]*a[2])); } // = |vector[3]|
void vector_sub(double *c,double *a,double *b) { for (int i=0;i<3;i++) c[i]=a[i]-b[i]; } // c[3] = a[3] - b[3]
void matrix_mul(double *c,double *a,double *b) // c[4x4] = a[4x4] * b [4x4]
{
double q[16];
q[ 0]=(a[ 0]*b[ 0])+(a[ 1]*b[ 4])+(a[ 2]*b[ 8])+(a[ 3]*b[12]);
q[ 1]=(a[ 0]*b[ 1])+(a[ 1]*b[ 5])+(a[ 2]*b[ 9])+(a[ 3]*b[13]);
q[ 2]=(a[ 0]*b[ 2])+(a[ 1]*b[ 6])+(a[ 2]*b[10])+(a[ 3]*b[14]);
q[ 3]=(a[ 0]*b[ 3])+(a[ 1]*b[ 7])+(a[ 2]*b[11])+(a[ 3]*b[15]);
q[ 4]=(a[ 4]*b[ 0])+(a[ 5]*b[ 4])+(a[ 6]*b[ 8])+(a[ 7]*b[12]);
q[ 5]=(a[ 4]*b[ 1])+(a[ 5]*b[ 5])+(a[ 6]*b[ 9])+(a[ 7]*b[13]);
q[ 6]=(a[ 4]*b[ 2])+(a[ 5]*b[ 6])+(a[ 6]*b[10])+(a[ 7]*b[14]);
q[ 7]=(a[ 4]*b[ 3])+(a[ 5]*b[ 7])+(a[ 6]*b[11])+(a[ 7]*b[15]);
q[ 8]=(a[ 8]*b[ 0])+(a[ 9]*b[ 4])+(a[10]*b[ 8])+(a[11]*b[12]);
q[ 9]=(a[ 8]*b[ 1])+(a[ 9]*b[ 5])+(a[10]*b[ 9])+(a[11]*b[13]);
q[10]=(a[ 8]*b[ 2])+(a[ 9]*b[ 6])+(a[10]*b[10])+(a[11]*b[14]);
q[11]=(a[ 8]*b[ 3])+(a[ 9]*b[ 7])+(a[10]*b[11])+(a[11]*b[15]);
q[12]=(a[12]*b[ 0])+(a[13]*b[ 4])+(a[14]*b[ 8])+(a[15]*b[12]);
q[13]=(a[12]*b[ 1])+(a[13]*b[ 5])+(a[14]*b[ 9])+(a[15]*b[13]);
q[14]=(a[12]*b[ 2])+(a[13]*b[ 6])+(a[14]*b[10])+(a[15]*b[14]);
q[15]=(a[12]*b[ 3])+(a[13]*b[ 7])+(a[14]*b[11])+(a[15]*b[15]);
for(int i=0;i<16;i++) c[i]=q[i];
}
void matrix_mul_vector(double *c,double *a,double *b) // c[3] = a[4x4] * (b[3],1)
{
double q[3];
q[0]=(a[ 0]*b[0])+(a[ 4]*b[1])+(a[ 8]*b[2])+(a[12]);
q[1]=(a[ 1]*b[0])+(a[ 5]*b[1])+(a[ 9]*b[2])+(a[13]);
q[2]=(a[ 2]*b[0])+(a[ 6]*b[1])+(a[10]*b[2])+(a[14]);
for(int i=0;i<3;i++) c[i]=q[i];
}
//---------------------------------------------------------------------------
class DragDrop3D // arrow translation controls (you need one for each objet)
{
public:
double *mm; // model matrix
double *mv; // view matrix
double *mp; // projection matrix
double o[3]; // start point
double l[3]; // length of the arrows
double a,b; // size of the arrow head a length, b width/2
int sel; // selected axis
DragDrop3D()
{
mm=NULL; mv=NULL; mp=NULL;
o[0]=-1.0; l[0]=3.5; a=0.5;
o[1]=-1.0; l[1]=3.5; b=0.25;
o[2]=-1.0; l[2]=3.5; sel=-1;
}
DragDrop3D(DragDrop3D& a) { *this=a; }
~DragDrop3D() {}
DragDrop3D* operator = (const DragDrop3D *a) { *this=*a; return this; }
//DragDrop3D* operator = (const DragDrop3D &a) { ...copy... return this; }
void project(double *scr,double *mmvp,double *obj) // obj -> scr
{
matrix_mul_vector(scr,mmvp,obj);
if (fabs(scr[2])>1e-10) scr[2]=1.0/scr[2]; else scr[2]=0.0;
scr[0]*=scr[2];
scr[1]*=scr[2];
}
void draw() // render arrows
{
int e;
double ang,dang=2.0*M_PI/36.0,u0,u1,v0,v1,q=1.0/sqrt((a*a)+(b*b));
// axis lines
glBegin(GL_LINES);
glColor3f(1.0,0.0,0.0); glVertex3dv(o); glVertex3d(o[0]+l[0],o[1],o[2]);
glColor3f(0.0,1.0,0.0); glVertex3dv(o); glVertex3d(o[0],o[1]+l[1],o[2]);
glColor3f(0.0,0.0,1.0); glVertex3dv(o); glVertex3d(o[0],o[1],o[2]+l[2]);
glEnd();
// cones
glBegin(GL_TRIANGLES);
u1=b*cos(-dang);
v1=b*sin(-dang);
for (e=1,ang=0.0;e;ang+=dang)
{
if (ang>=2.0*M_PI) { ang=2.0*M_PI; e=0; }
u0=u1; u1=b*cos(ang);
v0=v1; v1=b*sin(ang);
// X
if (sel==0) glColor3f(1.0,0.0,0.0); else glColor3f(0.5,0.1,0.1);
glNormal3f(a*q,(u0+u1)*0.5*q,(v0+v1)*0.5*q);
glVertex3d(o[0]+l[0] ,o[1] ,o[2] );
glVertex3d(o[0]+l[0]-a,o[1]+u0,o[2]+v0);
glVertex3d(o[0]+l[0]-a,o[1]+u1,o[2]+v1);
glNormal3f(-1.0,0.0,0.0);
glVertex3d(o[0]+l[0]-a,o[1],o[2]);
glVertex3d(o[0]+l[0]-a,o[1]+u1,o[2]+v1);
glVertex3d(o[0]+l[0]-a,o[1]+u0,o[2]+v0);
// Y
if (sel==1) glColor3f(0.0,1.0,0.0); else glColor3f(0.1,0.5,0.1);
glNormal3f((u0+u1)*0.5*q,a*q,(v0+v1)*0.5*q);
glVertex3d(o[0] ,o[1]+l[1] ,o[2] );
glVertex3d(o[0]+u1,o[1]+l[1]-a,o[2]+v1);
glVertex3d(o[0]+u0,o[1]+l[1]-a,o[2]+v0);
glNormal3f(0.0,-1.0,0.0);
glVertex3d(o[0] ,o[1]+l[1]-a,o[2] );
glVertex3d(o[0]+u0,o[1]+l[1]-a,o[2]+v0);
glVertex3d(o[0]+u1,o[1]+l[1]-a,o[2]+v1);
// Z
if (sel==2) glColor3f(0.0,0.0,1.0); else glColor3f(0.1,0.1,0.5);
glNormal3f((v0+v1)*0.5*q,(u0+u1)*0.5*q,a*q);
glVertex3d(o[0] ,o[1] ,o[2]+l[2] );
glVertex3d(o[0]+v1,o[1]+u1,o[2]+l[2]-a);
glVertex3d(o[0]+v0,o[1]+u0,o[2]+l[2]-a);
glNormal3f(0.0,0.0,-1.0);
glVertex3d(o[0] ,o[1] ,o[2]+l[2]-a);
glVertex3d(o[0]+v0,o[1]+u0,o[2]+l[2]-a);
glVertex3d(o[0]+v1,o[1]+u1,o[2]+l[2]-a);
}
glEnd();
}
bool mouse(double mx,double my,TShiftState sh) // handle mouse events return if redraw is needed
{
if ((mm==NULL)||(mv==NULL)||(mp==NULL)) return false;
int ql; double p[3],mmvp[16]; bool _redraw=false;
// MVP = M*V*P
matrix_mul(mmvp,mm,mv);
matrix_mul(mmvp,mmvp,mp);
// convert screen coords to <-1,+1> GL NDC
mx= (2.0*mx/double(xs))-1.0;
my=1.0-(2.0*my/double(ys)) ;
// mouse left button state (last,actual)
ql=sh.Contains(ssLeft);
// select (no mouse button)
if (!ql)
{
int sel0=sel; sel=-1;
// arrowhead center screen x,y distance to mouse select if close
p[0]=o[0]+l[0]-0.5*a; p[1]=o[1]; p[2]=o[2]; project(p,mmvp,p); p[0]-=mx; p[1]-=my; p[2]=0.0; if (vector_len(p)<=0.5*b) sel=0; // X
p[1]=o[1]+l[1]-0.5*a; p[0]=o[0]; p[2]=o[2]; project(p,mmvp,p); p[0]-=mx; p[1]-=my; p[2]=0.0; if (vector_len(p)<=0.5*b) sel=1; // Y
p[2]=o[2]+l[2]-0.5*a; p[1]=o[1]; p[0]=o[0]; project(p,mmvp,p); p[0]-=mx; p[1]-=my; p[2]=0.0; if (vector_len(p)<=0.5*b) sel=2; // Z
_redraw=(sel0!=sel);
}
// drag arrowhead center into mouse position (active button)
if ((ql)&&(sel>=0)&&(sel<3))
{
int i;
double len0,len;
double p0[3],dp[3]={0.0,0.0,0.0},t,dt,q[3]={mx,my,0.0};
// selected arrowhead position,direction
for (i=0;i<3;i++) p0[i]=o[i];
p0[sel]+=l[sel]-0.5*a;
dp[sel]=1.0;
// "closest" intersection between axis/mouse_ray
for (len0=-1.0,t=0.0,dt=1.0;fabs(dt)>1e-5;t+=dt)
{
// position on axis p(t) = p0 + t*dp
for (i=0;i<3;i++) p[i]=p0[i]+(t*dp[i]);
// len = distance to mouse
project(p,mmvp,p);
vector_sub(p,p,q); p[2]=0.0;
len=vector_len(p);
// handle iteration step
if (len0<-0.5) len0=len;
if (len>len0) dt=-0.1*dt;
len0=len;
}
// translate by t
double m[16]=
{
1.0,0.0,0.0,0.0,
0.0,1.0,0.0,0.0,
0.0,0.0,1.0,0.0,
0.0,0.0,0.0,1.0,
};
m[12+sel]=t;
matrix_mul(mm,m,mm);
_redraw=true;
}
return _redraw;
}
};
//---------------------------------------------------------------------------
DragDrop3D ctrl; // I got single cube so single arrow drag drop control suffice
//---------------------------------------------------------------------------
void gl_draw() // main rendering code
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnable(GL_CULL_FACE);
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
glEnable(GL_COLOR_MATERIAL);
// init
static bool _init=true;
if (_init)
{
_init=false;
// M,V init matrices
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glLoadIdentity();
glTranslated(0.0,0.0,-25.0);
glGetDoublev(GL_MODELVIEW_MATRIX,mview);
glLoadIdentity();
glTranslated(-2.0,-1.0,-1.0);
glRotated(-35.0,0.0,1.0,0.0);
glGetDoublev(GL_MODELVIEW_MATRIX,mmodel);
glPopMatrix();
// matrices -> ctrl
glGetDoublev(GL_PROJECTION_MATRIX,mproj);
ctrl.mp=mproj;
ctrl.mv=mview;
ctrl.mm=mmodel;
}
// matrices -> OpenGL
glMatrixMode(GL_MODELVIEW);
glLoadMatrixd(mview);
glMultMatrixd(mmodel);
// draw VAO cube
ctrl.draw();
vao_draw(); // here render your object instead
glFlush();
SwapBuffers(hdc);
}
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner):TForm(Owner)
{
// application init
gl_init(Handle);
vao_init();
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormDestroy(TObject *Sender)
{
// application exit
gl_exit();
vao_exit();
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormResize(TObject *Sender)
{
// window resize
gl_resize(ClientWidth,ClientHeight);
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormPaint(TObject *Sender)
{
// window repaint
gl_draw();
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormMouseWheel(TObject *Sender, TShiftState Shift, int WheelDelta, TPoint &MousePos, bool &Handled)
{
// mouse wheel translates camera (like zoom)
GLfloat dz=2.0;
if (WheelDelta<0) dz=-dz;
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glLoadMatrixd(mview);
glTranslatef(0,0,dz);
glGetDoublev(GL_MODELVIEW_MATRIX,mview);
glPopMatrix();
gl_draw();
}
//---------------------------------------------------------------------------
// mouse events
void __fastcall TForm1::FormMouseDown(TObject *Sender, TMouseButton Button,TShiftState Shift, int X, int Y) { if (ctrl.mouse(X,Y,Shift)) gl_draw(); }
void __fastcall TForm1::FormMouseUp(TObject *Sender, TMouseButton Button,TShiftState Shift, int X, int Y) { if (ctrl.mouse(X,Y,Shift)) gl_draw(); }
void __fastcall TForm1::FormMouseMove(TObject *Sender, TShiftState Shift, int X, int Y) { if (ctrl.mouse(X,Y,Shift)) gl_draw(); }
//---------------------------------------------------------------------------
It is based on this: simple complete GL+VAO/VBO+GLSL+shaders example in C++ where you will find more info and the gl_simple.h I am using for this. The code is VCL based so ignore the VCL stuff and port the events to your kind of programming.
The program is using just OpenGL 1.0 API (appart of the VAO/VBO cube representing my object) so it does not need anything apart math.h for sin,cos,fabs functions.
The idea is to have one control DragDrop3D object per each controlable object in the world/scene. Init each first and then call mouse for each on every mouse event and redraw if needed.
Here small preview:
Sadly my GIF capture SW does not catch mouse cursor but it matches the movement exactly.
I was too lazy to compute the intersection between axises directly instead I iterate to find closest match (that for loop with dt). That part could be replaced by intersection equation.
The axises are bounded to the x,y,z axises of the object coordinate system (mm,mmodel).
For more objects you should also add locks so only one object can be selected ...
PS. see related:
- OpenGL ray OBB intersection