Transform from window coordinate to OpenGL coordinate

[Debugger]

I am trying to use gluUnProject()transform window coordinate to OpenGL coordinate, but I found that I can only get correct coordinate for x axis, the y axis is a not correct, any idear about this?

I use a cross line to trace mouse position.
code:

#include <iostream>
#include <windows.h>
#include "GL/glut.h" 
 
using namespace std ;
 
//Threee variable indicate the coordiante after transformation
GLdouble	objX ;
GLdouble	objY ;
GLdouble	objZ ;
void MotionFunc(int x, int y)
{
 
	//Get Model matrix
	GLdouble *model = new GLdouble[16] ;
	glGetDoublev(GL_MODELVIEW_MATRIX,model) ;
	//Get project matrix
	GLdouble *proj = new GLdouble[16] ; 
	glGetDoublev(GL_PROJECTION_MATRIX,proj) ;
	//Get viewport 
	GLint *view = new GLint[4] ;
	glGetIntegerv(GL_VIEWPORT,view) ;
	//Transform
	gluUnProject( x, y, 1.0, model, proj, view, &amp;objX, &amp;objY, &amp;objZ) ;
 
}
 
void init(void)
{
	glClearColor(1.0, 1.0, 1.0, 1.0) ;
}
 
void display(void)
{
 
	glClear(GL_COLOR_BUFFER_BIT) ;
	glColor3f(1.0, 0.0, 0.0) ;
	//Draw a vertical line and a horizontal line
	glBegin(GL_LINES) ;
		glVertex2f((objX-4.0)<-2.0?-2.0:(objX-4.0), objY) ;
		glVertex2f((objX+4.0)>2.0?2.0:(objX+4.0), objY) ;
		glVertex2f(objX, (objY-3.0)<-1.5?-1.5:(objY-3.0)) ;
		glVertex2f(objX, (objY+3.0)>1.5?1.5:(objY+3.0)) ;
	glEnd() ;
	glutSwapBuffers() ;
 
}
 
void reshape(int w, int h)
{
	glViewport(0, 0, (GLsizei)w, (GLsizei)h) ;
	glMatrixMode(GL_PROJECTION) ;
	glLoadIdentity() ;
	if(w<=h)
		glOrtho(-1.5, 1.5, -1.5*(GLfloat)h/(GLfloat)w,
		1.5*(GLfloat)h/(GLfloat)w, -10.0, 10.0) ;
	else
		glOrtho(-1.5*(GLfloat)w/(GLfloat)h, 
		1.5*(GLfloat)w/(GLfloat)h, -1.5, 1.5, -10.0, 10.0) ;
	glMatrixMode(GL_MODELVIEW) ;
	glLoadIdentity() ;
}
 
int main(int argc, char **argv)
{
	glutInit(&amp;argc, argv) ;
	glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB) ;
	glutInitWindowSize(1024, 768) ;
	glutInitWindowPosition(0, 0) ;
	glutCreateWindow("MouseSample");	
	init() ;
	glutPassiveMotionFunc(MotionFunc);
	glutDisplayFunc(display);
	glutIdleFunc(display) ;
	glutReshapeFunc(reshape) ;
	glutMainLoop();
 
	return 0 ;
}

[Ido Ilan]

Hi,

Try this:
On windows the 0,0 is the upper left corner, but 0,0 for OpenGL is on the lower left corner.
You need to send: window heigh - y.

Ido

[Debugger]

Thank you very much! it works now, change it like the following:

glVertex2f((objX-4.0)<-2.0?-2.0:(objX-4.0), -objY) ;		
glVertex2f((objX+4.0)>2.0?2.0:(objX+4.0), -objY) ;