gluUnProject not working - c++

I am trying to use gluUnProject to get my mouse coordinates into world coordinates, however it seems to not be working, or I am just misunderstanding the functionality of the glUnProject function, here is the code I am working with, my matrices all check out fine and as for the -300 on the mouse x coordinate, I am using a C++ Win32 Dialog and the ScreenToClient is giving me funky results.
int appWidth = CApplication::GetInstance()->GetWidth();
int appHeight = CApplication::GetInstance()->GetHeight();
float fAspect = (float)appWidth / (float)appHeight;
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(60.0f, fAspect, 0.1f, 100000.0f);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(m_vecCamera.x, -m_vecCamera.y, m_vecCamera.z);
GLint viewport[4];
GLdouble modelview[16];
GLdouble projection[16];
GLfloat winX, winY, winZ;
GLdouble posX, posY, posZ;
glEnable(GL_DEPTH);
//Retrieve the Model/View, Projection, and Viewport Matrices
glGetDoublev( GL_MODELVIEW_MATRIX, modelview );
glGetDoublev( GL_PROJECTION_MATRIX, projection );
glGetIntegerv( GL_VIEWPORT, viewport );
//Retrieve the Mouse X and the flipped Mouse Y
winX = (float)pInput->msg.param1-300.0f;
winY = (float)viewport[3]-(float)pInput->msg.param2;
glReadPixels( int(winX), int(winY), 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &winZ );
gluUnProject(winX, winY, winZ, modelview, projection, viewport, &posX, &posY, &posZ);
This is however giving me coordinates relative to the center of my screen, and I am assuming is relative to my camera, I also tried implementing my own function
Vector2f MouseUnProject(int x, int y)
{
GLint viewport[4];
GLdouble modelview[16];
GLdouble projection[16];
GLfloat winX, winY, winZ;
GLdouble posX, posY, posZ;
glEnable(GL_DEPTH);
//Retrieve the Model/View, Projection, and Viewport Matrices
glGetDoublev( GL_MODELVIEW_MATRIX, modelview );
glGetDoublev( GL_PROJECTION_MATRIX, projection );
glGetIntegerv( GL_VIEWPORT, viewport );
//Retrieve the Mouse X and the flipped Mouse Y
winX = (float)x;
winY = (float)viewport[3]-y;
glReadPixels( int(winX), int(winY), 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &winZ );
double projectionX, projectionY;
double viewX, viewY;
double worldX, worldY;
//Convert from Screen Coords to Projection Coords
projectionX = (double)winX / ((double)viewport[2]/2.0) - 1.0;
projectionY = (double)winY / ((double)viewport[3]/2.0) + 1.0;
//Convert from projection Coords to View Coords
viewX = projectionX * modelview[14];
viewY = projectionY * modelview[14];
//Convert from View Coords to World Coords
worldX = viewX + modelview[12];
worldY = viewY - modelview[13];
return Vector2f(worldX, worldY);
}
It works to a certain mount, but when moving the camera, the numbers instantly go off a bit, the conversion from projection to view coords 'seems' to be ok, and the projection coords are definitely good.
I would really prefer to use glUnProject rather then my own function, but I can't get it to work for the life of me and all of the google searches I found don't seem to answer my question. What exactly does the GL documentation mean by 'object space' perhaps my understanding of that is wrong, and if so what do I additionally have to do to get my coordinates in the right space?

was posted a year ago,but anyways....so you are getting coordinates relative the the screen because you made a call to gluPerspective. this call internally calls glfrustum which will generate normalized coordinates in the range {-1, 1}. However if you called glfrustum directly with your near/far values you would have got the result from gluUnproject in that range.
To get back to your map editor coordinates, simply take the result from gluUnproject and manually range convert back to your editor coordinate system, ie{-1,1} => {0, max}
To get started you should test gluUnProject by inputting (0,0), (midX, midY), (maxX, maxY) and the result from gluUnProject should be (-1, -1, depth), (0, 0, depth) and (1, 1, depth). If you setup the projection matrix using glFrustum then the above result will be returned in the near/far range.

Related

OpenGL: Results by gluUnProject are not the expected ones

I am drawing a texture with z=0 as visible in the following image:
My near plane and far plane settings are 0.001 and 120.0. I can move around and zoom in and out using my keyboard.
What I want is to identify the world position of a mouse cursor position (e.g. red in the image) while using gluunproject.
Problem: The results posX, posY and posZ are somewhat close but not correct. E.g. for the center of the visible view (blue) I get posX=8.90000 and posY=53.80000. However if I move the mouse to the left I get posX=8.89894 (should be 3.xx). If I move the cursor to the right I get 8.90103 instead of approx. 14-16.
Here is my code:
glMatrixMode (GL_PROJECTION);
glLoadIdentity();
perspectiveGL(65.0,(GLdouble)width()/(GLdouble)height(), 0.001, 120.0);
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// Go to current World-Position
glTranslated(-m_posWorld.x(), -m_posWorld.y(), -m_posWorld.z());
// Try to project Screen(Mouse)-Coordinates to World Coordinates
GLint viewport[4];
GLdouble modelview[16];
GLdouble projection[16];
GLfloat winX, winY, winZ;
glGetDoublev( GL_MODELVIEW_MATRIX, modelview );
glGetDoublev( GL_PROJECTION_MATRIX, projection );
glGetIntegerv( GL_VIEWPORT, viewport );
winX = (float)m_lastPos.x(); // m_lastPos is a Point storing the last Mouse Cursor Position within the OpenGL-Widget (without borders)
winY = (float)viewport[3]-(float)m_lastPos.y();
winZ = -m_posWorld.z();
GLdouble posX, posY, posZ;
int success = glhUnProjectf( winX, winY, -m_posWorld.z(), modelview, projection, viewport, &posX, &posY, &posZ);
What might be the problem here?
To "unproject" something, you need window-space x,y and z.
    m_posWorld.z almost certainly is not in window-space.
Window-space z is what the depth buffer stores, it is a value between [0.0, 1.0] (assuming default depth range). Because the depth buffer gives you this value, you can easily figure it out by reading the depth buffer back at (winX, winY) (though performance will suffer).
You can transform your world-space coordinate into window-space:
vec4 posClip = projectionMatrix * viewMatrix * m_posWorld; // Project to clip-space
vec4 posNDC = posClip / posClip.w; // Perspective Divide
float winZ = (posNDC * vec4 (0.5) + vec4 (0.5)).z; // Adjust for Depth Range
The approach discussed above will work much quicker, but requires some matrix math. You are currently relying completely on OpenGL itself to do your matrix math for you, and if you want to keep doing that your only option will be to read the depth buffer back:
GLfloat winZ;
glReadPixels (winX, winY, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &winZ);

OpenGl getting mouse position

I have a function to create a vector with the mouse coordinates in 3d space.
Here is my code:
void myMouse(int x, int y){
GLint viewport[4];
GLdouble modelview[16];
GLdouble projection[16];
GLfloat winX, winY, winZ;
GLdouble posX, posY, posZ;
glGetDoublev( GL_MODELVIEW_MATRIX, modelview );
glGetDoublev( GL_PROJECTION_MATRIX, projection );
glGetIntegerv( GL_VIEWPORT, viewport );
winX = (float)x;
winY = (float)viewport[3] - (float)y; // Subtract The Current Mouse Y Coordinate
glReadPixels( x, winY, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &winZ );//Reads the depth buffer
gluUnProject( winX, winY, winZ, modelview, projection, viewport, &posX, &posY, &posZ);
vector.x=posX;
vector.y=posY;
vector.z=posZ;
}
The vector is then used as an attractor for some points that I'draw. The code works very well if i put the z position to 0, but then the points does not follow the cursor of the mouse when I rotate the scene. But if I set vector.z as the code above, the particles begin to move toward me and then they disappear (i.e. they go behind the viewpoint).
I'd like my points to follow the mouse only on the x/y axis when the z axis is pointed toward me, on the x/z axis when the y axis is pointed toward me and on the y/z axis when the x axis is pointed toward me.
Alternatively, how can I set the z position at a fixed distance from my point of view?
Most likely your problem lies in those lines:
glGetDoublev( GL_MODELVIEW_MATRIX, modelview );
glGetDoublev( GL_PROJECTION_MATRIX, projection );
glGetIntegerv( GL_VIEWPORT, viewport );
OpenGL is a state machine and what you query there could be anything. While drawing you normally manipulate the contents of those matrices in various ways, so what you query there may likely not be the matrices used initially for drawing.
To solve your problem you should make copies of the projection and modelview and viewport settings at the time of drawing right after you'Ve setup your initial view. You use then these copies instead of queried values, which may be very different from what you actually need.

gluUnproject returning 0, seems to be related to modelview matrix

I'm working on a 2D image viewer, I want to retrieve openGL mouse position on texture but I can't get it to work if glTranslatef() or glScalef() calls are made on the modelview matrix.
I'm using a QGLWidget , of the famous Qt library.
Here are the important calls :
Resize function :
void ViewerGL::resizeGL(int width, int height){
glViewport (0, 0, width, height);
Display function :
void ViewerGL::paintGL()
{ int w = width();
int h = height();
glMatrixMode (GL_PROJECTION);
glLoadIdentity();
//transX,transY are for panning around the image in the viewer
float left = (0.f+transX) ;
float right = (w+transX) ;
float bottom = (h-transY);
float top = (0.f-transY) ;
glOrtho(left, right, top, bottom, -1, 1);
... later in paintGL:
glMatrixMode (GL_MODELVIEW);
glLoadIdentity ();
//padx,pady are used to translate the image from the bottom left corner
// to the center of the viewer
float padx,pady;
padx= ((float)width() - _dw.w()*zoomFactor)/2.f; // _dw.w is the width of the texture
pady =((float)height() - _dw.h()*zoomFactor)/2.f ;// _dw.h is the height of the texture
glTranslatef( padx , pady, 0);
//zoomX,zoomY are the position at which the user required a zoom
glTranslatef(-zoomX,-zoomY, 0.f);
glScalef(zoomFactor, zoomFactor,0.f);
glTranslatef(zoomX ,zoomY, 0.f);
Now here is my function to retrieve the openGL coordinates :
QPoint ViewerGL::openGLpos(int x,int y){
GLint viewport[4];
GLdouble modelview[16];
GLdouble projection[16];
GLfloat winX=0, winY=0, winZ=0;
GLdouble posX=0, posY=0, posZ=0;
glGetDoublev( GL_MODELVIEW_MATRIX, modelview );
glGetDoublev( GL_PROJECTION_MATRIX, projection );
glGetIntegerv( GL_VIEWPORT, viewport );
winX = (float)x;
winY = height()- y;
if(winY == 0) winY =1.f;
glReadPixels( x, winY, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &winZ );
gluUnProject( winX, winY, winZ, modelview, projection, viewport, &posX, &posY, &posZ);
return QPoint(posX,posY);
}
So far , here is what I noticed:
The code like this returns always (0,0) and GLU_FALSE is returned from gluUnproject. I read somewhere on a forum that it could be because of the modelview matrix, so I put the identity matrix instead, but,if I do it, I get exactly the coordinates of the mouse in the window...
Before , I dealt with the zoom using the orthographic projection, but I couldn't make it work perfectly, so to make it simpler I decided to retrieve openGL position, and use glTranslatef/glScalef instead .
If I remove all the translating / scaling stuff in the paintGL function, everything is working...but the zoom doesn't work :x)
I'm requesting your help to make this damned zoom to point working, using the gluUnProject solution;)
Aigth , nevermind, I found the solution : I was zeroing out the z in glScalef(x,y,z)
so it made the matrix non-invertible...

Another zoom to point issue

I have a 2D application which is an image viewer.
I have the ability to pan around the image in the window and I have a basic zoom.
Now I'd like to improve the zoom so it zoom to the point under the mouse.
So far I've read everything possible on google and i've come close to something working,
but still can't find something working, here is what I got:
glMatrixMode (GL_PROJECTION);
glLoadIdentity();
// w and h are respectivly the width and height of the window
// newzoom_pos is the point in openGL coordinates where the user requested the zoom
// zoomFactor is between [0.1,10.0] , 0.1 -> 1.0 means downscale, 1.0 -> 10.0 means upscale
// transX and transY are used to pan around the image
float left = (0.f+transX -newzoom_pos.x())/zoomFactor +newzoom_pos.x();
float right = (w+transX -newzoom_pos.x())/zoomFactor +newzoom_pos.x();
float bottom = (h-transY-newzoom_pos.y())/zoomFactor +newzoom_pos.y();
float top = (0.f-transY -newzoom_pos.y())/zoomFactor +newzoom_pos.y();
glOrtho(left, right, top, bottom, -1, 1);
glMatrixMode (GL_MODELVIEW);
glLoadIdentity ();
It almost works, but it is not okay, it doesn't zoom exactly to the requested point and when the image is small and does not fit yet in the viewer entirely ( there's black around), well it is messy and does not work...
btw, here is the code when the user zoom-in, in the mouse wheel event handler:
zoomFactor+=0.1;
QPoint oglpos = openGLpos(new_zoomPoint.x(), new_zoomPoint.y());
this->newzoom_pos = oglpos;
the openGLpos function is the following:
QPoint ViewerGL::openGLpos(int x,int y){
GLint viewport[4];
GLdouble modelview[16];
GLdouble projection[16];
GLfloat winX=0, winY=0, winZ=0;
GLdouble posX=0, posY=0, posZ=0;
glGetDoublev( GL_MODELVIEW_MATRIX, modelview );
glGetDoublev( GL_PROJECTION_MATRIX, projection );
glGetIntegerv( GL_VIEWPORT, viewport );
winX = (float)x;
winY = viewport[3]- y;
if(winY == 0) winY =1.f;
glReadPixels( x, winY, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &winZ );
GLint b=gluUnProject( winX, winY, winZ, modelview, projection, viewport, &posX, &posY, &posZ);
if(b==GLU_FALSE) cout << "failed unprojection" << endl;
return QPoint(posX,posY);
}
Could anybody help me through this?

opengl mouse coordinate to world coordinate

I need to detect mouse motion and draw a ball at the mouse's position. I need the ball to be in world coordinate. So I'm trying to use glUnProject for this task and seems I'm not succeeding till now. This is my motionFunc:
void motionFunc( int x, int y)
{
GLint viewport[4];
GLdouble modelview[16];
GLdouble projection[16];
GLfloat winX, winY, winZ;
GLdouble posX, posY, posZ;
glGetDoublev( GL_MODELVIEW_MATRIX, modelview );
glGetDoublev( GL_PROJECTION_MATRIX, projection );
glGetIntegerv( GL_VIEWPORT, viewport );
winX = (float)x;
winY = (float)viewport[3] - (float)y;
glReadPixels( x, int(winY), 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &winZ );
gluUnProject( winX, winY, winZ, modelview, projection, viewport, &posX, &posY, &posZ); //printf("winz: %f posz: %f\n",winZ,posZ);
Ball.x=posX;
Ball.y=posY;
Ball.z=posZ;
//printf("%f %f %f\n",Ball.x,Ball.y,posZ);
glutPostRedisplay();
}
now, I added a breakpoint on glutPostRedisplay. Turns out when I click-drag mouse, the Ball's coordinates(Ball.x,Ball.y,Ball.z) are something like:
(Ball).x -727.175354
(Ball).y 407.310242
(Ball).z -865.000610
why is the z coordinate so far? My camera is at z=+135. And other objects in my model are like, at z= -3 to +3. I need the ball's z coordinate to be in the same range.
now, what exactly is winZ? Here, I checked it always turns out to be 1.00. I tried to hardcode winZ and I found at winZ=0.85, the ball seems like to be always under the mouse(I can drag the ball with my mouse and the ball is always under the pointer). But then the Ball's coordinates are like:
(Ball).x -4.67813921
(Ball).y 2.57806134
(Ball).z 128.370895
which is so close to the camera but x and y coordinates are not good for me. they always come out to be near the origin. which is not what I want. My other objects' x and y coordinates have a wider range.
Finally, my question is, what is the correct way to do glUnproject or something of the same sort?
A 2D mouse coordinate cannot unambiguously unmapped to a 3D world coordinate. The 2D coordinate corresponds with a line in 3D space. The winz influences which point on this line is returned. When you use 0.0 for winz you will get the point at the near clipping plane. When you use 1.0 you will get the point at the far clipping plane.
If you are using a depth buffer you could retrieve the value from the depth buffer using the glReadPixels function and use that as winz. Here a piece of code from a toy project of mine in Java
FloatBuffer depth = BufferUtils.createFloatBuffer(1);
glReadPixels(mouse_x, mouse_y, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, depth);
depth.rewind();
FloatBuffer farPos = BufferUtils.createFloatBuffer(3);
GLU.gluUnProject(mouse_x, mouse_y, depth.get(),
mainContext.getModelviewMatrix(),
mainContext.getProjectionMatrix(), viewport, farPos);
Most is the same in C/C++ except for the weird NIO buffers.