To zoom into the mouse position I was using:
glTranslatef(current.ScalePoint.x,current.ScalePoint.y,0);
glScalef(current.ScaleFactor,current.ScaleFactor,current.ScaleFactor);
glTranslatef(-current.ScalePoint.x,-current.ScalePoint.y,0);
so basically I translate to the new origin (the mouse position) then scale by the current scale factor, then translate back.
This kind of works generally well, but it can be a bit buggy. My issue is really that now I'v introduced a camera offset so I tried something like this:
glTranslatef(controls.MainGlFrame.GetCameraX(),
controls.MainGlFrame.GetCameraY(),0);
glTranslatef(current.ScalePoint.x,current.ScalePoint.y,0);
glScalef(current.ScaleFactor,current.ScaleFactor,current.ScaleFactor);
glTranslatef(-current.ScalePoint.x,-current.ScalePoint.y,0);
But this did not work as I intended. How could I properly do this knowing that:
The matrix's origin is the top left corner (0,0)
1 unit == 1 pixel
My scale factor
My camera's position relative to how far it is from (0,0) (the origin) and
the mouse position (screen to client).
Thanks
It is more safe (and also for code reuse) to un-project the mouse coordinate point (from window coordinates to model coordinates) first even though you know how projection is done.
You can use the following function:
void unProject(int ix, int iy, int &ox, int &oy)
{
// First, ensure that your OpenGL context is the selected one
GLint viewport[4];
GLdouble projection[16];
GLdouble modelview[16];
glGetIntegerv(GL_VIEWPORT, viewport);
glGetDoublev(GL_PROJECTION_MATRIX, projection);
glGetDoublev(GL_MODELVIEW_MATRIX, modelview);
int xx = ix;
int yy = viewport[3] - iy;
GLdouble x, y, z;
gluUnProject(xx, yy, 0 /*check*/, modelview, projection, viewport, &x, &y, &z);
ox = (int) x;
oy = (int) y;
}
The output then is the correct point on the model coordinates for your zooming
Related
I am trying to write a OpenGL application where an object is fired from a point( In this case 0,0,0 ) and flies to the x,y position of the mouse. This is the system I am currently using:
Create an object at the point 0,0,0
Get the x,y position of the mouse.
Convert the mouse to 3d co-ordinates.
Get a line between the start point and (mouse-X,m mouse-Y, far plane ) where the far plane is set to 4,294,967,295.
Use the parametric line equation to move the object along this line.
The problem is that the x,y on the far plane does not seem to correspond to the x,y mouse position so the object flies on the wrong line. I am pretty sure that the line/para,etric equation part is working ok, but the conversion between 2d and 3-d space may not. Here is what I have tried:
First convert to window co-ordinates:
POINT *mouse = new POINT();
mouse->x = mousePosition3D.x;
mouse->y = mousePosition3D.y;
ScreenToClient( windowHandle, mouse );
Then to 3-d co-ordinates
GLint viewport[4];
GLdouble modelview[16];
GLdouble projection[16];
GLfloat winX, winY, winZ;
GLdouble posX, posY, posZ;
OBJ_TriCo returnMe;
//All matrices in use need to be retrived
glGetDoublev( GL_MODELVIEW_MATRIX, modelview );
glGetDoublev( GL_PROJECTION_MATRIX, projection );
glGetIntegerv( GL_VIEWPORT, viewport );
//Set the co-ords to lookup, based on the mouse position passed to this
winX = (float)x;
winY = (float)viewport[3] - (float)y;
//Set the z to 0.99, for some reason the object will fly totally incorrectly otherwise
winZ = 0.999; //Get a point on the bettween FAR and NEAR-Clipping planes
//Convert the co-ords
gluUnProject( winX, winY, winZ, modelview, projection, viewport, &posX, &posY, &posZ);
//Return there values
returnMe.x = posX;
returnMe.y = posY;
returnMe.z = posZ;
return returnMe;
I am wondering has any body do anything similar to this or what maths i may need to do to get the objects to fly along the correct line.
You can calculate world space ray direction from screen-space coordinates (normalized to range [-1, 1]) like this:
vec4f r = projection_to_view_matrix * vec4f(screen_x, screen_y, 0, 1);
vec3f rdir = transpose(world_to_view_rotation_matrix) * vec3f(r.x, r.y, r.z);
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...
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.
I am trying to get the coordinates that the user clicks on on the plane y=0
I'm doing this by unprojecting the mouse coordinates to get the world coordinates on the near and far planes then using linear interpolation to find the coordinates on the plane but it's not giving me the correct coordinates.
My unprojection code:
int viewport[4];
double modelview[16];
double projection[16];
glGetIntegerv(GL_VIEWPORT, viewport);
glGetDoublev(GL_MODELVIEW_MATRIX, modelview);
glGetDoublev(GL_PROJECTION_MATRIX, projection);
double x, y, z;
//x_ and y_ are the x and y coordinates of the mouse
gluUnProject(x_, viewport[3] - y_, 0.0, modelview, projection, viewport, &x, &y, &z);
near.x = x;
near.y = y;
near.z = z;
gluUnProject(x_, viewport[3] - y_, 100.0, modelview, projection, viewport, &x, &y, &z);
far.x = x;
far.y = y;
far.z = z;
float t = -near.y / (far.y - near.y);
target_.y = 0.0f;
target_.x = near.x - t * (far.x - near.x);
target_.z = near.z - t * (far.z - near.z);
std::cout << target_ << std::endl;
but this always outputs:
x: a value between +-1 which seems to have a correlation to the click position just normalized even though I'm not normalizing anywhere
y: 0
z: -2
which I can't make sense of
Edit
Sorry, the error was me doing the unprojections before my transformations which you can't tell from the above code. I have solved it now.
Sorry, the error was me doing the unprojections before my transformations which you can't tell from the above code.
I am trying to implement an arcball interface and it seems that after rotation of 90 degrees the model stops rotating in that specific direction, I suspect that there is a problem with mapping clicks on the screen to the arcball, but it could be wrong math and/or wrong transformations accumulation, any help would be appreciated, here is the relevant code for the problem, when operating on vectors the ^ operator represents cross product, and * operator represents inner product
void mouseButton(int button,int state,int x,int y){
if(state==GLUT_DOWN){
GLdouble xx,yy,zz;
GLdouble modelMatrix[16];
glGetDoublev(GL_MODELVIEW_MATRIX,modelMatrix);
GLdouble projMatrix[16];
glGetDoublev(GL_PROJECTION_MATRIX,projMatrix);
int viewport[4];
glGetIntegerv(GL_VIEWPORT,viewport);
gluUnProject(x,height-y-1,0.755
,modelMatrix,projMatrix,viewport,&xx,&yy,&zz);
arcBall_begin(xx,yy);
}
}
void mouseMotion(int x,int y){
GLdouble xx,yy,zz;
GLdouble modelMatrix[16];
glGetDoublev(GL_MODELVIEW_MATRIX,modelMatrix);
GLdouble projMatrix[16];
glGetDoublev(GL_PROJECTION_MATRIX,projMatrix);
int viewport[4];
glGetIntegerv(GL_VIEWPORT,viewport);
gluUnProject(x,height-y-1,0.755
,modelMatrix,projMatrix,viewport,&xx,&yy,&zz);
arcBall_drag(xx,yy);
}
void arcBall_begin(GLdouble x,GLdouble y){
if(sqrt((x*x)+(y*y))>radius)
begin = vec(x,y,0);
else
begin = vec(x,y,sqrt((radius*radius)-(x*x)-(y*y)));
begin = begin.unit();
glGetDoublev(GL_MODELVIEW_MATRIX,mm);
}
void arcBall_drag(GLdouble x,GLdouble y){
if(sqrt((x*x)+(y*y))>radius)
end = vec(x,y,0);
else
end = vec(x,y,sqrt((radius*radius)-(x*x)-(y*y)));
end = end.unit();
rotationAxis = begin^end;
rotationAxis = rotationAxis.unit();
angle = -2*acos(begin*end);
angle = angle * (float(180)/float(PI));
}
float arcBall_rotate(){
if(angle!=0.0){
glLoadMatrixd(mm);
glRotatef(angle,rotationAxis.x,rotationAxis.y,rotationAxis.z);
angle = 0.0;
}
return angle;
}
Remember that in OpenGL pixel coordinates are (0,0) in the upper left corner of the screen, so when you want to map you have to reverse the y axis to map the coordinates to a sphere.