[osg-users] How to create a 3D ray from cursor position?

[Jad Killian]

Given a 2D cursor position from a mouse event, how do I compute a 3D ray into the scene?

This is my attempt so far but it's not giving sensible results:


Code:
float width = viewer->getCamera()->getViewport()->width();
float height = viewer->getCamera()->getViewport()->width();

float x = (2.0f * ea.getX()) / width - 1.0f;
float y = 1.0f - (2.0f * ea.getY()) / height;
float z = 1.0f;

osg::Vec3 ray_nds(x, y, z);

osg::Vec4 ray_clip(ray_nds.x(), ray_nds.y(), -1.0, 1.0);

osg::Matrixd proj_inv = viewer->getCamera()->getProjectionMatrix();
proj_inv = proj_inv.inverse(proj_inv);

osg::Vec4 ray_eye = proj_inv * ray_clip;
ray_eye.z() = -1.0;
ray_eye.w() = 0.0;

osg::Vec4 ray_wor4 = viewer->getCamera()->getInverseViewMatrix() * ray_eye;
osg::Vec3 ray_wor(ray_wor4.x(), ray_wor4.y(), ray_wor4.z());



P.S: I need such a ray so I can drag a 3D object around the scene like this:
new_position = camera_position + ray_direction * depth_value;
Or is there an easier way to accomplish this?

Thanks
[/code]

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Read this topic online here:
http://forum.openscenegraph.org/viewtopic.php?p=74349#74349

[Werner Modenbach]

Hi Jad,

this is how I do it:

double x = mEv->x();  double y = mEv->y();  double w =
view->getGraphicsWidth();  double h = view->getGraphicsHeight(); x =
x/w; y = y/h; // Normalize to range -1.0 - 1.0 x = (2.0 * _x) - 1.0; y =
-((2.0 * _y) - 1.0); // -1.0 is at bottom!!!  osg::Matrix MVPW(
view->getCamera()->getViewMatrix() *
view->getCamera()->getProjectionMatrix()); osg::Matrixd inverseMVPW =
osg::Matrixd::inverse(MVPW); osg::Vec3 near_point =
osg::Vec3(_x,_y,-1.0f) * inverseMVPW; osg::Vec3 far_point =
osg::Vec3(_x,_y, 1.0f) * inverseMVPW;

- Werner -

Post by Jad Killian
Given a 2D cursor position from a mouse event, how do I compute a 3D ray into the scene?
float width = viewer->getCamera()->getViewport()->width();
float height = viewer->getCamera()->getViewport()->width();
float x = (2.0f * ea.getX()) / width - 1.0f;
float y = 1.0f - (2.0f * ea.getY()) / height;
float z = 1.0f;
osg::Vec3 ray_nds(x, y, z);
osg::Vec4 ray_clip(ray_nds.x(), ray_nds.y(), -1.0, 1.0);
osg::Matrixd proj_inv = viewer->getCamera()->getProjectionMatrix();
proj_inv = proj_inv.inverse(proj_inv);
osg::Vec4 ray_eye = proj_inv * ray_clip;
ray_eye.z() = -1.0;
ray_eye.w() = 0.0;
osg::Vec4 ray_wor4 = viewer->getCamera()->getInverseViewMatrix() * ray_eye;
osg::Vec3 ray_wor(ray_wor4.x(), ray_wor4.y(), ray_wor4.z());
new_position = camera_position + ray_direction * depth_value;
Or is there an easier way to accomplish this?
Thanks
[/code]
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http://forum.openscenegraph.org/viewtopic.php?p=74349#74349
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