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

Jad Killian m.hasani at outlook.com
Wed Aug 15 00:09:45 PDT 2018

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:

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?


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