Implementing Ray Picking

by

If you can, do the picking on the CPU by calculating a ray from the eye through the mouse pointer and intersect it with your models.

If this isn’t an option I would go with some type of ID rendering. Assign each object you want to pick a unique color, render the objects with these colors and finally read out the color from the framebuffer under the mouse pointer.

EDIT: If the question is how to construct the ray from the mouse coordinates you need the following: a projection matrix P and the camera transform C. If the coordinates of the mouse pointer is (x, y) and the size of the viewport is (width, height) one position in clip space along the ray is:

mouse_clip = [
  float(x) * 2 / float(width) - 1,
  1 - float(y) * 2 / float(height),
  0,
  1]

(Notice that I flipped the y-axis since often the origin of the mouse coordinates are in the upper left corner)

The following is also true:

mouse_clip = P * C * mouse_worldspace

Which gives:

mouse_worldspace = inverse(C) * inverse(P) * mouse_clip

We now have:

p = C.position(); //origin of camera in worldspace
n = normalize(mouse_worldspace - p); //unit vector from p through mouse pos in worldspace

More Related Contents:

  1. Calculate distance between 2 GPS coordinates
  2. Generate a random point within a circle (uniformly)
  3. How to determine if a list of polygon points are in clockwise order?
  4. A simple algorithm for polygon intersection
  5. Turning a cylinder into a sphere without pinching at the poles
  6. How to calculate the volume of a 3D mesh object the surface of which is made up triangles
  7. Cone to box collision
  8. How do I calculate the normal vector of a line segment? [closed]
  9. Calculating area enclosed by arbitrary polygon on Earth’s surface
  10. How do I combine complex polygons?
  11. Using atan2 to find angle between two vectors
  12. correcting fisheye distortion programmatically
  13. Signed angle between two 3D vectors with same origin within the same plane
  14. How do I detect intersections between a circle and any other circle in the same plane?
  15. Projecting 3D points to 2D plane [closed]
  16. How to distribute points evenly on the surface of hyperspheres in higher dimensions?
  17. How to calculate Tangent and Binormal?
  18. Perpendicular on a line from a given point
  19. Finding the coordinates of points from distance matrix
  20. how map 2d grid points (x,y) onto sphere as 3d points (x,y,z)
  21. 3D coordinates on a sphere to Latitude and Longitude
  22. Calculate rotated rectangle size from known bounding box coordinates
  23. How to best approximate a geometrical arc with a Bezier curve?
  24. Get bounds of rotated rectangle
  25. OpenGL Math – Projecting Screen space to World space coords
  26. How to convert latitude or longitude to meters?
  27. Drawing Sphere in OpenGL without using gluSphere()?
  28. Calculating the angle between two lines without having to calculate the slope? (Java)
  29. Handling errors in math functions
  30. The algorithm to find the point of intersection of two 3D line segment

Leave a Comment