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POopengl select sphere with mouse
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  1. POopengl select sphere with mouse
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    copied!<p>I have a number of spheres in 3d space which the user should be able to select with a mouse click. Now I've seen some examples around using gluUnProject so I gave it a shot. So I have (please correct me every step of the way if I'm wrong because I'm not 100% sure of any part of it):</p> <pre><code>def compute_pos(x, y, z): ''' Compute the 3d opengl coordinates for 3 coordinates. @param x,y: coordinates from canvas taken with mouse position @param z: coordinate for z-axis @return; (gl_x, gl_y, gl_z) tuple corresponding to coordinates in OpenGL context ''' modelview = numpy.matrix(glGetDoublev(GL_MODELVIEW_MATRIX)) projection = numpy.matrix(glGetDoublev(GL_PROJECTION_MATRIX)) viewport = glGetIntegerv(GL_VIEWPORT) winX = float(x) winY = float(viewport[3] - float(y)) winZ = z return gluUnProject(winX, winY, winZ, modelview, projection, viewport) </code></pre> <p>Then, having the x and y of a mouse click and the position of the center of the sphere:</p> <pre><code>def is_picking(x, y, point): ray_start = compute_pos(x, y, -1) ray_end = compute_pos(x, y, 1) d = _compute_2d_distance( (ray_start[0], ray_start[1]), (ray_end[0], ray_end[1]), (point[0], point[1])) if d &gt; CUBE_SIZE: return False d = _compute_2d_distance( (ray_start[0], ray_start[2]), (ray_end[0], ray_end[2]), (point[0], point[2])) if d &gt; CUBE_SIZE: return False d = _compute_2d_distance( (ray_start[1], ray_start[2]), (ray_end[1], ray_end[2]), (point[1], point[2])) if d &gt; CUBE_SIZE: return False return True </code></pre> <p>So because my 3d geometry is not good at all, I compute two points as a ray start and end point, the go into 2d 3 times eliminating one dimension at a time and compute the distance there between my line and the center of the sphere. If any of those distances are bigger than my sphere ray the it's not clicked. I think the formula for the distance is correct but just in case:</p> <pre><code>def _compute_2d_distance(p1, p2, target): ''' Compute the distance between the line defined by two points and a target point. @param p1: first point that defines the line @param p2: second point that defines the line @param target: the point to which distance needs to be computed @return: distance from point to line ''' if p2[0] != p1[0]: if p2[1] == p1[1]: return abs(p2[0] - p1[0]) a = (p2[1] - p1[1])/(p2[0] - p1[0]) b = -1 c = p1[1] + p1[0] * (p2[1] - p1[1]) / (p2[0] - p1[0]) d = abs(a * target[0] + b * target[1] + c) / math.sqrt(a * a + b * b) return d if p2[0] == p1[0]: d = abs(p2[1] - p1[1]) return d return None </code></pre> <p>Now the code seems to work fine in the start position. But after you use to mouse and rotate the screen even for a little bit, nothing works as expected anymore.</p>
 

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