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+--- Thread: Opengl picking problem (zip file) (/thread-1961.html)
Opengl picking problem (zip file) - papillon68 - Jan 4, 2009 02:40 AM
I'm trying to get done with picking objects, but it doesn't work (I'm getting always a hit=TRUE value). I'm using the projected ray+sphere intersection tecnique but there is something wrong in the code.
I am providing the complete, commented project zip file (it's very simple and "clean" since it contains just the test code): http://rapidshare.com/files/179621768/experimenting.zip.html
I'd really appreciate if someone might help.
I'm basically calling two function, one to generate the ray:
// this is the function that creates the ray from x and y mouse position
void wuRayFromMousePos( int x, int y )
{
float value_fov = 0.7853; //45 degrees converted to radians
float value_aspect = 320.0/480.0; //the aspect ratio for a 320 x 480 window, in my case
float half_window_width = 160.0;
float half_window_height = 240.0;
float modifier_x; //mathematical handling of the difference between
float modifier_y; //mouse position and the 'center' of the window
float point[3]; //the untransformed ray
float point_dist = 10.0; //it'll be put this far on the Z plane
float camera_origin[3]; //this is where the camera sits, in 3dspace
float point_xformed[3]; //this is the transformed point
GLfloat pulledMatrix[16]; //pulledMatrix is the OpenGL matrix.
float final_point[3];
//This is where the mouse position is turned into a mathematical
//'relative' of 3d space. The conversion to an actual point
modifier_x = tan( value_fov * 0.5 )
* (( 1.0 - x / half_window_width ) * ( value_aspect ) );
modifier_y = tan( value_fov * 0.5 )
* -( 1.0 - y / half_window_height );
//These 3 take our modifier_x/y values and our 'casting' distance
//to throw out a point in space that lies on the point_dist plane.
point[0] = modifier_x * point_dist;
point[1] = modifier_y * point_dist;
point[2] = point_dist;
//openGL call to grab our MODELVIEW_MATRIX -
glGetFloatv(GL_MODELVIEW_MATRIX, pulledMatrix);
//Invert matrix results.
//First, to get the camera_origin, we transform the 12, 13, 14
//slots of our pulledMatrix - this gets us the actual viewing
//position we are 'sitting' at when the function is called
camera_origin[0] = -(pulledMatrix[0] * pulledMatrix[12] + pulledMatrix[1] * pulledMatrix[13] + pulledMatrix[2] * pulledMatrix[14]);
camera_origin[1] = -(pulledMatrix[4] * pulledMatrix[12] + pulledMatrix[5] * pulledMatrix[13] + pulledMatrix[6] * pulledMatrix[14]);
camera_origin[2] = -(pulledMatrix[8] * pulledMatrix[12] + pulledMatrix[9] * pulledMatrix[13] + pulledMatrix[10] * pulledMatrix[14]);
//Second, we transform the position we generated earlier - the '3d'
//mouse position - by our viewing matrix.
point_xformed[0] = -(pulledMatrix[0] * point[0] + pulledMatrix[1] * point[1] +
pulledMatrix[2] * point[2]);
point_xformed[1] = -( pulledMatrix[4] * point[0] + pulledMatrix[5] * point[1] + pulledMatrix[6] * point[2]);
point_xformed[2] = -(pulledMatrix[8] * point[0] + pulledMatrix[9] * point[1] +
pulledMatrix[10] * point[2]);
final_point[0] = point_xformed[0] + camera_origin[0];
final_point[1] = point_xformed[1] + camera_origin[1];
final_point[2] = point_xformed[2] + camera_origin[2];
vector3_t ray_dir;
ray_dir.x = final_point[0];
ray_dir.y = final_point[1];
ray_dir.z = final_point[2];
vector3_t ray_orig;
ray_orig.x = camera_origin[0];
ray_orig.y = camera_origin[1];
ray_orig.z = camera_origin[2];
float SphereRadius = 0.5;
GLboolean isHit = intersect_ray_sphere(ray_orig, ray_dir, SphereRadius);
}
The I'm doing sphere intersection:
GLboolean intersect_ray_sphere( vector3_t ray_orig, vector3_t ray_dir, GLfloat sphere_radius )
{
vector3_t sphereCenter;
sphereCenter.x=sphereCenter.y=sphereCenter.z = -7;
vector3_t v;
v = ray_orig - sphereCenter;
GLfloat b = 2.0f * scalar_product( ray_dir, v );
GLfloat c = scalar_product( v, v ) - sphere_radius*sphere_radius;
GLfloat d = b * b - 4.0f * c;
if ( d < 0.0f ) return GL_FALSE;
d = sqrtf(d);
GLfloat s0 = (d-b)*0.5f;
GLfloat s1 = (-d-b)*0.5f;
if ( s0 >=0.0f || s1 >= 0.0f ) return GL_TRUE;
return GL_FALSE;
}
Finally, this is the code in the Draw routine:
void Draw()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
renderSimpleTestQuad(); // this is drawn at 0,0,-5
wuRayFromMousePos(mouseX, mouseY);
}
Opengl picking problem (zip file) - chronus - Mar 1, 2009 08:49 PM
hey, did you ever figure out a solution to your opengl picking problem?