I try to set a good distance for the full view of a particles disk and in the same time have a valid line scale which represents the current value for the scale of the disk as a function of zooming with mouse.
The scene has the following parameters :
w_width = 600;
w_height = 600;
g_nearPlane = 0.1f;
g_farPlane = 1000.0f;
I do graphics initialization of 3D scene with the following code sample :
// Reset line scale value
lineScaleValue = 100.0f;
// Initialize View
glViewport(0, 0, w_width, w_height);
glMatrixMode(GL_PROJECTION); // Select The Projection Matrix
glLoadIdentity(); // Reset The Projection Matrix
// Perspective with angle set to 45 degrees
gluPerspective(45.0f, (float) w_width / w_height, g_nearPlane, g_farPlane);
glMatrixMode(GL_MODELVIEW); // Select The Modelview Matrix
glLoadIdentity(); // Reset The Modelview Matrixi
gluLookAt (0.0, 0.0, 3, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
glScalef(0.03f, 0.03f, 0.03f);
The above values for gluLookAt and glScalef have been chosen approximately, i.e manually without having an accurate calculation.
I would like to have only a full view for the disk (white particles).
For this, I know the maximum and minimum in the (x,y) plane of the disk :
-25 < x <25 and -22 < y < 22.
from this post set z good distance, I could do (with Fov/2 = 45 degrees) :
z_distance = 25*tan(pi/4) + dist = 50
with dist = 25 to be in front of the disk.
So can I do directly in my sample code (instead of
gluLookAt (0.0, 0.0, 3, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
glScalef(0.03f, 0.03f, 0.03f);
) :
gluLookAt (0.0, 0.0, 50, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
?
Thanks
The optimal distance can be calculated by the formula given in the post you already linked (not sure how you came to the z_distance equation?):
visible_range = 2 * tan(fov/2) * distance
In your case:
visible_range = 50 (-25 to 25)
=>
50 = 2 * tan(fov/2) * distance
distance = 50 / (2 * tan(fov/2)) = 25 / tan(fov/2)
Since the half field of view is in you're case 45° and tan(45°) = 1, the optimal solution is
distance = 25