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-- virtual trackball implementation
package Trackball is
type Quaternion is array (0 .. 3) of Float;
type Matrix is array (0 .. 3, 0 .. 3) of aliased Float;
type Vector is array (0 .. 2) of Float;
procedure Trackball (Q : out Quaternion;
P1x, P1y, P2x, P2y : Float);
-- Pass the x and y coordinates of the last and current positions of
-- the mouse, scaled so they are from (-1.0 ... 1.0).
-- The resulting rotation is returned as a quaternion rotation in the
-- first paramater.
procedure Add_Quats (Q1, Q2 : Quaternion;
Dest : out Quaternion);
-- Given two quaternions, add them together to get a third quaternion.
-- Adding quaternions to get a compound rotation is analagous to adding
-- translations to get a compound translation. When incrementally adding
-- rotations, the first argument here should be the new rotation, the
-- second and third the total rotation (which will be over-written with
-- the resulting new total rotation).
procedure Build_Rotmatrix (M : out Matrix; Q : Quaternion);
-- A useful function, builds a rotation matrix in Matrix based on given
-- quaternion.
procedure Axis_To_Quat (A : Vector; Phi : Float; Q : out Quaternion);
-- This function computes a quaternion based on an axis (defined by the
-- given vector) and an angle about which to rotate. The angle is
-- expressed in radians. The result is put into the third argument.
end Trackball;
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