Away3D 3.6.0: TargetCamera3D v2 – Fixed axes
View/download the Source files for this tutorial here, and view the main swf here. The tutorial also assumes you have a working build of Away3D 3.6.0.
Writing that last tutorial was enough to pique my old friend Jon‘s interest, who has provided me with the next bit of info I needed in order to improve my target cam. The last tutorial behaves in the following way:
Position 2 is a 45 degree rotation around the X axis, which in the above diagram would be facing directly towards us. In rotation jargon, this is referred to as a change in “pitch”. You can move the camera to this position yourself by opening this example, clicking the Flash to gain focus and holding the W key until you’re halfway towards the topmost point of the sphere. What we’re actually doing here is rotating the camera’s internal coordinate space around it’s 0,0,0 point, positioned in line with the centre of the sphere. If you now hold the A key to rotate left around the Y axis (referred to in the jargon as “yaw”), you are rotated around the Y axis you see in position 2, not the Y axis in position 1. This is fine as it’s logically consistent, though it’s apparently not what you would expect from camera functionality in most 3D editor programs. As with the functionality in the tutorial that inspired me to write these tutorials, the camera is expected to behave as follows:
This behaviour is a result of the fact that the X,Y and Z axes are fixed, so holding the A key will result in a leftward rotation around the fixed Y axis; the closer you are to the topmost point of the target object, the narrower your orbit. If you have a play with the latest version below, you can see this is now working.
So how was this achieved? Our main app class remains unchanged from the previous tutorial, but we’ve overridden the pitch(), yaw() and roll() methods the TargetCamera3D2 class inherits from Object3D:
private var _pitch:Number = 0;
private var _yaw:Number = 0;
private var _roll:Number = 0;
override public function pitch(angle:Number):void
{
_pitch += angle;
transform = buildMatrix();
}
override public function yaw(angle:Number):void
{
_yaw += angle;
transform = buildMatrix();
}
override public function roll(angle:Number):void
{
_roll += angle;
transform = buildMatrix();
}
Our new methods update the _pitch, _yaw and _roll values, which are used to store absolute values for our rotation along the 3 axes. When these values are updated we update the object’s transform by calling the following method:
private function buildMatrix():Matrix3D
{
var matrix:Matrix3D = new Matrix3D();
matrix.appendRotation( _pitch, Vector3D.X_AXIS );
matrix.appendRotation( _yaw, Vector3D.Y_AXIS );
matrix.appendRotation( _roll, Vector3D.Z_AXIS );
matrix.appendTranslation(position.x, position.y, position.z);
return matrix;
}
Instead of incrementally updating our object’s rotation using the current position of the axes as per the first diagram, the buildMatrix() method starts from scratch each time with a new Matrix3D, applies each rotation in turn and finally updates it’s 0,0,0 position to align with the centre of the target object. This approach ensures that the object’s rotations happen relative to fixed X,Y,Z axes which correlate with the world’s coordinate space. And there you have it. Thanks Jon!
