Bzw 2.0 3d transformations howto

Changes

In version 1.10.8 and older bzflag, objects position, rotation and size where defined by, logically, position, rotation and size keywords. When 2.0 introduced 3d rotation, this had to change. Position and rotation have been obsoleted by their superiors, shift and spin. Size could be replaced with scale, but there is no need for that on traditional objects (mesh are a bit different).

box
	position 50 100 0
	size 20 20 5
	rotation 45
end

can now be written:

meshbox
	size 20 20 5
	spin 45 0 0 1
	shift 50 100 0
end

All keywords are order-specific. If you do shift before spin, it will still spin the object around 0 0 0, moving it somewhere else than what it was ment to.

Spin

Spin can be used to rotate object around a specific axis. First value after spin-keyword is rotation in degrees. Axis is a line, defined by two points. Other one is always 0 0 0, other one is defined by the three values after rotation. It is usually simple to think rotation around the standard axises. They are defined as:

You can spin around any axis, diagonal or anything. Anyway, all rotations can be made by rotating around standard axises, and they are usually most simple to think of.

Shifting

Shifting means moving the object. It is used in same manner as old position-keyword. Without position-keyword, object is placed around 0 0 0. When shift moves it from origo, coordinates are just like with position. However, shift is repeatable, and sequent moves will use last point as origo.

Shearing

Shearing is, as ibot knows, "a deformation of an object in which parallel planes remain parallel but are shifted in a direction parallel to themselves." If you don't understand, look at the image below. In next example, we use shear to make an escalator with nice ends.

physics
	name escalator
	linear 15 0 15
end
meshbox
	size 10 10 100
	shear 2 0 0
	phydrv escalator
end

The three values after shear-keyword define a vector. Vectors lenght represents change per Z-axis unit. If you have 10 units high meshbox, and shear it by 1 0 0, top will move 10 * 1 away from the bottom in X-axis direction.

meshbox
	size 10 10 10
	shear 1 0 0
end

Would be like:

Scaling

Scale is simple. It scales object by specific amount. It is useful mostly with groups and meshes. Attention must be paid to order - If you shift before scale, scale will scale the distance from origo too. Example:

define MyBox
	meshbox  # Really complicated box - we don't want to type this more than once
		size 5 5 10 
		# We could have phydrv, matref etc. here.
	end
enddef

group MyBox
	scale 2 2 2 # Double the size, 10 10 20
	shift -50 0 0 # Our box was around 0 0 0, so this translates to position -50 0 0
end

group MyBox
	# No shift - position is 0 0 0
	# No scale - defined size ( 5 5 10 )
end

group MyBox
	scale 0.5 0.5 0.5 # Half the size, 2.5 2.5 5
	shift 50 0 0 # Position 50 0 0
end # Nice line of boxes is ready.

group MyBox
	shift 0 50 0 # Notice order
	scale 2 2 2 # This goes much farther than others, because 50 * 2 = 100
end

©Petteri Aimonen 2005