Houdini tip | CAMERA AUTO FOCUS

Hello,
in this post I will show a quick way of adding auto-focus support to Houdini camera. By setting a target, following couple lines of code will determine correct distance to focus on. This approach will work for any renderer.

 

The setup is pretty simple, we need to add two parameters to our camera: target which is a string pointing to OBJ node we want to focus on and dist parameter which will contain following Python expression.

	# our cam object
	cam = hou.pwd()
	# get 4×4 matrix representing transformation of our camera
	cam_xform = cam.worldTransform()
	# get position of our camera
	cam_pos = hou.Vector4(0, 0, 0, 1) * cam_xform
	cam_pos = hou.Vector3(cam_pos)
	# view axis of our camera
	view_axis = hou.Vector4(0, 0, -1, 0) * cam_xform
	# get target path
	target_path = cam.evalParm("target")
	# get target object
	target_node = hou.node(target_path)
	# get target's transformation
	target_xform = target_node.worldTransform()
	# get target's position
	target_pos = hou.Vector4(0, 0, 0, 1) * target_xform
	# cast from Vector4 to Vector3
	view_axis = hou.Vector3(view_axis)
	target_pos = hou.Vector3(target_pos)
	# normalize our view axis
	view_axis = view_axis.normalized()
	# get a vector pointing from camera to target
	cam_target = hou.Vector3( target_pos – cam_pos )
	# project cam_target vector on view_axis, because view_axis is normalized, this results in length of our projected vector, what represents focus distance in our case
	focus_dist = cam_target.dot(view_axis)
	return focus_dist

view raw

parm.py

hosted with ❤ by GitHub

 

After that we can link Focal Distance parameter to our dist. Feel free to drop a helper Null object for visualizing focus plane 🙂

 

You can download project file here.