Create locator on surface of any visible mesh object

snap_loc_to_geo.py

import maya.cmds as cmds
import pymel.core as pm
import maya.api.OpenMaya as om
import maya.api.OpenMayaUI as omui

class SamsClass():
	
	def __init__(self):
		pass

	def pointLocator(self, *args):
		'''
		pass in the name of a mesh, or just select one
		'''
		
		self.meshSelection = cmds.ls( type='mesh' )
		self.Context='Context'
		
		# clear any previous contexts
		if cmds.draggerContext(Context, exists=True):
			print 'deleting'
			cmds.deleteUI(Context)
		cmds.setToolTo('selectSuperContext')
			
		# parse args and selection
		mesh = None
		self.geo = None
	
		# create context and set tool
		cmds.draggerContext( self.Context, pressCommand=self.onPress, dragCommand=self.onDrag, name=Context, cursor='crossHair')
		cmds.setToolTo(Context)


	def onPress(self):
		vpX, vpY, _ = cmds.draggerContext( self.Context, query=True, anchorPoint=True)
		pos = om.MPoint()
		direction = om.MVector()
		omui.M3dView().active3dView().viewToWorld(int(vpX)	 , int(vpY), pos, direction)
		
		for mesh in self.meshSelection:
			selectionList = om.MSelectionList()
			selectionList.add(mesh)
			dagPath = selectionList.getDagPath(0)
			self.fnMesh = om.MFnMesh(dagPath)
               
			self.intersection = self.fnMesh.closestIntersection( om.MFloatPoint( pos	), om.MFloatVector(direction), om.MSpace.kWorld, 99999, False )
	
			if self.intersection: 
				hitPoint, hitRayParam, hitFace, hitTriangle, hitBary1, hitBary2 = self.intersection
	
			if hitTriangle != -1:
				self.loc1= pm.spaceLocator(p=(hitPoint[0],hitPoint[1],hitPoint[2]), a=True)
				cmds.refresh() 


	def onDrag(self):
		vpX, vpY, _ = cmds.draggerContext( self.Context, query=True, dragPoint=True)
		pos = om.MPoint()
		direction = om.MVector()
		omui.M3dView().active3dView().viewToWorld(int(vpX)	 , int(vpY), pos, direction)
		for mesh in self.meshSelection:
			selectionList = om.MSelectionList()
			selectionList.add(mesh)
			dagPath = selectionList.getDagPath(0)
			self.fnMesh = om.MFnMesh(dagPath)
              
			dragIntersection = self.fnMesh.closestIntersection( om.MFloatPoint( pos	), om.MFloatVector(direction), om.MSpace.kWorld, 99999, False )
	
			if dragIntersection: 
				hitPoint, hitRayParam, hitFace, hitTriangle, hitBary1, hitBary2 = dragIntersection
					
			if hitTriangle != -1:
				self.loc1.localPosition.set( 0,0,0 )
				pos = pm.datatypes.Point(*hitPoint)
				'''
				closest = None
				minLength = None
				verts = [self.geo.vtx[i] for i in self.geo.f[hitFace].getVertices()]
				for v in verts:
					vpos = v.getPosition(space='world')
					thisLength = (pos - vpos).length()
					if minLength is None or thisLength < minLength:
						minLength = thisLength
						closest = vpos
				'''
				self.loc1.setTranslation( pos , space='world')
				cmds.refresh()
			
'''
Select the base mesh before running the following
'''			
a = SamsClass()
a.pointLocator()