dragger.py

import maya.OpenMaya as om
import maya.OpenMayaUI as omui
import maya.cmds as cmds

ctx = 'myCtx'
sel = cmds.ls(sl=True)[0]
selectedMesh = cmds.listRelatives(sel, s=True)[0]

'''
closestIntersection(raySource, rayDirection, space, maxParam,
    testBothDirections, faceIds=None, triIds=None, idsSorted=False,
    accelParams=None, tolerance=kIntersectTolerance)
    
  -> (hitPoint, hitRayParam, hitFace, hitTriangle, hitBary1, hitBary2)
'''

def onDrag():
	vpX, vpY, _ = cmds.draggerContext(ctx, query=True, dragPoint=True)
	#print(vpX, vpY)
	pos = om.MPoint()
	dir = om.MVector()
	
	omui.M3dView().active3dView().viewToWorld(int(vpX), int(vpY), pos, dir)
	pos2 = om.MFloatPoint(pos.x, pos.y, pos.z)
	#for mesh in cmds.ls(type='mesh'):
	selectionList = om.MSelectionList()
	selectionList.add(selectedMesh)
	dagPath = om.MDagPath()
	selectionList.getDagPath(0, dagPath)
	fnMesh = om.MFnMesh(dagPath)
	
	raySource = om.MFloatPoint(pos2)
	rayDirection = om.MFloatVector(dir)
	faceIds = None
	triIds = None
	idsSorted = False
	maxParamPtr = 99999999
	testBothDirections = False
	accelParams = None
	
	hitpoint = om.MFloatPoint()
	hitRayParam = None
	hitFacePtr = om.MScriptUtil().asIntPtr()
	hitTriangle = None
	hitBary1 = None
	hitBary2 = None
	intersection = fnMesh.closestIntersection(raySource,
	                                          rayDirection,
	                                          faceIds,
											  triIds,
											  idsSorted,
											  om.MSpace.kWorld,
											  maxParamPtr,
											  testBothDirections,
											  accelParams,
											  hitpoint,
											  hitRayParam,
											  hitFacePtr,
											  hitTriangle,
											  hitBary1,
											  hitBary2)
	
	if intersection:
		print hitFacePtr
		#x = hitpoint.x
		#y = hitpoint.y
		#z = hitpoint.z
		#print x, y, z
		#cmds.spaceLocator(p=(x,y,z))


def main():
	if cmds.draggerContext(ctx, exists=True):
		cmds.deleteUI(ctx)
	
	cmds.draggerContext(ctx, dragCommand=onDrag, name=ctx, cursor='crossHair')
	cmds.setToolTo(ctx)
    
if __name__ == '__main__':
	main()