Inserts object inside mesh just in the middle of the of the intersection of the camera ray and all geo in the scene

inMeshPlace

'''
Instructions:

To run the script just ise the code:
________________________________________________________________
import inMeshPlace
inMeshPlace.start()
________________________________________________________________

This script works in 3 modes:

1. If you run the script without any mesh selected, it will insert object in the approximate point of the ray that intersect all visible meshes in the scene.
2. If you run the script with one/many selected meshes, it will insert object in the approximate point of the ray that intersect all selected meshes in the scene.
3. If you select components and run the script, it will consider in computations only that component, i.e. it will compute approximate point under cursor only that was already selected.

Nota bene:
If you've clicked in the mesh and changed your mind about exact position, you can slide cursor before LMB release

'''


import maya.api.OpenMaya as om2
import maya.OpenMayaUI as omui
import maya.api.OpenMayaUI as omui2
import maya.cmds as mc
from functools import partial

try:
	from PySide import QtGui, QtCore
	import shiboken as shiboken
	from shiboken import wrapInstance
except ImportError:
	from PySide2 import QtGui, QtCore
	import PySide2.QtWidgets as QtWidgets
	import shiboken2 as shiboken
	from shiboken2 import wrapInstance


class InMeshPlace( object ):

	def __init__( self ):
		self.obj = 'joint'

	def UI( self ):
		winName = 'InMeshPlace'
		if mc.window( winName, ex=1 ):
			mc.deleteUI( winName )
		mainWin = mc.window( winName, s=1, mxb=0, mnb=0 )
		mainLayout = mc.formLayout( p=mainWin )

		objects = [ 'joint', 'spaceLocator', 'group', 'circle', 'polyCube' ]

		self.inplaceTF = mc.textField( cc=partial(self.insetText, 0 ), p=mainLayout )
		mc.popupMenu()
		for o in xrange( len(objects) ):
			exec( 'self.menuItem%i = mc.menuItem( l="%s", c=partial(self.insetText,"%s") ) ' % ( o, objects[o], objects[o] ) ) in globals(), locals()
		self.inplaceBN = mc.button( l='Place', h=30, c=lambda *x: self.startContext(1) )

		if mc.optionVar( ex='inmeshplace' ):
			txt = mc.optionVar( q='inmeshplace' )
			mc.textField( self.inplaceTF, e=1, tx=txt )

		mainWindow = shiboken.wrapInstance( long( omui.MQtUtil.findControl(mainWin) ), QtWidgets.QWidget )
		mainWindow.setStyleSheet( 'QWidget {background-color:#3a404e;}' )
		widgets = mainWindow.findChildren(QtWidgets.QWidget)
		for w in widgets:
			wtType = w.metaObject().className()
			if wtType == 'QmayaField':
				w.setStyleSheet( 'QmayaField {background-color:#282e35; border: 1px solid #1e2328; border-radius: 3px; color: #9dbfd5 }' )
			elif wtType == 'QPushButton':
				w.setStyleSheet( 'QPushButton {background-color:#495572; border: 1px solid #4a6288; border-radius: 3px; color: #aac6dc  }' )

		mc.formLayout( mainLayout, e=1, af=( self.inplaceTF, "top", 15 ) )
		mc.formLayout( mainLayout, e=1, af=( self.inplaceTF, "left", 15 ) )
		mc.formLayout( mainLayout, e=1, af=( self.inplaceTF, "right", 15 ) )
		mc.formLayout( mainLayout, e=1, ac=( self.inplaceBN, "top", 10, self.inplaceTF ) )
		mc.formLayout( mainLayout, e=1, af=( self.inplaceBN, "left", 15 ) )
		mc.formLayout( mainLayout, e=1, af=( self.inplaceBN, "right", 15 ) )
		mc.showWindow(mainWin)
		mc.window( winName, e=1, wh=( 150, 90 ) )

	def insetText( self, name, part):
		if name:
			mc.textField( self.inplaceTF, e=1, tx=name )
		else:
			name = mc.textField( self.inplaceTF, q=1, tx=1 )
		mc.optionVar( sv=( 'inmeshplace', name ) )

	def startContext( self, mode=0 ):
		self.ctx = 'mContext'
		if mode == 1:
			self.obj = mc.textField( self.inplaceTF, q=1, tx=1 )
		if mc.draggerContext(self.ctx, exists=1):
			mc.deleteUI(self.ctx)
		mc.draggerContext(self.ctx, releaseCommand=self.onRelease, name=self.ctx, cursor='crossHair')
		mc.setToolTo(self.ctx)
		self.pId = None
		self.allMeshTransform = mc.ls( sl=1, v=1  )
		if not self.allMeshTransform:
			self.allMesh = mc.ls( type='mesh', v=1 )
		elif self.allMeshTransform:
			vertextCheck = mc.filterExpand( self.allMeshTransform[0], sm=31 )
			edgeCheck = mc.filterExpand( self.allMeshTransform[0], sm=32 )
			faceCheck = mc.filterExpand( self.allMeshTransform[0], sm=34 )
			if vertextCheck or edgeCheck or faceCheck:
				self.allMesh = [ mc.listRelatives( x, p=1, typ='mesh' )[0] for x in self.allMeshTransform if mc.listRelatives( x, p=1, typ='mesh' ) ]
				borderComp = mc.polyListComponentConversion( self.allMeshTransform, tf=1, border=1 )
				allComp = mc.polyListComponentConversion( self.allMeshTransform, tf=1 )
				if self.allMeshTransform:
					if vertextCheck:
						self.pId = [ int( x[x.find("[") + 1:x.find("]")] ) for x in mc.ls( allComp, fl=1 ) if x not in mc.ls( borderComp, fl=1 ) ]
					else:
						self.pId = [ int( x[x.find("[") + 1:x.find("]")] ) for x in mc.ls( allComp, fl=1 ) ]
				else:
					return
			else:
				self.allMesh = [ mc.listRelatives( x, s=1, typ='mesh' )[0] for x in self.allMeshTransform if mc.listRelatives( x, s=1, typ='mesh' ) ]

	def onRelease( self ):
		allVectors = {}
		pos = om2.MPoint()
		dir = om2.MVector()
		vp = mc.draggerContext( self.ctx, q=1, dp=1 )
		omui2.M3dView().active3dView().viewToWorld(int(vp[0]), int(vp[1]), pos, dir)
		for mesh in self.allMesh:
			selectionList = om2.MSelectionList()
			selectionList.add(mesh)
			dagPath = selectionList.getDagPath(0)
			fnMesh = om2.MFnMesh(dagPath)
			if self.pId:
				intersection = fnMesh.allIntersections(om2.MFloatPoint(pos), om2.MFloatVector(dir), om2.MSpace.kWorld, 99999, 0, faceIds=self.pId )
			else:
				intersection = fnMesh.allIntersections(om2.MFloatPoint(pos), om2.MFloatVector(dir), om2.MSpace.kWorld, 99999, 0 )
			for i in intersection[0]:
				allVectors[ ( om2.MVector( pos ) - om2.MVector( i ) ).length() ] = om2.MVector( i )

		if allVectors:
			mc.select( cl=1 )
			maxLength = max( allVectors, key=float )
			minLength = min( allVectors, key=float )
			fVec = allVectors[ maxLength ]
			sVec = allVectors[ minLength ]
			point = [ (x + y) / 2 for x, y in zip( fVec, sVec ) ]
			if self.obj == 'group':
				newObj = eval( 'mc.' + self.obj + '(em=1)' )
				mc.setAttr( newObj + '.displayHandle', 1 )
			else:
				newObj = eval( 'mc.' + self.obj + '()' )
			mc.xform( newObj, ws=1, t=point )
			if self.allMeshTransform:
				mc.select( cl=1 )
				mc.select( self.allMeshTransform, r=1 )
			else:
				mc.select( cl=1 )


def start():
	InMeshPlace().UI()