3D旋转猴头示例中的坐标

Question

我想更改此代码以添加一个on-unu-touch-up事件，该事件将告诉她猴头是否被点击。但我很难弄清楚坐标系是怎么工作的。我知道变量touch返回鼠标点击的坐标，左下角是（0,0）。如果我检查模型（猴头）的位置，它会返回（0,0）。有谁能帮我解答一下这个问题吗？提前谢谢。在

from kivy.app import App
from kivy.clock import Clock
from kivy.core.window import Window
from kivy.uix.widget import Widget
from kivy.resources import resource_find
from kivy.graphics.transformation import Matrix
from kivy.graphics.opengl import *
from kivy.graphics import *
from objloader import ObjFile


class Renderer(Widget):
  def __init__(self, **kwargs):
    self.canvas = RenderContext(compute_normal_mat=True)
    self.canvas.shader.source = resource_find('simple.glsl')
    self.scene = ObjFile(resource_find("monkey.obj"))
    super(Renderer, self).__init__(**kwargs)
    with self.canvas:
      self.cb = Callback(self.setup_gl_context)
      PushMatrix()
      self.setup_scene()
      PopMatrix()
      self.cb = Callback(self.reset_gl_context)
    Clock.schedule_interval(self.update_glsl, 1 / 60.)

def setup_gl_context(self, *args):
    glEnable(GL_DEPTH_TEST)

def reset_gl_context(self, *args):
    glDisable(GL_DEPTH_TEST)

def update_glsl(self, delta):
    asp = self.width / float(self.height)
    proj = Matrix().view_clip(-asp, asp, -1, 1, 1, 100, 1)
    self.canvas['projection_mat'] = proj
    self.canvas['diffuse_light'] = (1.0, 1.0, 0.8)
    self.canvas['ambient_light'] = (0.1, 0.1, 0.1)
    self.rot.angle += delta * 100

def setup_scene(self):
    Color(1, 1, 1, 1)
    PushMatrix()
    Translate(0, 0, -3)
    self.rot = Rotate(1, 0, 1, 0)
    m = list(self.scene.objects.values())[0]
    UpdateNormalMatrix()
    self.mesh = Mesh(
        vertices=m.vertices,
        indices=m.indices,
        fmt=m.vertex_format,
        mode='triangles',
    )
    PopMatrix()

def on_touch_up(self, touch):
  print "touch: ({}, {})".format(touch.pos[0], touch.pos[1])

def _on_keyboard_down(self,  keyboard, keycode, text, modifiers):
   if keycode[1] == 'right':
       self.update_glsl(1/60.)
   elif keycode[1] == 'left':
       self.rot.angle -= 1/60. * 100

class RendererApp(App):
  def build(self):
    return Renderer()

if __name__ == "__main__":
  RendererApp().run()