Kivy : Move image following mouse movement without kv - kivy

Question

I want to move a image following mouse movement.
Especially, I'm at a loss how do I get mouse movement amount and translate coordinates.
I tried to_local , to_window , to_parent but I could not get it well...
Here is my minimal code. How should I modify this?
import kivy
from kivy.app import App
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.image import Image
class TestLayer(FloatLayout):
def __init__(self, **kwargs):
super(TestLayer, self).__init__(**kwargs)
self.pos_hint = {'top':1, 'x':0}
self.size_hint_x = 1
self.size_hint_y = 1
def build(self):
# specify your image dir and name
self.img = Image(source='0.png', size=(100, 100))
self.add_widget(self.img)
def on_touch_down(self, touch):
if self.collide_point(*touch.pos):
if touch.button == 'left':
# Hold value of touch downed pos
pass
return super(TestLayer, self).on_touch_down(touch)
def on_touch_move(self, touch):
if self.collide_point(*touch.pos):
if touch.button == 'left':
# self.img.x = self.img.x + (mouse movements distance)
# self.img.y = self.img.y + (mouse movements distance)
pass
return super(TestLayer, self).on_touch_move(touch)
def on_touch_up(self, touch):
if self.collide_point(*touch.pos):
if touch.button == 'left':
# process after movement or something?
pass
return super(TestLayer, self).on_touch_up(touch)
class TestScreen(Screen):
def __init__(self, **kwargs):
super(TestScreen, self).__init__(**kwargs)
layer = TestLayer()
self.add_widget(layer)
layer.build()
sm = ScreenManager()
class DemoApp(App):
def build(self):
sm.add_widget(TestScreen(name='test'))
return sm
if __name__ == '__main__':
DemoApp().run()

Answer 1

The code is set up in the correct way. What you need to do is save where the mouse was at each touch event (touch_down or touch_move) and compare to where it is now. Then you take the difference of those two, and move your image by that much.
The x and y coordinate of a touch are in the touch.pos[0] and touch.pos[1] variables respectively.
For example:
def on_touch_down(self, touch):
if self.collide_point(*touch.pos):
if touch.button == 'left':
# Hold value of touch downed pos
self.last_touch = touch.pos # Need this line
return super(TestLayer, self).on_touch_down(touch)
and
def on_touch_move(self, touch):
if self.collide_point(*touch.pos):
if touch.button == 'left':
self.img.x = self.img.x + touch.pos[0] - self.last_touch[0] # Add the x distance between this mouse event and the last
self.img.y = self.img.y + touch.pos[1] - self.last_touch[1] # Add the y distance between this mouse event and the last
self.last_touch = touch.pos # Update the last position of the mouse
return super(TestLayer, self).on_touch_move(touch)