Enable pressure for touches in android (and ios?) (#7684)

* enable pressure four touches in android (and some ios devices)

* style fixes

examples/demo/touchtracer/main.py

@@ -32,6 +32,7 @@ from kivy.app import App
 from kivy.uix.floatlayout import FloatLayout
 from kivy.uix.label import Label
 from kivy.graphics import Color, Rectangle, Point, GraphicException
+from kivy.metrics import dp
 from random import random
 from math import sqrt
 
@@ -54,14 +55,23 @@ def calculate_points(x1, y1, x2, y2, steps=5):
 
 class Touchtracer(FloatLayout):
 
+    def normalize_pressure(self, pressure):
+        print(pressure)
+        # this might mean we are on a device whose pressure value is
+        # incorrectly reported by SDL2, like recent iOS devices.
+        if pressure == 0.0:
+            return 1
+        return dp(pressure * 10)
+
     def on_touch_down(self, touch):
         win = self.get_parent_window()
         ud = touch.ud
         ud['group'] = g = str(touch.uid)
         pointsize = 5
+        print(touch.profile)
         if 'pressure' in touch.profile:
             ud['pressure'] = touch.pressure
-            pointsize = (touch.pressure * 100000) ** 2
+            pointsize = self.normalize_pressure(touch.pressure)
         ud['color'] = random()
 
         with self.canvas:
@@ -92,16 +102,20 @@ class Touchtracer(FloatLayout):
                 points = ud['lines'][index].points
                 oldx, oldy = points[-2], points[-1]
                 break
-            except:
+            except IndexError:
                 index -= 1
 
         points = calculate_points(oldx, oldy, touch.x, touch.y)
 
         # if pressure changed create a new point instruction
         if 'pressure' in ud:
-            if not .95 < (touch.pressure / ud['pressure']) < 1.05:
+            old_pressure = ud['pressure']
+            if (
+                not old_pressure
+                or not .99 < (touch.pressure / old_pressure) < 1.01
+            ):
                 g = ud['group']
-                pointsize = (touch.pressure * 100000) ** 2
+                pointsize = self.normalize_pressure(touch.pressure)
                 with self.canvas:
                     Color(ud['color'], 1, 1, mode='hsv', group=g)
                     ud['lines'].append(

kivy/core/window/_window_sdl2.pyx

@@ -641,13 +641,15 @@ cdef class _WindowSDL2Storage:
             fid = event.tfinger.fingerId
             x = event.tfinger.x
             y = event.tfinger.y
-            return ('fingermotion', fid, x, y)
+            pressure = event.tfinger.pressure
+            return ('fingermotion', fid, x, y, pressure)
         elif event.type == SDL_FINGERDOWN or event.type == SDL_FINGERUP:
             fid = event.tfinger.fingerId
             x = event.tfinger.x
             y = event.tfinger.y
+            pressure = event.tfinger.pressure
             action = 'fingerdown' if event.type == SDL_FINGERDOWN else 'fingerup'
-            return (action, fid, x, y)
+            return (action, fid, x, y, pressure)
         elif event.type == SDL_JOYAXISMOTION:
             return (
                 'joyaxismotion',

kivy/core/window/window_sdl2.py

@@ -107,8 +107,8 @@ SDLK_F15 = 1073741896
 class SDL2MotionEvent(MotionEvent):
     def depack(self, args):
         self.is_touch = True
-        self.profile = ('pos', )
-        self.sx, self.sy = args
+        self.profile = ('pos', 'pressure', )
+        self.sx, self.sy, self.pressure = args
         win = EventLoop.window
         super(SDL2MotionEvent, self).depack(args)
 
@@ -126,13 +126,15 @@ class SDL2MotionEventProvider(MotionEventProvider):
             except IndexError:
                 return
 
-            action, fid, x, y = value
+            action, fid, x, y, pressure = value
             y = 1 - y
             if fid not in touchmap:
-                touchmap[fid] = me = SDL2MotionEvent('sdl', fid, (x, y))
+                touchmap[fid] = me = SDL2MotionEvent(
+                    'sdl', fid, (x, y, pressure)
+                )
             else:
                 me = touchmap[fid]
-                me.move((x, y))
+                me.move((x, y, pressure))
             if action == 'fingerdown':
                 dispatch_fn('begin', me)
             elif action == 'fingerup':