Alpha problem with ui.ImageContext.get_image()

[WillW68]

I have modified the Sketch.py code to draw a succession of ovals instead of using path.stroke(), with the intention of using the pencil pressure to change the alpha at different points along the path. In the code below I have kept it constant for simplicity. But the alpha value does not seem to be captured correctly in ctx.get_image(), causing it to change when path_action() is called at the end of the path. Just add the code below to the Sketch.py example, and change the definition in touch_began() to self.path = MyPath() to see the problem when you lift the pencil/finger at the end of the stroke.

import math
def distanceBetween(point1, point2):
  return math.sqrt((point2[0] - point1[0])**2 + (point2[1] - point1[1])**2)

def angleBetween(point1, point2):
  return math.atan2( point2[0] - point1[0], point2[1] - point1[1] )

class MyPath():

	def move_to(self,x,y):
		self.path = [(x,y)]

	def line_to(self,x,y):
		self.path.append((x,y))
	
	def stroke(self):
		w = 20
		ui.set_alpha(0.006)
		lastPoint = self.path[0]
		for i in range(1,len(self.path)):
			currentPoint = self.path[i]
			dist = distanceBetween(lastPoint, currentPoint)
			angle = angleBetween(lastPoint, currentPoint)
			for j in range(int(dist)):
				x = lastPoint[0] + (math.sin(angle) * j)
				y = lastPoint[1] + (math.cos(angle) * j)
				circle = ui.Path.oval(x, y, w, w)
				circle.fill()
			lastPoint = currentPoint

[JonB]

sure you didnt change anything else? your code works for me:

https://gist.github.com/48675c9f598a1a8ade648391b429d63c

[WillW68]

I copied and pasted your code into a new script, and get the same result - when I lift my finger off at the end of a stroke, the alpha value of the whole stroke changes (gets lighter).

I am running the latest version of Pythonista (3.2) using python 3.6 on a 10.5” iPad Pro with iOS 11.2