# Alpha problem with ui.ImageContext.get_image() browsing

• posted
0

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 - point1)**2 + (point2 - point1)**2)

def angleBetween(point1, point2):
return math.atan2( point2 - point1, point2 - point1 )

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
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 + (math.sin(angle) * j)
y = lastPoint + (math.cos(angle) * j)
circle = ui.Path.oval(x, y, w, w)
circle.fill()
lastPoint = currentPoint``````

• posted
0

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

• posted
0

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

Internal error.

Oops! Looks like something went wrong!