Ellipse Tool in Python part 2

Question

I am currently making changes to the way my ellipse tool works as it was not working the correct way previously. I am creating it for my paint program using python 2.7.5 and pygame. I have recently encountered this error:

Traceback (most recent call last):
File "C:\Users\Wisdom1\Desktop\Comp Science Files\Canvas.py", line 164, in <module>
draw.ellipse(screen,(c),(x,y,radx,rady),sz2)
ValueError: width greater than ellipse radius

This occurs when I try to create an ellipse going in every direction except downward to the right from a point. I understand the error I just do not know how to fix it. Here is my ellipse tool:

if mb[0] == 1 and canvas.collidepoint(mx,my):
        screen.set_clip(canvas)
        if tool == "ellipse":
            screen.blit(copy,(0,0))
            radx = max(mx-x,1)
            rady = max(my-y,1)
            draw.ellipse(screen,(c),(x,y,radx,rady),sz2)
        screen.set_clip(None)

Sz2 is a size variable that begins at 10 and decreases or increases by 3 each time the mouse wheel is moved down or up. Any help is appreciated. Thank you

Answer 1

You could also use a ternary statement in the form of:

draw.ellipse(screen,(c),(x,y,radx,rady), sz2 if sz2 < max(radx, raxy) else 0)

Sincerely,

Another Massey student working on a Sunday night ;)

Answer 2

If sz2, the thickness of the curve, is greater than the minor radius of the ellipse, pygame raises a ValueError. So you could protect against this by using an if-statement:

if sz2 < min(radx, rady)//2:
    pygame.draw.ellipse(self.screen, green, box, sz2)
else:
    # sz2=0 fills the ellipse
    pygame.draw.ellipse(self.screen, green, box, 0)

radx, rady is the width and height of the Rect bounding the ellipse. So the minor radius is half the smaller of radx and rady.

---

Here is some runnable code showing that the if-statement works:

"""Based on http://www.pygame.org/docs/tut/intro/intro.html"""
import sys
import pygame

pygame.init()
size = (width, height) = (320, 240)
screen = pygame.display.set_mode(size)
black = (0,0,0)
green = [0, 255, 0]
radx, rady = 50, 70
box = [160-radx//2, 120-rady//2, radx, rady]
width = 1
delta = 2
while True:
    for event in pygame.event.get():
        if ((event.type == pygame.QUIT) or 
            (event.type == pygame.KEYDOWN and 
             event.key == pygame.K_ESCAPE)): 
            sys.exit()
    screen.fill(black)
    if 0 < width < min(radx, rady)//2:
        pygame.draw.ellipse(screen, green, box, width)
    else:
        if width > 0:
            pygame.draw.ellipse(screen, green, box, 0)
        delta *= -1
    width += delta
    pygame.display.flip()
    pygame.time.delay(100)