0

I have this code:

platform.window:invalidate()

function on.paint(gc)
    gc:setColorRGB(0,0,0)

    for i=1,8,1 do
        gc:fillArc(230,(i*30)-40,30,30,45,360-(i*60))
    end
end

if you look at the first iteration, where i=1, the circle should be drawn from 45° - 300° counter-clockwise. This isn't what happens. The circle is drawn from what looks like 45° to 345°, which obviously is undesirable.

Some other odd occurrences happen when drawing other circles, which makes them seem flipped, or mirrored or something like that when drawn. This oddity can be replicated by inputting different values into the 2 last arguments of fillArc(). 90 and 270 draws from 90 to 360. 180 and 270 draws from 180 to 90. Why is this occurring?

an expected input and 2 circles

https://i.stack.imgur.com/4Uk2X.jpg

crazicrafter1
  • 309
  • 5
  • 18
  • BTW, irrelevant to your issue, but multiplication in Lua (as in most languages) has precedence over addition & subtraction so parentheses are redundant. – tonypdmtr Jan 31 '18 at 17:17

1 Answers1

1

I don't have a device to test this on, but from what you are describing it looks like the "end angle" argument is taken to be relative to the "start angle", so 90 and 270 will be drawn from 90 to 90+270. This would not be my reading of the documentation -- "The arc is drawn beginning at startAngle degrees and ending at endAngle." -- but it can probably be interpreted either way.

Paul Kulchenko
  • 25,884
  • 3
  • 38
  • 56
  • I think you're right, it does seem to be calculated from start to the end as a relative position; the Wiki should be more specific besides just stating "The arc is drawn beginning at startAngle degrees and ending at endAngle." – crazicrafter1 Jan 31 '18 at 12:13