isMouseInCircleSector?

[Captain07]

Hello,

I'm working with circles (dxDrawCircle) recently and I need a function to check if the player's cursor is within a circle's sector (a button). Is there a function to do this? I found the isMouseInCircle function, but it's not enough. Any ideas?

[MRmihailZH]

use a triple check, first whether the cursor is in a large circle, then whether the cursor is in a small circle, and whether the cursor is in a triangle

 

x, y - cursor coordinates

x1, y1, x2, y2, x3, y3 - coordinates of the angles of the triangle

the function returns true if the point x, y belongs to a triangle

function getPosition(x, y, x1, y1, x2, y2, x3, y3)
    local k = (x1 - x) * (y2 - y1) - (x2 - x1) * (y1 - y)
    local m = (x2 - x) * (y3 - y2) - (x3 - x2) * (y2 - y)
    local n = (x3 - x) * (y1 - y3) - (x1 - x3) * (y3 - y)
    return ((k >= 0 and m >= 0 and n >= 0) or (k <= 0 and m <= 0 and n <= 0))
end

Edited February 2, 2021 by MRmihailZH

[Captain07]

Thanks, I'll check it out!

[Zango]

If you only want to see if the point is inside one of the circle's quadrants, it can be done really simple.

If you want to check for any sector, I have made the following, where you define the sector from two angles. It would also be possible to define the sectors from vectors instead.

local sx, sy = guiGetScreenSize( )
function isMouseInCircleSector(cx, cy, r, angleStart, angleEnd)
	local mx, my = getCursorPosition()
	if not mx then return end
	
	-- Relativise mouse position to circle center
	mx = mx * sx - cx
	my = my * sy - cy
	
	-- Convert angles to vectors
	local x1, y1 = r * math.cos(angleStart), r * math.sin(angleStart)
	local x2, y2 = r * math.cos(angleEnd), r * math.sin(angleEnd)
	
	return mx^2 + my^2 <= r^2 and -- Check if within radius
	-x1*my + y1*mx <= 0 and -- Check if counterclockwise to angleStart
	-x2*my + y2*mx > 0 -- Check if clockwise to angleEnd
end

Where:

cx, cy = Circle center

r = Circle radius

angleStart = start of sector, in radians

angleEnd = end of sector, in radians

So as an example, here are the angleStart and angleEnd values for each quadrant

270, 0 - First quadrant
180, 270 - Second quadrant
90, 180 - Third quadrant
0, 90 - Fourth quadrant

Hope it's useful

[Captain07]

Thank you! I tested it and for some reason it's not working properly, did I mess something up? I wanted make it green when it's within the sector, otherwise red. 
 

-- 1st test

if isMouseInCircleSector(sx/2, sy/2, 330, 0, 90) then
    dxDrawCircle(sx/2, sy/2, 330, 0, 90, tocolor(0, 255, 0, 255))
else
    dxDrawCircle(sx/2, sy/2, 330, 0, 90, tocolor(255, 0, 0, 255))
end


-- 2nd test

if isMouseInCircleSector(sx/2, sy/2, 330, 0, 180) then
    dxDrawCircle(sx/2, sy/2, 330, 0, 180, tocolor(0, 255, 0, 255))
else
    dxDrawCircle(sx/2, sy/2, 330, 0, 180, tocolor(255, 0, 0, 255))
end

https://imgur.com/a/g6udD5L
 

[Zango]

You need to parse radians to it, like this

isMouseInCircleSector(sx/2, sy/2, 330, math.rad(0), math.rad(90))

 

[Captain07]

Oops... thanks! Now it's working like a charm!