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Cart #invertedcircle-1 | 2020-11-05 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA
4


I noticed that people relatively often ask for a way to draw an inverted circle and don't have an easy way to implement it, since it requires a bit of math that can be difficult to derive without experience. I decided to make a quick cart and standalone function to do that! This isn't amazingly efficient, and it only does circles (not ellipses), but it is a drop in function:
Update: new function utilizing trig, faster and now subpixel!

 
x=x or 64
	y=y or 64
	r=r or 32
	left=left or 0
	right=right or 128
	top=top or 0
	bottom=bottom or 128
	local p=r*6.28
	if(top<y-r)rectfill(left,top,right,y-r,c)
	if(bottom>y+r)rectfill(left,y+r,right,bottom,c)
	for d=-.001,.25,1/p do
		local ex,ey=r*cos(d),r*sin(d)
		if(x-ex>left) then
			if(y-ey>top) then
				rect(left,y-ey,x-ex,y-ey,c)
			end
			if(y+ey<bottom) then
				rect(left,y+ey,x-ex,y+ey,c)
			end
		end
		if(x+ex<right) then
			if(y-ey>top) then
				rect(x+ex,y-ey,right,y-ey,c)
			end
			if(y+ey<bottom) then
				rect(x+ex,y+ey,right,y+ey,c)
			end
		end
	end

Old versions:


Cart #invertedcircle-0 | 2020-11-05 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA
4

 
function invertedcircle(x,y,r,left,right,top,bottom,c)
	x=x or 64
	y=y or 64
	r=r or 32
	left=left or 0
	right=right or 128
	top=top or 0
	bottom=bottom or 128

	local rsqr=r*r
	for i=flr(top),bottom do
		local yr=i-y
		local w=max(0,(rsqr-yr*yr)^.5)
		if(x-w>left)rect(left,i,x-w,i,c)
		if(x+w<right)rect(right,i,x+w,i,c)
	end
end

4

Mind if I use this in a project I'm working on?

Hi @ValerADHD.

It should be no difficult feat to make an inverted circle that does not require vectors or rectangles if CPU usage is not a consideration.

It doesn't go above 30.22% in any case.

Cart #sapatofujo-0 | 2022-08-31 | Code ▽ | Embed ▽ | No License

Use LEFT and RIGHT arrow keys to vanish or appear the picture behind it.

. . .

Cart #someyubafo-0 | 2022-08-31 | Code ▽ | Embed ▽ | No License

Here is a faster version using rectangles ^^
The CPU does not go above 19%.

. . .

Cart #fupujefaso-0 | 2022-08-31 | Code ▽ | Embed ▽ | No License

Here it is ^^ not manually redrawing the rectangles every time, decreasing the CPU usage to 13%.

. . .

There should be a way to get this even faster.

Cart #gejemodafi-0 | 2022-09-01 | Code ▽ | Embed ▽ | No License

Ah, even using memory transfer, it is spr() that is slowing me down and not much else. This method ^^ uses 18% CPU.
And chomps up memory 0x8000-0xBFFF besides.

. . .

I think what we really need is invcircfill(x1,y1,x2,y2,x3,y3,r,c)
Where x1,y1 are top-left of the rectangle.
Where x2,y2 are bottom-right of the rectangle.
Where x3,y3 is the transparent circle location.
Where r,c is radius and color.



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