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2d doughnut

BlitzMax Forums/BlitzMax Programming/2d doughnut

zambani(Posted 2008) [#1]
Does anyone have an idea how to quickly draw a 2d doughnut(filled circle with a hole in the middle)

I've already tried faking it by drawing another smaller circle on top of the first with the background color. But the problem is that the "hole" is not transparent


dynaman(Posted 2008) [#2]
Why are you not using a transparent background color? (not trying to be rude, just confused why you are not using a donut image and pasting it so the background color is transparent)


zambani(Posted 2008) [#3]
Why are you not using a transparent background color? (not trying to be rude, just confused why you are not using a donut image and pasting it so the background color is transparent)


The doughnut size needs to change dynamically. When I resize an image, Blixmax tends to blur the edges.


_JIM(Posted 2008) [#4]
You could draw this to a pixmap and then process pixels so that the ones colored like the background would be transparent. Not sure how fast this is though.

A second suggestion would be to make the doughnut image the same size as your maximum size inside the application. Then it won't blur anymore, but it will get a bit sharper when you scale down


smilertoo(Posted 2008) [#5]
Draw quite a big doughnut and shrink it? instead of enlarging a small one?


tonyg(Posted 2008) [#6]
I tried a doughnut with transparent psp7 background and it doesn't seem to blur when being enlarged.
Have you got the code and image that has the problem?


Brucey(Posted 2008) [#7]
Blue donut :-)

cairo.Arc(320, 240, 30, 0, 360)
cairo.Arc(320, 240, 70, 0, 360)

cairo.SetFillRule(CAIRO_FILL_RULE_EVEN_ODD)

cairo.SetSourceRGB(0, 0, 1)
cairo.FillPreserve()

cairo.SetSourceRGB(0, 0, 0)
cairo.Stroke()

Inner radius 30, outer radius 70 pixels.


SSS(Posted 2008) [#8]
If you felt like doing it in a less efficient way you could use the function,
Function DrawDonut(x:Float,y:Float,ir:Float,er:Float,quads:Int = 20)
	Local xy:Float[] = New Float[6]
	For Local i:Int = 0 To (quads-1)
		Local angle:Float = i*360.0/quads
		Local angleTo:Float = (i+1)*360.0/quads
		xy[0] = x+er*Cos(angle)
		xy[1] = y+er*Sin(angle)
		xy[2] = x+ir*Cos(angle)
		xy[3] = y+ir*Sin(angle)
		xy[4] = x+ir*Cos(angleTo)
		xy[5] = y+ir*Sin(angleTo)
		DrawPoly(xy)
		xy[0] = x+er*Cos(angle)
		xy[1] = y+er*Sin(angle)
		xy[2] = x+er*Cos(angleTo)
		xy[3] = y+er*Sin(angleTo)
		xy[4] = x+ir*Cos(angleTo)
		xy[5] = y+ir*Sin(angleTo)
		DrawPoly(xy)
	Next
End Function


You could probably make it a good deal faster by precalculating the array and then upscaling it.