DrawOval improvement

BlitzMax Forums/BlitzMax Module Tweaks/DrawOval improvement

fredborg

(Posted 2004) [#1]

Hi,

A small fix to make DrawOval work with a width+height less than 5. Ie. DrawOval(x,y,2,2)

Replace the original DrawOval method in:

'\mod\brl.mod\glmax2d.mod\glmax2d.bmx'

With this:

	Method DrawOval( x0#,y0#,x1#,y1#,tx#,ty# )
		DisableTex
		Local	i,x#,y#,w#,h#,c
		glBegin GL_POLYGON
		w=(x1-x0)*.5
		h=(y1-y0)*.5
		x0:+w
		y0:+h
		c=(Abs(w)+Abs(h))
		If c<3 c=3 ' <- My genius fix
		c=360/c
		If c<1 c=1 
		i=0
		While i<360
			x=x0+Cos(i)*w
			y=y0-Sin(i)*h
			glVertex2f x*ix+y*iy+tx,x*jx+y*jy+ty
			i:+c
		Wend
		glEnd
	End Method

(As I'm the first to post here, I don't know if this is what this board is intended to be used for...so feel free to remove this topic elsewhere, if it isn't)

marksibly

(Posted 2004) [#2]

Cheer Fredborg!

Yep, this is the right place for that sort of thing.

marksibly

(Posted 2004) [#3]

Actually, this isn't correct.

The 'front end' bit in max2d converts the x,y,w,h to x0,y0,x1,y1

Here's a little test that seems to indicate everything's OK 'as-is':


Strict

Graphics 640,480

Type TPixie

	Field x#=Rnd(640),y#=Rnd(480)

	Field width#=Rnd(32),height#=Rnd(32)
	
	Field scale_x#=Rnd(1,3),scale_y#=Rnd(1,3)
	
	Field rot#,rot_speed#=Rnd(3,6)

	Method Render()
	
		rot:+rot_speed
		SetRotation rot
		SetScale scale_x,scale_y
		SetHandle width/2,height/2
		
		SetColor 255,255,255
		DrawRect x,y,width,height
		SetColor 0,0,255
		DrawOval x,y,width,height
	
	End Method

End Type

Local list:TList=New TList

For Local i=0 Until 100
	list.Addlast New TPixie
Next

While Not KeyHit(KEY_ESCAPE)

	Cls

	For Local p:TPixie=EachIn list
		p.Render()
	Next
	
	Flip
	FlushMem
Wend

matt!

(Posted 2004) [#4]

Hi Mark,

Any ideas why my other Oval probelm is happening? The Oval is a different, rough, non-oval shape depending on where I draw it on my window.

http://www.blitzbasic.com/Community/posts.php?topic=41393

Very strange

matt!

(Posted 2004) [#5]

Try substituting this code in Mark's example. Take a screen shot using Apple+Shift+3 and then load that into a paint program and zoom in.

Field width#=5,height#=5
Field scale_x#= 1,scale_y#= 1

fredborg

(Posted 2004) [#6]

Well, there you go...Just me being silly again :D

I guess I'll have to wait for the Windows version to try it out for real. So I'll just keep quiet now :)

fredborg

(Posted 2004) [#7]

Ok, in my strive to make this topic less pointless, I've changed the code at the top, to handle ovals with a width+ height less than 5.

This should be a real fix, and not just some mumbo jumbo I invented in my wait for BMax for PC :)

matt!

(Posted 2004) [#8]

Are you coding blind or have you actually tried your code on BMX?

fredborg

(Posted 2004) [#9]

Well, I have to admit I'm coding more or less in blind.

But this one should be correct. Here's a quick explanation:

When width+height is less than 5, then (width*0.5)+(height*0.5) <= 2 which is what is used to calculate how many points/vertices are needed to form a visually correct circle of a given size. And since two points/vertices doesn't render in OpenGL unless you have it set to 'Point (or Wire) Rendering Mode' instead of 'Solid Rendering Mode' you will end up with no visual output. So my fix is that if the number of points/vertices created is less than 3 then set it to 3, so the circle will at least render as a triangle if it's very small.

I sure hope that's correct, or I'll now officially be known as 'The Stupidest BMax User'...So please confirm :)

Perturbatio

(Posted 2004) [#10]

you were wrong then huh? :)

TommyBear

(Posted 2004) [#11]

Can't you tell from his username????? Sheesh! :p