Create a circle or ellipse with the GL class

Question

I am trying to create a simple circle. I don't want to use the LineRenderer because I need the circle to be a 1px line at all times. So I am using the GL class.

I am uncertain how to create a Quadratic Bezier Curve using the GL class.

Here is the modified code from the Wiki:

var numberOfPoints = 60; var lineColor = Color.white; var drawLines = true;

private var lineMaterial : Material; private var linePoints : Vector2[]; private var lineWidth = 1;

function Awake () { //create line material color lineMaterial = new Material( "Shader \"Lines/Colored Blended\" {" + "SubShader { Pass {" + " BindChannels { Bind \"Color\",color }" + " Blend SrcAlpha OneMinusSrcAlpha" + " ZWrite Off Cull Off Fog { Mode Off }" + "} } }"); lineMaterial.hideFlags = HideFlags.HideAndDontSave; lineMaterial.shader.hideFlags = HideFlags.HideAndDontSave; }

function Start () { linePoints = new Vector2[numberOfPoints];

 // Plot points on a circle
 var radians : float = 360.0/(numberOfPoints-1)*Mathf.Deg2Rad;
 var p = 0.0;
 for (i = 0; i &lt; numberOfPoints; i++) {
     linePoints[i] = Vector2(0.5 + .25*Mathf.Cos(p), 0.5 + 0.25*Mathf.Sin(p));
     p += radians;
     //print(p);
 }

function OnPostRender () { if (!drawLines || !linePoints || linePoints.Length < 2) {return;}

 var cam = camera; // Cache GetComponent call in local variable for speed
 var nearClip = cam.nearClipPlane+0.01; // Add a bit, else there's flickering when the camera moves
 var pWidth = (1.0/Screen.width)*((Screen.width+0.0)/Screen.height)*0.22;
 var end = linePoints.Length-1;

 lineMaterial.SetPass(0);
 GL.Begin(GL.LINES);
 GL.Color(lineColor);

 for (i = 0; i &lt; end; i++) {
     var v1 = cam.ViewportToWorldPoint(Vector3(linePoints[i].x, linePoints[i].y, nearClip));
     var v2 = cam.ViewportToWorldPoint(Vector3(linePoints[i+1].x, linePoints[i+1].y, nearClip));
     GL.Vertex(v1);
     GL.Vertex(v2);
 }
 GL.End();

function OnApplicationQuit () { DestroyImmediate(lineMaterial); }

@script RequireComponent(Camera)

Any help would be awesome. Thanks in advance!

Answer 1

Best Answer

Answer by Eric5h5 · Apr 27, 2010 at 12:05 AM

Have a look at this vector line script on the wiki, which has an example that plots a circle (and then animates it in a funky way, but you can leave that part out of course).

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Adam D. · Apr 27, 2010 at 12:24 AM 0

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Thanks Eric! I did find that script, and boiled it down to draw a circle (I have updated my original question, with the modified wiki script). I am struggling getting this to work in world space, instead of camera space. I basically want to supply a center transform point, and I want the circle to be drawn around the center point, using an outer transform point to get the radius. Think of "the Moons orbit path around the Earth."

I have tried converting some of the Vector2 points to Vector3, but things got messy fast.

Thanks!

Eric5h5 · Apr 27, 2010 at 12:35 AM 0

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@Adam D. You can use WorldToViewportSpace in order to supply the center transform point, as well as the outer transform point. Actually in this case using screen space would be more convenient for plotting circles since you don't have to compensate for the aspect ratio to get a perfect circle.

Adam D. · Apr 27, 2010 at 01:07 AM 0

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Thanks, I'll give it a go... My math is rusty, so we'll see ;) And I'm still a bit confused on how to create my array of points in world space like you are doing here: linePoints[i] = Vector2(0.5 + .25*Mathf.Cos(p), 0.5 + 0.25*Mathf.Sin(p));

Adam D. · Apr 27, 2010 at 02:15 AM 0

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Got it working thanks! Replaced "0.5 + .25" with the transform.position of my target object. Works great.

AhmedMTawfik · Aug 04, 2020 at 06:35 PM 0

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Link is dead; any replacements?

Eno-Khaon AhmedMTawfik · Aug 04, 2020 at 07:25 PM 1

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Same place, new location:

http://wiki.unity3d.com/index.php?title=VectorLine

AhmedMTawfik Eno-Khaon · Aug 05, 2020 at 07:17 PM 0

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Thanks for the link!

Create a circle or ellipse with the GL class

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