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jPCT - a 3d engine for Java => Support => Topic started by: stormp on August 13, 2007, 09:35:39 pm

Title: project3D2D: how to tell if center is behind the viewplane and clip
Post by: stormp on August 13, 2007, 09:35:39 pm

Hi,

Still working on my grid lines.  ;D 

project3D2D wont render if "the center is behind the viewplane".   How can I adjust my vectors to clip at the approriate end?

Much thanks.

S.

Code: [Select]

   
    private void drawLine(FrameBuffer fb, Graphics2D g, SimpleVector v1, SimpleVector v2)
    {
        SimpleVector point1 = Interact2D.project3D2D(theWorld.getCamera(), fb, v1);
        SimpleVector point2 = Interact2D.project3D2D(theWorld.getCamera(), fb, v2);


        if(point1 != null && point2 != null)
        {
            g.drawLine((int)point1.x, (int)point1.y, (int)point2.x, (int)point2.y);
        }  // if
    }


Title: Re: project3D2D: how to tell if center is behind the viewplane and clip
Post by: EgonOlsen on August 13, 2007, 09:48:20 pm

By clipping them in 3D if one lies behind the plane (if both are behind, the line is hidden anyway). That's quite simple, but i suggest to clip them against plane+small-value to avoid rounding errors. Here's some code to get you started:

Code: [Select]

SimpleVector start=new SimpleVector(10,10,10);
SimpleVector end=new SimpleVector(30,30,-10);
float planeAt=1.01f;

SimpleVector dir=end.calcSub(start);
float mul=(planeAt-start.z)/dir.z;
float x=start.x+mul*dir.x;
float y=start.y+mul*dir.y;

SimpleVector intersect=new SimpleVector(x,y,planeAt);