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Extruding a 2D path

Posted on 2004-09-18
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Last Modified: 2013-12-26
Hi guys,

I have developed a 2d graphics app which can create simple outlines (consisting of straight lines only).  Using DirextX, I would like to extrude each line into a face based on a height parameter.  Each Shape (2D) has an array of Point objects (X & Y values).  

Can anyone help?

I'm using C# but i'll accept the algorythm in pseudo code if you're not familiar with c# as long as it uses standard verticies / vertex buffers / index buffers etc.

Thanks in advance

Chris
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Question by:chrisevans123
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davebytes earned 1840 total points
ID: 12109431
If you aren't using too many lines to begin with, don't even bother worrying about optimization.

You may want to swap Y and Z in the following, depending on how you want things to look initially.

For each point, you want to make it a 3D point at say Z=100 to start with.  Then you also need the extruded matching point at Z=100+height.

A final vertex array can be rendered as a triangle strip if the points are interlaced.  That is, assuming your initial vertices are in a 2d float structure, and you have a 3d point structure (which D3D does), you want to do something like:

Point2D *array_orig; // already filled in.
int vertex_count; // already filled in...
float extrude_height; // same...

Point3D *array_3d = new Point3D[vertex_count];
int sub;
for (int i=0; i<vertex_count; i++)
{
  subi = 2*i;
  array_3d[subi].x = array_orig[i].x;
  array_3d[subi].y = array_orig[i].y;
  array_3d[subi].z = 100;
  array_3d[subi+1].x = array_orig[i].x;
  array_3d[subi+1].y = array_orig[i].y;
  array_3d[subi+1].z = 100 + extrude_height;
}

Then array_3d can be rendered as a triangle-strip.  You might need to play with clockwise vs counter-clockwise culling (or turn culling off).

-d
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