Game Structure - C# Game Programming: For Serious Game Creation - page 141

private Vector GetCenter()
{

double halfWidth = GetWidth() / 2;
double halfHeight = GetHeight() / 2;

return new Vector(
_vertexPositions[0].X + halfWidth,
_vertexPositions[0].Y - halfHeight,
_vertexPositions[0].Z);

}

private void InitVertexPositions(Vector position, double width, double
height)
{

double halfWidth = width / 2;
double halfHeight = height / 2;
// Clockwise creation of two triangles to make a quad.

// TopLeft, TopRight, BottomLeft
_vertexPositions[0] = new Vector(position.X - halfWidth, position.Y +
halfHeight, position.Z);
_vertexPositions[1]= new Vector(position.X + halfWidth, position.Y +
halfHeight, position.Z);
_vertexPositions[2]= new Vector(position.X - halfWidth, position.Y -
halfHeight, position.Z);

// TopRight, BottomRight, BottomLeft
_vertexPositions[3]= new Vector(position.X + halfWidth, position.Y +
halfHeight, position.Z);
_vertexPositions[4]= new Vector(position.X + halfWidth, position.Y -
halfHeight, position.Z);
_vertexPositions[5]= new Vector(position.X - halfWidth, position.Y -
halfHeight, position.Z);
}

public double GetWidth()
{

// topright - topleft
return _vertexPositions[1].X - _vertexPositions[0].X;

}