// NumVertsPerPrimitive is a boring helper function that tells how many vertices
// it will take to draw each kind of primitive.
static private int NumVertsPerPrimitive(ePrimitiveType primitive)
{
int numVertsPerPrimitive;
switch (primitive)
{
case ePrimitiveType.PointList:
numVertsPerPrimitive = 1;
break;
case ePrimitiveType.LineList:
numVertsPerPrimitive = 2;
break;
case ePrimitiveType.TriangleList:
numVertsPerPrimitive = 3;
break;
case ePrimitiveType.RoundedLineList:
numVertsPerPrimitive = 2;
break;
default:
throw new InvalidOperationException("primitive is not valid");
}
return(numVertsPerPrimitive);
}
// Begin is called to tell the PrimitiveBatch what kind of primitives will be
// drawn, and to prepare the graphics card to render those primitives.
public void Begin(ePrimitiveType primitiveType)
{
if (hasBegun)
{
throw new InvalidOperationException
("End must be called before Begin can be called again.");
}
this.primitiveType = primitiveType;
// how many verts will each of these primitives require?
this.numVertsPerPrimitive = NumVertsPerPrimitive(primitiveType);
// prepare the graphics device for drawing by setting the vertex declaration
// and telling our basic effect to begin.
if (primitiveType != ePrimitiveType.RoundedLineList)
{
device.VertexDeclaration = vertexDeclaration;
basicEffect.Begin();
basicEffect.CurrentTechnique.Passes[0].Begin();
}
// flip the error checking boolean. It's now ok to call AddVertex, Flush,
// and End.
hasBegun = true;
}
