There are two types of overloads of DrawUserIndexedPrimitive: Those accepting 16-bit indices and those accepting 32-bit indices.
When using 16-bit indices, everything works fine. When using 32-bit indices, I get an InvalidOperationException with the "helpful" error text An unexpected error has occurred (no inner exceptions) when DrawUserIndexedPrimitive is called. When I enable "Unmanaged Code Debugging" in the project properties, I get the lines
First-chance exception at 0x75a5b9bc in DrawUserPrimitives.exe: Microsoft C++ exception: long at memory location 0x0032e6b4..
First-chance exception at 0x75a5b9bc in DrawUserPrimitives.exe: Microsoft C++ exception: long at memory location 0x0032e728..
in the debug window right before the exception is thrown.
Why does this happen? Since both overloads are available, I would imagine that both would work (or at least throw a meaningful exception if only one of them is supported). Here's a complete minimal sample program that can be used to reproduce this issue. I'm using XNA 3.0.
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
public class GameTest : Microsoft.Xna.Framework.Game
{
static void Main(string[] args)
{
using (var game = new GameTest())
{
game.Run();
}
}
GraphicsDeviceManager manager;
public GameTest() { manager = new GraphicsDeviceManager(this); }
protected override void Draw(GameTime gameTime)
{
GraphicsDevice.Clear(Color.SteelBlue);
GraphicsDevice.VertexDeclaration = new VertexDeclaration(GraphicsDevice, VertexPositionColor.VertexElements);
var basicEffect = new BasicEffect(GraphicsDevice, null);
basicEffect.VertexColorEnabled = true;
basicEffect.View = Matrix.CreateLookAt(new Vector3(0.0f, 0.0f, 1.0f), Vector3.Zero, Vector3.Up);
basicEffect.Projection = Matrix.CreateOrthographicOffCenter(-1, 2, 2, -1, 1.0f, 1000.0f);
// two simple points
var pointList = new VertexPositionColor[] {
new VertexPositionColor(new Vector3(0,0,0), Color.White),
new VertexPositionColor(new Vector3(0,1,0), Color.White)
};
// one simple line between those two points
var lineListIndices = new short[] { 0, 1 }; // works fine
// var lineListIndices = new int[] { 0, 1 }; // causes exception below
basicEffect.Begin();
foreach (EffectPass pass in basicEffect.CurrentTechnique.Passes)
{
pass.Begin();
GraphicsDevice.DrawUserIndexedPrimitives<VertexPositionColor>(
PrimitiveType.LineList, pointList, 0, 2,
lineListIndices, 0, 1); // exception occurs here
pass.End();
}
basicEffect.End();
base.Draw(gameTime);
}
}
