/// <summary>
/// The indexes in which order the rendering command renders vertexes.
/// </summary>
/// <param name="bufferId">用glGenBuffers()得到的VBO的Id。<para>Id got from glGenBuffers();</para></param>
/// <param name="elementType">type in glDrawElements(uint mode, int count, uint type, IntPtr indices);</param>
/// <param name="byteLength">此VBO中的数据在内存中占用多少个字节？<para>How many bytes in this buffer</para></param>
internal IndexBuffer(uint bufferId, IndexBufferElementType elementType, int byteLength)
: base(bufferId, byteLength / elementType.GetSize(), byteLength)
{
this.Target = BufferTarget.ElementArrayBuffer;
this.ElementType = elementType;
}
/// <summary>
/// Creates a <see cref="IndexBuffer"/> object directly in server side(GPU) without initializing its value.
/// </summary>
/// <param name="type"></param>
/// <param name="length">How many indexes are there?(How many uint/ushort/bytes?)</param>
/// <param name="usage"></param>
/// <returns></returns>
public static IndexBuffer Create(IndexBufferElementType type, int length, BufferUsage usage)
{
int byteLength = type.GetSize() * length;
uint[] buffers = new uint[1];
{
glGenBuffers(1, buffers);
const uint target = GL.GL_ELEMENT_ARRAY_BUFFER;
glBindBuffer(target, buffers[0]);
glBufferData(target, byteLength, IntPtr.Zero, (uint)usage);
glBindBuffer(target, 0);
}
var buffer = new IndexBuffer(buffers[0], type, byteLength);
return(buffer);
}
/// <summary>
/// Creates a <see cref="OneIndexBuffer"/> object directly in server side(GPU) without initializing its value.
/// </summary>
/// <param name="array"></param>
/// <param name="type"></param>
/// <param name="mode"></param>
/// <param name="usage"></param>
/// <returns></returns>
public static OneIndexBuffer GenIndexBuffer <T>(this T[] array, IndexBufferElementType type, DrawMode mode, BufferUsage usage) where T : struct
{
GCHandle pinned = GCHandle.Alloc(array, GCHandleType.Pinned);
IntPtr header = pinned.AddrOfPinnedObject();
// same result with: IntPtr header = Marshal.UnsafeAddrOfPinnedArrayElement(array, 0);
UnmanagedArrayBase unmanagedArray = new TempUnmanagedArray <T>(header, array.Length);// It's not neecessary to call Dispose() for this unmanaged array.
int byteLength = unmanagedArray.ByteLength;
uint[] buffers = new uint[1];
{
glGenBuffers(1, buffers);
const uint target = GL.GL_ELEMENT_ARRAY_BUFFER;
glBindBuffer(target, buffers[0]);
glBufferData(target, byteLength, unmanagedArray.Header, (uint)usage);
glBindBuffer(target, 0);
}
pinned.Free();
var buffer = new OneIndexBuffer(
buffers[0], mode, type, byteLength / type.GetSize(), byteLength);
return(buffer);
}
