// Here you can disable rendering geometry (then nothing is visible on screen,

// should be used together with DISABLE_SWAP_BUFFERS_FOR_PERFORMANCE_TESTING).

// This tests CPU performance much closer without having to wait for GPU each

// frame. This only makes a difference for very high fps (>5000 on fast PCs).

// Note: Also useful to find native memory leaks related to geometry rendering!

//#define DISABLE_GEOMETRY_RENDERING_FOR_PERFORMANCE_TESTING



using System;

using Delta.ContentSystem.Rendering;

using Delta.Engine;

using Delta.Graphics.BaseOpenGL;

using Delta.Utilities;

using Delta.Utilities.Helpers;

using OpenTK.Graphics.OpenGL;



namespace Delta.Graphics.OpenTK

{

	/// <summary>

	/// OpenTK geometry implementation (with VAO if supported to improve

	/// performance). We use also VBO and IBO for this implementation. For

	/// details see http://nehe.gamedev.net/data/lessons/lesson.asp?lesson=45

	/// </summary>

	public class OpenTKGeometry : BaseOpenGLGeometry

	{

		#region drawMode (Private)

		/// <summary>

		/// The cached draw mode of this geometry which is either Lines or Triangles.

		/// </summary>

		private readonly BeginMode drawMode;

		#endregion



		#region Constructor

		/// <summary>

		/// Create mesh from already created MeshData (for creating dynamic meshes,

		/// like for Lines, UI rendering or Effects).

		/// </summary>

		/// <param name="setMeshData">The set mesh data.</param>

		public OpenTKGeometry(GeometryData setMeshData)

			: base(setMeshData)

		{

			drawMode =

				Data.IsLineData

					? BeginMode.Lines

					: BeginMode.Triangles;

		}

		#endregion



		#region Create

		/// <summary>

		/// Create native mesh data (vertex buffers, vertex array objects, etc.).

		/// Used to create the native vertex buffer, etc. when we have not created

		/// it yet or if the content gets updated by the content system.

		/// </summary>

		internal override void Create(BaseShader shader)

		{

			if (OpenTKGraphic.VaoSupport)

			{

				// Create and bind our VAO if we have not created it yet.

				if (nativeVertexArrayID == MathHelper.InvalidIndex)

				{

					// Create and setup vertex format

					GL.GenVertexArrays(1, out nativeVertexArrayID);

				}



				// Always bind it

				GL.BindVertexArray(nativeVertexArrayID);

				ErrorCode error = GL.GetError();

				if (error != ErrorCode.NoError)

				{

					Log.Warning(

						"There was an OpenGL error while creating the Vertex " +

						"Array Object: '" + error + "'. This usually happens when " +

						"something went wrong a little earlier, enable OpenTK debugging " +

						"and figure the problem out at the original place.");

				}

			}



			bool vertexDataChanged;

			bool indexDataChanged;

			CheckIfDataChanged(out vertexDataChanged, out indexDataChanged);



			#region VBO

			if (vertexDataChanged)

			{

				// Increase VBO if needed

				if (Data.MaxNumberOfVertices > currentMaxNumberOfVertices)

				{

					currentMaxNumberOfVertices = Data.MaxNumberOfVertices;

					int vertexSizeInBytes =

						Data.MaxNumberOfVertices * Data.Format.LengthInBytes;

					// Create or update VBO

					if (nativeVertexBufferID == MathHelper.InvalidIndex)

					{

						GL.GenBuffers(1, out nativeVertexBufferID);

						GL.BindBuffer(BufferTarget.ArrayBuffer, nativeVertexBufferID);

						// Reserve space for currentMaxNumberOfVertices

						GL.BufferData(BufferTarget.ArrayBuffer,

							new IntPtr(vertexSizeInBytes), IntPtr.Zero,

							Data.IsStatic

								? BufferUsageHint.StaticDraw

								: BufferUsageHint.StreamDraw);

					}

					else

					{

						GL.BindBuffer(BufferTarget.ArrayBuffer, nativeVertexBufferID);

						GL.BufferData(BufferTarget.ArrayBuffer,

							new IntPtr(vertexSizeInBytes), IntPtr.Zero,

							BufferUsageHint.StreamDraw);

					}



					if (OpenTKGraphic.VaoSupport)

					{

						//Not helping at all, the issue is with SetupVertexFormat!

						//VaoSupport: return false;



						// Setup the vertex format for all geometry we will render.

						// Note: Needs to be done for every geometry, else pointers are

						// not correct! See

						// http://stackoverflow.com/questions/3665671/is-vertexattribpointer-needed-after-each-bindbuffer

						BaseOpenGLGraphic.SetupVertexFormat(shader as BaseOpenGLShader,

							Data.Format);

					}

				}

				else

				{

					// Just bind the buffer. Note: gDEBugger might report that this is

					// not needed, but it is not already set from last time causing

					// skipped geometry and other render errors, do not remove this!

					GL.BindBuffer(BufferTarget.ArrayBuffer, nativeVertexBufferID);

				}



				// changing geometries might be a lot more efficient!

				// This need to be re-thinked even of Engine side, we need to create

				// some kind of vertices atlas.



				// Update data in VBO

				byte[] dataBytes = Data.GetVerticesBytes();

				int dataSize =

					Data.VertexDataLengthInBytes * Data.NumberOfUsedVertices;



				GL.BufferSubData<byte>(BufferTarget.ArrayBuffer, IntPtr.Zero,

					(IntPtr)dataSize, dataBytes);

			}

			#endregion



			#region IBO

			if (Data.NumberOfUsedIndices > 0 &&

					indexDataChanged)

			{

				// recreate IBO if needed

				if (Data.Indices.Length > currentMaxNumberOfIndices)

				{

					currentMaxNumberOfIndices = Data.Indices.Length;

					// Create or update IBO

					if (nativeIndexBufferID == MathHelper.InvalidIndex)

					{

						GL.GenBuffers(1, out nativeIndexBufferID);

						GL.BindBuffer(BufferTarget.ElementArrayBuffer,

							nativeIndexBufferID);

						// Reserve space for currentMaxNumberOfIndices

						// 2 is the size of an ushort

						GL.BufferData(BufferTarget.ElementArrayBuffer,

							new IntPtr(currentMaxNumberOfIndices * 2), IntPtr.Zero,

							Data.IsStatic

								? BufferUsageHint.StaticDraw

								: BufferUsageHint.StreamDraw);

					}

					else

					{

						GL.BindBuffer(BufferTarget.ElementArrayBuffer,

							nativeIndexBufferID);

						// 2 is the size of an ushort

						GL.BufferData(BufferTarget.ElementArrayBuffer,

							new IntPtr(currentMaxNumberOfIndices * 2), IntPtr.Zero,

							BufferUsageHint.StreamDraw);

					}

				}

				else

				{

					// Just bind the buffer. Note: gDEBugger might report that this is

					// not needed, but it is not already set from last time causing

					// skipped geometry and other render errors, do not remove this!

					GL.BindBuffer(BufferTarget.ElementArrayBuffer, nativeIndexBufferID);

				}



				// Update data in IBO (2 is the size of an ushort)

				int dataSize = Data.NumberOfUsedIndices * 2;

				GL.BufferSubData<ushort>(BufferTarget.ElementArrayBuffer, IntPtr.Zero,

					(IntPtr)dataSize, Data.Indices);

			}

			#endregion



			#region Dispose geometry data for static geometry

			// For static geometry we can get rid of the vertices and indices as

			// we have them now on the GPU. This saves memory and the content can

			// be reloaded at any time too.

			if (Data.IsStaticAndLoadedFromContent)

			{

				Data.Dispose();

			}

			#endregion

		}

		#endregion



		#region Render

		/// <summary>

		/// Draw the current mesh at the already specified location (handled in

		/// MaterialManager and ModelManager).

		/// </summary>

		/// <param name="shader">The shader.</param>

		internal override void Render(BaseShader shader)

		{

			// Nothing to draw? Then quit!

			if (Data.NumberOfUsedVertices == 0)

			{

				Log.Warning("Nothing to render, you should not call Render!");

				return;

			}





			// Dynamic vertex data needs to be updated each frame (if there are used

			// vertices for this frame). We also need to create the native vertex

			// buffer if that has not been done yet (the very first draw time here).

			if (Data.IsStatic == false &&

			    Data.HasDataChanged ||

			    nativeVertexArrayID == MathHelper.InvalidIndex)

			{

				try

				{

					Create(shader);

				}

				catch (Exception ex)

				{

					// Note: This should never happen, but if debug mode OpenTK is on

					// this might catch some errors and report some useful details.

					Log.Warning("Failed to create vertex buffer geometry for data=" +

					            Data + ": " + ex);

				}

			} // if



			if (Graphic.Instance.HasShaderSupport == false)

			{

				GL.BindBuffer(BufferTarget.ArrayBuffer, nativeVertexBufferID);



				// If no support for shaders bind out FFP.

				BaseOpenGLGraphic.SetupFFPVertexFormat(Data.Format);

			}

			else

			{

				if (OpenTKGraphic.VaoSupport == false)

				{

					BaseOpenGLGraphic.SetupVertexFormat(

						shader as BaseOpenGLShader, Data.Format);

				}

				else

				{

					// Bind our VAO object

					GL.BindVertexArray(nativeVertexArrayID);

				}

			}



			// Line rendering needs some extra checks

			if (Data.IsLineData)

			{

				bool useAA = Settings.Extra.UseAntiAliasing;

				// Disable Depth writes when rendering anti aliased lines

				if (useAA)

				{

					GL.DepthMask(false);

				}



				// Lines are always drawn without index buffer

				GL.DrawArrays(drawMode, 0, Data.NumberOfUsedVertices);



				// Enable Depth writes when finished rendering anti aliased lines

				if (useAA)

				{

					GL.DepthMask(true);

				}

			}

				// Draw stuff normally

			else if (Data.NumberOfUsedIndices <= 0)

			{

				// Without index buffer

				GL.DrawArrays(drawMode, 0, Data.NumberOfUsedVertices);

			}

			else

			{

				// Bind our index buffer for correct rendering.

				GL.BindBuffer(BufferTarget.ElementArrayBuffer, nativeIndexBufferID);



				// With index buffer. Note since an IBO was setup above

				// we do not need the last parameter: See

				// http://www.opengl.org/discussion_boards/ubbthreads.php?ubb=showflat&Number=258926

				GL.DrawElements(drawMode, Data.NumberOfUsedIndices,

					DrawElementsType.UnsignedShort, IntPtr.Zero);

			}

		}

		#endregion

	}

}