// ClassicalSharp copyright 2014-2016 UnknownShadow200 | Licensed under MIT
using System;

namespace ClassicalSharp.GraphicsAPI {
	
	/// <summary> Abstracts a 3D graphics rendering API. </summary>
	public abstract partial class IGraphicsApi {	
		
		protected void InitDynamicBuffers() {
			quadVb = CreateDynamicVb( VertexFormat.P3fC4b, 4 );
			texVb = CreateDynamicVb( VertexFormat.P3fT2fC4b, 4 );
		}
		
		public virtual void Dispose() {
			DeleteDynamicVb( ref quadVb );
			DeleteDynamicVb( ref texVb );
		}
		
		internal VertexP3fC4b[] quadVerts = new VertexP3fC4b[4];
		internal int quadVb;
		public virtual void Draw2DQuad( float x, float y, float width, float height, 
		                               FastColour col ) {
			int c = col.Pack();
			quadVerts[0] = new VertexP3fC4b( x, y, 0, c );
			quadVerts[1] = new VertexP3fC4b( x + width, y, 0, c );
			quadVerts[2] = new VertexP3fC4b( x + width, y + height, 0, c );
			quadVerts[3] = new VertexP3fC4b( x, y + height, 0, c );
			SetBatchFormat( VertexFormat.P3fC4b );
			UpdateDynamicIndexedVb( DrawMode.Triangles, quadVb, quadVerts, 4, 6 );
		}
		
		public virtual void Draw2DQuad( float x, float y, float width, float height, 
		                               FastColour topCol, FastColour bottomCol ) {
			int c = topCol.Pack();
			quadVerts[0] = new VertexP3fC4b( x, y, 0, c );
			quadVerts[1] = new VertexP3fC4b( x + width, y, 0, c );
			c = bottomCol.Pack();
			quadVerts[2] = new VertexP3fC4b( x + width, y + height, 0, c );
			quadVerts[3] = new VertexP3fC4b( x, y + height, 0, c );
			SetBatchFormat( VertexFormat.P3fC4b );
			UpdateDynamicIndexedVb( DrawMode.Triangles, quadVb, quadVerts, 4, 6 );
		}
		
		internal VertexP3fT2fC4b[] texVerts = new VertexP3fT2fC4b[4];
		internal int texVb;
		public virtual void Draw2DTexture( ref Texture tex, FastColour col ) {
			int index = 0;
			Make2DQuad( ref tex, col, texVerts, ref index );
			SetBatchFormat( VertexFormat.P3fT2fC4b );
			UpdateDynamicIndexedVb( DrawMode.Triangles, texVb, texVerts, 4, 6 );
		}
		
		public static void Make2DQuad( ref Texture tex, FastColour col,
		                              VertexP3fT2fC4b[] vertices, ref int index ) {
			float x1 = tex.X, y1 = tex.Y, x2 = tex.X + tex.Width, y2 = tex.Y + tex.Height;
			#if USE_DX
			// NOTE: see "https://msdn.microsoft.com/en-us/library/windows/desktop/bb219690(v=vs.85).aspx",
			// i.e. the msdn article called "Directly Mapping Texels to Pixels (Direct3D 9)" for why we have to do this.
			x1 -= 0.5f; x2 -= 0.5f;
			y1 -= 0.5f; y2 -= 0.5f;
			#endif
			int c = col.Pack();
			vertices[index++] = new VertexP3fT2fC4b( x1, y1, 0, tex.U1, tex.V1, c );
			vertices[index++] = new VertexP3fT2fC4b( x2, y1, 0, tex.U2, tex.V1, c );
			vertices[index++] = new VertexP3fT2fC4b( x2, y2, 0, tex.U2, tex.V2, c );
			vertices[index++] = new VertexP3fT2fC4b( x1, y2, 0, tex.U1, tex.V2, c );
		}
		
		/// <summary> Updates the various matrix stacks and properties so that the graphics API state
		/// is suitable for rendering 2D quads and other 2D graphics to. </summary>
		public void Mode2D( float width, float height, bool setFog ) {
			SetMatrixMode( MatrixType.Projection );
			PushMatrix();
			LoadOrthoMatrix( width, height );
			SetMatrixMode( MatrixType.Modelview );
			PushMatrix();
			LoadIdentityMatrix();
			
			DepthTest = false;
			AlphaBlending = true;
			if( setFog ) Fog = false;
		}
		
		/// <summary> Updates the various matrix stacks and properties so that the graphics API state
		/// is suitable for rendering 3D vertices. </summary>
		public void Mode3D( bool setFog ) {
			SetMatrixMode( MatrixType.Projection );
			PopMatrix(); // Get rid of orthographic 2D matrix.
			SetMatrixMode( MatrixType.Modelview );
			PopMatrix();
			
			DepthTest = true;
			AlphaBlending = false;
			if( setFog ) Fog = true;
		}
		
		internal unsafe int MakeDefaultIb() {
			const int maxIndices = 65536 / 4 * 6;
			int element = 0;
			ushort* indices = stackalloc ushort[maxIndices];
			IntPtr ptr = (IntPtr)indices;
			
			for( int i = 0; i < maxIndices; i += 6 ) {
				*indices = (ushort)(element + 0); indices++;
				*indices = (ushort)(element + 1); indices++;
				*indices = (ushort)(element + 2); indices++;
				
				*indices = (ushort)(element + 2); indices++;
				*indices = (ushort)(element + 3); indices++;
				*indices = (ushort)(element + 0); indices++;
				element += 4;
			}
			return CreateIb( ptr, maxIndices );
		}
	}

	public enum VertexFormat {
		P3fC4b = 0, P3fT2fC4b = 1,
	}
	
	public enum DrawMode {
		Triangles = 0, Lines = 1,
	}
	
	public enum CompareFunc {
		Always = 0,
		NotEqual = 1,
		Never = 2,
		
		Less = 3,
		LessEqual = 4,
		Equal = 5,
		GreaterEqual = 6,
		Greater = 7,
	}
	
	public enum BlendFunc {
		Zero = 0,
		One = 1,
		
		SourceAlpha = 2,
		InvSourceAlpha = 3,
		DestAlpha = 4,
		InvDestAlpha = 5,
	}
	
	public enum Fog {
		Linear = 0, Exp = 1, Exp2 = 2,
	}
	
	public enum MatrixType {
		Projection = 0, Modelview = 1, Texture = 2,
	}
}