/*=============================================================================

  Project:   SharpImage
  Module:    siOpenGlShader.cs
  Language:  C#
  Author:    Dan Mueller
  Date:      $Date: 2007-07-06 10:57:00 +1000 (Fri, 06 Jul 2007) $
  Revision:  $Revision: 2 $

  Copyright (c) Queensland University of Technology (QUT) 2007.
  All rights reserved.

  This software is distributed WITHOUT ANY WARRANTY; without even
  the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
  PURPOSE.  See the above copyright notices for more information.
  
=============================================================================*/

using System;
using System.IO;
using System.Text;
using System.Drawing;
using System.Collections;
using System.Diagnostics;
using System.Windows.Forms;
using System.Runtime.InteropServices;

using System.Reflection;
using System.Reflection.Emit;

using Tao.OpenGl;
using Tao.FreeGlut;
using Tao.Platform.Windows;

namespace SharpImage.Rendering
{
    /// <summary>
    /// Encapsulates a vertex and fragment shading program in OGSL (OpenGL Shading Language).
    /// </summary>
    public class siOpenGlShader
    {
        #region Instance Variables
        //============================================================================
        private int m_VertexHandle = 0;
        private int m_FragmentHandle = 0;
        private int m_ProgramHandle = 0;
        //============================================================================
        #endregion

        #region Construction and Disposal
        //============================================================================
        /// <summary>
        /// Default constructor.
        /// </summary>
        public siOpenGlShader()
        {

        }
        //============================================================================
        #endregion

        #region Properties
        //============================================================================

        #region VertexProgramPath
        //============================================================================
        private String m_VertexProgramPath = string.Empty;

        /// <summary>
        /// Gets the vertex shader program absolute path and filename.
        /// </summary>
        public String VertexProgramPath
        {
            get { return this.m_VertexProgramPath; }
            set { this.m_VertexProgramPath = value; }
        }
        //============================================================================
        #endregion

        #region FragmentProgramPath
        //============================================================================
        private String m_FragmentProgramPath = string.Empty;

        /// <summary>
        /// Gets the fragment shader program absolute path and filename.
        /// </summary>
        public String FragmentProgramPath
        {
            get { return this.m_FragmentProgramPath; }
            set { this.m_FragmentProgramPath = value; }
        }
        //============================================================================
        #endregion

        #region IsLoaded
        //============================================================================
        private bool m_IsLoaded = false;

        /// <summary>
        /// Gets if the program has been loaded.
        /// </summary>
        public bool IsLoaded
        {
            get { return this.m_IsLoaded; }
        }
        //============================================================================
        #endregion

        #region IsCompiled
        //============================================================================
        private bool m_IsCompiled = false;

        /// <summary>
        /// Gets if the program has been compiled.
        /// </summary>
        public bool IsCompiled
        {
            get { return this.m_IsCompiled; }
        }
        //============================================================================
        #endregion

        #region IsAttached
        //============================================================================
        private bool m_IsAttached = false;

        /// <summary>
        /// Gets if the program has been attached.
        /// </summary>
        public bool IsAttached
        {
            get { return this.m_IsAttached; }
        }
        //============================================================================
        #endregion

        #region IsLinked
        //============================================================================
        private bool m_IsLinked = false;

        /// <summary>
        /// Gets if the program has been linked.
        /// </summary>
        public bool IsLinked
        {
            get { return this.m_IsLinked; }
        }
        //============================================================================
        #endregion

        #region IsReady
        //============================================================================
        /// <summary>
        /// Gets if the program is ready for use.
        /// </summary>
        public bool IsReady
        {
            get { return this.IsLoaded && this.IsCompiled && this.IsLinked; }
        }
        //============================================================================
        #endregion

        //============================================================================
        #endregion

        #region Main Methods
        //============================================================================
        /// <summary>
        /// Initialises the vertex and fragment shader programs for use.
        /// This method MUST be called before the programs can be used (via Begin/End).
        /// An exception is thrown on failure.
        /// </summary>
        /// <param name="pathVertex">The absolute path to the vertex program source.</param>
        /// <param name="pathFragment">The absolute path to the fragment program source.</param>
        public void Initialise(String pathVertex, String pathFragment)
        {
            // Set member variables
            this.m_VertexProgramPath = pathVertex;
            this.m_FragmentProgramPath = pathFragment;

            // Do the work
            this.Initialise();
        }

        /// <summary>
        /// Initialises the vertex and fragment shader programs for use.
        /// Uses the VertexProgramPath and FragmentProgramPath variables.
        /// This method MUST be called before the programs can be used (via Begin/End).
        /// An exception is thrown on failure.
        /// </summary>
        public void Initialise()
        {
            // Do the init work
            this.LoadExtensions();
            this.LoadPrograms(this.m_VertexProgramPath, this.m_FragmentProgramPath);
            this.CompilePrograms();
            this.AttachPrograms();
            this.LinkPrograms();

            // Check init suceeded
            if (!this.IsReady)
                throw new ApplicationException("Could not initialise the vertex and fragment shader programs.");
        }
        
        /// <summary>
        /// Specifies that OpenGL should switch from the fixed lighting functionality to the
        /// functionality specified by the vertex and fragment shader programs.
        /// </summary>
        public void Begin()
        {
            if (!this.IsReady)
                throw new ApplicationException("The vertex and fragment shader programs are not ready for use.");
            
            Gl.glUseProgramObjectARB(this.m_ProgramHandle);
        }

        /// <summary>
        /// Specifies that OpenGL should switch back to the fixed functionality.
        /// </summary>
        public void End()
        {
            if (!this.IsReady)
                throw new ApplicationException("The vertex and fragment shader programs are not ready for use.");
            
            Gl.glUseProgramObjectARB(0);
        }        
        //============================================================================
        #endregion

        #region Uniforms, Attributes, Varying
        //============================================================================		
        /// <summary>
        /// Sets the given sampler to the given texture unit.
        /// </summary>
        /// <param name="sampler">The name of the sampler variable in the program.</param>
        /// <param name="texunit">The texture unit value.</param>
        public void SetTextureUnit(string sampler, int texunit)
        {
            this.SetUniformInt(sampler, texunit);
        }

        /// <summary>
        /// Sets the given uniform (type vec4) to the given values.
        /// </summary>
        /// <param name="uniform">The name of the vec4 uniform variable.</param>
        /// <param name="v0"></param>
        /// <param name="v1"></param>
        /// <param name="v2"></param>
        /// <param name="v3"></param>
        public void SetUniformVec4(string uniform, float v0, float v1, float v2, float v3)
        {
            int location = Gl.glGetUniformLocationARB(this.m_ProgramHandle, uniform);
            if (location != -1)
            {
                this.Begin();
                Gl.glUniform4fARB(location, v0, v1, v2, v3);
                this.End();
            }
        }

        /// <summary>
        /// Sets the given uniform (type vec3) to the given values.
        /// </summary>
        /// <param name="uniform">The name of the vec3 uniform variable.</param>
        /// <param name="v0"></param>
        /// <param name="v1"></param>
        /// <param name="v2"></param>
        public void SetUniformVec3(string uniform, float v0, float v1, float v2)
        {
            int location = Gl.glGetUniformLocationARB(this.m_ProgramHandle, uniform);
            if (location != -1)
            {
                this.Begin();
                Gl.glUniform3fARB(location, v0, v1, v2);
                this.End();
            }
        }


        /// <summary>
        /// Sets the given uniform (type int) to the given value.
        /// </summary>
        /// <param name="uniform">The name of the int uniform variable</param>
        /// <param name="v0"></param>
        public void SetUniformInt(string uniform, int v0)
        {
            int location = Gl.glGetUniformLocationARB(this.m_ProgramHandle, uniform);
            if (location != -1)
            {
                this.Begin();
                Gl.glUniform1iARB(location, v0);
                this.End();
            }
        }

        /// <summary>
        /// Sets the given uniform (type float) to the given value.
        /// </summary>
        /// <param name="uniform">The name of the int uniform variable</param>
        /// <param name="v0">The value</param>
        public void SetUniformFloat(string uniform, float v0)
        {
            int location = Gl.glGetUniformLocationARB(this.m_ProgramHandle, uniform);
            if (location != -1)
            {
                this.Begin();
                Gl.glUniform1fARB(location, v0);
                this.End();
            }
        }
        //============================================================================
        #endregion

        #region Private Methods
        //============================================================================		
        /// <summary>
        /// Loads the required extensions.
        /// </summary>
        private void LoadExtensions()
        {
            // List the extensions to load
            string[] extensionsToLoad = new string[]
			{
				"GL_ARB_fragment_shader",
				"GL_ARB_shader_objects"
			};

            // Try to load the extensions
            bool result = true;
            foreach (string extensionToLoad in extensionsToLoad)
                result &= GlExtensionLoader.LoadExtension(extensionToLoad);
            if (!result)
            {
                string formattedExtensionsToLoad = string.Empty;
                for (int i = 0; i < extensionsToLoad.Length; i++)
                    formattedExtensionsToLoad += extensionsToLoad[i] + ", ";
                throw new ApplicationException("The OpenGL extensions required for fragment shader programs are not available: " + formattedExtensionsToLoad.Trim(',', ' '));
            }
        }

        /// <summary>
        /// Loads a shader program using the given vertex and fragment shader code.
        /// An exception is thrown on failure.
        /// </summary>
        /// <param name="pathVertex">The absolute path to the vertex program source.</param>
        /// <param name="pathFragment">The absolute path to the fragment program source.</param>
        private void LoadPrograms(string pathVertex, string pathFragment)
        {
            // Check file paths
            if (pathVertex == null || pathVertex.Length == 0 || !File.Exists(pathVertex))
                throw new FileNotFoundException("The vertex shader program file is not valid.", pathVertex);
            if (pathFragment == null || pathFragment.Length == 0 || !File.Exists(pathFragment))
                throw new FileNotFoundException("The fragment shader program file is not valid.", pathFragment);

            // Read files
            StreamReader readerVertex = File.OpenText(pathVertex);
            string contentsVertex = readerVertex.ReadToEnd();
            int lengthVertex = contentsVertex.Length;

            StreamReader readerFragment = File.OpenText(pathFragment);
            string contentsFragment = readerFragment.ReadToEnd();
            int lengthFragment = contentsFragment.Length;

            // Create handles
            this.m_VertexHandle = Gl.glCreateShaderObjectARB(Gl.GL_VERTEX_SHADER_ARB);
            this.m_FragmentHandle = Gl.glCreateShaderObjectARB(Gl.GL_FRAGMENT_SHADER_ARB);

            // Load both programs
            Gl.glShaderSourceARB(this.m_VertexHandle, 1, ref contentsVertex, ref lengthVertex);
            Gl.glShaderSourceARB(this.m_FragmentHandle, 1, ref contentsFragment, ref lengthFragment);

            // Set that we have loaded the programs
            this.m_IsLoaded = true;
        }

        /// <summary>
        /// Compiles the shader program	(vertex and fragment programs).
        /// An exception is thrown on failure.
        /// </summary>
        private void CompilePrograms()
        {
            // Check the programs have been loaded
            if (!this.IsLoaded)
                throw new ApplicationException("The programs have not been loaded.");
            
            // Compile both programs
            this.CompileProgram("vertex", this.m_VertexHandle);
            this.CompileProgram("fragment", this.m_FragmentHandle);

            // Set that we have compiled
            this.m_IsCompiled = true;
        }

        /// <summary>
        /// Compiles the given program. An exception is thrown on failure.
        /// </summary>
        /// <param name="type">Either "vertex" or "fragment".</param>
        /// <param name="handle"></param>
        /// <returns></returns>
        private void CompileProgram(string type, int handle)
        {
            //Compile
            Gl.glCompileShaderARB(handle);

            //Get result
            int result = 0;
            int lenLog = 0;
            Gl.glGetObjectParameterivARB(handle, Gl.GL_OBJECT_COMPILE_STATUS_ARB, out result);
            Gl.glGetObjectParameterivARB(handle, Gl.GL_OBJECT_INFO_LOG_LENGTH_ARB, out lenLog);

            //Show log if compilation failed
            if (result == 0)
            {
                // Get the log
                int lenLogActual = 0;
                string strLog = new string((char)0, 0);
                IntPtr ptrLog = Marshal.StringToHGlobalAnsi(strLog);
                Gl.glGetInfoLogARB(handle, lenLog, out lenLogActual, ptrLog);
                strLog = Marshal.PtrToStringAnsi(ptrLog);

                // Format the log
                string formattedLog = strLog.Replace("\n", "\r\n").ToString().TrimEnd('\r', '\n');
                if (formattedLog.Length < 1)
                    formattedLog = "Log not available.";

                // Create a message
                string message = "An error occured compiling the " + type + " shader program.\r\n";
                message += "Handle=" + handle + "\r\n";
                message += formattedLog;

                // Throw exception
                throw new ApplicationException(message);
            }
        }

        /// <summary>
        /// Attaches the vertex and fragment programs to a global shader program.
        /// An exception is thrown on failure.
        /// </summary>
        private void AttachPrograms()
        {
            // Check the programs have been compiled
            if (!this.IsCompiled)
                throw new ApplicationException("The programs have not been compiled.");
            
            // Create container object
            this.m_ProgramHandle = Gl.glCreateProgramObjectARB();

            // Attach
            Gl.glAttachObjectARB(this.m_ProgramHandle, this.m_VertexHandle);
            Gl.glAttachObjectARB(this.m_ProgramHandle, this.m_FragmentHandle);

            // Set that we have attached
            this.m_IsAttached = true;
        }

        /// <summary>
        /// Links the program. An exception with the log information is thrown on failure.
        /// </summary>
        private void LinkPrograms()
        {
            // Check the programs have been attached
            if (!this.IsAttached)
                throw new ApplicationException("The programs have not been attached.");

            // Link
            Gl.glLinkProgramARB(this.m_ProgramHandle);

            // Get result
            int result = 0;
            int lenLog = 0;
            Gl.glGetObjectParameterivARB(this.m_ProgramHandle, Gl.GL_OBJECT_LINK_STATUS_ARB, out result);
            Gl.glGetObjectParameterivARB(this.m_ProgramHandle, Gl.GL_OBJECT_INFO_LOG_LENGTH_ARB, out lenLog);

            // Check if the link was successful
            if (result == 1)
            {
                this.m_IsLinked = true;
            }
            else
            {
                // Get the log
                int lenLogActual = 0;
                string strLog = new string((char)0, 0);
                IntPtr ptrLog = Marshal.StringToHGlobalAnsi(strLog);
                Gl.glGetInfoLogARB(this.m_ProgramHandle, lenLog, out lenLogActual, ptrLog);
                strLog = Marshal.PtrToStringAnsi(ptrLog);

                // Format the log
                string formattedLog = strLog.Replace("\n", "\r\n").ToString().TrimEnd('\r', '\n');
                if (formattedLog.Length < 1)
                    formattedLog = "Log not available.";
                
                // Create a message
                string message = "An error occured linking the vertex and fragment shader program.\r\n";
                message += "ProgramHandle=" + this.m_ProgramHandle.ToString() + " VertexHandle=" + this.m_VertexHandle.ToString() + " FragmentHandle=" + this.m_FragmentHandle.ToString() + "\r\n";
                message += formattedLog;

                // Throw exception
                throw new ApplicationException(message);
            }
        }        
        //============================================================================
        #endregion
    }
}