Implementation

Let's start laying out the skeleton of the main class and implementing the helper class. One of the new things you will notice is i have blocks of functions wrapped in #region and #endregion tags.

These tags have no effect on the final executable, they are there to visually help the code be more easily readable and navigatable. They get compiled out like comments.

using System;
using System.Drawing;
using System.Drawing.Imaging;
using OpenTK.Graphics.OpenGL;
using System.Collections.Generic;

namespace GameFramework {
    public class TextureManager {

#region Singleton
        private static TextureManager instance = null;
        public static TextureManager Instance {
            get {
                if (instance == null) {
                    instance = new TextureManager();
                }
                return instance;
            }
        }

        private TextureManager() {

        }
#endregion

#region HelperClass
        private class TextureInstance {
            public int glHandle = -1;
            public string path = string.Empty;
            public int refCount = 0;
            public int width = 0;
            public int height = 0;
        }
#endregion

#region MemberVariables
        private List<TextureInstance> managedTextures = null;
        private bool isInitialized = false;
#endregion

#region HelperFunctions
        private void Error(string error) { }
        private void Warning(string error) { }
        private void InitCheck(string errorMessage) { }
        private void IndexCheck(int index, string function) { }
        private bool IsPowerOfTwo(int x) { }
        private int LoadGLTexture(string filename, out int width, out int height, bool nearest) { }
#endregion

#region PublicAPI
        public void Initialize() { }
        public void Shutdown() { }
        public int LoadTexture(string texturePath, bool UseNearestFiltering = false) { }
        public void UnloadTexture(int textureId) { }
        public int GetTextureWidth(int textureId) { }
        public int GetTextureHeight(int textureId) { }
        public Size GetTextureSize(int textureId) { }
        public int GetGLHandle(int textureId) { }
#endregion
    }
}

As you can see this class is a singleton, therefore it has a public Instance accessor, and it's constructor is marked as private to ensure that only this class can make a new instance of it's self.

We defined a private inner class called TextureInstance. Because it's an inner class, you can only make a new instance of it as new TextureManager.TextureInstance outside of TextureManager, but inside you can just use new TextureInstance. This however doesn't matter, because the inner class is private, nothing outside of TextureManager can ever reference it.

We have two member variables, one is a list of TextureInstance, this is all the textures we are managing, the other is a bool to keep track of weather the manager has been initialized or not.

We have 6 private helper functions. These are private because they will never be used outside of the texture manager class. We will talk about them more in detail as we implement each of them.

Finally, the public API consists of 8 functions. These are the functions that the rest of the code can use to interact with our manager. Again, we will talk about these in more detail as we implement them