CSharpGL(38)带初始数据创建Vertex Buffer Object的情形汇总

开始

总的来说，OpenGL应用开发者会遇到为如下三种数据创建Vertex Buffer Object的情形：

  1. 任意一个struct类型T data；
  2. 任意一个元素类型为struct的数组T[] array；
  3. 任意一个非托管数组UnmanagedArray<T> array；

而可创建的Vertex Buffer Object也分为如下的类别：

  1. 描述顶点属性（位置、颜色、法线等）的VertexBuffer；
  2. 描述索引的IndexBuffer；
  3. 描述其他自定义内容的各种Buffer；

本文介绍用C#如何实现上述功能。

非托管数组->VertexBuffer

最基本的功能是通过非托管数组UnmanagedArrayBase创建一个VBO，我们首先实现这个功能。

         public static VertexBuffer GetVertexBuffer(this UnmanagedArrayBase array, VBOConfig config, string varNameInVertexShader, BufferUsage usage, uint instancedDivisor = , int patchVertexes = )

         {

             uint[] buffers = new uint[];

             glGenBuffers(, buffers);

             const uint target = OpenGL.GL_ARRAY_BUFFER;

             glBindBuffer(target, buffers[]);

             glBufferData(target, array.ByteLength, array.Header, (uint)usage);

             glBindBuffer(target, );

             var buffer = new VertexBuffer(

                 varNameInVertexShader, buffers[], config, array.Length, array.ByteLength, instancedDivisor, patchVertexes);

             return buffer;

         }

T[] -> VertexBuffer

很多时候，大家都是在用习惯了的托管数组（int[]、Point[]、vec3[]等）。那么能不能直接用托管数组创建VBO呢？当然可以。虽然是托管数组，但是在内存中毕竟也还是连续存放的一块内存。我们只需找到它的地址就可以了。找地址这件事通过 Marshal.UnsafeAddrOfPinnedArrayElement(); 就可以做到。

         public static VertexBuffer GetVertexBuffer<T>(this T[] array, VBOConfig config, string varNameInVertexShader, BufferUsage usage, uint instancedDivisor = , int patchVertexes = ) where T : struct

         {

             GCHandle pinned = GCHandle.Alloc(array, GCHandleType.Pinned);

             IntPtr header = Marshal.UnsafeAddrOfPinnedArrayElement(array, );

             UnmanagedArrayBase unmanagedArray = new UnmanagedArray<T>(header, array.Length);// It's not neecessary to call Dispose() for this unmanaged array.

             VertexBuffer buffer = GetVertexBuffer(unmanagedArray, config, varNameInVertexShader, usage, instancedDivisor, patchVertexes);

             pinned.Free();

             return buffer;

         }

T -> VertexBuffer

那么单独的一个struct变量，如何为之创建VBO？只需用一个 var array = new T[]{ data }; 将其封装起来，就可以用上面的方法了。

         public static VertexBuffer GetVertexBuffer<T>(this T data, VBOConfig config, string varNameInVertexShader, BufferUsage usage, uint instancedDivisor = , int patchVertexes = ) where T : struct

         {

             var array = new T[] { data };

             return GetVertexBuffer(array, config, varNameInVertexShader, usage, instancedDivisor, patchVertexes);

             // another way to do this:

             //using (UnmanagedArrayBase unmanagedArray = new UnmanagedArray<T>(1))

             //{

             //    Marshal.StructureToPtr(data, unmanagedArray.Header, false);

             //    VertexBuffer buffer = GetVertexBufferObject(unmanagedArray, config, varNameInVertexShader, usage, instancedDivisor, patchVertexes);

             //    return buffer;

             //}

         }

非托管数组->IndexBuffer

非托管数组->OneIndexBuffer

从非托管数组到OneIndexBuffer的思路和上面一致。要注意的是，OneIndexBuffer能接受的元素类型只能是byte、ushort、uint三者之一。

         public static OneIndexBuffer GetOneIndexBuffer(this UnmanagedArray<byte> array, DrawMode mode, BufferUsage usage, int primCount = )

         {

             return GetOneIndexBuffer(array, mode, usage, IndexElementType.UByte, primCount);

         }

         public static OneIndexBuffer GetOneIndexBuffer(this UnmanagedArray<ushort> array, DrawMode mode, BufferUsage usage, int primCount = )

         {

             return GetOneIndexBuffer(array, mode, usage, IndexElementType.UShort, primCount);

         }

         public static OneIndexBuffer GetOneIndexBuffer(this UnmanagedArray<uint> array, DrawMode mode, BufferUsage usage, int primCount = )

         {

             return GetOneIndexBuffer(array, mode, usage, IndexElementType.UInt, primCount);

         }

         private static OneIndexBuffer GetOneIndexBuffer(this UnmanagedArrayBase array, DrawMode mode, BufferUsage usage, IndexElementType elementType, int primCount = )

         {

             if (glGenBuffers == null)

             {

                 InitFunctions();

             }

             uint[] buffers = new uint[];

             glGenBuffers(, buffers);

             const uint target = OpenGL.GL_ELEMENT_ARRAY_BUFFER;

             glBindBuffer(target, buffers[]);

             glBufferData(target, array.ByteLength, array.Header, (uint)usage);

             glBindBuffer(target, );

             var buffer = new OneIndexBuffer(buffers[], mode, elementType, array.Length, array.ByteLength, primCount);

             return buffer;

         }

T[] -> OneIndexBuffer

思路同上。

         public static OneIndexBuffer GetOneIndexBuffer(this byte[] array, DrawMode mode, BufferUsage usage, int primCount = )

         {

             GCHandle pinned = GCHandle.Alloc(array, GCHandleType.Pinned);

             IntPtr header = Marshal.UnsafeAddrOfPinnedArrayElement(array, );

             var unmanagedArray = new UnmanagedArray<byte>(header, array.Length);// It's not neecessary to call Dispose() for this unmanaged array.

             OneIndexBuffer buffer = GetOneIndexBuffer(unmanagedArray, mode, usage, IndexElementType.UByte, primCount);

             pinned.Free();

             return buffer;

         }

         public static OneIndexBuffer GetOneIndexBuffer(this ushort[] array, DrawMode mode, BufferUsage usage, int primCount = )

         {

             GCHandle pinned = GCHandle.Alloc(array, GCHandleType.Pinned);

             IntPtr header = Marshal.UnsafeAddrOfPinnedArrayElement(array, );

             var unmanagedArray = new UnmanagedArray<ushort>(header, array.Length);// It's not neecessary to call Dispose() for this unmanaged array.

             OneIndexBuffer buffer = GetOneIndexBuffer(unmanagedArray, mode, usage, IndexElementType.UShort, primCount);

             pinned.Free();

             return buffer;

         }

         public static OneIndexBuffer GetOneIndexBuffer(this uint[] array, DrawMode mode, BufferUsage usage, int primCount = )

         {

             GCHandle pinned = GCHandle.Alloc(array, GCHandleType.Pinned);

             IntPtr header = Marshal.UnsafeAddrOfPinnedArrayElement(array, );

             var unmanagedArray = new UnmanagedArray<uint>(header, array.Length);// It's not neecessary to call Dispose() for this unmanaged array.

             OneIndexBuffer buffer = GetOneIndexBuffer(unmanagedArray, mode, usage, IndexElementType.UInt, primCount);

             pinned.Free();

             return buffer;

         }

T -> OneIndexBuffer

只有1个元素的索引数组，比较奇葩，不过也是可以实现的。

         public static OneIndexBuffer GetOneIndexBuffer(this byte data, DrawMode mode, BufferUsage usage, int primCount = )

         {

             var array = new byte[] { data };

             return GetOneIndexBuffer(array, mode, usage, primCount);

         }

         public static OneIndexBuffer GetOneIndexBuffer(this ushort data, DrawMode mode, BufferUsage usage, int primCount = )

         {

             var array = new ushort[] { data };

             return GetOneIndexBuffer(array, mode, usage, primCount);

         }

         public static OneIndexBuffer GetOneIndexBuffer(this uint data, DrawMode mode, BufferUsage usage, int primCount = )

         {

             var array = new uint[] { data };

             return GetOneIndexBuffer(array, mode, usage, primCount);

         }

ZeroIndexBuffer

这事一个特殊的Buffer，因为实际上在OpenGL的server端并没有真正创建一个Buffer。但是逻辑上把它也视作一个Buffer是方便合理的。既然没有真正创建Buffer，那么也就不存在用非托管数组创建ZeroIndexBuffer的情形了。

非托管数组->自定义Buffer

自定义Buffer都有哪些

所谓自定义Buffer，是那些用途各异的特殊Buffer，目前CSharpGL包含了：

 AtomicCounterBuffer

 PixelPackBuffer

 PixelUnpackBuffer

 ShaderStorageBuffer

 TextureBuffer

 UniformBuffer

下面以 AtomicCounterBuffer 为例，其他雷同。

非托管数组->自定义Buffer

思路同上。

        public static AtomicCounterBuffer GetAtomicCounterBuffer(this UnmanagedArrayBase array, BufferUsage usage)

        {

            return GetIndependentBuffer(array, IndependentBufferTarget.AtomicCounterBuffer, usage) as AtomicCounterBuffer;

        }

        private static Buffer GetIndependentBuffer(this UnmanagedArrayBase array, IndependentBufferTarget bufferTarget, BufferUsage usage)

        {

            uint[] buffers = new uint[];

            glGenBuffers(, buffers);

            var target = (uint)bufferTarget;

            glBindBuffer(target, buffers[]);

            glBufferData(target, array.ByteLength, array.Header, (uint)usage);

            glBindBuffer(target, );

            Buffer buffer = null;

            switch (bufferTarget)

            {

                case IndependentBufferTarget.AtomicCounterBuffer:

                    buffer = new AtomicCounterBuffer(buffers[], array.Length, array.ByteLength);

                    break;

                case IndependentBufferTarget.PixelPackBuffer:

                    buffer = new PixelPackBuffer(buffers[], array.Length, array.ByteLength);

                    break;

                case IndependentBufferTarget.PixelUnpackBuffer:

                    buffer = new PixelUnpackBuffer(buffers[], array.Length, array.ByteLength);

                    break;

                case IndependentBufferTarget.ShaderStorageBuffer:

                    buffer = new ShaderStorageBuffer(buffers[], array.Length, array.ByteLength);

                    break;

                case IndependentBufferTarget.TextureBuffer:

                    buffer = new TextureBuffer(buffers[], array.Length, array.ByteLength);

                    break;

                case IndependentBufferTarget.UniformBuffer:

                    buffer = new UniformBuffer(buffers[], array.Length, array.ByteLength);

                    break;

                default:

                    throw new NotImplementedException();

            }

            return buffer;

        }

T[] –> 自定义Buffer

思路同上。

         public static AtomicCounterBuffer GetAtomicCounterBuffer<T>(this T[] array, BufferUsage usage) where T : struct

         {

             GCHandle pinned = GCHandle.Alloc(array, GCHandleType.Pinned);

             IntPtr header = Marshal.UnsafeAddrOfPinnedArrayElement(array, );

             var unmanagedArray = new UnmanagedArray<T>(header, array.Length);// It's not neecessary to call Dispose() for this unmanaged array.

             AtomicCounterBuffer buffer = GetIndependentBuffer(unmanagedArray, IndependentBufferTarget.AtomicCounterBuffer, usage) as AtomicCounterBuffer;

             pinned.Free();

             return buffer;

         }

T -> 自定义Buffer

思路同上。这个方式还是比较常见的一种用法。

         public static AtomicCounterBuffer GetAtomicCounterBuffer<T>(this T data, BufferUsage usage) where T : struct

         {

             var array = new T[] { data };

             return GetAtomicCounterBuffer(array, usage);

         }

如何使用

实现了上面那些看起来比较啰嗦的功能，现在来看看使用的时候是什么情形。

-> VertexBuffer

最基本的功能是通过数组UnmanagedArrayBase或T[]创建一个VBO，我们首先使用这个功能。可见只需一行代码即可实现，且调用方式也相同。

     vec3 position = GetPositions();

     VertexBuffer buffer = position.GetVertexBuffer(VBOConfig.Vec3, varNameInShader, BufferUsage.StaticDraw);

     //

     vec3[] positions = GetPositions();

     VertexBuffer buffer = positions.GetVertexBuffer(VBOConfig.Vec3, varNameInShader, BufferUsage.StaticDraw);

     //

     UnmanagedArray<vec3> positions = GetPositions();

     VertexBuffer buffer = positions.GetVertexBuffer(VBOConfig.Vec3, varNameInShader, BufferUsage.StaticDraw);

-> OneIndexBuffer

同上，不解释。

     uint position = GetIndexes();

     VertexBuffer buffer = position.GetOneIndexBuffer(DrawMode.Triangles, BufferUsage.StaticDraw);

     //

     uint[] positions = GetIndexes();

     VertexBuffer buffer = positions.GetOneIndexBuffer(DrawMode.Triangles, BufferUsage.StaticDraw);

     //

     UnmanagedArray<uint> positions = GetIndexes();

     VertexBuffer buffer = positions.GetOneIndexBuffer(DrawMode.Triangles, BufferUsage.StaticDraw);

-> 自定义Buffer

同上，不解释。

     SomeStruct data = GetIndexes();

     VertexBuffer buffer = position.GetUniformBuffer(BufferUsage.StaticDraw);

     //

     SomeStruct[] data = GetIndexes();

     VertexBuffer buffer = data.GetUniformBuffer(BufferUsage.StaticDraw);

     //

     UnmanagedArray<SomeStruct> data = GetIndexes();

     VertexBuffer buffer = data.GetUniformBuffer(BufferUsage.StaticDraw);

总结

业务数据是核心，其他参数辅助，按照这一思路，就实现了现在的一行创建VBO的功能。

CSharpGL已经有点深度，所以笔记很难写出让人直接就能眼前一亮的感觉了。

目前CSharpGL中已经涵盖了我所知的所有OpenGL知识点。下一步就是精心读书，继续深挖。

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