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：
- 任意一个struct类型T data；
- 任意一个元素类型为struct的数组T[] array；
- 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：
- 描述顶点属性（位置、颜色、法线等）的VertexBuffer；
- 描述索引的IndexBuffer；
- 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。