坐标系与基本图元（2）

创建顶点缓冲区

在创建顶点缓冲区之前，需要先定义一个表示顶点的结构类型，描述顶点保存格式的FVF和一个保存顶点的结构数组。

struct sCustomVertex
{
	float x, y, z, rhw;
	DWORD color;
};

#define D3DFVF_CUSTOM_VERTEX (D3DFVF_XYZRHW | D3DFVF_DIFFUSE) 

sCustomVertex vertices[] =
{
    { 100.0f, 400.0f, 1.0f, 1.0f, 0xffffff00, },
    { 300.0f,  50.0f, 1.0f, 1.0f, 0xff00ff00, }, 
    { 500.0f, 400.0f, 1.0f, 1.0f, 0xffff00ff, },
};

创建顶点缓冲区的函数IDirect3DDevice9::CreateVertexBuffer()声明如下：

Creates a vertex buffer.

HRESULT CreateVertexBuffer(
  UINT Length,
  DWORD Usage,
  DWORD FVF,
  D3DPOOL Pool,
  IDirect3DVertexBuffer9** ppVertexBuffer,
  HANDLE* pSharedHandle
);

Parameters

Length

[in] Size of the vertex buffer, in bytes. For FVF vertex buffers, Length must be large enough to contain at least one vertex, but it need not be a multiple of the vertex size. Length is not validated for non-FVF buffers. See Remarks.

Usage

[in] Usage can be 0, which indicates no usage value. However, if usage is desired, use a combination of one or more D3DUSAGE constants. It is good practice to match the usage parameter in CreateVertexBuffer with the behavior flags in IDirect3D9::CreateDevice. For more information, see Remarks.

FVF

[in] Combination of D3DFVF, a usage specifier that describes the vertex format of the vertices in this buffer. If this parameter is set to a valid FVF code, the created vertex buffer is an FVF vertex buffer (see Remarks). Otherwise, if this parameter is set to zero, the vertex buffer is a non-FVF vertex buffer.

Pool

[in] Member of the D3DPOOL enumerated type, describing a valid memory class into which to place the resource. Do not set to D3DPOOL_SCRATCH.

ppVertexBuffer

[out, retval] Address of a pointer to an IDirect3DVertexBuffer9 interface, representing the created vertex buffer resource.

pSharedHandle

[in] Reserved. Set this parameter to NULL.

Return Values

If the method succeeds, the return value is D3D_OK. If the method fails, the return value can be one of the following: D3DERR_INVALIDCALL, D3DERR_OUTOFVIDEOMEMORY, E_OUTOFMEMORY.

Defines the memory class that holds the buffers for a resource.

typedef enum D3DPOOL
{
    D3DPOOL_DEFAULT = 0,
    D3DPOOL_MANAGED = 1,
    D3DPOOL_SYSTEMMEM = 2,
    D3DPOOL_SCRATCH = 3,
    D3DPOOL_FORCE_DWORD = 0x7fffffff,
} D3DPOOL, *LPD3DPOOL;

Constants

D3DPOOL_DEFAULT

Resources are placed in the memory pool most appropriate for the set of usages requested for the given resource. This is usually video memory, including both local video memory and AGP memory. The D3DPOOL_DEFAULT pool is separate from D3DPOOL_MANAGED and D3DPOOL_SYSTEMMEM, and it specifies that the resource is placed in the preferred memory for device access. Note that D3DPOOL_DEFAULT never indicates that either D3DPOOL_MANAGED or D3DPOOL_SYSTEMMEM should be chosen as the memory pool type for this resource. Textures placed in the D3DPOOL_DEFAULT pool cannot be locked unless they are dynamic textures or they are private, FOURCC, driver formats. To access unlockable textures, you must use functions such as IDirect3DDevice9::UpdateSurface, IDirect3DDevice9::UpdateTexture, IDirect3DDevice9::GetFrontBufferData, and IDirect3DDevice9::GetRenderTargetData. D3DPOOL_MANAGED is probably a better choice than D3DPOOL_DEFAULT for most applications. Note that some textures created in driver-proprietary pixel formats, unknown to the Direct3D runtime, can be locked. Also note that - unlike textures - swap chain back buffers, render targets, vertex buffers, and index buffers can be locked. When a device is lost, resources created using D3DPOOL_DEFAULT must be released before calling IDirect3DDevice9::Reset. For more information, see Lost Devices (Direct3D 9).

When creating resources with D3DPOOL_DEFAULT, if video card memory is already committed, managed resources will be evicted to free enough memory to satisfy the request.

D3DPOOL_MANAGED

Resources are copied automatically to device-accessible memory as needed. Managed resources are backed by system memory and do not need to be recreated when a device is lost. See Managing Resources (Direct3D 9) for more information. Managed resources can be locked. Only the system-memory copy is directly modified. Direct3D copies your changes to driver-accessible memory as needed.

D3DPOOL_SYSTEMMEM

Resources are placed in memory that is not typically accessible by the Direct3D device. This memory allocation consumes system RAM but does not reduce pageable RAM. These resources do not need to be recreated when a device is lost. Resources in this pool can be locked and can be used as the source for a IDirect3DDevice9::UpdateSurface or IDirect3DDevice9::UpdateTexture operation to a memory resource created with D3DPOOL_DEFAULT.

D3DPOOL_SCRATCH

Resources are placed in system RAM and do not need to be recreated when a device is lost. These resources are not bound by device size or format restrictions. Because of this, these resources cannot be accessed by the Direct3D device nor set as textures or render targets. However, these resources can always be created, locked, and copied.

D3DPOOL_FORCE_DWORD

Forces this enumeration to compile to 32 bits in size. Without this value, some compilers would allow this enumeration to compile to a size other than 32 bits. This value is not used.

 

创建顶点缓冲区的代码如下：

g_device->CreateVertexBuffer(sizeof(vertices), 0, D3DFVF_CUSTOM_VERTEX, D3DPOOL_DEFAULT, &g_vertex_buffer, NULL);

现在，已经创建了顶点缓冲区g_vertex_buffer，接下来把顶点数据vertices[]中保存的顶点数据复制到顶点缓冲区中:

void* ptr;

g_vertex_buffer->Lock(0, sizeof(vertices), (void**)&ptr, 0);
memcpy(ptr, vertices, sizeof(vertices));
g_vertex_buffer->Unlock();

IDirect3DVertexBuffer9::Lock()通知Direct3D将要对顶点缓冲区进行内存操作，并获得顶点缓冲区的内存指针，顶点数据复制完成后，IDirect3DVertexBuffer9::Unlock()通知Direct3D操作结束。

Locks a range of vertex data and obtains a pointer to the vertex buffer memory.

HRESULT Lock(
  UINT OffsetToLock,
  UINT SizeToLock,
  VOID ** ppbData,
  DWORD Flags
);

Parameters

OffsetToLock

[in] Offset into the vertex data to lock, in bytes. To lock the entire vertex buffer, specify 0 for both parameters, SizeToLock and OffsetToLock.

SizeToLock

[in] Size of the vertex data to lock, in bytes. To lock the entire vertex buffer, specify 0 for both parameters, SizeToLock and OffsetToLock.

ppbData

[out] VOID* pointer to a memory buffer containing the returned vertex data.

Flags

[in] Combination of zero or more locking flags that describe the type of lock to perform. For this method, the valid flags are:

• D3DLOCK_DISCARD
• D3DLOCK_NO_DIRTY_UPDATE
• D3DLOCK_NOSYSLOCK
• D3DLOCK_READONLY
• D3DLOCK_NOOVERWRITE

For a description of the flags, see D3DLOCK.

Return Values

If the method succeeds, the return value is D3D_OK. If the method fails, the return value can be D3DERR_INVALIDCALL.

Remarks

When working with vertex buffers, you are allowed to make multiple lock calls; however, you must ensure that the number of lock calls match the number of unlock calls. DrawPrimitive calls will not succeed with any outstanding lock count on any currently set vertex buffer.

The D3DLOCK_DISCARD and D3DLOCK_NOOVERWRITE flags are valid only on buffers created with D3DUSAGE_DYNAMIC.

For information about using D3DLOCK_DISCARD or D3DLOCK_NOOVERWRITE with IDirect3DVertexBuffer9::Lock, see Using Dynamic Vertex and Index Buffers.

参数Flags表示顶点缓冲区的加锁属性，它可以取0（默认值）或者下表中任意值的逻辑或。

执行Lock()函数需要一定的时间，默认状态下，Direct3D会暂停其他的显示操作，直至Lock()函数执行结束。设置D3DLOCK_NOSYSLOCK属性，可以使Direct3D在执行对缓冲区加锁的同时执行其他的显示操作，比如移动鼠标。