ID3DXMesh接口的主要功能繼承自ID3DXBaseMesh父接口，了解這些是很重要的，其它一些mesh接口如ID3DXPMesh也是繼承自ID3DXBaseMesh。
ID3DXBaseMesh接口包含一個用來存儲網格頂點的頂點緩存和一個用來定義這些頂點怎樣連接在一起組成網格三角形的索引緩存。我們使用下面的方法來得到這些緩存的指針：
|
HRESULT
ID3DXMesh::GetVertexBuffer(LPDIRECT3DVERTEXBUFFER9* ppVB);
HRESULT
ID3DXMesh::GetIndexBuffer(LPDIRECT3DINDEXBUFFER9* ppIB);
|
這里有一些使用這些方法的例子：
|
IDirect3DVertexBuffer9* vb
= 0;
Mesh->GetVertexBuffer( &vb
);
IDirect3DIndexBuffer9* ib =
0;
Mesh->GetIndexBuffer( &ib
);
|
假如想鎖定這些緩存來讀寫數據，那么我們能夠使用下面的方法。注意這些方法鎖定整個頂點/索引緩存。
Locks a vertex buffer and obtains a pointer to the
vertex buffer memory.
HRESULT LockVertexBuffer(
DWORD Flags,
LPVOID * ppData
);
Parameters
- Flags
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
- [in] For a description of the flags, see D3DLOCK.
- ppData
- [out, retval] VOID* pointer to a buffer containing
the vertex data.
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.
Locks an index buffer and obtains a pointer to the
index buffer memory.
HRESULT LockIndexBuffer(
DWORD Flags,
LPVOID * ppData
);
Parameters
- Flags
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
- [in] For a description of the flags, see D3DLOCK.
- ppData
- [out, retval] VOID* pointer to a buffer containing
the index data. The count of indices in this buffer will be equal to
ID3DXBaseMesh::GetNumFaces * 3.
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 index 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 index buffer.
D3DLOCK
A combination of zero or more locking options that
describe the type of lock to perform.
| #define |
Description |
| D3DLOCK_DISCARD |
The application discards all memory within the
locked region. For vertex and index buffers, the entire buffer will be
discarded. This option is only valid when the resource is created with
dynamic usage (see D3DUSAGE). |
| D3DLOCK_DONOTWAIT |
Allows an application to gain back CPU cycles
if the driver cannot lock the surface immediately. If this flag is set
and the driver cannot lock the surface immediately, the lock call will
return D3DERR_WASSTILLDRAWING. This flag can only be used when locking a
surface created using IDirect3DDevice9::CreateOffscreenPlainSurface,
IDirect3DDevice9::CreateRenderTarget, or
IDirect3DDevice9::CreateDepthStencilSurface. This flag can also be used
with a back buffer. |
| D3DLOCK_NO_DIRTY_UPDATE |
By default, a lock on a resource adds a dirty
region to that resource. This option prevents any changes to the dirty
state of the resource. Applications should use this option when they
have additional information about the set of regions changed during the
lock operation. |
| D3DLOCK_NOOVERWRITE |
Indicates that memory that was referred to in
a drawing call since the last lock without this flag will not be
modified during the lock. This can enable optimizations when the
application is appending data to a resource. Specifying this flag
enables the driver to return immediately if the resource is in use,
otherwise, the driver must finish using the resource before returning
from locking. |
| D3DLOCK_NOSYSLOCK |
The default behavior of a video memory lock is
to reserve a system-wide critical section, guaranteeing that no display
mode changes will occur for the duration of the lock. This option causes
the system-wide critical section not to be held for the duration of the
lock.
The lock operation is time
consuming, but can enable the system to perform other duties, such as
moving the mouse cursor. This option is useful for long-duration locks,
such as the lock of the back buffer for software rendering that would
otherwise adversely affect system responsiveness.
|
| D3DLOCK_READONLY |
The application will not write to the buffer.
This enables resources stored in non-native formats to save the
recompression step when unlocking. |
當然在你鎖定以后一定要記得解鎖：
|
HRESULT
ID3DXMesh::UnlockVertexBuffer();
HRESULT
ID3DXMesh::UnlockIndexBuffer();
|
下面是另外一些與mesh幾何結構有關的ID3DXMesh接口方法：
DWORD
GetFVF() — 返回頂點的格式
DWORD
GetNumVertices() —
返回頂點緩存中的頂點數
DWORD
GetNumBytesPerVertex() —
返回一個頂點所占的字節數
DWORD GetNumFaces()
— 返回在mesh中的面（三角形）數
一個mesh由一個或數個子集組成。一個子集（subset）是在mesh中的使用相同屬性渲染的一組三角形。這里的屬性是指材質，紋理和渲染狀態。圖10.1顯示了一座房子mesh可能被分成的幾個子集。
在mesh中的每個三角形都與一個屬性ID相關聯，表示該三角形屬于該子集。例如，圖10.1中組成地板的三角形具有屬性ID0，它表示這些三角形屬于子集0。同樣，組成墻的三角形具有屬性ID1，它表示這些三角形屬于子集1。
三角形的屬性ID存儲在mesh的屬性緩存中，它是一個DWORD數組。因為每個面對應屬性緩存中的一項，所以屬性緩存中的項目數等于mesh中的面的個數。屬性緩存中的項目和索引緩存中定義的三角形一一對應。即，屬性緩存中的第i項和索引緩存中的第i個三角形相對應。三角形i由下面三個索引緩存中的索引項定義：
A = i * 3
B = i * 3 + 1
C = i * 3 + 2
圖10.2顯示了這個對應關系：
我們可以通過LockAttributeBuffer()鎖定屬性緩存:
Locks the mesh buffer that contains the mesh attribute
data, and returns a pointer to it.
HRESULT LockAttributeBuffer(
DWORD Flags,
DWORD ** ppData
);
Parameters
- Flags
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
- [in] For a description of the flags, see D3DLOCK.
- ppData
- [out] Address of a pointer to a buffer containing
a DWORD for each face in the mesh.
Return Values
If the method succeeds, the return value is D3D_OK. If
the method fails, the return value can be D3DERR_INVALIDCALL.
Remarks
If ID3DXMesh::Optimize has been called, the mesh will
also have an attribute table that can be accessed using the
ID3DXBaseMesh::GetAttributeTable method.
就象下面的代碼片段：
|
DWORD* buffer = 0;
Mesh->LockAttributeBuffer(lockingFlags, &buffer);
// Read or
write to attribute buffer...
Mesh->UnlockAttributeBuffer();
|
ID3DXMesh接口提供了DrawSubset（DWORD
AttribId）方法來繪制AttribId指示的子集中的各個三角形。
Draws a subset of a mesh.
HRESULT DrawSubset(
DWORD AttribId
);
Parameters
- AttribId
- [in] DWORD that specifies which subset of the mesh
to draw. This value is used to differentiate faces in a mesh as belonging to
one or more attribute groups.
Return Values
If the method succeeds, the return value is D3D_OK. If
the method fails, the return value can be D3DERR_INVALIDCALL.
Remarks
The subset that is specified by AttribId will be
rendered by the IDirect3DDevice9::DrawIndexedPrimitive method, using the
D3DPT_TRIANGLELIST primitive type, so an index buffer must be properly
initialized.
An attribute table is used to identify areas of the
mesh that need to be drawn with different textures, render states, materials,
and so on. In addition, the application can use the attribute table to hide
portions of a mesh by not drawing a given attribute identifier (AttribId)
when drawing the frame.
例如，要繪制子集0中的所有三角形，我們將這樣寫：
為了繪制整個mesh，我們必須繪制mesh的所有子集。這是非常方便的用0，1，2，…，n-1來標識子集，這里的n是子集的總數。且有一個相對應的材質和紋理數組，即子集i與材質和紋理數組的第i項對應。這就使我們能夠簡單的用循環來渲染mesh：
|
for(int
i = 0; i < numSubsets; i++)
{
Device->SetMaterial(
mtrls[i] );
Device->SetTexture(
0, textures[i] );
Mesh->DrawSubset(i);
}
|