渲染圖形
使用Direct3D繪制三維圖形和使用GDI繪制二維圖形的方法非常類似，Direct3D程序中的Direct3D設備對象相當于GDI程序中的hdc(設備描述表)，使用 GDI繪制圖形前，通常需要先利用hdc進行相關設置，然后通過hdc進行繪圖。同樣在Direct3D程序中通常先通過Direct3D設備接口進行相關的渲染設備設置，然后再渲染圖形。而且所有的渲染圖形操作必須在函數BeginScene()和EndScene()之間進行。
void render()
{
g_device->Clear(0, NULL, D3DCLEAR_TARGET, D3DCOLOR_X#2d32aa, 1.0f, 0);
g_device->BeginScene();
// render game scene here
g_device->EndScene();
g_device->Present(NULL, NULL, NULL, NULL);
}
IDirect3DDevice9::Clear()函數的作用是清空一個或多個表面的內容。Direct3D在繪制圖形前，需要使用該函數清空視口（viewport）的顏色緩沖區、深度緩沖區或者模板緩沖區。
Clears one or more surfaces such as a render target,
multiple render targets, a stencil buffer, and a depth buffer.
HRESULT Clear(
DWORD Count,
CONST D3DRECT * pRects,
DWORD Flags,
D3DCOLOR Color,
float Z,
DWORD Stencil
);
Parameters
- Count
- [in] Number of rectangles in the array at pRects.
Must be set to 0 if pRects is NULL. May not be 0 if pRects is a valid
pointer.
- pRects
- [in] Pointer to an array of D3DRECT structures
that describe the rectangles to clear. Set a rectangle to the dimensions of
the rendering target to clear the entire surface. Each rectangle uses screen
coordinates that correspond to points on the render target. Coordinates are
clipped to the bounds of the viewport rectangle. To indicate that the entire
viewport rectangle is to be cleared, set this parameter to NULL and Count to
0.
- Flags
- [in] Combination of one or more D3DCLEAR flags
that specify the surface(s) that will be cleared.
- Color
- [in] Clear a render target to this ARGB color.
- Z
- [in] Clear the depth buffer to this new z value
which ranges from 0 to 1. See remarks.
- Stencil
- [in] Clear the stencil buffer to this new value
which ranges from 0 to 2n - 1 (n is the bit depth of the stencil
buffer). See remarks.
Return Values
If the method succeeds, the return value is D3D_OK. If
the method fails, the return value can be: D3DERR_INVALIDCALL.
Remarks
Use this method to clear a surface including: a render
target, all render targets in an MRT, a stencil buffer, or a depth buffer. Flags
determines how many surfaces are cleared. Use pRects to clear a subset of a
surface defined by an array of rectangles.
IDirect3DDevice9::Clear will fail if you:
- Try to clear either the depth buffer or the
stencil buffer of a render target that does not have an attached depth
buffer.
- Try to clear the stencil buffer when the depth
buffer does not contain stencil data.
大多數三維圖形程序擁有2個或者更多顏色緩沖區。用于當前屏幕刷新的顏色緩沖區稱為前臺緩沖區，而將用于圖形繪制的其他顏色緩沖區稱為后臺緩沖區。同時擁有前臺緩沖區和后臺緩沖區的圖形程序可以同時進行圖形繪制和屏幕刷新工作，系統的運行性能優于僅有單個顏色緩沖區的圖形程序。在Direct3D程序中最常見的情況是有一個前臺緩沖區和一個后臺緩沖區。
在繪制圖形開始之前，必須先調用函數IDirect3DDevice9::BeginScene()函數，通知Direct3D設備開始繪制圖形（又稱渲染），否則Direct3D程序就會出錯返回；渲染程序完成后，也必須調用函數IDirect3DDevice9::EndScene()通知Direct3D設備結束渲染。而且這兩個函數必須成對出現，不允許嵌套和交錯的情況發生。任何Direct3D渲染函數都必須在函數BeginScene()和函數EndScene()的中間出現。
Direct3D在后臺緩沖區進行圖形繪制操作，當所有的圖形繪制操作結束之后，調用函數IDirect3DDevice9::Present()將在后臺緩沖區繪制的內容提交到前臺顯示，這樣繪制的圖形就顯示在屏幕上了。
Presents the contents of the next buffer in the
sequence of back buffers owned by the device.
HRESULT Present(
CONST RECT * pSourceRect,
CONST RECT * pDestRect,
HWND hDestWindowOverride,
CONST RGNDATA * pDirtyRegion
);
Parameters
- pSourceRect
- [in] Pointer to a value that must be NULL unless
the swap chain was created with D3DSWAPEFFECT_COPY. pSourceRect is a pointer
to a RECT structure containing the source rectangle. If NULL, the entire
source surface is presented. If the rectangle exceeds the source surface,
the rectangle is clipped to the source surface.
- pDestRect
- [in] Pointer to a value that must be NULL unless
the swap chain was created with D3DSWAPEFFECT_COPY. pDestRect is a pointer
to a RECT structure containing the destination rectangle, in window client
coordinates. If NULL, the entire client area is filled. If the rectangle
exceeds the destination client area, the rectangle is clipped to the
destination client area.
- hDestWindowOverride
- [in] Pointer to a destination window whose client
area is taken as the target for this presentation. If this value is NULL,
then the hWndDeviceWindow member of D3DPRESENT_PARAMETERS is taken.
- pDirtyRegion
- [in] Value must be NULL unless the swap chain was
created with D3DSWAPEFFECT_COPY. For more information about swap chains, see
Flipping Surfaces (Direct3D 9) and D3DSWAPEFFECT. If this value is non-NULL,
the contained region is expressed in back buffer coordinates. The rectangles
within the region are the minimal set of pixels that need to be updated.
This method takes these rectangles into account when optimizing the
presentation by copying only the pixels within the region, or some suitably
expanded set of rectangles. This is an aid to optimization only, and the
application should not rely on the region being copied exactly. The
implementation can choose to copy the whole source rectangle.
Return Values
Possible return values include: D3D_OK or
D3DERR_DEVICEREMOVED (see D3DERR).
Remarks
If necessary, a stretch operation is applied to
transfer the pixels within the source rectangle to the destination rectangle in
the client area of the target window.
IDirect3DDevice9::Present will fail, returning
D3DERR_INVALIDCALL, if called between BeginScene and EndScene pairs unless the
render target is not the current render target (such as the back buffer you get
from creating an additional swap chain). This is a new behavior for Direct3D 9.