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設置燈光

在Direct3D的一個場景中，最多可設置8個光源，設置光源由IDirect3DDevice9::SetLight()函數完成。該函數的聲明如下：

Assigns a set of lighting properties for this device.

HRESULT SetLight(
  DWORD Index,
  CONST D3DLight9 * pLight
);

Parameters

Index

[in] Zero-based index of the set of lighting properties to set. If a set of lighting properties exists at this index, it is overwritten by the new properties specified in pLight.

pLight

[in] Pointer to a D3DLIGHT9 structure, containing the lighting parameters to set.

Return Values

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

Remarks

Set light properties by preparing a D3DLIGHT9 structure and then calling the IDirect3DDevice9::SetLight method. The IDirect3DDevice9::SetLight method accepts the index at which the device should place the set of light properties to its internal list of light properties, and the address of a prepared D3DLIGHT9 structure that defines those properties. You can call IDirect3DDevice9::SetLight with new information as needed to update the light's illumination properties.

The system allocates memory to accommodate a set of lighting properties each time you call the IDirect3DDevice9::SetLight method with an index that has never been assigned properties. Applications can set a number of lights, with only a subset of the assigned lights enabled at a time. Check the MaxActiveLights member of the D3DCAPS9 structure when you retrieve device capabilities to determine the maximum number of active lights supported by that device. If you no longer need a light, you can disable it or overwrite it with a new set of light properties.

The following example prepares and sets properties for a white point-light whose emitted light will not attenuate over distance.

// Assume d3dDevice is a valid pointer to an IDirect3DDevice9 interface.
D3DLight9 d3dLight;
HRESULT   hr;
    
// Initialize the structure.
ZeroMemory(&D3dLight, sizeof(d3dLight));
    
// Set up a white point light.
d3dLight.Type = D3DLIGHT_POINT;
d3dLight.Diffuse.r  = 1.0f;
d3dLight.Diffuse.g  = 1.0f;
d3dLight.Diffuse.b  = 1.0f;
d3dLight.Ambient.r  = 1.0f;
d3dLight.Ambient.g  = 1.0f;
d3dLight.Ambient.b  = 1.0f;
d3dLight.Specular.r = 1.0f;
d3dLight.Specular.g = 1.0f;
d3dLight.Specular.b = 1.0f;
    
// Position it high in the scene and behind the user.
// Remember, these coordinates are in world space, so
// the user could be anywhere in world space, too. 
// For the purposes of this example, assume the user
// is at the origin of world space.
d3dLight.Position.x = 0.0f;
d3dLight.Position.y = 1000.0f;
d3dLight.Position.z = -100.0f;
    
// Don't attenuate.
d3dLight.Attenuation0 = 1.0f; 
d3dLight.Range        = 1000.0f;
    
// Set the property information for the first light.
hr = d3dDevice->SetLight(0, &d3dLight);
if (SUCCEEDED(hr))
    // Handle Success
else
    // Handle failure

Enable a light source by calling the IDirect3DDevice9::LightEnable method for the device.

函數IDirect3DDevice9::SetLight()只是設置光源，在默認情況下，設置的任何光源都還不起作用，具體使用哪些光源，由函數IDirect3DDevice9::LightEnable()確定，該函數聲明如下:

Enables or disables a set of lighting parameters within a device.

HRESULT LightEnable(
  DWORD LightIndex,
  BOOL bEnable
);

Parameters

LightIndex

[in] Zero-based index of the set of lighting parameters that are the target of this method.

bEnable

[in] Value that indicates if the set of lighting parameters are being enabled or disabled. Set this parameter to TRUE to enable lighting with the parameters at the specified index, or FALSE to disable it.

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 a value for LightIndex is outside the range of the light property sets assigned within the device, the IDirect3DDevice9::LightEnable method creates a light source represented by a D3DLIGHT9 structure with the following properties and sets its enabled state to the value specified in bEnable.

因為鏡面反射的計算量很大，所以Direct3D在默認狀態下不進行鏡面反射運算。如果想得到鏡面反射效果，可以先設置好結構體D3DLIGHT9的Specular成員和物體表面材質結構體D3DMATERIAL9的Specular和Power成員，然后通過下面的代碼激活鏡面反射運算。

g_device->SetRenderState(D3DRS_SPECULARENABLE, TRUE);

如果需要進行漫反射或鏡面反射運算，那么在頂點緩沖區中必須包含頂點的法向量信息，這是因為Direct3D在進行光照運算時，要用到頂點法向量。

材質

對于光照計算，光源和材質兩者缺一不可，物體表面材質屬性決定了它能反射什么顏色的光線以及能反射多少，在Direct3D中，物體表面材質屬性由結構體D3DMATERIAL9定義：

Specifies material properties.

typedef struct D3DMATERIAL9 {
    D3DCOLORVALUE Diffuse;
    D3DCOLORVALUE Ambient;
    D3DCOLORVALUE Specular;
    D3DCOLORVALUE Emissive;
    float Power;
} D3DMATERIAL9, *LPD3DMATERIAL9;

Members

Diffuse

Value specifying the diffuse color of the material. See D3DCOLORVALUE.

Ambient

Value specifying the ambient color of the material. See D3DCOLORVALUE.

Specular

Value specifying the specular color of the material. See D3DCOLORVALUE.

Emissive

Value specifying the emissive color of the material. See D3DCOLORVALUE.

Power

Floating-point value specifying the sharpness of specular highlights. The higher the value, the sharper the highlight.

Remarks

To turn off specular highlights, set D3DRS_SPECULARENABLE to FALSE, using D3DRENDERSTATETYPE. This is the fastest option because no specular highlights will be calculated.

For more information about using the lighting engine to calculate specular lighting, see Specular Lighting (Direct3D 9).

浮點成員Power為鏡面反射指數，即鏡面反射光照計算模型計算公式中的n，Power值越大，高光強度和周圍亮度相差越大。

Emissive表示物體自身的發光度，以R、G、B表示。

物體頂點的顏色亮度總和為：

I_total = I_ambient + I_diffuse + I_specular + I_emissive

I表示物體的顏色值，上式表示物體的顏色總和 = 物體反射環境光 + 物體反射漫反射光 + 物體反射鏡面光 + 物體自發光。

設置材質

函數IDirect3DDevice9::SetMaterial()用來設置Direct3D當前材質屬性，該函數聲明如下：

Sets the material properties for the device.

HRESULT SetMaterial(
  CONST D3DMATERIAL9 * pMaterial
);

Parameters

pMaterial

[in] Pointer to a D3DMATERIAL9 structure, describing the material properties to set.

Return Values

If the method succeeds, the return value is D3D_OK. D3DERR_INVALIDCALL if the pMaterial parameter is invalid.

下面的示例代碼設置當前材質為能漫反射50%紅光、80%綠光和60%藍光的表面。

D3DMATERIAL9 material;
ZeroMemory(&material, sizeof(material));

material.Diffuse.r = 0.5f;
material.Diffuse.g = 0.8f;
material.Diffuse.b = 1.6f;
material.Diffuse.a = 0.0f;

g_device->SetMaterial(&material);

Direct3D圖形系統在進行光照計算時，會根據3種光照計算模型分別進行計算，然后將計算結果疊加在一起，作為頂點的光照顏色值，如果物體表面只能進行漫反射，則鏡面反射系數應當為0，這時鏡面反射計算得到的顏色值顯然為0，從而使物體不具有鏡面反射效果，但是實際上鏡面反射計算也在進行。因為鏡面反射計算量大，會對性能造成沖擊，所以如果物體表面不具有鏡面反射效果，就不要啟用鏡面反射計算。

如果應用程序沒有指定材質屬性，系統將使用默認材質。默認材質反射所有漫反射光，沒有環境反射和鏡面反射，也沒有自發光顏色。

默認材質的光照屬性

獲取材質屬性

通過調用接口函數IDirect3DDevice9::GetMaterial()可獲取渲染設備當前正在使用的材質屬性。

Retrieves the current material properties for the device.

HRESULT GetMaterial(
  D3DMATERIAL9 * pMaterial
);

Parameters

pMaterial

[out] Pointer to a D3DMATERIAL9 structure to fill with the currently set material properties.

Return Values

If the method succeeds, the return value is D3D_OK. D3DERR_INVALIDCALL if the pMaterial parameter is invalid.

Remarks

This method will not return device state for a device that is created using D3DCREATE_PUREDEVICE. If you want to use this method, you must create your device with any of the other values in D3DCREATE.