Introduction to 3D Game Programming with DirectX.9.0 - F. D. Luna

19.6.1 Obtaining a Handle to an Effect

The first step to using a technique is to obtain a D3DXHANDLE to that technique. A handle to a technique can be obtained using this method:

D3DXHANDLE ID3DXEffect::GetTechniqueByName( LPCSTR pName // Name of the technique.

);

Note: In practice, an effect file typically contains several techniques, where each is designed for a particular set of hardware capabilities. Therefore, the application normally runs some capability tests on the system to determine its hardware and then selects the best technique based on those tests. See ID3DXEffect::ValidateTechnique in the following section.

19.6.2 Activating an Effect

Once the handle to the desired technique has been obtained, we must activate that technique. This is done with the following method:

HRESULT ID3DXEffect::SetTechnique(

D3DXHANDLE hTechnique // Handle to the technique to set.

);

Note: Before activating a technique you will want to validate it with the current device. That is, you will want to ensure that the hardware supports the features the technique uses and the configuration of features the technique uses. You can use the following method to do so:

HRESULT ID3DXEffect::ValidateTechnique(

D3DXHANDLE hTechnique // Handle to the technique to validate.

);

Recall that an effect file may have several techniques, each attempting to implement a particular effect using different hardware features, hoping that the implementation of at least one technique will work on the user’s system. For an effect, you will want to iterate through each technique and run it through ID3DXEffect::ValidateTechnique so that you can verify which techniques are supported and which ones are not, and then act appropriately.

19.6.3 Beginning an Effect

To render geometry using an effect, we must surround the drawing function calls between the ID3DXEffect::Begin and ID3DXEffect ::End methods. These functions essentially enable and disable the effect, respectively.

HRESULT ID3DXEffect::Begin(

UINT* pPasses,

DWORD Flags

);

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As a warm-up, let’s create an effect file that handles lighting and texturing a 3D model. The sample runs entirely in the fixed function pipeline, implying that the effects framework is not limited to effects that use shaders. Figure 19.1 shows a screen shot of the Lighting and Texturing sample.

Figure 19.1: Screen shot from the Lighting and Texturing sample. The texture, material, and lighting states are specified inside the effect file.

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ProjectionTransform = (ProjMatrix);

//

//Set a light source at light index 0. We fill out all the

//components for light[0] because the Direct3D

//documentation recommends filling out all components

//for best performance.

// Finally, enable the light:

LightEnable[0] = true;

//

//Set material components. This is like calling

//IDirect3DDevice9::SetMaterial.

MaterialAmbient = {1.0f, 1.0f, 1.0f, 1.0f};

MaterialDiffuse = {1.0f, 1.0f, 1.0f, 1.0f};

MaterialEmissive = {0.0f, 0.0f, 0.0f, 0.0f};

MaterialPower = 1.0f;

MaterialSpecular = {1.0f, 1.0f, 1.0f, 1.0f};

//

//Hook up the sampler object ‘S0’ to sampler stage 0,

//which is given by Sampler[0].

Sampler[0] = (S0);

}

}

In this effect file we are primarily setting device states, as covered in section 19.3. For instance, we set a light source and a material directly in the effect file. Furthermore, we specify transformation matrices and the texture and sampler states to apply. These specified states are then applied to any geometry that is rendered using technique LightAndTexture and rendering pass P0.

Note: Observe that to refer to variables in an effect file, we must enclose them in parentheses. For example, to refer to matrix variables, we had to write (WorldMatrix), (ViewMatrix), and (ProjMatrix). Leaving the parentheses off is illegal.

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::MessageBox(0, "D3DXCreateEffectFromFile() - FAILED", 0, 0); return false;

}

//

// Save Frequently Accessed Parameter Handles

//

WorldMatrixHandle=LightTexEffect->GetParameterByName(0,

"WorldMatrix");

LightTexTechHandle =

LightTexEffect->GetTechniqueByName("LightAndTexture");

//

//Set effect parameters

//Matrices

D3DXMATRIX W, P;

D3DXMatrixIdentity(&W);

LightTexEffect->SetMatrix( WorldMatrixHandle, &W);

D3DXMatrixPerspectiveFovLH(

&P, D3DX_PI * 0.25f, // 45 - degree (float)Width / (float)Height, 1.0f, 1000.0f);

LightTexEffect->SetMatrix( ProjMatrixHandle, &P);

// Texture: IDirect3DTexture9* tex = 0;

D3DXCreateTextureFromFile(Device, "Terrain_3x_diffcol.jpg", &tex);

LightTexEffect->SetTexture(TexHandle, tex);

d3d::Release<IDirect3DTexture9*>(tex);

return true;

}

The Display function is straightforward and performs the steps outlined in section 19.6:

bool Display(float timeDelta)

{

if( Device )

{

//

// ...[Camera update snipped]

//

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As you can see, linear vertex fog can be controlled through five simple render states:

FogVertexMode—Specifies the fog function to use for vertex fog. The fog function specifies how the fog increases with distance, as naturally fog is less thick near the viewpoint and becomes thicker as the distance increases. Valid assignment types are LINEAR, EXP, and EXP2. These functions are defined as:

(d is the distance from the viewpoint.)

Note: If you use the EXP or EXP2 fog functions, you do not need to set FogStart and FogEnd because they are not used in these types of fog functions; instead you must set the fog density render state (e.g.,

FogDensity = someFloatType;).

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