Programming with DirectX : Shading and Surfaces - Implementing Texture Mapping (part 2) - Multi Texture Demo

1/21/2011 11:53:17 AM

Multi Texture Demo

Multi-texturing is a technique that is used to display multiple textures on one surface. In Direct3D 10 this can be done by loading a second texture image and sending it to the pixel shader. Inside the pixel shader both shaders are sampled, and the results are blended together. How you blend them is up to you. You can multiply the colors together, add them, interpolate between them, and so forth. An example of multi-texturing is shown in Figure 2 .

Figure 2. Texture A (left), texture B (middle), and A and B multi-textured (right).

In the Multi Texture demo’s shader file we declare a second Texture2D object. Inside the pixel shader we sample from both shaders using the same sampler state and the same texture coordinates. This is shown in Listing 7 . If you wanted, you could use different sampler states and even different texture coordinates. In the pixel shader we combine colors by multiplying them together. Since colors are in the range of 0.0 to 1.0, two white colors will be white, two black colors will be black, and anything in between will be a blend. We could also have added them together to get a different effect, subtracted, linearly interpolated, and so forth.

Listing 7. The Shader from the Multi Texture Demo

Texture2D decal1;

Texture2D decal2;

SamplerState DecalSampler
{
   Filter = MIN_MAG_MIP_LINEAR;
   AddressU = Wrap;
   AddressV = Wrap;
};

cbuffer cbChangesEveryFrame
{
   matrix World;
   matrix View;
};

cbuffer cbChangeOnResize
{
   matrix Projection;
};

struct VS_INPUT
{
   float4 Pos : POSITION;
   float2 Tex : TEXCOORD;
};

struct PS_INPUT
{
   float4 Pos : SV_POSITION;
   float2 Tex : TEXCOORD0;
};


PS_INPUT VS(VS_INPUT input)
{
   PS_INPUT output = (PS_INPUT)0;

   output.Pos = mul(input.Pos, World);
   output.Pos = mul(output.Pos, View);
   output.Pos = mul(output.Pos, Projection);

   output.Tex = input.Tex;

   return output;
}

float4 PS(PS_INPUT input)  : SV_Target
{
   return decal1.Sample(DecalSampler, input.Tex) *
          decal2.Sample(DecalSampler, input.Tex);
}


technique10 MultiTextureMapping
{
   pass P0
   {
      SetVertexShader(CompileShader(vs_4_0, VS()));
      SetGeometryShader(NULL);
      SetPixelShader(CompileShader(ps_4_0, PS()));
   }
}

The source code from the Multi Texture demo builds directly off of the code from the Texture Mapping demo. In the global section another shader resource view and shader resource variable were added for the second texture. This addition is shown in Listing 8. In the InitializeDemo() function the second texture is loaded along with binding to the shader variable decal2, which is shown in Listing 9.

Listing 8. The Altered Globals in the Multi Texture Demo from Texture Mapping

ID3D10ShaderResourceView *g_squareDecal1 = NULL;
ID3D10ShaderResourceView *g_squareDecal2 = NULL;

ID3D10EffectShaderResourceVariable *g_decalEffectVar1 = NULL;
ID3D10EffectShaderResourceVariable *g_decalEffectVar2 = NULL;

Listing 6.9. The altered InitializeDemo() function from the Multi Texture demo.

bool InitializeDemo()
{
   …

   g_textureMapTech = g_shader->GetTechniqueByName(
      "MultiTextureMapping");

   g_worldEffectVar = g_shader->GetVariableByName(
      World")->AsMatrix();

   g_viewEffectVar = g_shader->GetVariableByName(
      "View")->AsMatrix();

   g_projEffectVar = g_shader->GetVariableByName(
      "Projection")->AsMatrix();

   g_decalEffectVar1 = g_shader->GetVariableByName(
      "decal1")->AsShaderResource();

   g_decalEffectVar2 = g_shader->GetVariableByName(
      "decal2")->AsShaderResource();
   // Load the textures.
   hr = D3DX10CreateShaderResourceViewFromFile(g_d3dDevice,
     "brick.dds", NULL, NULL, &g_squareDecal1, NULL);

   if(FAILED(hr))
      return false;

   hr = D3DX10CreateShaderResourceViewFromFile(g_d3dDevice,
      "wavystars.dds", NULL, NULL, &g_squareDecal2, NULL);

   if(FAILED(hr))
      return false;

   …
}

The last modified code in the Multi Texture demo from the Texture Mapping demo can be seen in the RenderScene() and Shutdown() functions. In the RenderScene() function a new line of code is added to send the second texture to the decal2 shader variable. In the Shutdown() function the second shader resource view and its texture object are released from memory directly under the first texture. Both of these functions are shown in Listing 10 . A screenshot of the application is shown in Figure 3.

Listing 10. The RenderScene() and Shutdown() Functions from the Multi Texture Demo

Code View: Scroll / Show All

void RenderScene()
{
   float col[4] = { 0, 0, 0, 1 };

   g_d3dDevice->ClearRenderTargetView(g_renderTargetView, col);

   g_worldEffectVar->SetMatrix((float*)&g_worldMat);
   g_decalEffectVar1->SetResource(g_squareDecal1);
   g_decalEffectVar2->SetResource(g_squareDecal2);
   unsigned int stride = sizeof(DX10Vertex);
   unsigned int offset = 0;

   g_d3dDevice->IASetInputLayout(g_layout);
   g_d3dDevice->IASetVertexBuffers(0, 1, &g_squareVB,
      &stride, &offset);
   g_d3dDevice->IASetPrimitiveTopology(
      D3D10_PRIMITIVE_TOPOLOGY_TRIANGLELIST);

   D3D10_TECHNIQUE_DESC techDesc;
   g_textureMapTech->GetDesc(&techDesc);

   for(unsigned int i = 0; i < techDesc.Passes; i++)
   {
      g_textureMapTech->GetPassByIndex(i)->Apply(0);
      g_d3dDevice->Draw(6, 0);
   }

   g_swapChain->Present(0, 0);
}


void Shutdown()
{
   if(g_d3dDevice) g_d3dDevice->ClearState();
   if(g_swapChain) g_swapChain->Release();
   if(g_renderTargetView) g_renderTargetView->Release();

   if(g_shader) g_shader->Release();
   if(g_layout) g_layout->Release();
   if(g_squareVB) g_squareVB->Release();

   if(g_squareDecal1)
   {
      ID3D10Resource *pRes;
      g_squareDecal1->GetResource(&pRes);

      pRes->Release();
      g_squareDecal1->Release();
   }

   if(g_squareDecal2)
   {
      ID3D10Resource *pRes;
      g_squareDecal2->GetResource(&pRes);

      pRes->Release();
      g_squareDecal2->Release();
   }

   if(g_d3dDevice) g_d3dDevice->Release();
}