Programming with DirectX : Rendering Geometry - Colors

typedef struct D3DXCOLOR {
   FLOAT r;
   FLOAT g;
   FLOAT b;
   FLOAT a;
} D3DXCOLOR, *LPD3DXCOLOR;

Colors Demo

This demo application builds off of the Primitives demo and adds a color property to the vertices that are rendered. In the Primitives demo the pixel shader used yellow for the rendering. In this demo the color is specified per vertex. The first change in the Colors demo is the addition of a D3DXCOLOR object to the vertex structure. The addition of colors to the vertex structure is shown in Listing 1.

Listing 1. The Global Section from the Colors Demo

// Direct3D 10 objects.
ID3D10Device *g_d3dDevice = NULL;
IDXGISwapChain *g_swapChain = NULL;
ID3D10RenderTargetView *g_renderTargetView = NULL;

// Effect objects.
ID3D10Effect *g_shader = NULL;
ID3D10EffectTechnique *g_technique = NULL;

// Display object to store scene geometry.
ID3D10InputLayout *g_layout = NULL;
ID3D10Buffer *g_vertexBuffer = NULL;

// Structure used to represent a single vertex.
struct DX10_Vertex
{
   D3DXVECTOR3 pos;
   D3DXCOLOR col;
};

Since the vertex structure requires a color now, the data that makes up the object must be updated to reflect this. This can be seen in the initialize function for the Colors demo, where the input layout is given a different property and the list of vertices specifies a color for each vertex point. The initialization code that is specific to the Colors demo is shown in Listing 2. Note that the alignment offset (third to last property for each input element) is 12 for the color element. This is because the element that comes before it takes up 12 bytes, so to get to the color data, Direct3D must move past the first 12 bytes of each vertex to obtain the start of the color.

Listing 2. The Initialize Code Specific to the Colors Demo

bool InitializeDemo()
{
   // Load the shader.

   …


   // Create the geometry. The layout of each vertex is made up
   // of just a position so that is all we need.

   D3D10_INPUT_ELEMENT_DESC layout[] =
   {
     { "POSITION", 0, DXGI_FORMAT_R32G32B32_FLOAT, 0, 0,
        D3D10_INPUT_PER_VERTEX_DATA, 0 },
     { "COLOR", 0, DXGI_FORMAT_R32G32B32A32_FLOAT, 0, 12,
        D3D10_INPUT_PER_VERTEX_DATA, 0 },
   };


   …


   DX10_Vertex vertices[] =
   {
     { D3DXVECTOR3( 0.0f,  0.5f, 0.5f), D3DXCOLOR(1, 0, 0, 1) },
     { D3DXVECTOR3( 0.5f, -0.5f, 0.5f), D3DXCOLOR(0, 1, 0, 1) },
     { D3DXVECTOR3(-0.5f, -0.5f, 0.5f), D3DXCOLOR(0, 0, 1, 1) },
   };
   // Create the vertex buffer.

   D3D10_BUFFER_DESC buffDesc;

   buffDesc.Usage = D3D10_USAGE_DEFAULT;
   buffDesc.ByteWidth = sizeof(DX10_Vertex) * 3;
   buffDesc.BindFlags = D3D10_BIND_VERTEX_BUFFER;
   buffDesc.CPUAccessFlags = 0;
   buffDesc.MiscFlags = 0;

   D3D10_SUBRESOURCE_DATA resData;
   resData.pSysMem = vertices;

   hr = g_d3dDevice->CreateBuffer(&buffDesc, &resData,
                                  &g_vertexBuffer);

   if(FAILED(hr))
      return false;

   return true;
}

					    

The rendering code from the Colors demo is the same as the Primitives demo, with the exception that we are rendering three vertices instead of six. The shader for the Colors demo is slightly different than the Primitives demo. We have added a color semantic to the vertex and pixel shader input structures. This occurs because now we are bringing in a vertex color from the application into the vertex shader input, and we are sending the color from the vertex shader into the pixel shader input. The pixel shader simply uses this incoming vertex color instead of specifying a hard-coded value like the Primitives demo did for its output color value. The shader from the Colors demo is shown in Listing 3. Figure 1 shows a screenshot from the Colors demo. To get a better appreciation of the demo in action it is recommended that you execute it.

Listing 3. The Colors Demo’s Shader

struct VS_INPUT { float4 Pos : POSITION; float4 Color : COLOR; }; struct PS_INPUT { float4 Pos : SV_POSITION; float4 Color : COLORO; }; PS_INPUT VS(VS_INPUT input) { PS_INPUT output = (PS_INPUT)0; output.Pos = input.Pos; output.Color = input.Color; return output; } float4 PS(PS_INPUT input) : SV_Target { return input.Color; } technique10 PassThrough { pass P0 { SetVertexShader(CompileShader(vs_4_0, VS())); SetGeometryShader(NULL); SetPixelShader(CompileShader(ps_4_0, PS())); } }

Figure 1. A screenshot from the Colors demo.