Phong shading

This tutorial shows how we generate a custom mesh and perform Phong illumination using a shader.

This sample displays a Phong shaded white sphere lit by a single red light.

// The 4x4 world view projection matrix.
float4x4 worldViewProjection : WorldViewProjection;

// positions of the light and camera
float3 light_pos;
float3 camera_pos;

// phong lighting components of the light source
float4 light_ambient;
float4 light_diffuse;
float4 light_specular;

//  shininess of the material. (for specular lighting)
float shininess;

// input parameters for our vertex shader
struct VertexShaderInput {
  float4 postion : POSITION;
  float3 normal : NORMAL;
  float4 color : COLOR;
};

// input parameters for our pixel shader
// also the output parameters for our vertex shader
struct PixelShaderInput {
  float4 postion : POSITION;
  float3 lightVector : TEXCOORD0;
  float3 normal : TEXCOORD1;
  float3 viewPosition : TEXCOORD2;
  float4 color : COLOR;
};

/**
 * Vertex Shader - vertex shader for phong illumination
 */
PixelShaderInput vertexShaderFunction(VertexShaderInput input) {
  /**
   * We use the standard phong illumination equation here.
   * We restrict (clamp) the dot products so that we
   * don't get any negative values.
   * All vectors are normalized for proper calculations.
   *
   * The output color is the summation of the
   * ambient, diffuse, and specular contributions.
   *
   * Note that we have to transform each vertex and normal
   * by the world view projection matrix first.
   */
  PixelShaderInput output;

output.postion = mul(input.postion, worldViewProjection);

/**
   * lightVector - light vector
   * normal - normal vector
   * viewPosition - view vector (from camera)
   */

// NOTE: In this case we do not need to multiply by any matrices since the
  // WORLD transformation matrix is the identity. If you were moving the
  // object such that the WORLD transform matrix was not the identity, you
  // would need to multiply the normal by the WORLDINVERSETTRANSFORM matrix
  // since the normal is in object space. Other values (light_pos, camera_pos)
  // are already in world space.
  float3 lightVector = light_pos - input.postion.xyz;
  float3 normal = input.normal;
  float3 viewPosition = camera_pos - input.postion.xyz;

output.lightVector = lightVector;
  output.normal = normal;
  output.viewPosition = viewPosition;
  output.color = input.color;
  return output;
}

/**
 * Pixel Shader
 */
float4 pixelShaderFunction(PixelShaderInput input): COLOR {
  float3 lightVector = normalize(input.lightVector);
  float3 normal = normalize(input.normal);
  float3 viewPosition = normalize(input.viewPosition);
  float3 halfVector = normalize(lightVector + viewPosition);

// use lit function to calculate phong shading
  // x component contains the ambient coefficient
  // y component contains the diffuse coefficient:
  //     max(dot(normal, lightVector),0)
  // z component contains the specular coefficient:
  //     dot(normal, lightVector) < 0 || dot(normal, halfVector) < 0 ?
  //         0 : pow(dot(normal, halfVector), shininess)
  // NOTE: This is actually Blinn-Phong shading, not Phong shading
  // which would use the reflection vector instead of the half vector

float4 phong_coeff = lit(dot(normal, lightVector),
                           dot(normal, halfVector), shininess);

float4 ambient = light_ambient * phong_coeff.x * input.color;
  float4 diffuse = light_diffuse * phong_coeff.y * input.color;
  float4 specular = light_specular * phong_coeff.z * input.color;

return ambient + diffuse + specular;
}

// Here we tell our effect file *which* functions are
// our vertex and pixel shaders.

// #o3d VertexShaderEntryPoint vertexShaderFunction
// #o3d PixelShaderEntryPoint pixelShaderFunction
// #o3d MatrixLoadOrder RowMajor