Volume Rendering.

mouse_wheel = zoom | click_drag = rotate

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

// The texture sampler is used to access the texture bitmap in the fragment
// shader.
sampler texSampler0;
  
// 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;
  float2 tex : TEXCOORD0;  // Texture coordinates
};

// input parameters for our pixel shader
// also the output parameters for our vertex shader
struct PixelShaderInput {
  float4 postion : POSITION;
  float2 tex : TEXCOORD0;  // Texture coordinates
  float3 normal : TEXCOORD1;
  float3 lightVector : TEXCOORD3;
  float3 viewPosition : TEXCOORD2;
  float4 color : COLOR;
};

/**
 * Vertex Shader - vertex shader for phong illumination
 */
PixelShaderInput vertexShaderFunction(VertexShaderInput input) {

PixelShaderInput output;

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

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

float3 lightVector = light_pos - input.postion.xyz;
  float3 normal = mul(input.normal, World);
  float3 viewPosition = camera_pos - input.postion.xyz;

output.lightVector = lightVector;
  output.normal = normal;
  output.viewPosition = viewPosition;
  output.color = input.color;
  output.tex = input.tex;
  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);

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;*/

float4 texval = tex2D(texSampler0, input.tex);
  texval.a = texval.r;
  //float4 lighting = diffuse + specular; 
  
  return texval;
}

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

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