History: Fading Object Shader

            !!Description
This shader applies to an object a color that fade to dark when getting away from the camera. I use it for large object, to emphase the feeling of largeness. The object is not textured, but just colorized.

{img src="img/wiki_up/Gradient_shader.jpg" alt="Gradient_shader.jpg"}

!!Usage
To use the shader, you will need to give 2 custom parameters:
* the color of the object.
* the radius of the object.

And then apply the __shader/gradient__ material to your object.
Example :
{CODE(wrap="1", colors="c++")} Vector4 vColour = Vector4(circlecolour.r, circlecolour.g, circlecolour.b, circlecolour.a);
 Vector4 vRadius = Vector4(mRadius,0,0,0);
 mObject->setCustomParameter(0,vColour);
 mObject->setCustomParameter(1,vRadius);
 mObject->setMaterial("shader/gradient");
{CODE}
!!Gradientshader.cg

{CODE(wrap="1", colors="c++")} // --------------------------------------------------------------------
 // Gradient shader : vertex program
 // Author : David de Lorenzo
 // -----------------------------------------------------------------
 void gradient_vp( in      float4   position  : POSITION,
                  uniform float4x4 worldViewProj,
                  uniform float3   camera_position_object_space,
                  uniform float4   customParamColour,
                  uniform float4   customParamRadius,
                  out     float4   oPosition : POSITION,
                  out     float4   oColor    : COLOR
              )
 {
     // Get the custom parameters
     float  objectradius = customParamRadius.x;
 
     // calculate output position
     oPosition = mul(worldViewProj, position);
 
     // Calculate the color value, depending on the position
     float3 vect_center_to_cam =  camera_position_object_space;
     float3 position_closest   =  normalize(vect_center_to_cam) * objectradius;
 
     float Rc = (position_closest.z * position.z ) + (position_closest.x * position.x);  // Ratio on Center-to-Cam axis
     Rc =  Rc / (objectradius * objectradius);   // recalibrate (-1..1)
     float ratio  = (1+Rc);                      // recalibrate ( 0..2) - (x2 to emphasis the color)
 
     oColor= ratio * customParamColour;
 }
  
 // -----------------------------------------------------------------
 // Gradient shader : fragment program
 // Author : David de Lorenzo
 // -----------------------------------------------------------------
 float4 main_fp(in  float4 color  : COLOR) :  COLOR0
 {
   return (color);
 }
{CODE}

!!Gradientshader.material
{CODE(wrap="1", colors="c++")} vertex_program shader/gradientVP cg
 {
      source gradientshader.cg
     entry_point gradient_vp
     profiles vs_1_1
 
     default_params    
     {
        param_named_auto worldViewProj  worldviewproj_matrix
           param_named_auto camera_position_object_space camera_position_object_space
        }
 } 
 
 fragment_program shader/gradientFP cg
 {
     source gradientshader.cg
     entry_point main_fp
     profiles ps_1_1
 }
 
 material shader/gradient
 { 
      technique
     {
         pass
         {
             vertex_program_ref shader/gradientVP
             {
                          param_named_auto customParamColour custom 0
                          param_named_auto customParamRadius custom 1
             }
             fragment_program_ref shader/gradientFP
             {
             }
         }
     }
 }
{CODE}

---
Alias: (alias(Fading_Object_Shader))