//-----------------------------------------------------------------------------
// --- GNNViz:  PIXEL shader for terrain used in GNNViz with the Torque Shader
// --- Engine
// --- 
// --- This is a custom shader derived from the original TSE Atlas Vertex
// --- shader code.  It has been modified to allow for multiple detail texture
// --- scales to remove tiling effects, plus a fade factor to allow terrain
// --- to fade from detail texture close up to a "satellite overview" texture
// --- for distant terrain.
// ---
// --- This shader was developed as part of the GNNViz project who's website is
// --- at http://www.fsl.orst.edu/lemma/gnnviz/index.php
// ---
// --- For more information, contact Tim Holt at tim.holt@oregonstate.edu
//-----------------------------------------------------------------------------

//-----------------------------------------------------------------------------
// --- Ideas for Improvement
// ---
// --- Need multiple detail textures applied using a blending map style
// ---
// --- Apply normal and parallax shaders to overview texture.  The idea here is
// --- that we could make the distant forest landscape be bumpy looking, which
// --- would look like you were seeing the tops of the forest canopy.  If you
// --- think about it, when viewing a forested landscape from far away you are
// --- just seeing bumpy tops of trees, not the smooth flat ground.
// ---
// --- Apply normal map shader to detail textures to give it more texture.
// --- The normal map could be placed in the unused alpha channel.
// ---
// --- Store shadow information in the alpha channel of the overview texture
// --- and apply it to the detail texture.  When GNNViz generates a fake
// --- satellite-like overview image to be used on the terrain, it also gives
// --- the trees shadows.  By making the unused alpha layer hold a basic 0..1
// --- level of shadow intensity, we could turn around and apply it to the 
// --- detail texture to shade the ground under trees.  This would probably be
// --- a very visually powerful addition to realism, however it would require
// --- that the foliage replicator place tree models at the same locations as
// --- the fake satellite overview image.  That means that the code which 
// --- makes the fake sat image has to share the same random number generator
// --- and seed as the foliage replicator.
//-----------------------------------------------------------------------------

//-----------------------------------------------------------------------------
// Structures                                                                  
//-----------------------------------------------------------------------------
struct ConnectData
{
   float2 texCoord        : TEXCOORD0;
   float2 fogCoord        : TEXCOORD1;
   float2 detailCoord     : TEXCOORD2;
   float2 detailCoord2    : TEXCOORD3;
   float2 distCoord       : TEXCOORD4;
};


struct Fragout
{
   float4 col : COLOR0;
};


//-----------------------------------------------------------------------------
// Main                                                                        
//-----------------------------------------------------------------------------
Fragout main( ConnectData IN,
              uniform sampler2D diffuseMap      : register(S0),
              uniform sampler2D fogMap          : register(S1),
              uniform sampler2D detailMap       : register(S2),
              uniform sampler2D detailMap2      : register(S3)
              )
{
   //--------------------------------------------------------------------------
   // --- GNNViz:  Pixel shader main body
   // --- 
   // --- The job of this shader code is to return the actual color value to be
   // --- drawn at the current pixel.  This code works in conjunction with the
   // --- vertex shader code in GNNVizAtlasSurfaceV.hlsl to decide how to
   // --- render the pixel data.
   //--------------------------------------------------------------------------
   Fragout OUT;
   
   //--------------------------------------------------------------------------
   // --- Compute the color contribution of the overview texture which is
   // --- draped over the entire Atlas terrain surface.
   //--------------------------------------------------------------------------
   float4 overlayColor = tex2D(diffuseMap, IN.texCoord);
   overlayColor.a = diffuseColor.r;
   overlayColor.r = diffuseColor.b;
   overlayColor.b = diffuseColor.a;
   overlayColor.a = 1.0;

   //--------------------------------------------------------------------------
   // --- Compute the amount of fog (0..1) to apply to the pixel being 
   // --- rendered.
   //--------------------------------------------------------------------------
   float4 fogColor     = tex2D(fogMap,     IN.fogCoord);

   //--------------------------------------------------------------------------
   // --- Compute the amount of fade (0..1) between close up and distant 
   // --- texture.
   //--------------------------------------------------------------------------
   float4 fadeColor    = tex2D(fogMap,     IN.distCoord);

   //--------------------------------------------------------------------------
   // ---- Compute the color contribution of the detail texture.
   // ---
   // --- Note that we are combining the same detail texture at two different
   // --- scale values here.  This removes tiling in the detail texture.
   //--------------------------------------------------------------------------
   float4 detailColor  =  tex2D(detailMap,   IN.detailCoord);
   detailColor  += tex2D(detailMap,  IN.detailCoord2);
   detailColor /= 2;

   //--------------------------------------------------------------------------
   // --- Now based on distance from viewers eye to pixel's coordinate in 
   // --- space, blend between the overlay texture color contribution and the 
   // --- detail texture contribution.
   //--------------------------------------------------------------------------
   overlayColor = lerp (detailColor, overlayColor, fadeColor.a);

   //--------------------------------------------------------------------------
   // --- Now factor in the fog contribution, interpolating between the terrain
   // --- color and the fog color using the fogColor alpha value as the weight.
   //--------------------------------------------------------------------------
   OUT.col = lerp( overlayColor, fogColor, fogColor.a ); 
   
   // --- original shader output calc
   // OUT.col = lerp(overlayColor, fogColor, fogColor.a ); 

   return OUT;
}