adresses #1704: partial reversion to 3.8 specs regarding layer blending.

Engine/source/terrain/glsl/terrFeatureGLSL.cpp

@@ -568,7 +568,7 @@ void TerrainDetailMapFeatGLSL::processPix(   Vector<ShaderComponent*> &component
    }
 
    // Add to the blend total.
-   meta->addStatement( new GenOp( "   @ += @;\r\n", blendTotal, detailBlend ) );
+   meta->addStatement(new GenOp("   @ = max( @, @ );\r\n", blendTotal, blendTotal, detailBlend));
 
    // If we had a parallax feature... then factor in the parallax
    // amount so that it fades out with the layer blending.
@@ -820,7 +820,7 @@ void TerrainMacroMapFeatGLSL::processPix(   Vector<ShaderComponent*> &componentL
    }
 
    // Add to the blend total.
-   meta->addStatement( new GenOp( "   @ += @;\r\n", blendTotal, detailBlend ) );
+   meta->addStatement(new GenOp("   @ = max( @, @ );\r\n", blendTotal, blendTotal, detailBlend));
 
    Var *detailColor = (Var*)LangElement::find( "macroColor" ); 
    if ( !detailColor )

Engine/source/terrain/hlsl/terrFeatureHLSL.cpp

@@ -509,7 +509,8 @@ void TerrainDetailMapFeatHLSL::processPix(   Vector<ShaderComponent*> &component
    }
 
    // Add to the blend total.
-   meta->addStatement( new GenOp( "   @ += @;\r\n", blendTotal, detailBlend ) );
+
+   meta->addStatement(new GenOp("   @ = max( @, @ );\r\n", blendTotal, blendTotal, detailBlend));
 
    // If we had a parallax feature... then factor in the parallax
    // amount so that it fades out with the layer blending.
@@ -856,7 +857,7 @@ void TerrainMacroMapFeatHLSL::processPix(   Vector<ShaderComponent*> &componentL
    }
 
    // Add to the blend total.
-   meta->addStatement( new GenOp( "   @ += @;\r\n", blendTotal, detailBlend ) );
+   meta->addStatement(new GenOp("   @ = max( @, @ );\r\n", blendTotal, blendTotal, detailBlend));
 
    Var *detailColor = (Var*)LangElement::find( "macroColor" ); 
    if ( !detailColor )