From 304214e0df2334a2aaba85ea394f05330cca5ec3 Mon Sep 17 00:00:00 2001
From: Robert Osfield <robert@openscenegraph.com>
Date: Thu, 25 Mar 2010 11:11:35 +0000
Subject: [PATCH] Introduced the use of linear interpolation of evelvations
 when sampling

---
 include/osgTerrain/Layer             | 47 ++++++++++++++++++++++++++++
 src/osgTerrain/GeometryTechnique.cpp | 23 ++++++--------
 2 files changed, 56 insertions(+), 14 deletions(-)

diff --git a/include/osgTerrain/Layer b/include/osgTerrain/Layer
index f8058dfa1..11f9dd931 100644
--- a/include/osgTerrain/Layer
+++ b/include/osgTerrain/Layer
@@ -191,6 +191,53 @@ class OSGTERRAIN_EXPORT Layer : public osg::Object
             return false;
         }
 
+        inline bool getInterpolatedValidValue(double ndc_x, double ndc_y, float& value)
+        {
+            unsigned int i,j;
+            double ir, jr;
+            computeIndices(ndc_x, ndc_y, i, j, ir, jr);
+            value = 0.0f;
+            double div = 0.0f;
+            float v,r;
+
+            r = (1.0f-ir)*(1.0f-jr);
+            if (r>0.0 && getValidValue(i,j,v))
+            {
+                value += v*r;
+                div += r;
+            }
+
+            r = (ir)*(1.0f-jr);
+            if (r>0.0 && getValidValue(i+1,j,v))
+            {
+                value += v*r;
+                div += r;
+            }
+
+            r = (ir)*(jr);
+            if (r>0.0 && getValidValue(i+1,j+1,v))
+            {
+                value += v*r;
+                div += r;
+            }
+
+            r = (1.0f-ir)*(jr);
+            if (r>0.0 && getValidValue(i,j+1,v))
+            {
+                value += v*r;
+                div += r;
+            }
+
+            if (div != 0.0)
+            {
+                value /= div;
+                return true;
+            }
+
+            value = 0.0;
+            return false;
+        }
+
         /** increment the modified count."*/
         virtual void dirty() {};
 
diff --git a/src/osgTerrain/GeometryTechnique.cpp b/src/osgTerrain/GeometryTechnique.cpp
index 883d9264d..30bd8cd5e 100644
--- a/src/osgTerrain/GeometryTechnique.cpp
+++ b/src/osgTerrain/GeometryTechnique.cpp
@@ -310,7 +310,7 @@ void GeometryTechnique::generateGeometry(Locator* masterLocator, const osg::Vec3
 
                 Locator* locator = colorLayer->getLocator();
                 if (!locator)
-                {            
+                {
                     osgTerrain::SwitchLayer* switchLayer = dynamic_cast<osgTerrain::SwitchLayer*>(colorLayer);
                     if (switchLayer)
                     {
@@ -321,8 +321,8 @@ void GeometryTechnique::generateGeometry(Locator* masterLocator, const osg::Vec3
                             locator = switchLayer->getLayer(switchLayer->getActiveLayer())->getLocator();
                         }
                     }
-                }            
-            
+                }
+
                 TexCoordLocatorPair& tclp = layerToTexCoordMap[colorLayer];
                 tclp.first = new osg::Vec2Array;
                 tclp.first->reserve(numVertices);
@@ -355,25 +355,20 @@ void GeometryTechnique::generateGeometry(Locator* masterLocator, const osg::Vec3
         {
             unsigned int iv = j*numColumns + i;
             osg::Vec3d ndc( ((double)i)/(double)(numColumns-1), ((double)j)/(double)(numRows-1), 0.0);
-     
+
             bool validValue = true;
-     
-            
-            unsigned int i_equiv = i_sampleFactor==1.0 ? i : (unsigned int) (double(i)*i_sampleFactor);
-            unsigned int j_equiv = i_sampleFactor==1.0 ? j : (unsigned int) (double(j)*j_sampleFactor);
-            
             if (elevationLayer)
             {
                 float value = 0.0f;
-                validValue = elevationLayer->getValidValue(i_equiv,j_equiv, value);
-                // OSG_INFO<<"i="<<i<<" j="<<j<<" z="<<value<<std::endl;
+                if (sampleRatio==1.0) validValue = elevationLayer->getValidValue(i,j,value);
+                else validValue = elevationLayer->getInterpolatedValidValue(ndc.x(), ndc.y(), value);
                 ndc.z() = value*scaleHeight;
             }
-            
+
             if (validValue)
             {
                 indices[iv] = vertices->size();
-            
+
                 osg::Vec3d model;
                 masterLocator->convertLocalToModel(ndc, model);
 
@@ -416,7 +411,7 @@ void GeometryTechnique::generateGeometry(Locator* masterLocator, const osg::Vec3
             }
         }
     }
-    
+
     // populate primitive sets
 //    bool optimizeOrientations = elevations!=0;
     bool swapOrientation = !(masterLocator->orientationOpenGL());