From 79276b316980042e5fdcb80a8e461a8439900cf4 Mon Sep 17 00:00:00 2001
From: Robert Osfield <robert@openscenegraph.com>
Date: Thu, 28 Feb 2008 10:56:03 +0000
Subject: [PATCH] From He Sicong, "fixed shader calculation of ray tracing"

---
 examples/osgvolume/osgvolume.cpp | 45 ++++++++++++++++----------------
 1 file changed, 22 insertions(+), 23 deletions(-)

diff --git a/examples/osgvolume/osgvolume.cpp b/examples/osgvolume/osgvolume.cpp
index 5b99ca873..885ac63c4 100644
--- a/examples/osgvolume/osgvolume.cpp
+++ b/examples/osgvolume/osgvolume.cpp
@@ -792,13 +792,13 @@ osg::Node* createShaderModel(osg::ref_ptr<osg::Image>& image_3d, osg::ref_ptr<os
     {
         char vertexShaderSource[] = 
             "varying vec3 texcoord;\n"
-            "varying vec3 deltaTexCoord;\n"
+            "varying vec3 cameraPos;\n"
             "\n"
             "void main(void)\n"
             "{\n"
-            "    texcoord = gl_MultiTexCoord0.xyz;\n"
-            "    gl_Position     = ftransform();  \n"
-            "    deltaTexCoord = normalize(gl_ModelViewMatrixInverse * vec4(0,0,0,1) - gl_Vertex);\n"
+            "        texcoord = gl_MultiTexCoord0.xyz;\n"
+            "        gl_Position     = ftransform();\n"
+            "        cameraPos=vec4(gl_ModelViewMatrixInverse*vec4(0,0,0,1)).xyz;\n"
             "}\n";
 
         osg::Shader* vertex_shader = new osg::Shader(osg::Shader::VERTEX, vertexShaderSource);
@@ -822,27 +822,26 @@ osg::Node* createShaderModel(osg::ref_ptr<osg::Image>& image_3d, osg::ref_ptr<os
             "uniform float transparency;\n"
             "uniform float alphaCutOff;\n"
             "\n"
-            "varying vec3 deltaTexCoord;\n"
+            "varying vec3 cameraPos;\n"
             "varying vec3 texcoord;\n"
-            "void main(void) \n"
-            "{ \n"
-            "    vec3 deltaTexCoord2 = normalize(deltaTexCoord)*sampleDensity; \n"
             "\n"
-            "    gl_FragColor = vec4(0.0, 0.0, 0.0, 0.0); \n"
-            "    \n"
-            "    while (texcoord.x>=0.0 && texcoord.x<=1.0 &&\n"
-            "           texcoord.y>=0.0 && texcoord.y<=1.0 &&\n"
-            "           texcoord.z>=0.0 && texcoord.z<=1.0)\n"
-            "    {\n"
-            "       vec4 color = texture3D( baseTexture, texcoord);\n"
-            "       float r = color[3]*transparency;\n"
-            "       if (r>alphaCutOff)\n"
-            "       {\n"
-            "         gl_FragColor.xyz = gl_FragColor.xyz*(1.0-r)+color.xyz*r;\n"
-            "         gl_FragColor.w += r;\n"
-            "       }\n"
-            "       texcoord += deltaTexCoord2; \n"
-            "    }\n"
+            "void main(void)\n"
+            "{ \n"
+            "        vec3 deltaTexCoord=normalize(cameraPos-texcoord.xyz)*sampleDensity;\n"
+            "        gl_FragColor = vec4(0.0, 0.0, 0.0, 0.0); \n"
+            "        while (texcoord.x>=0.0 && texcoord.x<=1.0 &&\n"
+            "               texcoord.y>=0.0 && texcoord.y<=1.0 &&\n"
+            "               texcoord.z>=0.0 && texcoord.z<=1.0)\n"
+            "        {\n"
+            "            vec4 color = texture3D( baseTexture, texcoord);\n"
+            "            float r = color[3]*transparency;\n"
+            "            if (r>alphaCutOff)\n"
+            "            {\n"
+            "                gl_FragColor.xyz = gl_FragColor.xyz*(1.0-r)+color.xyz*r;\n"
+            "                gl_FragColor.w += r;\n"
+            "            }\n"
+            "            texcoord += deltaTexCoord; \n"
+            "        }\n"
             "    if (gl_FragColor.w>1.0) gl_FragColor.w = 1.0; \n"
             "}\n";