Improved distance sorting for objects; fixes the case when a small satellite orbiting close to a planet was incorrectly occluded.

src/celengine/render.cpp

@@ -21,6 +21,7 @@
 #include <celutil/debug.h>
 #include <celmath/frustum.h>
 #include <celmath/distance.h>
+#include <celmath/intersect.h>
 #include "gl.h"
 #include "astro.h"
 #include "glext.h"
@@ -264,6 +265,44 @@ static float calcPixelSize(float fovY, float windowHeight)
 }
 
 
+bool operator<(const RenderListEntry& a, const RenderListEntry& b)
+{
+    // This comparison functions tries to determine which of two objects is
+    // closer to the viewer.  Looking just at the distances of the centers
+    // is not enough, nor is comparing distances to the bounding spheres.
+    // Here we trace a ray from the viewer to the center of the smaller
+    // of the two objects and see which object it intersects first.  If the
+    // ray doesn't intersect the larger object at all, it's safe to use
+    // the distance to bounding sphere test.
+    if (a.radius < b.radius)
+    {
+        Vec3f dir = a.position - Point3f(0.0f, 0.0f, 0.0f);
+        float distance;
+        dir.normalize();
+        if (testIntersection(Ray3f(Point3f(0.0f, 0.0f, 0.0f), dir),
+                             Spheref(b.position, b.radius),
+                             distance))
+        {
+            return a.distance - a.radius < distance;
+        }
+    }
+    else
+    {
+        Vec3f dir = b.position - Point3f(0.0f, 0.0f, 0.0f);
+        float distance;
+        dir.normalize();
+        if (testIntersection(Ray3f(Point3f(0.0f, 0.0f, 0.0f), dir),
+                             Spheref(a.position, a.radius),
+                             distance))
+        {
+            return distance < b.distance - b.radius;
+        }
+    }
+
+    return a.distance - a.radius < b.distance - b.radius;
+}
+
+
 bool Renderer::init(int winWidth, int winHeight)
 {
     // Initialize static meshes and textures common to all instances of Renderer
@@ -843,6 +882,7 @@ void Renderer::autoMag(float& faintestMag)
       
 }
 
+
 void Renderer::render(const Observer& observer,
                       const Universe& universe,
                       float faintestMagNight,
@@ -3647,7 +3687,7 @@ public:
     Vec3f viewNormal;
 
     vector<Renderer::Particle>* glareParticles;
-    vector<Renderer::RenderListEntry>* renderList;
+    vector<RenderListEntry>* renderList;
     Renderer::StarVertexBuffer* starVertexBuffer;
 
     float faintestMagNight;
@@ -3759,7 +3799,7 @@ void StarRenderer::process(const Star& star, float distance, float appMag)
         }
         else
         {
-            Renderer::RenderListEntry rle;
+            RenderListEntry rle;
             rle.star = &star;
             rle.body = NULL;
             rle.isCometTail = false;

src/celengine/render.h

@@ -18,6 +18,21 @@
 #include <celtxf/texturefont.h>
 
 
+struct RenderListEntry
+{
+    const Star* star;
+    Body* body;
+    Point3f position;
+    Vec3f sun;
+    float distance;
+    float radius;
+    float nearZ;
+    float farZ;
+    float discSizeInPixels;
+    float appMag;
+    bool isCometTail;
+};
+
 class Renderer
 {
  public:
@@ -126,27 +141,6 @@ class Renderer
         float pad0, pad1, pad2;
     };
 
-    typedef struct _RenderListEntry
-    {
-        const Star* star;
-        Body* body;
-        Point3f position;
-        Vec3f sun;
-        float distance;
-        float radius;
-        float nearZ;
-        float farZ;
-        float discSizeInPixels;
-        float appMag;
-        bool isCometTail;
-
-        bool operator<(const _RenderListEntry& r) const
-        {
-            return distance - radius < r.distance - r.radius;
-            // return z > r.z;
-        }
-    } RenderListEntry;
-
     struct EclipseShadow
     {
         Point3f origin;