Add cloud movement direction and speed

simgear/scene/sky/cloud.cxx

@@ -285,7 +285,7 @@ bool SGCloudLayer::repaint( sgVec3 fog_color ) {
 // spin specifies a rotation about the new Z axis (and orients the
 // sunrise/set effects
 bool SGCloudLayer::reposition( sgVec3 p, sgVec3 up, double lon, double lat,
-        		       double alt )
+        		       double alt, double dt )
 {
     sgMat4 T1, LON, LAT;
     sgVec3 axis;
@@ -343,15 +343,35 @@ bool SGCloudLayer::reposition( sgVec3 p, sgVec3 up, double lon, double lat,
         last_lat = lat;
     }
 
-    if ( lon != last_lon || lat != last_lat ) {
+    double sp_dist = speed*dt;
+
+    if ( lon != last_lon || lat != last_lat || sp_dist != 0 ) {
         Point3D start( last_lon, last_lat, 0.0 );
         Point3D dest( lon, lat, 0.0 );
-        double course, dist;
-        calc_gc_course_dist( dest, start, &course, &dist );
+        double course = 0.0, dist = 0.0;
+
+        if (dest != start) {
+            calc_gc_course_dist( dest, start, &course, &dist );
+         }
         // cout << "course = " << course << ", dist = " << dist << endl;
 
-        double xoff = cos( course ) * dist / (2 * scale);
-        double yoff = sin( course ) * dist / (2 * scale);
+
+        // calculate cloud movement due to external forces
+        double ax = 0.0, ay = 0.0, bx = 0.0, by = 0.0;
+
+        if (dist > 0.0) {
+            ax = cos(course) * dist;
+            ay = sin(course) * dist;
+        }
+
+        if (sp_dist > 0) {
+            bx = cos(-direction * SGD_DEGREES_TO_RADIANS) * sp_dist;
+            by = sin(-direction * SGD_DEGREES_TO_RADIANS) * sp_dist;
+        }
+
+
+        double xoff = (ax + bx) / (2 * scale);
+        double yoff = (ay + by) / (2 * scale);
 
         const float layer_scale = layer_span / scale;
 

simgear/scene/sky/cloud.hxx

@@ -98,6 +98,7 @@ public:
      * visibility.
      */
     float getTransition_m () const;
+
     /**
      * set the transition layer size in meters
      * @param transition_m the transition layer size in meters
@@ -106,12 +107,31 @@ public:
 
     /** get coverage type */
     Coverage getCoverage () const;
+
     /**
      * set coverage type
      * @param coverage the coverage type
      */
     void setCoverage (Coverage coverage);
 
+    /**
+     * set the cloud movement direction
+     * @param dir the cloud movement direction
+     */
+    inline void setDirection(float dir) { direction = dir; }
+
+    /** get the cloud movement direction */
+    inline float getDirection() { return direction; }
+
+    /**
+     * set the cloud movement speed 
+     * @param sp the cloud movement speed
+     */
+    inline void setSpeed(float sp) { speed = sp; }
+
+    /** get the cloud movement speed */
+    inline float getSpeed() { return speed; }
+
     /** build the cloud object */
     void rebuild();
 
@@ -130,8 +150,10 @@ public:
      * @param lat specifies a rotation about the new Y axis
      * @param spin specifies a rotation about the new Z axis
      *        (and orients the sunrise/set effects)
+     * @param dt the time elapsed since the last call
      */
-    bool reposition( sgVec3 p, sgVec3 up, double lon, double lat, double alt );
+    bool reposition( sgVec3 p, sgVec3 up, double lon, double lat, double alt,
+                     double dt = 0.0 );
 
     /** draw the cloud layer */
     void draw();
@@ -154,6 +176,8 @@ private:
     float layer_transition;
     Coverage layer_coverage;
     float scale;
+    float speed;
+    float direction;
 
     // for handling texture coordinates to simulate cloud movement
     // from winds, and to simulate the clouds being tied to ground

simgear/scene/sky/sky.cxx

@@ -139,7 +139,7 @@ bool SGSky::repaint( const SGSkyColor &sc )
 // spin specifies a rotation about the new Z axis (this allows
 // additional orientation for the sunrise/set effects and is used by
 // the skydome and perhaps clouds.
-bool SGSky::reposition( SGSkyState &st )
+bool SGSky::reposition( SGSkyState &st, double dt )
 {
 
     double angle = st.gst * 15;	// degrees
@@ -159,7 +159,7 @@ bool SGSky::reposition( SGSkyState &st )
     for ( int i = 0; i < (int)cloud_layers.size(); ++i ) {
         if ( cloud_layers[i]->getCoverage() != SGCloudLayer::SG_CLOUD_CLEAR ) {
             cloud_layers[i]->reposition( st.zero_elev, st.view_up,
-                                         st.lon, st.lat, st.alt );
+                                         st.lon, st.lat, st.alt, dt );
         }
     }
 

simgear/scene/sky/sky.hxx

@@ -308,7 +308,7 @@ public:
      * @param moon_dec the moon's current declination
      * @param moon_dist the moon's distance from the current view point. 
      */
-    bool reposition( SGSkyState &st );
+    bool reposition( SGSkyState &st, double dt = 0.0 );
 
     /**
      * Modify the given visibility based on cloud layers, thickness,