Add a method to SGCloudLayer to set overall cloud alpha. This gives us the

capability to slowly fade a cloud layer in or out.

We use this effect in combination with lowering visibility as we approach
a cloud layer to hide the fact that it is simply a 2d textured polygon being
drawn across the sky.

diff --git a/simgear/scene/sky/cloud.cxx b/simgear/scene/sky/cloud.cxx
index dbc7d03d67d22cf5153fc671a6a16f52e46df644..d567f729b67d67bf880ba99afb50a795664bced9 100644 (file)
--- a/simgear/scene/sky/cloud.cxx
+++ b/simgear/scene/sky/cloud.cxx
@@ -197,9 +197,12 @@ generateNormalizationCubeMap()
 
 // Constructor
 SGCloudLayer::SGCloudLayer( const string &tex_path ) :
+    vertices(0),
+    indices(0),
     layer_root(new ssgRoot),
     layer_transform(new ssgTransform),
     state_sel(0),
+    cloud_alpha(1.0),
     texture_path(tex_path),
     layer_span(0.0),
     layer_asl(0.0),
@@ -210,9 +213,7 @@ SGCloudLayer::SGCloudLayer( const string &tex_path ) :
     speed(0.0),
     direction(0.0),
     last_lon(0.0),
-    last_lat(0.0),
-    vertices(0),
-    indices(0)
+    last_lat(0.0)
 {
     cl[0] = cl[1] = cl[2] = cl[3] = NULL;
     vl[0] = vl[1] = vl[2] = vl[3] = NULL;
@@ -495,7 +496,7 @@ SGCloudLayer::rebuild()
                            cos( j * half_angle ),
                            -sin( j * half_angle ) );
                 sgVectorProductVec3( v1.normal, v1.tTangent, v1.sTangent );
-                sgSetVec4( v1.color, 1.0f, 1.0f, 1.0f, (i == 0) ? 0.0f : 0.15f );
+                sgSetVec4( v1.color, 1.0f, 1.0f, 1.0f, (i == 0) ? 0.0f : cloud_alpha * 0.15f );
             }
         }
         /*
@@ -630,10 +631,27 @@ bool SGCloudLayer::repaint( sgVec3 fog_color ) {
         float *color;
 
         for ( int i = 0; i < 4; i++ ) {
-            for ( int j = 0; j < 10; ++j ) {
-                color = cl[i]->get( j );
+            color = cl[i]->get( 0 );
+            sgCopyVec3( color, fog_color );
+            color[3] = (i == 0) ? 0.0f : 0.15f;
+
+            for ( int j = 0; j < 4; ++j ) {
+                color = cl[i]->get( (2*j) );
                 sgCopyVec3( color, fog_color );
+                color[3] = 
+                    ((j == 0) || (i == 3)) ?
+                    ((j == 0) && (i == 3)) ? 0.0f : 0.15f : 1.0f;
+
+                color = cl[i]->get( (2*j) + 1 );
+                sgCopyVec3( color, fog_color );
+                color[3] = 
+                    ((j == 3) || (i == 0)) ?
+                    ((j == 3) && (i == 0)) ? 0.0f : 0.15f : 1.0f;
             }
+
+            color = cl[i]->get( 9 );
+            sgCopyVec3( color, fog_color );
+            color[3] = (i == 3) ? 0.0f : 0.15f;
         }
     }
 

diff --git a/simgear/scene/sky/cloud.hxx b/simgear/scene/sky/cloud.hxx
index 73ca832232d2af9e118bf7c130274e3cb5b9adb0..dbd7c8fb1cdfe154584d00fdcfd53a9a8f76ebf9 100644 (file)
--- a/simgear/scene/sky/cloud.hxx
+++ b/simgear/scene/sky/cloud.hxx
@@ -143,6 +143,18 @@ public:
     /** get the cloud movement speed */
     inline float getSpeed() { return speed; }
 
+    /**
+     * set the alpha component of the cloud base color.  Normally this
+     * should be 1.0, but you can set it anywhere in the range of 0.0
+     * to 1.0 to fade a cloud layer in or out.
+     * @param alpha cloud alpha value (0.0 to 1.0)
+     */
+    inline void setAlpha( float alpha ) {
+        if ( alpha < 0.0 ) { alpha = 0.0; }
+        if ( alpha > 1.0 ) { alpha = 1.0; }
+        cloud_alpha = alpha;
+    }
+
     /** build the cloud object */
     void rebuild();
 
@@ -191,6 +203,8 @@ private:
     ssgLeaf *layer[4];
     ssgStateSelector *state_sel;
 
+    float cloud_alpha;          // 1.0 = drawn fully, 0.0 faded out completely
+
     ssgColourArray *cl[4]; 
     ssgVertexArray *vl[4];
     ssgTexCoordArray *tl[4];

diff --git a/simgear/scene/sky/sky.cxx b/simgear/scene/sky/sky.cxx
index ad8e8ae05caea36f555f0a397f6f2fea55c76590..ae1a2c0af161f117c1e364e755c64beb90a0e607 100644 (file)
--- a/simgear/scene/sky/sky.cxx
+++ b/simgear/scene/sky/sky.cxx
@@ -171,34 +171,34 @@ bool SGSky::reposition( SGSkyState &st, double dt )
 void SGSky::preDraw( float alt, float fog_exp2_density ) {
     ssgCullAndDraw( pre_root );
 
-       // if we are closer than this to a cloud layer, don't draw clouds
+    // if we are closer than this to a cloud layer, don't draw clouds
     static const float slop = 5.0;
     int i;
 
     // check where we are relative to the cloud layers
     in_cloud = -1;
     for ( i = 0; i < (int)cloud_layers.size(); ++i ) {
-       float asl = cloud_layers[i]->getElevation_m();
-       float thickness = cloud_layers[i]->getThickness_m();
-
-       if ( alt < asl - slop ) {
-           // below cloud layer
-       } else if ( alt < asl + thickness + slop ) {
-           // in cloud layer
-
-           // bail now and don't draw any clouds
-           in_cloud = i;
-       } else {
-           // above cloud layer
-       }
+        float asl = cloud_layers[i]->getElevation_m();
+        float thickness = cloud_layers[i]->getThickness_m();
+
+        if ( alt < asl - slop ) {
+            // below cloud layer
+        } else if ( alt < asl + thickness + slop ) {
+            // in cloud layer
+
+            // bail now and don't draw any clouds
+            in_cloud = i;
+        } else {
+            // above cloud layer
+        }
     }
 
     // determine rendering order
     cur_layer_pos = 0;
     while ( cur_layer_pos < (int)cloud_layers.size() &&
-           alt > cloud_layers[cur_layer_pos]->getElevation_m())
+            alt > cloud_layers[cur_layer_pos]->getElevation_m() )
     {
-       ++cur_layer_pos;
+        ++cur_layer_pos;
     }
 
     // FIXME: This should not be needed, but at this time (08/15/2003)
@@ -266,7 +266,10 @@ void SGSky::modify_vis( float alt, float time_factor ) {
 
        double ratio = 1.0;
 
-        if ( cloud_layers[i]->getCoverage() == SGCloudLayer::SG_CLOUD_CLEAR || cloud_layers[i]->getCoverage() == SGCloudLayer::SG_CLOUD_FEW || cloud_layers[i]->getCoverage() == SGCloudLayer::SG_CLOUD_SCATTERED) {
+        if ( cloud_layers[i]->getCoverage() == SGCloudLayer::SG_CLOUD_CLEAR ||
+             cloud_layers[i]->getCoverage() == SGCloudLayer::SG_CLOUD_FEW ||
+             cloud_layers[i]->getCoverage() == SGCloudLayer::SG_CLOUD_SCATTERED)
+        {
            // less than 50% coverage -- assume we're in the clear for now
            ratio = 1.0;
         } else if ( alt < asl - transition ) {
@@ -286,9 +289,15 @@ void SGSky::modify_vis( float alt, float time_factor ) {
            ratio = 1.0;
        }
 
+        // set the alpha fade value for the cloud layer
+        float temp = ratio * 2.0;
+        if ( temp > 1.0 ) { temp = 1.0; }
+        cloud_layers[i]->setAlpha( temp );
+
        // accumulate effects from multiple cloud layers
        effvis *= ratio;
 
+#if 0
        if ( ratio < 1.0 ) {
            if ( ! in_puff ) {
                // calc chance of entering cloud puff
@@ -345,12 +354,14 @@ void SGSky::modify_vis( float alt, float time_factor ) {
                    in_puff = false; 
                }
            }
-
-           // never let visibility drop below 25 meters
-           if ( effvis <= 25.0 ) {
-               effvis = 25.0;
-           }
        }
+#endif
+
+        // never let visibility drop below 25 meters
+        if ( effvis <= 25.0 ) {
+            effvis = 25.0;
+        }
+
     } // for
 
     effective_visibility = effvis;