Beginning work on a restructure of the sky code.

simgear/ephemeris/sky.cxx

@@ -55,14 +55,14 @@
 // in meters of course
 #define CENTER_ELEV   25000.0
 
-#define INNER_RADIUS  50000.0
+#define UPPER_RADIUS  50000.0
-#define INNER_ELEV    20000.0
+#define UPPER_ELEV    20000.0
 
 #define MIDDLE_RADIUS 70000.0
 #define MIDDLE_ELEV    8000.0
 
-#define OUTER_RADIUS  80000.0
+#define LOWER_RADIUS  80000.0
-#define OUTER_ELEV        0.0
+#define LOWER_ELEV        0.0
 
 #define BOTTOM_RADIUS 50000.0
 #define BOTTOM_ELEV   -2000.0
@@ -73,13 +73,214 @@ static float middle_vertex[12][3];
 static float outer_vertex[12][3];
 static float bottom_vertex[12][3];
 
-static GLubyte inner_color[12][4];
+static GLubyte upper_color[12][4];
 static GLubyte middle_color[12][4];
-static GLubyte outer_color[12][4];
+static GLubyte lower_color[12][4];
+
+
+// Constructor
+FGSky::FGSky( void ) {
+}
+
+
+// Destructor
+FGSky::~FGSky( void ) {
+}
+
+
+// initialize the sky object and connect it into the scene graph
+bool FGSky::initialize() {
+    sgVec3 vertex;
+    sgVec3 color;
+
+    float theta;
+    int i;
+
+    // initialize arrays
+    upper_ring_vl = new ssgVertexArray( 12 );
+    upper_ring_cl = new ssgColourArray( 12 );
+
+    middle_ring_vl = new ssgVertexArray( 12 );
+    middle_ring_cl = new ssgColourArray( 12 );
+
+    lower_ring_vl = new ssgVertexArray( 12 );
+    lower_ring_cl = new ssgColourArray( 12 );
+
+    bottom_ring_vl = new ssgVertexArray( 12 );
+    bottom_ring_cl = new ssgColourArray( 12 );
+
+    // generate the sky dome vertices
+
+    sgSetVec3( color, 0.0, 0.0, 1.0 ); // seed to all blue
+
+    for ( i = 0; i < 12; i++ ) {
+	theta = (i * 30.0) * DEG_TO_RAD;
+
+	sgSetVec3( vertex,
+		   cos(theta) * UPPER_RADIUS,
+		   sin(theta) * UPPER_RADIUS,
+		   UPPER_ELEV );
+	upper_ring_vl->add( vertex );
+	upper_ring_cl->add( color );
+	
+	sgSetVec3( vertex,
+		   cos((double)theta) * MIDDLE_RADIUS,
+		   sin((double)theta) * MIDDLE_RADIUS,
+		   MIDDLE_ELEV );
+	middle_ring_vl->add( vertex );
+	middle_ring_cl->add( color );
+
+	sgSetVec3( vertex,
+		   cos((double)theta) * LOWER_RADIUS,
+		   sin((double)theta) * LOWER_RADIUS,
+		   LOWER_ELEV );
+	lower_ring_vl->add( vertex );
+	lower_ring_cl->add( color );
+
+	sgSetVec3( vertex,
+		   cos((double)theta) * BOTTOM_RADIUS,
+		   sin((double)theta) * BOTTOM_RADIUS,
+		   BOTTOM_ELEV );
+	bottom_ring_vl->add( vertex );
+	bottom_ring_cl->add( color );
+    }
+
+    // force a rebuild of the colors
+    rebuild();
+
+    return true;
+}
+
+
+// rebuild the sky colors based on current value of sun_angle, sky,
+// and fog colors.  This updates the color arrays for ssgVtxTable.
+bool FGSky::rebuild() {
+    double diff;
+    sgVec3 outer_param, outer_amt, outer_diff;
+    sgVec3 middle_param, middle_amt, middle_diff;
+    int i, j;
+
+    if ( (sun_angle > 80.0) && (sun_angle < 100.0) ) {
+	// 0.0 - 0.4
+	sgSetVec3( outer_param,
+		   (10.0 - fabs(90.0 - sun_angle)) / 20.0,
+		   (10.0 - fabs(90.0 - sun_angle)) / 40.0,
+		   -(10.0 - fabs(90.0 - sun_angle)) / 30.0 );
+
+	sgSetVec3( middle_param,
+		   (10.0 - fabs(90.0 - sun_angle)) / 40.0,
+		   (10.0 - fabs(90.0 - sun_angle)) / 80.0,
+		   0.0 );
+
+	sgScaleVec3( outer_diff, outer_param, 1.0 / 6.0 );
+
+	sgScaleVec3( middle_diff, middle_param, 1.0 / 6.0 );
+    } else {
+	sgSetVec3( outer_param, 0.0, 0.0, 0.0 );
+	sgSetVec3( middle_param, 0.0, 0.0, 0.0 );
+
+	sgSetVec3( outer_diff, 0.0, 0.0, 0.0 );
+	sgSetVec3( middle_diff, 0.0, 0.0, 0.0 );
+    }
+    // printf("  outer_red_param = %.2f  outer_red_diff = %.2f\n", 
+    //        outer_red_param, outer_red_diff);
+
+    // calculate transition colors between sky and fog
+    sgCopyVec3( outer_amt, outer_param );
+    sgCopyVec3( middle_amt, middle_param );
+
+    // float *upper_color, *middle_color, *lower_color;
+
+    for ( i = 0; i < 6; i++ ) {
+	// inner_color = 
+	for ( j = 0; j < 3; j++ ) {
+	    diff = sky_color[j] - fog_color[j];
+
+	    // printf("sky = %.2f  fog = %.2f  diff = %.2f\n", 
+	    //        l->sky_color[j], l->fog_color[j], diff);
+
+	    upper_color[i][j] = (GLubyte)((sky_color[j] - diff * 0.3) * 255);
+	    middle_color[i][j] = (GLubyte)((sky_color[j] - diff * 0.9 
+					   + middle_amt[j]) * 255);
+	    lower_color[i][j] = (GLubyte)((fog_color[j] + outer_amt[j]) 
+					  * 255);
+
+	    if ( upper_color[i][j] > 255 ) { upper_color[i][j] = 255; }
+	    if ( upper_color[i][j] < 25 ) { upper_color[i][j] = 25; }
+	    if ( middle_color[i][j] > 255 ) { middle_color[i][j] = 255; }
+	    if ( middle_color[i][j] < 25 ) { middle_color[i][j] = 25; }
+	    if ( lower_color[i][j] > 255 ) { lower_color[i][j] = 255; }
+	    if ( lower_color[i][j] < 25 ) { lower_color[i][j] = 25; }
+	}
+	upper_color[i][3] = middle_color[i][3] = lower_color[i][3] = 
+	    (GLubyte)(sky_color[3] * 255);
+
+	for ( j = 0; j < 3; j++ ) {
+	    outer_amt[j] -= outer_diff[j];
+	    middle_amt[j] -= middle_diff[j];
+	}
+
+	/*
+	printf("upper_color[%d] = %.2f %.2f %.2f %.2f\n", i, upper_color[i][0],
+	       upper_color[i][1], upper_color[i][2], upper_color[i][3]);
+	printf("middle_color[%d] = %.2f %.2f %.2f %.2f\n", i, 
+	       middle_color[i][0], middle_color[i][1], middle_color[i][2], 
+	       middle_color[i][3]);
+	printf("lower_color[%d] = %.2f %.2f %.2f %.2f\n", i, 
+	       lower_color[i][0], lower_color[i][1], lower_color[i][2], 
+	       lower_color[i][3]);
+	*/
+    }
+
+    sgSetVec3( outer_amt, 0.0, 0.0, 0.0 );
+    sgSetVec3( middle_amt, 0.0, 0.0, 0.0 );
+
+    for ( i = 6; i < 12; i++ ) {
+	for ( j = 0; j < 3; j++ ) {
+	    diff = sky_color[j] - fog_color[j];
+
+	    // printf("sky = %.2f  fog = %.2f  diff = %.2f\n", 
+	    //        sky_color[j], fog_color[j], diff);
+
+	    upper_color[i][j] = (GLubyte)((sky_color[j] - diff * 0.3) * 255);
+	    middle_color[i][j] = (GLubyte)((sky_color[j] - diff * 0.9 
+					    + middle_amt[j]) * 255);
+	    lower_color[i][j] = (GLubyte)((fog_color[j] + outer_amt[j]) 
+					  * 255);
+
+	    if ( upper_color[i][j] > 255 ) { upper_color[i][j] = 255; }
+	    if ( upper_color[i][j] < 25 ) { upper_color[i][j] = 25; }
+	    if ( middle_color[i][j] > 255 ) { middle_color[i][j] = 255; }
+	    if ( middle_color[i][j] < 25 ) { middle_color[i][j] = 25; }
+	    if ( lower_color[i][j] > 255 ) { lower_color[i][j] = 255; }
+	    if ( lower_color[i][j] < 35 ) { lower_color[i][j] = 35; }
+	}
+	upper_color[i][3] = middle_color[i][3] = lower_color[i][3] = 
+	    (GLubyte)(sky_color[3] * 255);
+
+	for ( j = 0; j < 3; j++ ) {
+	    outer_amt[j] += outer_diff[j];
+	    middle_amt[j] += middle_diff[j];
+	}
+
+	/*
+	printf("upper_color[%d] = %.2f %.2f %.2f %.2f\n", i, upper_color[i][0],
+	       upper_color[i][1], upper_color[i][2], upper_color[i][3]);
+	printf("middle_color[%d] = %.2f %.2f %.2f %.2f\n", i, 
+	       middle_color[i][0], middle_color[i][1], middle_color[i][2], 
+	       middle_color[i][3]);
+	printf("lower_color[%d] = %.2f %.2f %.2f %.2f\n", i, 
+	       lower_color[i][0], lower_color[i][1], lower_color[i][2], 
+	       lower_color[i][3]);
+	*/
+    }
+
+    return true;
+}
 
 
 // Calculate the sky structure vertices
-void fgSkyVerticesInit( void ) {
+void fgSkyVerticesInit() {
     float theta;
     int i;
 
@@ -88,20 +289,20 @@ void fgSkyVerticesInit( void ) {
     for ( i = 0; i < 12; i++ ) {
 	theta = (i * 30.0) * DEG_TO_RAD;
 	
-	inner_vertex[i][0] = cos(theta) * INNER_RADIUS;
+	inner_vertex[i][0] = cos(theta) * UPPER_RADIUS;
-	inner_vertex[i][1] = sin(theta) * INNER_RADIUS;
+	inner_vertex[i][1] = sin(theta) * UPPER_RADIUS;
-	inner_vertex[i][2] = INNER_ELEV;
+	inner_vertex[i][2] = UPPER_ELEV;
 	
-	// printf("    %.2f %.2f\n", cos(theta) * INNER_RADIUS, 
+	// printf("    %.2f %.2f\n", cos(theta) * UPPER_RADIUS, 
-	//        sin(theta) * INNER_RADIUS);
+	//        sin(theta) * UPPER_RADIUS);
 
 	middle_vertex[i][0] = cos((double)theta) * MIDDLE_RADIUS;
 	middle_vertex[i][1] = sin((double)theta) * MIDDLE_RADIUS;
 	middle_vertex[i][2] = MIDDLE_ELEV;
 	    
-	outer_vertex[i][0] = cos((double)theta) * OUTER_RADIUS;
+	outer_vertex[i][0] = cos((double)theta) * LOWER_RADIUS;
-	outer_vertex[i][1] = sin((double)theta) * OUTER_RADIUS;
+	outer_vertex[i][1] = sin((double)theta) * LOWER_RADIUS;
-	outer_vertex[i][2] = OUTER_ELEV;
+	outer_vertex[i][2] = LOWER_ELEV;
 	    
 	bottom_vertex[i][0] = cos((double)theta) * BOTTOM_RADIUS;
 	bottom_vertex[i][1] = sin((double)theta) * BOTTOM_RADIUS;
@@ -111,7 +312,7 @@ void fgSkyVerticesInit( void ) {
 
 
 // (Re)calculate the sky colors at each vertex
-void fgSkyColorsInit( void ) {
+void fgSkyColorsInit() {
     fgLIGHT *l;
     double sun_angle, diff;
     double outer_param[3], outer_amt[3], outer_diff[3];
@@ -169,20 +370,20 @@ void fgSkyColorsInit( void ) {
 	    // printf("sky = %.2f  fog = %.2f  diff = %.2f\n", 
 	    //        l->sky_color[j], l->fog_color[j], diff);
 
-	    inner_color[i][j] = (GLubyte)((l->sky_color[j] - diff * 0.3) * 255);
+	    upper_color[i][j] = (GLubyte)((l->sky_color[j] - diff * 0.3) * 255);
 	    middle_color[i][j] = (GLubyte)((l->sky_color[j] - diff * 0.9 
 					   + middle_amt[j]) * 255);
-	    outer_color[i][j] = (GLubyte)((l->fog_color[j] + outer_amt[j]) 
+	    lower_color[i][j] = (GLubyte)((l->fog_color[j] + outer_amt[j]) 
 					  * 255);
 
-	    if ( inner_color[i][j] > 255 ) { inner_color[i][j] = 255; }
+	    if ( upper_color[i][j] > 255 ) { upper_color[i][j] = 255; }
-	    if ( inner_color[i][j] < 25 ) { inner_color[i][j] = 25; }
+	    if ( upper_color[i][j] < 25 ) { upper_color[i][j] = 25; }
 	    if ( middle_color[i][j] > 255 ) { middle_color[i][j] = 255; }
 	    if ( middle_color[i][j] < 25 ) { middle_color[i][j] = 25; }
-	    if ( outer_color[i][j] > 255 ) { outer_color[i][j] = 255; }
+	    if ( lower_color[i][j] > 255 ) { lower_color[i][j] = 255; }
-	    if ( outer_color[i][j] < 25 ) { outer_color[i][j] = 25; }
+	    if ( lower_color[i][j] < 25 ) { lower_color[i][j] = 25; }
 	}
-	inner_color[i][3] = middle_color[i][3] = outer_color[i][3] = 
+	upper_color[i][3] = middle_color[i][3] = lower_color[i][3] = 
 	    (GLubyte)(l->sky_color[3] * 255);
 
 	for ( j = 0; j < 3; j++ ) {
@@ -191,14 +392,14 @@ void fgSkyColorsInit( void ) {
 	}
 
 	/*
-	printf("inner_color[%d] = %.2f %.2f %.2f %.2f\n", i, inner_color[i][0],
+	printf("upper_color[%d] = %.2f %.2f %.2f %.2f\n", i, upper_color[i][0],
-	       inner_color[i][1], inner_color[i][2], inner_color[i][3]);
+	       upper_color[i][1], upper_color[i][2], upper_color[i][3]);
 	printf("middle_color[%d] = %.2f %.2f %.2f %.2f\n", i, 
 	       middle_color[i][0], middle_color[i][1], middle_color[i][2], 
 	       middle_color[i][3]);
-	printf("outer_color[%d] = %.2f %.2f %.2f %.2f\n", i, 
+	printf("lower_color[%d] = %.2f %.2f %.2f %.2f\n", i, 
-	       outer_color[i][0], outer_color[i][1], outer_color[i][2], 
+	       lower_color[i][0], lower_color[i][1], lower_color[i][2], 
-	       outer_color[i][3]);
+	       lower_color[i][3]);
 	*/
     }
 
@@ -215,20 +416,20 @@ void fgSkyColorsInit( void ) {
 	    // printf("sky = %.2f  fog = %.2f  diff = %.2f\n", 
 	    //        l->sky_color[j], l->fog_color[j], diff);
 
-	    inner_color[i][j] = (GLubyte)((l->sky_color[j] - diff * 0.3) * 255);
+	    upper_color[i][j] = (GLubyte)((l->sky_color[j] - diff * 0.3) * 255);
 	    middle_color[i][j] = (GLubyte)((l->sky_color[j] - diff * 0.9 
 					    + middle_amt[j]) * 255);
-	    outer_color[i][j] = (GLubyte)((l->fog_color[j] + outer_amt[j]) 
+	    lower_color[i][j] = (GLubyte)((l->fog_color[j] + outer_amt[j]) 
 					  * 255);
 
-	    if ( inner_color[i][j] > 255 ) { inner_color[i][j] = 255; }
+	    if ( upper_color[i][j] > 255 ) { upper_color[i][j] = 255; }
-	    if ( inner_color[i][j] < 25 ) { inner_color[i][j] = 25; }
+	    if ( upper_color[i][j] < 25 ) { upper_color[i][j] = 25; }
 	    if ( middle_color[i][j] > 255 ) { middle_color[i][j] = 255; }
 	    if ( middle_color[i][j] < 25 ) { middle_color[i][j] = 25; }
-	    if ( outer_color[i][j] > 255 ) { outer_color[i][j] = 255; }
+	    if ( lower_color[i][j] > 255 ) { lower_color[i][j] = 255; }
-	    if ( outer_color[i][j] < 35 ) { outer_color[i][j] = 35; }
+	    if ( lower_color[i][j] < 35 ) { lower_color[i][j] = 35; }
 	}
-	inner_color[i][3] = middle_color[i][3] = outer_color[i][3] = 
+	upper_color[i][3] = middle_color[i][3] = lower_color[i][3] = 
 	    (GLubyte)(l->sky_color[3] * 255);
 
 	for ( j = 0; j < 3; j++ ) {
@@ -237,21 +438,21 @@ void fgSkyColorsInit( void ) {
 	}
 
 	/*
-	printf("inner_color[%d] = %.2f %.2f %.2f %.2f\n", i, inner_color[i][0],
+	printf("upper_color[%d] = %.2f %.2f %.2f %.2f\n", i, upper_color[i][0],
-	       inner_color[i][1], inner_color[i][2], inner_color[i][3]);
+	       upper_color[i][1], upper_color[i][2], upper_color[i][3]);
 	printf("middle_color[%d] = %.2f %.2f %.2f %.2f\n", i, 
 	       middle_color[i][0], middle_color[i][1], middle_color[i][2], 
 	       middle_color[i][3]);
-	printf("outer_color[%d] = %.2f %.2f %.2f %.2f\n", i, 
+	printf("lower_color[%d] = %.2f %.2f %.2f %.2f\n", i, 
-	       outer_color[i][0], outer_color[i][1], outer_color[i][2], 
+	       lower_color[i][0], lower_color[i][1], lower_color[i][2], 
-	       outer_color[i][3]);
+	       lower_color[i][3]);
 	*/
     }
 }
 
 
 // Initialize the sky structure and colors
-void fgSkyInit( void ) {
+void fgSkyInit() {
     FG_LOG( FG_ASTRO, FG_INFO, "Initializing the sky" );
 
     fgSkyVerticesInit();
@@ -263,13 +464,13 @@ void fgSkyInit( void ) {
 
 
 // Draw the Sky
-void fgSkyRender( void ) {
+void fgSkyRender() {
     FGInterface *f;
     fgLIGHT *l;
     GLubyte sky_color[4];
-    GLubyte inner_color[4];
+    GLubyte upper_color[4];
     GLubyte middle_color[4];
-    GLubyte outer_color[4];
+    GLubyte lower_color[4];
     double diff;
     int i;
 
@@ -285,11 +486,11 @@ void fgSkyRender( void ) {
 	// printf("sky = %.2f  fog = %.2f  diff = %.2f\n", 
 	//        l->sky_color[j], l->adj_fog_color[j], diff);
 
-	inner_color[i] = (GLubyte)((l->sky_color[i] - diff * 0.3) * 255);
+	upper_color[i] = (GLubyte)((l->sky_color[i] - diff * 0.3) * 255);
 	middle_color[i] = (GLubyte)((l->sky_color[i] - diff * 0.9) * 255);
-	outer_color[i] = (GLubyte)(l->adj_fog_color[i] * 255);
+	lower_color[i] = (GLubyte)(l->adj_fog_color[i] * 255);
     }
-    inner_color[3] = middle_color[3] = outer_color[3] = 
+    upper_color[3] = middle_color[3] = lower_color[3] = 
 	(GLubyte)(l->adj_fog_color[3] * 255);
 
     xglPushMatrix();
@@ -315,10 +516,10 @@ void fgSkyRender( void ) {
     xglColor4fv(l->sky_color);
     xglVertex3f(0.0, 0.0, CENTER_ELEV);
     for ( i = 11; i >= 0; i-- ) {
-	xglColor4ubv( inner_color );
+	xglColor4ubv( upper_color );
 	xglVertex3fv( inner_vertex[i] );
     }
-    xglColor4ubv( inner_color );
+    xglColor4ubv( upper_color );
     xglVertex3fv( inner_vertex[11] );
     xglEnd();
 
@@ -331,17 +532,17 @@ void fgSkyRender( void ) {
 	//        middle_color[i][3]);
 	// xglColor4f(1.0, 0.0, 0.0, 1.0);
 	xglVertex3fv( middle_vertex[i] );
-	xglColor4ubv( inner_color );
+	xglColor4ubv( upper_color );
-	// printf("inner_color[%d] = %.2f %.2f %.2f %.2f\n", i, 
+	// printf("upper_color[%d] = %.2f %.2f %.2f %.2f\n", i, 
-	//        inner_color[i][0], inner_color[i][1], inner_color[i][2], 
+	//        upper_color[i][0], upper_color[i][1], upper_color[i][2], 
-	//        inner_color[i][3]);
+	//        upper_color[i][3]);
 	// xglColor4f(0.0, 0.0, 1.0, 1.0);
 	xglVertex3fv( inner_vertex[i] );
     }
     xglColor4ubv( middle_color );
     // xglColor4f(1.0, 0.0, 0.0, 1.0);
     xglVertex3fv( middle_vertex[0] );
-    xglColor4ubv( inner_color );
+    xglColor4ubv( upper_color );
     // xglColor4f(0.0, 0.0, 1.0, 1.0);
     xglVertex3fv( inner_vertex[0] );
     xglEnd();
@@ -349,12 +550,12 @@ void fgSkyRender( void ) {
     // Draw the outer ring
     xglBegin( GL_TRIANGLE_STRIP );
     for ( i = 0; i < 12; i++ ) {
-	xglColor4ubv( outer_color );
+	xglColor4ubv( lower_color );
 	xglVertex3fv( outer_vertex[i] );
 	xglColor4ubv( middle_color );
 	xglVertex3fv( middle_vertex[i] );
     }
-    xglColor4ubv( outer_color );
+    xglColor4ubv( lower_color );
     xglVertex3fv( outer_vertex[0] );
     xglColor4ubv( middle_color );
     xglVertex3fv( middle_vertex[0] );
@@ -362,7 +563,7 @@ void fgSkyRender( void ) {
 
     // Draw the bottom skirt
     xglBegin( GL_TRIANGLE_STRIP );
-    xglColor4ubv( outer_color );
+    xglColor4ubv( lower_color );
     for ( i = 0; i < 12; i++ ) {
 	xglVertex3fv( bottom_vertex[i] );
 	xglVertex3fv( outer_vertex[i] );

simgear/ephemeris/sky.hxx

@@ -33,19 +33,82 @@
 #include <plib/ssg.h>		// plib include
 
 
-class fgSky : ssgLeaf
+class FGSky {
-{
+    double sun_angle;		// sun angle in degrees relative to verticle
+				// 0 degrees = high noon
+				// 90 degrees = sun rise/set
+				// 180 degrees = darkest midnight
+
+    sgVec3 sky_color;		// base sky color
+    sgVec3 fog_color;		// fog color
+
+    sgVec3 origin;		// coordinates of sky placement origin
+				// I recommend (lon, lat, 0) relative to
+				// your world coordinate scheme
+
+    double lon, lat;		// current lon and lat (for properly rotating
+				// sky)
+
+
+    ssgVertexArray *upper_ring_vl;
+    ssgColourArray *upper_ring_cl;
+
+    ssgVertexArray *middle_ring_vl;
+    ssgColourArray *middle_ring_cl;
+
+    ssgVertexArray *lower_ring_vl;
+    ssgColourArray *lower_ring_cl;
+
+    ssgVertexArray *bottom_ring_vl;
+    ssgColourArray *bottom_ring_cl;
+
+public:
+
+    // Constructor
+    FGSky( void );
+
+    // Destructor
+    ~FGSky( void );
+
+    // initialize the sky object and connect it into the scene graph
+    bool initialize();
+
+    // rebuild the sky colors based on current value of sun_angle,
+    // sky, and fog colors.  This updates the color arrays for
+    // ssgVtxTable.
+    bool rebuild();
+
+    // enable the sky in the scene graph (default)
+    bool enable();
+
+    // disable the sky in the scene graph.  The leaf node is still
+    // there, how ever it won't be traversed on the cullandrender
+    // phase.
+    bool disable();
+
+    inline void set_sun_angle( double a ) { sun_angle = a; }
+    inline void set_sky_color( sgVec3 color ) { 
+	sgCopyVec3(sky_color, color);
+    }
+    inline void set_fog_color( sgVec3 color ) { 
+	sgCopyVec3(fog_color, color);
+    }
+    inline void set_origin( sgVec3 p ) { 
+	sgCopyVec3(origin, p);
+    }
+    inline void set_lon( double l ) { lon = l; }
+    inline void set_lat( double l ) { lat = l; }
 };
 
 
 // (Re)generate the display list
-void fgSkyInit( void );
+void fgSkyInit();
 
 // (Re)calculate the sky colors at each vertex
-void fgSkyColorsInit( void );
+void fgSkyColorsInit();
 
 // Draw the Sky
-void fgSkyRender( void );
+void fgSkyRender();
 
 
 #endif // _SKY_HXX