[Kstars-devel] branches/kstars/unfrozen/kstars/kstars

[Jason Harris]

SVN commit 829326 by harris:

Introducing variable-speed slewing.  When you move to a new position, rather than 
slewing at a uniform rate, the speed will gradually increase to a maximum value, 
then slow down as the target is approached.

Try it out and let me know what you think.  Is this appealing enough that we can 
just discard uniform slews, or should users be given the option?

CCMAIL: kstars-devel at kde.org



 M  +33 -3     skymap.cpp  


--- branches/kstars/unfrozen/kstars/kstars/skymap.cpp #829325:829326
@@ -718,8 +718,12 @@
 }
 
 void SkyMap::slewFocus( void ) {
-    double dX, dY, fX, fY, r;
+    double dX, dY, fX, fY, r, r0;
+    double rslowdown = 0.0;
     double step = 1.0;
+    double maxstep = 10.0;
+    double grow = 1.1;
+    
     SkyPoint newFocus;
 
     //Don't slew if the mouse button is pressed
@@ -742,9 +746,11 @@
             if ( dX < -180.0 ) dX = 360.0 + dX;
             else if ( dX > 180.0 ) dX = -360.0 + dX;
 
-            r = sqrt( dX*dX + dY*dY );
-
+            r0 = sqrt( dX*dX + dY*dY );
+            r = r0;
             while ( r > step ) {
+                //DEBUG
+                //kDebug() << step << ": " << r << ": " << r0 << endl;
                 fX = dX / r;
                 fY = dY / r;
 
@@ -780,6 +786,30 @@
                 else if ( dX > 180.0 ) dX = -360.0 + dX;
 
                 r = sqrt( dX*dX + dY*dY );
+                
+                //rslowdown is set when we have reached the maximum slew speed
+                //check to see if we are approaching the target position
+                //if so, start slowing down
+                if ( rslowdown > 0.0 ) {
+                    if ( r <= rslowdown && step > 1.0 ) {
+                        step /= grow;
+                    }
+
+                } else {
+                    //stop accelerating when we pass the midpoint
+                    if ( r/r0 < 0.5 && step < maxstep ) { maxstep = step; }
+                    //accelerate if we're more than 2 steps away and 
+                    //not already at maxstep
+                    if ( r/step > 2.0 && step < maxstep ) {
+                        step *= grow;
+                        if ( step > maxstep ) { step = maxstep; }
+                    }
+                    //if we're at maxstep, set rslowdown to the distance 
+                    //traversed so far (this will make a symmetric slowdown)
+                    if ( step >= maxstep && rslowdown == 0.0 ) {
+                        rslowdown = 1.25*(r0 - r);
+                    }
+                }
             }
         }