add getTranslation and setGeoPosition to transform.nas, adapt element.nas accordingly;

improve readability and comments

Nasal/canvas/api/element.nas

@@ -13,10 +13,11 @@ var Element = {
     #
     # @param ghost    Element ghost as retrieved from core methods
     new: func(ghost) {
-        return {
-            parents: [PropertyElement, Element, ghost],
-            _node: props.wrapNode(ghost._node_ghost)
+        var obj = {
+            parents: [Element, PropertyElement, ghost],
+            _node: props.wrapNode(ghost._node_ghost),
         };
+        return obj;
     },
 
     # Get parent group/element
@@ -26,7 +27,7 @@ var Element = {
             return nil;
 
         var type = props.wrapNode(parent_ghost._node_ghost).getName();
-        var factory = me._getFactory(type);
+        var factory = Group._getFactory(type);
         if (factory == nil)
             return parent_ghost;
 
@@ -72,8 +73,7 @@ var Element = {
     },
 
     setGeoPosition: func(lat, lon) {
-        me._getTf()._node.getNode("m-geo[4]", 1).setValue("N"~lat);
-        me._getTf()._node.getNode("m-geo[5]", 1).setValue("E"~lon);
+        me._getTf().setGeoPosition(lat, lon);
         return me;
     },
 
@@ -94,10 +94,10 @@ var Element = {
 
     # Get translation set with #setTranslation
     getTranslation: func() {
-        if (me["_tf"] == nil)
+        if (me["_tf"] == nil) {
             return [0, 0];
-
-        return [me._tf.e.getValue(), me._tf.f.getValue()];
+        }
+        return me._tf.getTranslation();
     },
 
     # Set rotation around transformation center (see #setCenter).
@@ -182,6 +182,7 @@ var Element = {
         return center;
     },
 
+    #return vector [sx, sy] with dimensions of bounding box
     getSize: func {
         var bb = me.getTightBoundingBox();
         return [bb[2] - bb[0], bb[3] - bb[1]];
@@ -189,7 +190,7 @@ var Element = {
 
     # convert bounding box vector into clip string (yes, different order)
     boundingbox2clip: func(bb) {
-        return sprintf("rect(%d,%d,%d,%d)", bb[1], bb[2], bb[3], bb[0])
+        return sprintf("rect(%d,%d,%d,%d)", bb[1], bb[2], bb[3], bb[0]);
     },
 
     # set clip by bounding box

Nasal/canvas/api/transform.nas

@@ -9,6 +9,7 @@
 #  0 0 1
 #
 # See http://www.w3.org/TR/SVG/coords.html#TransformMatrixDefined for details.
+#     https://www.w3.org/TR/css-transforms-1/#mathematical-description
 #
 var Transform = {
     new: func(node, vals = nil) {
@@ -44,7 +45,11 @@ var Transform = {
 
         return me;
     },
-
+    
+    getTranslation: func() {
+        return [me.e.getValue(), me.f.getValue()];
+    },
+    
     # Set rotation (Optionally around a specified point instead of (0,0))
     #
     #    setRotation(rot)
@@ -58,6 +63,7 @@ var Transform = {
         var s = math.sin(angle);
         var c = math.cos(angle);
 
+        # rotation goes to the top-left 2x2 part of the matrix
         me.a.setDoubleValue(c);     me.c.setDoubleValue(-s);
         me.b.setDoubleValue(s);     me.d.setDoubleValue(c);
 
@@ -76,15 +82,24 @@ var Transform = {
     #    setScale([x, y])
     setScale: func {
         var scale = _arg2valarray(arg);
-
+        # the scale factors go to the diagonal elements of the matrix
         me.a.setDoubleValue(scale[0]);
         me.d.setDoubleValue(size(scale) >= 2 ? scale[1] : scale[0]);
-
         return me;
     },
 
     getScale: func() {
         # TODO handle rotation
         return [me.a.getValue(), me.d.getValue()];
-    }
+    },
+    
+    # this function is called very often, if a canvas map is active and
+    # the aircraft symbol is shown.
+    setGeoPosition: func(lat, lon) {
+        if (me["_gn"] == nil) { me._gn = me._node.getNode("m-geo[4]", 1); }
+        if (me["_ge"] == nil) { me._ge = me._node.getNode("m-geo[5]", 1); }
+        me._gn.setValue("N" ~ lat);
+        me._ge.setValue("E" ~ lon);
+        return me;
+    },
 };