Footprints with pads taking most of area are kept in the selection menu

Improved the selection heuristics to keep footprints in the
disambiguation menu when they contain pads with high pad-to-footprint
area ratio.
In other words: make it possible to select a footprint when
most of its area is taken by a pad. Previously pads were given the
priority, so it was very tricky to select the parent footprint.

Fixes: lp:1739425
* https://bugs.launchpad.net/kicad/+bug/1739425

pcbnew/tools/selection_tool.cpp

@@ -1761,18 +1761,23 @@ double calcRatio( double a, double b )
 void SELECTION_TOOL::guessSelectionCandidates( GENERAL_COLLECTOR& aCollector ) const
 {
     std::set<BOARD_ITEM*> rejected;
-
-    const double footprintAreaRatio = 0.2;
-    const double modulePadMinCoverRatio = 0.45;
-    const double padViaAreaRatio = 0.5;
-    const double trackViaLengthRatio = 2.0;
-    const double trackTrackLengthRatio = 0.3;
-    const double textToFeatureMinRatio = 0.2;
-    const double textToFootprintMinRatio = 0.4;
+    std::set<BOARD_ITEM*> forced;
+
+    constexpr double footprintAreaRatio = 0.2;
+    // footprints containing pads with pad-to-footprint area ratio smaller than this will be dropped
+    constexpr double modulePadMinCoverRatio = 0.45;
+    // footprints containing pads with pad-to-footprint area ratio higher than this will be
+    // forced to stay on the list
+    constexpr double modulePadMaxCoverRatio = 0.80;
+    constexpr double padViaAreaRatio = 0.5;
+    constexpr double trackViaLengthRatio = 2.0;
+    constexpr double trackTrackLengthRatio = 0.3;
+    constexpr double textToFeatureMinRatio = 0.2;
+    constexpr double textToFootprintMinRatio = 0.4;
     // If the common area of two compared items is above the following threshold, they cannot
     // be rejected (it means they overlap and it might be hard to pick one by selecting
     // its unique area).
-    const double commonAreaRatio = 0.6;
+    constexpr double commonAreaRatio = 0.6;
 
     PCB_LAYER_ID actLayer = (PCB_LAYER_ID) view()->GetTopLayer();
 
@@ -1846,6 +1851,27 @@ void SELECTION_TOOL::guessSelectionCandidates( GENERAL_COLLECTOR& aCollector ) c
         }
     }
 
+    if( aCollector.CountType( PCB_PAD_T ) > 0 )
+    {
+        for( int i = 0; i < aCollector.GetCount(); ++i )
+        {
+            if( D_PAD* pad = dyn_cast<D_PAD*>( aCollector[i] ) )
+            {
+                double ratio = pad->GetParent()->PadCoverageRatio();
+
+                // when pad area is small compared to the parent footprint,
+                // then it is a clear sign the pad is the selection target
+                if( ratio < modulePadMinCoverRatio )
+                    rejected.insert( pad->GetParent() );
+                // for pads covering most of the footprint area the parent footprint
+                // should be kept in the disambiguation menu, otherwise it is very hard
+                // to select the footprint
+                else if( ratio > modulePadMaxCoverRatio )
+                    forced.insert( pad->GetParent() );
+            }
+        }
+    }
+
     if( aCollector.CountType( PCB_MODULE_T ) > 0 )
     {
         double maxArea = calcMaxArea( aCollector, PCB_MODULE_T );
@@ -1856,6 +1882,10 @@ void SELECTION_TOOL::guessSelectionCandidates( GENERAL_COLLECTOR& aCollector ) c
         {
             if( MODULE* mod = dyn_cast<MODULE*>( aCollector[i] ) )
             {
+                // do not check the module if it is forced on the list
+                if( forced.count( mod ) )
+                    continue;
+
                 double normalizedArea = calcRatio( calcArea( mod ), maxArea );
 
                 if( normalizedArea > footprintAreaRatio
@@ -1868,20 +1898,6 @@ void SELECTION_TOOL::guessSelectionCandidates( GENERAL_COLLECTOR& aCollector ) c
         }
     }
 
-    if( aCollector.CountType( PCB_PAD_T ) > 0 )
-    {
-        for( int i = 0; i < aCollector.GetCount(); ++i )
-        {
-            if( D_PAD* pad = dyn_cast<D_PAD*>( aCollector[i] ) )
-            {
-                double ratio = pad->GetParent()->PadCoverageRatio();
-
-                if( ratio < modulePadMinCoverRatio )
-                    rejected.insert( pad->GetParent() );
-            }
-        }
-    }
-
     if( aCollector.CountType( PCB_VIA_T ) > 0 )
     {
         for( int i = 0; i < aCollector.GetCount(); ++i )