Add z distance checking to entity picking. Fixes issue 521

src/draw.cpp

@@ -342,6 +342,8 @@ GraphicsWindow::Selection GraphicsWindow::ChooseFromHoverToSelect() {
     Group *activeGroup = SK.GetGroup(SS.GW.activeGroup);
     int bestOrder = -1;
     int bestZIndex = 0;
+    double bestDepth = VERY_POSITIVE;
+    
     for(const Hover &hov : hoverList) {
         hGroup hg = {};
         if(hov.selection.entity.v != 0) {
@@ -353,8 +355,11 @@ GraphicsWindow::Selection GraphicsWindow::ChooseFromHoverToSelect() {
         Group *g = SK.GetGroup(hg);
         if(g->order > activeGroup->order) continue;
         if(bestOrder != -1 && (bestOrder > g->order || bestZIndex > hov.zIndex)) continue;
+        // we have hov.zIndex is >= best and hov.group is >= best (but not > active group)
+        if(hov.depth > bestDepth && bestOrder == g->order && bestZIndex == hov.zIndex) continue;
         bestOrder  = g->order;
         bestZIndex = hov.zIndex;
+        bestDepth = hov.depth;
         sel = hov.selection;
     }
     return sel;
@@ -370,6 +375,8 @@ GraphicsWindow::Selection GraphicsWindow::ChooseFromHoverToDrag() {
     Group *activeGroup = SK.GetGroup(SS.GW.activeGroup);
     int bestOrder = -1;
     int bestZIndex = 0;
+    double bestDepth = VERY_POSITIVE;
+
     for(const Hover &hov : hoverList) {
         hGroup hg = {};
         if(hov.selection.entity.v != 0) {
@@ -383,6 +390,8 @@ GraphicsWindow::Selection GraphicsWindow::ChooseFromHoverToDrag() {
         Group *g = SK.GetGroup(hg);
         if(g->order > activeGroup->order) continue;
         if(bestOrder != -1 && (bestOrder > g->order || bestZIndex > hov.zIndex)) continue;
+        // we have hov.zIndex is >= best and hov.group is >= best (but not > active group)
+        if(hov.depth > bestDepth && bestOrder == g->order && bestZIndex == hov.zIndex) continue;
         bestOrder  = g->order;
         bestZIndex = hov.zIndex;
         sel = hov.selection;
@@ -439,6 +448,7 @@ void GraphicsWindow::HitTestMakeSelection(Point2d mp) {
             Hover hov = {};
             hov.distance = canvas.minDistance;
             hov.zIndex   = canvas.maxZIndex;
+            hov.depth    = canvas.minDepth;
             hov.selection.entity = e.h;
             hoverList.Add(&hov);
         }

src/render/render.cpp

@@ -343,9 +343,10 @@ void UiCanvas::DrawBitmapText(const std::string &str, int x, int y, RgbaColor co
 // A canvas that performs picking against drawn geometry.
 //-----------------------------------------------------------------------------
 
-void ObjectPicker::DoCompare(double distance, int zIndex, int comparePosition) {
+void ObjectPicker::DoCompare(double depth, double distance, int zIndex, int comparePosition) {
     if(distance > selRadius) return;
     if((zIndex == maxZIndex && distance < minDistance) || (zIndex > maxZIndex)) {
+        minDepth    = depth;
         minDistance = distance;
         maxZIndex   = zIndex;
         position    = comparePosition;
@@ -372,10 +373,10 @@ void ObjectPicker::DoQuad(const Vector &a, const Vector &b, const Vector &c, con
 
     bool insideQuad = (minNegative == VERY_NEGATIVE || maxPositive == VERY_POSITIVE);
     if(insideQuad) {
-        DoCompare(0.0, zIndex, comparePosition);
+        DoCompare(0, 0.0, zIndex, comparePosition);
     } else {
         double distance = std::min(fabs(minNegative), fabs(maxPositive));
-        DoCompare(distance, zIndex, comparePosition);
+        DoCompare(0, distance, zIndex, comparePosition);
     }
 }
 
@@ -384,7 +385,8 @@ void ObjectPicker::DrawLine(const Vector &a, const Vector &b, hStroke hcs) {
     Point2d ap = camera.ProjectPoint(a);
     Point2d bp = camera.ProjectPoint(b);
     double distance = point.DistanceToLine(ap, bp.Minus(ap), /*asSegment=*/true);
-    DoCompare(distance - stroke->width / 2.0, stroke->zIndex);
+    double depth = 0.5 * (camera.ProjectPoint3(a).z + camera.ProjectPoint3(b).z) ;
+    DoCompare(depth, distance - stroke->width / 2.0, stroke->zIndex);
 }
 
 void ObjectPicker::DrawEdges(const SEdgeList &el, hStroke hcs) {
@@ -393,7 +395,8 @@ void ObjectPicker::DrawEdges(const SEdgeList &el, hStroke hcs) {
         Point2d ap = camera.ProjectPoint(e.a);
         Point2d bp = camera.ProjectPoint(e.b);
         double distance = point.DistanceToLine(ap, bp.Minus(ap), /*asSegment=*/true);
-        DoCompare(distance - stroke->width / 2.0, stroke->zIndex, e.auxB);
+        double depth = 0.5 * (camera.ProjectPoint3(e.a).z + camera.ProjectPoint3(e.b).z) ;
+        DoCompare(depth, distance - stroke->width / 2.0, stroke->zIndex, e.auxB);
     }
 }
 
@@ -423,7 +426,8 @@ void ObjectPicker::DrawQuad(const Vector &a, const Vector &b, const Vector &c, c
 void ObjectPicker::DrawPoint(const Vector &o, Canvas::hStroke hcs) {
     Stroke *stroke = strokes.FindById(hcs);
     double distance = point.DistanceTo(camera.ProjectPoint(o)) - stroke->width / 2;
-    DoCompare(distance, stroke->zIndex);
+    double depth = camera.ProjectPoint3(o).z;
+    DoCompare(depth, distance, stroke->zIndex);
 }
 
 void ObjectPicker::DrawPolygon(const SPolygon &p, hFill hcf) {
@@ -445,6 +449,7 @@ void ObjectPicker::DrawPixmap(std::shared_ptr<const Pixmap> pm,
 }
 
 bool ObjectPicker::Pick(const std::function<void()> &drawFn) {
+    minDepth = VERY_POSITIVE;
     minDistance = VERY_POSITIVE;
     maxZIndex = INT_MIN;
 

src/render/render.h

@@ -232,6 +232,7 @@ public:
     double      selRadius   = 0.0;
     // Picking state.
     double      minDistance = 0.0;
+    double      minDepth    = 1e10;
     int         maxZIndex   = 0;
     uint32_t    position    = 0;
 
@@ -257,7 +258,7 @@ public:
                     const Point2d &ta, const Point2d &tb, hFill hcf) override;
     void InvalidatePixmap(std::shared_ptr<const Pixmap> pm) override {}
 
-    void DoCompare(double distance, int zIndex, int comparePosition = 0);
+    void DoCompare(double depth, double distance, int zIndex, int comparePosition = 0);
     void DoQuad(const Vector &a, const Vector &b, const Vector &c, const Vector &d,
                 int zIndex, int comparePosition = 0);
 

src/ui.h

@@ -727,6 +727,7 @@ public:
     public:
         int         zIndex;
         double      distance;
+        double      depth;
         Selection   selection;
     };