Nodes: Improve readability of selected node links

This commit improves the drawing of selected node links:
 - Highlight the entire link to make it easier to spot where the link
   is going/coming from.
 - Always draw selected links on top, so they are always clearly
   visible.
 - Don't fade selected node links when the sockets they are connected
   to are out out view.
 - Dragged node links still get a partial highlight when they are only
   attached to one socket.

Differential Revision: https://developer.blender.org/D11930

source/blender/blenkernel/BKE_node.h

@@ -681,6 +681,7 @@ void nodeRemLink(struct bNodeTree *ntree, struct bNodeLink *link);
 void nodeRemSocketLinks(struct bNodeTree *ntree, struct bNodeSocket *sock);
 void nodeMuteLinkToggle(struct bNodeTree *ntree, struct bNodeLink *link);
 bool nodeLinkIsHidden(const struct bNodeLink *link);
+bool nodeLinkIsSelected(const struct bNodeLink *link);
 void nodeInternalRelink(struct bNodeTree *ntree, struct bNode *node);
 
 void nodeToView(const struct bNode *node, float x, float y, float *rx, float *ry);

source/blender/blenkernel/intern/node.cc

@@ -2438,6 +2438,11 @@ bool nodeLinkIsHidden(const bNodeLink *link)
   return nodeSocketIsHidden(link->fromsock) || nodeSocketIsHidden(link->tosock);
 }
 
+bool nodeLinkIsSelected(const bNodeLink *link)
+{
+  return (link->fromnode->flag & NODE_SELECT) || (link->tonode->flag & NODE_SELECT);
+}
+
 /* Adjust the indices of links connected to the given multi input socket after deleting the link at
  * `deleted_index`. This function also works if the link has not yet been deleted. */
 static void adjust_multi_input_indices_after_removed_link(bNodeTree *ntree,

source/blender/editors/space_node/drawnode.cc

@@ -1967,9 +1967,10 @@ void node_draw_link_bezier(const bContext &C,
                            const bNodeLink &link,
                            const int th_col1,
                            const int th_col2,
-                           const int th_col3)
+                           const int th_col3,
+                           const bool selected)
 {
-  const float dim_factor = node_link_dim_factor(v2d, link);
+  const float dim_factor = selected ? 1.0f : node_link_dim_factor(v2d, link);
   float thickness = 1.5f;
   float dash_factor = 1.0f;
 
@@ -2025,19 +2026,17 @@ void node_draw_link_bezier(const bContext &C,
     }
 
     /* Highlight links connected to selected nodes. */
-    const bool is_fromnode_selected = link.fromnode && link.fromnode->flag & SELECT;
+    if (selected) {
-    const bool is_tonode_selected = link.tonode && link.tonode->flag & SELECT;
-    if (is_fromnode_selected || is_tonode_selected) {
       float color_selected[4];
       UI_GetThemeColor4fv(TH_EDGE_SELECT, color_selected);
       const float alpha = color_selected[3];
 
       /* Interpolate color if highlight color is not fully transparent. */
       if (alpha != 0.0) {
-        if (is_fromnode_selected) {
+        if (link.fromsock) {
           interp_v3_v3v3(colors[1], colors[1], color_selected, alpha);
         }
-        if (is_tonode_selected) {
+        if (link.tosock) {
           interp_v3_v3v3(colors[2], colors[2], color_selected, alpha);
         }
       }
@@ -2102,7 +2101,8 @@ void node_draw_link_bezier(const bContext &C,
 void node_draw_link(const bContext &C,
                     const View2D &v2d,
                     const SpaceNode &snode,
-                    const bNodeLink &link)
+                    const bNodeLink &link,
+                    const bool selected)
 {
   int th_col1 = TH_WIRE_INNER, th_col2 = TH_WIRE_INNER, th_col3 = TH_WIRE;
 
@@ -2146,7 +2146,7 @@ void node_draw_link(const bContext &C,
     }
   }
 
-  node_draw_link_bezier(C, v2d, snode, link, th_col1, th_col2, th_col3);
+  node_draw_link_bezier(C, v2d, snode, link, th_col1, th_col2, th_col3, selected);
 }
 
 }  // namespace blender::ed::space_node

source/blender/editors/space_node/node_draw.cc

@@ -660,7 +660,7 @@ static void node_draw_mute_line(const bContext &C,
   GPU_blend(GPU_BLEND_ALPHA);
 
   LISTBASE_FOREACH (const bNodeLink *, link, &node.internal_links) {
-    node_draw_link_bezier(C, v2d, snode, *link, TH_WIRE_INNER, TH_WIRE_INNER, TH_WIRE);
+    node_draw_link_bezier(C, v2d, snode, *link, TH_WIRE_INNER, TH_WIRE_INNER, TH_WIRE, false);
   }
 
   GPU_blend(GPU_BLEND_NONE);
@@ -2650,10 +2650,18 @@ static void node_draw_nodetree(const bContext &C,
   nodelink_batch_start(snode);
 
   LISTBASE_FOREACH (bNodeLink *, link, &ntree.links) {
-    if (!nodeLinkIsHidden(link)) {
+    if (!nodeLinkIsHidden(link) && !nodeLinkIsSelected(link)) {
-      node_draw_link(C, region.v2d, snode, *link);
+      node_draw_link(C, region.v2d, snode, *link, false);
     }
   }
+
+  /* Draw selected node links after the unselected ones, so they are shown on top. */
+  LISTBASE_FOREACH (bNodeLink *, link, &ntree.links) {
+    if (!nodeLinkIsHidden(link) && nodeLinkIsSelected(link)) {
+      node_draw_link(C, region.v2d, snode, *link, true);
+    }
+  }
+  
   nodelink_batch_end(snode);
   GPU_blend(GPU_BLEND_NONE);
 
@@ -2838,7 +2846,7 @@ void node_draw_space(const bContext &C, ARegion &region)
     GPU_line_smooth(true);
     if (snode.runtime->linkdrag) {
       for (const bNodeLink *link : snode.runtime->linkdrag->links) {
-        node_draw_link(C, v2d, snode, *link);
+        node_draw_link(C, v2d, snode, *link, true);
       }
     }
     GPU_line_smooth(false);

source/blender/editors/space_node/node_intern.hh

@@ -196,7 +196,8 @@ void nodelink_batch_end(SpaceNode &snode);
 void node_draw_link(const bContext &C,
                     const View2D &v2d,
                     const SpaceNode &snode,
-                    const bNodeLink &link);
+                    const bNodeLink &link,
+                    bool selected);
 /**
  * Don't do shadows if th_col3 is -1.
  */
@@ -206,7 +207,8 @@ void node_draw_link_bezier(const bContext &C,
                            const bNodeLink &link,
                            int th_col1,
                            int th_col2,
-                           int th_col3);
+                           int th_col3,
+                           bool selected);
 /** If v2d not nullptr, it clips and returns 0 if not visible. */
 bool node_link_bezier_points(const View2D *v2d,
                              const SpaceNode *snode,