Clip-Drag: introduce sub-interface for canvas metric

...previously this was modelled as part of the CanvasHook abstraction,
and in fact it will in any case be implemented by delegation to the
TimelineLayout or some kind of display manager.

We need this to tanslate mouse pixel movements into a time change

src/stage/model/canvas-hook.hpp

@@ -67,6 +67,27 @@ namespace model {
   
   
   
+  /**
+   * Mix-in interface to allow for concrete CanvasHooked widgets
+   * to adapt themselves to the metric currently employed on the canvas.
+   * In some cases, most notably when a timeline canvas is calibrated to
+   * represent temporal extension precisely, the widgets (clips, effects)
+   * within such a display need to adjust themselves. A relevant special
+   * case is when such a widget _is dragged_ -- receiving mouse move events
+   * in screen coordinates -- which need to be translated into a resulting
+   * temporal offset or change as a result of this _interaction gesture._
+   */
+  class DisplayMetric
+    {
+    public:
+      virtual ~DisplayMetric() { }    ///< this is an interface
+      
+      /** extension point for time axis zoom management. */
+      virtual int translateTimeToPixels (TimeValue)  const      =0;
+    };
+  
+  
+  
   /**
    * Interface to represent _"some presentation layout entity",_
    * with the ability to _place_ widgets (managed elsewhere) onto it,
@@ -80,6 +101,7 @@ namespace model {
    */
   template<class WID>
   class CanvasHook
+    : public DisplayMetric
     {
     public:
       virtual ~CanvasHook() { }    ///< this is an interface
@@ -117,9 +139,6 @@ namespace model {
         {
           return hookedAt (translateTimeToPixels (start), downshift);
         }
-      
-      /** extension point for time axis zoom management. */
-      virtual int translateTimeToPixels (TimeValue)  const      =0;
     };
   
   

src/stage/timeline/body-canvas-widget.cpp

@@ -553,7 +553,7 @@ namespace timeline {
   }
   
   
-  /* ==== Interface: ViewHook ===== */
+  /* ==== Interface: CanvasHook ===== */
   
   void
   BodyCanvasWidget::hook (Gtk::Widget& widget, int xPos, int yPos)

src/stage/timeline/display-manager.hpp

@@ -61,6 +61,13 @@
  ** This builds the foundation for implementing UI structures recursively, leading to somewhat
  ** simplified code, which hopefully is also easier to maintain and extend in the long run.
  ** 
+ ** \par Avoiding the double-indirect calls?
+ ** In theory, it would be possible to avoid the double forwarding indirect calls in all the
+ ** operations of RelativeCanvasHook: We'd have to provide a concrete mix-in to be used already
+ ** within body-canvas-widget.cpp, and this mixin would hold a _direct reference_ to the embedded
+ ** Gtk::Layout and provide an additional API to adjust the offset. However, the savings through
+ ** such an implementation scheme would be dwarfed by the effort for actually rendering a widget.
+ ** 
  ** @todo as of 10/2018 timeline display in the UI is rebuilt to match the architecture
  ** @todo WIP-WIP-WIP - drafting the DisplayEvaluation as of 3/2020
  ** @todo WIP as of 1/2021 about to build a first preliminary Clip representation
@@ -98,6 +105,8 @@ namespace timeline {
    * @note the ctor uses #getAnchorHook, thus effectively,
    *       for a chain of RelativeCanvasHook instances,
    *       the #refHook_ holds the top level anchor.
+   * @remark avoiding this 2-step indirect dispatch is not
+   *       justified here, given the overhead of drawing.
    */
   template<class WID>
   class RelativeCanvasHook

wiki/thinkPad.ichthyo.mm

@@ -33130,10 +33130,46 @@
 <node CREATED="1619698300242" ID="ID_498514293" MODIFIED="1619698315566" TEXT="und der Wrapper ebenfalls"/>
 <node CREATED="1619698316317" ID="ID_629600190" MODIFIED="1619698329643" TEXT="dann kann der Wrapper seine Sub-Komponente vom Delegate initialisieren"/>
 </node>
-<node CREATED="1619697887065" ID="ID_1694064911" MODIFIED="1619697892300" TEXT="RelativeCanvasHook">
+<node CREATED="1619697887065" ID="ID_1694064911" MODIFIED="1619788146033" TEXT="RelativeCanvasHook">
+<icon BUILTIN="button_cancel"/>
 <node CREATED="1619698448530" ID="ID_231932844" MODIFIED="1619698455469" TEXT="ist zu 100% ein Dekorator"/>
 <node CREATED="1619698460320" ID="ID_1397414962" MODIFIED="1619698473284" TEXT="erbt zudem vom gleichen Interface wie sein Delegate"/>
 <node CREATED="1619698474655" ID="ID_609667543" MODIFIED="1619698501783" TEXT="&#x27f9; klassishe linearisierte Vererbung"/>
+<node CREATED="1619787501628" ID="ID_1894601265" MODIFIED="1619787526640" TEXT="trotzdem wird es stets zwei indirekte Aufrufe geben">
+<icon BUILTIN="messagebox_warning"/>
+</node>
+<node CREATED="1619787529209" ID="ID_1165327118" MODIFIED="1619787547480" TEXT="kann man einen davon einsparen?">
+<icon BUILTIN="stop-sign"/>
+<node CREATED="1619787550612" ID="ID_1297192304" MODIFIED="1619787577240" TEXT="jaa man kannnn...">
+<icon BUILTIN="idea"/>
+</node>
+<node CREATED="1619787584274" FOLDED="true" ID="ID_1256984812" MODIFIED="1619788141013" TEXT="das wird aber durchaus komplex">
+<icon BUILTIN="flag-orange"/>
+<node CREATED="1619787756234" ID="ID_566753329" MODIFIED="1619787782836" TEXT="das konkrete Body-Canvas-Widget m&#xfc;&#xdf;te umgeschrieben werden"/>
+<node CREATED="1619787783758" ID="ID_955157823" MODIFIED="1619787838923" TEXT="die eigentliche Implementierung des CanvasHook m&#xfc;&#xdf;te per Mix-In realisiert werden"/>
+<node CREATED="1619787839607" ID="ID_736108938" MODIFIED="1619787853365" TEXT="und zwar ein konkretes Implementieruns-Mix-in"/>
+<node CREATED="1619787854247" ID="ID_1799143382" MODIFIED="1619787870551" TEXT="dieses bekommt einen konkreten GTK-Canvas als Referenz"/>
+<node CREATED="1619787894264" ID="ID_982929479" MODIFIED="1619787918928" TEXT="und au&#xdf;erdem m&#xfc;&#xdf;te es bereits den Offset als Ctor-Parameter mitbekommen"/>
+<node CREATED="1619787926203" ID="ID_166173193" MODIFIED="1619788009055" TEXT="und der Nutzer (DisplayFrame im TrackPresenter) m&#xfc;&#xdf;te dieses konkrete Objekt-API sehen"/>
+<node CREATED="1619788024275" ID="ID_1728948599" MODIFIED="1619788043839" TEXT="allerdings k&#xf6;nnte man trotzdem die Impl. in einem separaten Translation-Unit &quot;verbergen&quot;"/>
+<node CREATED="1619788065160" ID="ID_1004040494" MODIFIED="1619788100395" TEXT="Ergebnis: alle Aufrufe gehen direkt durch die VTable in dieses konkrete Canvas-Mixin"/>
+</node>
+<node CREATED="1619787626757" ID="ID_1522870458" MODIFIED="1619799442131" TEXT="und ist hier nicht gerechtfertigt">
+<richcontent TYPE="NOTE"><html>
+  <head>
+    
+  </head>
+  <body>
+    <p>
+      das Platzieren auf den Canvas ist <b>keine</b>&#160;high-Performance-Operation;<br />vielmehr ist es sogar <i>vernachl&#228;ssigbar im Vergleich </i>zum Aufwand der Zeichen-Operationen; und letztere werden eben genau aus Performance-Gr&#252;nden gebatcht und geb&#252;ndelt....
+    </p>
+  </body>
+</html>
+</richcontent>
+<linktarget COLOR="#6775b4" DESTINATION="ID_1522870458" ENDARROW="Default" ENDINCLINATION="125;10;" ID="Arrow_ID_565826448" SOURCE="ID_1388699771" STARTARROW="None" STARTINCLINATION="290;14;"/>
+<icon BUILTIN="yes"/>
+</node>
+</node>
 </node>
 <node CREATED="1619698512378" ID="ID_333159714" MODIFIED="1619698546465" TEXT="Metrik-&#xdc;bersetzung">
 <node CREATED="1619698551205" ID="ID_994295604" MODIFIED="1619698871778" TEXT="sieht nach einem isolierten Belang aus">
@@ -33143,6 +33179,24 @@
 <node CREATED="1619698583671" ID="ID_1092960475" MODIFIED="1619698623962" TEXT="ein Sub-Interface w&#xfc;rde das Design versbessern">
 <icon BUILTIN="yes"/>
 </node>
+<node CREATED="1619799300329" ID="ID_170912303" MODIFIED="1619799331661" TEXT="direkt im Gesture-Controller nutzen">
+<icon BUILTIN="idea"/>
+<node CREATED="1619799349705" ID="ID_281542411" MODIFIED="1619799359972" TEXT="in diesem Fall dann nur noch eine Indirektion"/>
+<node CREATED="1619799367600" ID="ID_1388699771" MODIFIED="1619799442130">
+<richcontent TYPE="NODE"><html>
+  <head>
+    
+  </head>
+  <body>
+    <p>
+      im Gegensatz zum CanvasHook ist <i>das hier durchaus relevant</i>
+    </p>
+  </body>
+</html>
+</richcontent>
+<arrowlink COLOR="#6775b4" DESTINATION="ID_1522870458" ENDARROW="Default" ENDINCLINATION="125;10;" ID="Arrow_ID_565826448" STARTARROW="None" STARTINCLINATION="290;14;"/>
+</node>
+</node>
 </node>
 <node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1619698607118" ID="ID_239118181" MODIFIED="1619698618056" TEXT="Umbau sehr w&#xfc;nschenswert">
 <icon BUILTIN="flag-yellow"/>