add getWantPreNote()

currently only C64 system requires this

src/engine/dispatch.h

@@ -399,6 +399,12 @@ class DivDispatch {
      */
     virtual bool getDCOffRequired();
 
+    /**
+     * check whether PRE_NOTE command is desired.
+     * @return truth.
+     */
+    virtual bool getWantPreNote();
+
     /**
      * get a description of a dispatch-specific effect.
      * @param effect the effect.

src/engine/platform/abstract.cpp

@@ -90,6 +90,10 @@ bool DivDispatch::getDCOffRequired() {
   return false;
 }
 
+bool DivDispatch::getWantPreNote() {
+  return false;
+}
+
 const char* DivDispatch::getEffectName(unsigned char effect) {
   return NULL;
 }

src/engine/platform/c64.cpp

@@ -513,6 +513,10 @@ bool DivPlatformC64::getDCOffRequired() {
   return true;
 }
 
+bool DivPlatformC64::getWantPreNote() {
+  return true;
+}
+
 void DivPlatformC64::reset() {
   for (int i=0; i<3; i++) {
     chan[i]=DivPlatformC64::Channel();

src/engine/platform/c64.h

@@ -97,6 +97,7 @@ class DivPlatformC64: public DivDispatch {
     void setFlags(unsigned int flags);
     void notifyInsChange(int ins);
     bool getDCOffRequired();
+    bool getWantPreNote();
     DivMacroInt* getChanMacroInt(int ch);
     void notifyInsDeletion(void* ins);
     void poke(unsigned int addr, unsigned short val);

src/engine/playback.cpp

@@ -866,7 +866,9 @@ void DivEngine::nextRow() {
     if (!(pat->data[curRow][0]==0 && pat->data[curRow][1]==0)) {
       if (pat->data[curRow][0]!=100 && pat->data[curRow][0]!=101 && pat->data[curRow][0]!=102) {
         if (!chan[i].legato) {
-          dispatchCmd(DivCommand(DIV_CMD_PRE_NOTE,i,ticks));
+          if (disCont[dispatchOfChan[i]].dispatch!=NULL) {
+            if (disCont[dispatchOfChan[i]].dispatch->getWantPreNote()) dispatchCmd(DivCommand(DIV_CMD_PRE_NOTE,i,ticks));
+          }
 
           if (song.oneTickCut) {
             bool doPrepareCut=true;