Amiga: take loop pos into account

src/engine/engine.cpp

@@ -1314,7 +1314,7 @@ bool DivEngine::loadFur(unsigned char* file, size_t len) {
       // reserved
       for (int j=0; j<3; j++) reader.readC();
 
-      if (ds.version>=18) {
+      if (ds.version>=19) {
         sample->loopStart=reader.readI();
       } else {
         reader.readI();

src/engine/platform/amiga.cpp

@@ -20,7 +20,11 @@ void DivPlatformAmiga::acquire(short* bufL, short* bufR, size_t start, size_t le
             chan[i].audDat=s->rendData[chan[i].audPos++]>>8;
           }
           if (chan[i].audPos>=s->rendLength) {
-            chan[i].sample=-1;
+            if (s->loopStart>=0 && s->loopStart<=(int)s->rendLength) {
+              chan[i].audPos=s->loopStart;
+            } else {
+              chan[i].sample=-1;
+            }
           }
           chan[i].audSub+=chan[i].freq;
         }

src/gui/gui.cpp

@@ -1214,6 +1214,19 @@ void FurnaceGUI::drawSampleEdit() {
         if (sample->rate>32000) sample->rate=32000;
       }
       ImGui::Text("effective rate: %dHz",e->getEffectiveSampleRate(sample->rate));
+      bool doLoop=(sample->loopStart>=0);
+      if (ImGui::Checkbox("Loop",&doLoop)) {
+        if (doLoop) {
+          sample->loopStart=0;
+        } else {
+          sample->loopStart=-1;
+        }
+      }
+      if (doLoop) if (ImGui::SliderInt("##LoopPosition",&sample->loopStart,0,sample->length-1)) {
+        if (sample->loopStart<0 || sample->loopStart>=sample->length) {
+          sample->loopStart=0;
+        }
+      }
       if (ImGui::SliderScalar("Volume",ImGuiDataType_S8,&sample->vol,&_ZERO,&_ONE_HUNDRED,fmt::sprintf("%d%%%%",sample->vol*2).c_str())) {
         if (sample->vol<0) sample->vol=0;
         if (sample->vol>100) sample->vol=100;