better volume slide accuracy

volume slide seems to be kind of quirky:
- sliding all the way down and then up suddenly sets the vol to max
- apparently there is an overflow and the slide stops when it reaches
  its boundaries (instead of continuing)

src/engine/dispatch.h

@@ -9,6 +9,7 @@ enum DivDispatchCmds {
   DIV_CMD_INSTRUMENT,
   DIV_CMD_VOLUME,
   DIV_CMD_GET_VOLUME,
+  DIV_CMD_GET_VOLMAX,
   DIV_CMD_NOTE_PORTA,
   DIV_CMD_PITCH,
   DIV_CMD_PANNING,

src/engine/engine.cpp

@@ -697,6 +697,11 @@ bool DivEngine::init() {
   blip_set_rates(bb[0],dispatch->rate,got.rate);
   blip_set_rates(bb[1],dispatch->rate,got.rate);
 
+  for (int i=0; i<chans; i++) {
+    chan[i].volMax=dispatch->dispatch(DivCommand(DIV_CMD_GET_VOLMAX,i))<<8;
+    chan[i].volume=chan[i].volMax;
+  }
+
   if (!output->setRun(true)) {
     logE("error while activating!\n");
     return false;

src/engine/engine.h

@@ -8,7 +8,7 @@
 struct DivChannelState {
   std::vector<DivDelayedCommand> delayed;
   int note, pitch, portaSpeed, portaNote;
-  int volume, volSpeed, cut, rowDelay;
+  int volume, volSpeed, cut, rowDelay, volMax;
   int vibratoDepth, vibratoRate, vibratoPos;
   int tremoloDepth, tremoloRate, tremoloPos;
   unsigned char arp, arpStage;

src/engine/platform/dummy.cpp

@@ -32,6 +32,9 @@ int DivPlatformDummy::dispatch(DivCommand c) {
     case DIV_CMD_GET_VOLUME:
       return chan[c.chan].vol;
       break;
+    case DIV_CMD_GET_VOLMAX:
+      return 15;
+      break;
     default:
       break;
   }

src/engine/platform/genesis.cpp

@@ -301,6 +301,9 @@ int DivPlatformGenesis::dispatch(DivCommand c) {
       
       break;
     }
+    case DIV_CMD_GET_VOLMAX:
+      return 127;
+      break;
     default:
       printf("WARNING: unimplemented command %d\n",c.cmd);
       break;

src/engine/platform/genesisext.cpp

@@ -20,6 +20,9 @@ int DivPlatformGenesisExt::dispatch(DivCommand c) {
     case DIV_CMD_VOLUME:
       chan[c.chan].vol=c.value;
       break;
+    case DIV_CMD_GET_VOLMAX:
+      return 127;
+      break;
     default:
       break;
   }

src/engine/platform/sms.cpp

@@ -144,6 +144,9 @@ int DivPlatformSMS::dispatch(DivCommand c) {
     case DIV_CMD_PRE_PORTA:
       chan[c.chan].std.init(parent->getIns(chan[c.chan].ins));
       break;
+    case DIV_CMD_GET_VOLMAX:
+      return 15;
+      break;
     default:
       break;
   }

src/engine/playback.cpp

@@ -134,9 +134,11 @@ void DivEngine::processRow(int i, bool afterDelay) {
 
   // volume
   if (pat->data[curRow][3]!=-1) {
+    if ((chan[i].volume>>8)!=pat->data[curRow][3]) {
       chan[i].volume=pat->data[curRow][3]<<8;
       dispatch->dispatch(DivCommand(DIV_CMD_VOLUME,i,chan[i].volume>>8));
     }
+  }
 
   // effects
   for (int j=0; j<song.pat[i]->effectRows; j++) {
@@ -342,11 +344,19 @@ void DivEngine::nextTick() {
       }
     }
     if (chan[i].volSpeed!=0) {
-      chan[i].volume=(chan[i].volume&0xff)|(dispatch->dispatch(DivCommand(DIV_CMD_GET_VOLUME,i))<<8);
+      //chan[i].volume=(chan[i].volume&0xff)|(dispatch->dispatch(DivCommand(DIV_CMD_GET_VOLUME,i))<<8);
       chan[i].volume+=chan[i].volSpeed;
-      if (chan[i].volume>0x7f00) chan[i].volume=0x7f00;
+      if (chan[i].volume>chan[i].volMax) {
-      if (chan[i].volume<0) chan[i].volume=0;
+        chan[i].volume=chan[i].volMax;
+        chan[i].volSpeed=0;
         dispatch->dispatch(DivCommand(DIV_CMD_VOLUME,i,chan[i].volume>>8));
+      } else if (chan[i].volume<0) {
+        chan[i].volSpeed=0;
+        chan[i].volume=chan[i].volMax;
+        dispatch->dispatch(DivCommand(DIV_CMD_VOLUME,i,0));
+      } else {
+        dispatch->dispatch(DivCommand(DIV_CMD_VOLUME,i,chan[i].volume>>8));
+      }
     }
     if (chan[i].vibratoDepth>0) {
       chan[i].vibratoPos+=chan[i].vibratoRate;