add ability to play by one row

src/engine/engine.cpp

@@ -4756,6 +4756,7 @@ void DivEngine::playSub(bool preserveDrift, int goalRow) {
   int goal=curOrder;
   curOrder=0;
   curRow=0;
+  stepPlay=0;
   int prevDrift;
   prevDrift=clockDrift;
   clockDrift=0;
@@ -4815,8 +4816,12 @@ int DivEngine::calcFreq(int base, int pitch, bool period, int octave) {
 
 void DivEngine::play() {
   isBusy.lock();
-  freelance=false;
-  playSub(false);
+  if (stepPlay==0) {
+    freelance=false;
+    playSub(false);
+  } else {
+    stepPlay=0;
+  }
   isBusy.unlock();
 }
 
@@ -4827,11 +4832,23 @@ void DivEngine::playToRow(int row) {
   isBusy.unlock();
 }
 
+void DivEngine::stepOne(int row) {
+  isBusy.lock();
+  if (!isPlaying()) {
+    freelance=false;
+    playSub(false,row);
+  }
+  stepPlay=2;
+  ticks=1;
+  isBusy.unlock();
+}
+
 void DivEngine::stop() {
   isBusy.lock();
   freelance=false;
   playing=false;
   extValuePresent=false;
+  stepPlay=0;
   remainingLoops=-1;
   isBusy.unlock();
 }
@@ -5086,6 +5103,10 @@ bool DivEngine::isPlaying() {
   return (playing && !freelance);
 }
 
+bool DivEngine::isStepping() {
+  return !(stepPlay==0);
+}
+
 bool DivEngine::isChannelMuted(int chan) {
   return isMuted[chan];
 }

src/engine/engine.h

@@ -150,7 +150,7 @@ class DivEngine {
   bool halted;
   bool forceMono;
   int ticks, curRow, curOrder, remainingLoops, nextSpeed, divider;
-  int cycles, clockDrift;
+  int cycles, clockDrift, stepPlay;
   int changeOrd, changePos, totalSeconds, totalTicks, totalTicksR, totalCmds, lastCmds, cmdsPerSecond, globalPitch;
   unsigned char extValue;
   unsigned char speed1, speed2;
@@ -288,6 +288,9 @@ class DivEngine {
     // play to row
     void playToRow(int row);
 
+    // play by one row
+    void stepOne(int row);
+
     // stop
     void stop();
 
@@ -406,6 +409,9 @@ class DivEngine {
     // is playing
     bool isPlaying();
 
+    // is stepping
+    bool isStepping();
+
     // is exporting
     bool isExporting();
 
@@ -587,6 +593,7 @@ class DivEngine {
       divider(60),
       cycles(0),
       clockDrift(0),
+      stepPlay(0),
       changeOrd(-1),
       changePos(0),
       totalSeconds(0),

src/engine/playback.cpp

@@ -844,7 +844,7 @@ bool DivEngine::nextTick(bool noAccum) {
   }
 
   if (!freelance) {
-    if (--ticks<=0) {
+    if (stepPlay!=1) if (--ticks<=0) {
       ret=endOfSong;
       if (endOfSong) {
         if (song.loopModality!=2) {
@@ -852,6 +852,7 @@ bool DivEngine::nextTick(bool noAccum) {
         }
       }
       endOfSong=false;
+      if (stepPlay==2) stepPlay=1;
       nextRow();
     }
     // process stuff

src/gui/gui.cpp

@@ -645,6 +645,10 @@ void FurnaceGUI::drawEditControls() {
         if (ImGui::Checkbox("Repeat pattern",&repeatPattern)) {
           e->setRepeatPattern(repeatPattern);
         }
+        ImGui::SameLine();
+        if (ImGui::Button(ICON_FA_ARROW_DOWN "##StepOne")) {
+          e->stepOne(cursor.y);
+        }
       }
       if (ImGui::IsWindowFocused(ImGuiFocusedFlags_ChildWindows)) curWindow=GUI_WINDOW_EDIT_CONTROLS;
       ImGui::End();
@@ -658,6 +662,10 @@ void FurnaceGUI::drawEditControls() {
         if (ImGui::Button(ICON_FA_PLAY "##Play")) {
           play();
         }
+        ImGui::SameLine();
+        if (ImGui::Button(ICON_FA_ARROW_DOWN "##StepOne")) {
+          e->stepOne(cursor.y);
+        }
 
         ImGui::SameLine();
         bool repeatPattern=e->getRepeatPattern();
@@ -722,6 +730,9 @@ void FurnaceGUI::drawEditControls() {
         if (ImGui::Button(ICON_FA_STOP "##Stop")) {
           stop();
         }
+        if (ImGui::Button(ICON_FA_ARROW_DOWN "##StepOne")) {
+          e->stepOne(cursor.y);
+        }
 
         bool repeatPattern=e->getRepeatPattern();
         ImGui::PushStyleColor(ImGuiCol_Button,ImVec4(0.2f,(repeatPattern)?0.6f:0.2f,0.2f,1.0f));
@@ -792,6 +803,10 @@ void FurnaceGUI::drawEditControls() {
         if (ImGui::Button(ICON_FA_PLAY_CIRCLE "##PlayAgain")) {
           play();
         }
+        ImGui::SameLine();
+        if (ImGui::Button(ICON_FA_ARROW_DOWN "##StepOne")) {
+          e->stepOne(cursor.y);
+        }
 
         ImGui::SameLine();
         ImGui::PushStyleColor(ImGuiCol_Button,ImVec4(0.2f,(edit)?0.6f:0.2f,0.2f,1.0f));
@@ -4719,6 +4734,9 @@ void FurnaceGUI::keyDown(SDL_Event& ev) {
           doUndo();
         }
         break;
+      case SDLK_RETURN:
+        e->stepOne(cursor.y);
+        break;
     }
   } else switch (ev.key.keysym.sym) {
     case SDLK_F5:
@@ -4758,7 +4776,7 @@ void FurnaceGUI::keyDown(SDL_Event& ev) {
       }
       break;
     case SDLK_RETURN:
-      if (e->isPlaying()) {
+      if (e->isPlaying() && !e->isStepping()) {
         stop();
       } else {
         if (ev.key.keysym.mod&KMOD_SHIFT) {