add PlayButton: drop previewing HotcueButton onto it to latch play

CMakeLists.txt

@@ -1554,6 +1554,7 @@ add_library(
   src/widget/wnumberrate.cpp
   src/widget/woverview.cpp
   src/widget/wpixmapstore.cpp
+  src/widget/wplaybutton.cpp
   src/widget/wpushbutton.cpp
   src/widget/wraterange.cpp
   src/widget/wstarratingaction.cpp

res/skins/LateNight/controls/button_play_2state_right_display.xml

@@ -0,0 +1,59 @@
+<!--
+Description:
+  A button that has click or display controls.
+  Left-click control is one of the play controls.
+  HotcueButtons of the same player (engine, not necessarily same player in skin)
+  can be dropped onto it in order to latch play when previewing from hotcue.
+
+  Make sure to use one of the 'play' ToolTipIDs so the dnd behavior is discoverable.
+
+Variables:
+  ObjectName        : object name
+  ToolTipID         : standard Tooltip from mixxx db
+    see: https://github.com/mixxxdj/mixxx/blob/main/src/skin/legacy/tooltips.cpp
+  Group             : BasePlayer group
+  Size              : button size
+  state_X_text      : label text for state X
+  state_X_pressed   : background graphic for pressed state X
+  state_X_unpressed : background graphic for unpressed state X
+  Align             : alignment of text
+  ConfigKey         : left-click control
+  ConfigKeyRight    : right-click control
+  ConfigKeyDisp     : display control
+-->
+<Template>
+  <PlayButton>
+    <TooltipId><Variable name="TooltipId"/></TooltipId>
+    <ObjectName><Variable name="ObjectName"/></ObjectName>
+    <Size><Variable name="Size"/></Size>
+    <NumberStates>2</NumberStates>
+    <RightClickIsPushButton>true</RightClickIsPushButton>
+    <Group><Variable name="Group"/></Group>
+    <State>
+      <Number>0</Number>
+      <Text><Variable name="state_0_text"/></Text>
+      <Alignment><Variable name="Align"/></Alignment>
+      <Unpressed scalemode="STRETCH">skins:LateNight/<Variable name="BtnScheme"/>/buttons/btn_<Variable name="BtnType"/>_<Variable name="BtnSize"/>.svg</Unpressed>
+      <Pressed scalemode="STRETCH">skins:LateNight/<Variable name="BtnScheme"/>/buttons/btn_<Variable name="BtnType"/>_<Variable name="BtnSize"/>_active.svg</Pressed>
+    </State>
+    <State>
+      <Number>1</Number>
+      <Text><Variable name="state_1_text"/></Text>
+      <Alignment><Variable name="Align"/></Alignment>
+      <Unpressed scalemode="STRETCH">skins:LateNight/<Variable name="BtnScheme"/>/buttons/btn_<Variable name="BtnType"/>_<Variable name="BtnSize"/>_active.svg</Unpressed>
+      <Pressed scalemode="STRETCH">skins:LateNight/<Variable name="BtnScheme"/>/buttons/btn_<Variable name="BtnType"/>_<Variable name="BtnSize"/>_active.svg</Pressed>
+    </State>
+    <Connection>
+      <ConfigKey><Variable name="ConfigKey"/></ConfigKey>
+      <ButtonState>LeftButton</ButtonState>
+    </Connection>
+    <Connection>
+      <ConfigKey><Variable name="ConfigKeyRight"/></ConfigKey>
+      <ButtonState>RightButton</ButtonState>
+    </Connection>
+    <Connection>
+      <ConfigKey><Variable name="ConfigKeyDisp"/></ConfigKey>
+      <ConnectValueFromWidget>false</ConnectValueFromWidget>
+    </Connection>
+  </PlayButton>
+</Template>

res/skins/LateNight/decks/row_5_transportLoopJump.xml

@@ -71,7 +71,7 @@
                 <Layout>stacked</Layout>
                 <Size>68f,26f</Size>
                 <Children>
-                  <Template src="skins:LateNight/controls/button_2state_right_display.xml">
+                  <Template src="skins:LateNight/controls/button_play_2state_right_display.xml">
                     <SetVariable name="TooltipId">play_cue_set</SetVariable>
                     <SetVariable name="ObjectName">PlayDeck</SetVariable>
                     <SetVariable name="Size">68f,26f</SetVariable>

res/skins/LateNight/samplers/sampler.xml

@@ -85,7 +85,7 @@
                         <Layout>stacked</Layout>
                         <SizePolicy>max,max</SizePolicy>
                         <Children>
-                          <Template src="skins:LateNight/controls/button_2state_right_display.xml">
+                          <Template src="skins:LateNight/controls/button_play_2state_right_display.xml">
                             <SetVariable name="TooltipId">cue_gotoandplay_cue_default</SetVariable>
                             <SetVariable name="ObjectName">PlaySampler</SetVariable>
                             <SetVariable name="Size">34f,34f</SetVariable>

src/skin/legacy/legacyskinparser.cpp

@@ -63,6 +63,7 @@
 #include "widget/wnumberrate.h"
 #include "widget/woverview.h"
 #include "widget/wpixmapstore.h"
+#include "widget/wplaybutton.h"
 #include "widget/wpushbutton.h"
 #include "widget/wraterange.h"
 #include "widget/wrecordingduration.h"
@@ -536,6 +537,8 @@ QList<QWidget*> LegacySkinParser::parseNode(const QDomElement& node) {
         result = wrapWidget(parseStandardWidget<WSliderComposed>(node));
     } else if (nodeName == "PushButton") {
         result = wrapWidget(parseStandardWidget<WPushButton>(node));
+    } else if (nodeName == "PlayButton") {
+        result = wrapWidget(parsePlayButton(node));
     } else if (nodeName == "EffectPushButton") {
         result = wrapWidget(parseEffectPushButton(node));
     } else if (nodeName == "HotcueButton") {
@@ -1942,6 +1945,18 @@ QWidget* LegacySkinParser::parseHotcueButton(const QDomElement& element) {
     return pWidget;
 }
 
+QWidget* LegacySkinParser::parsePlayButton(const QDomElement& element) {
+    QString group = lookupNodeGroup(element);
+    WPlayButton* pWidget = new WPlayButton(m_pParent, group);
+    commonWidgetSetup(element, pWidget);
+    pWidget->setup(element, *m_pContext);
+    pWidget->installEventFilter(m_pKeyboard);
+    pWidget->installEventFilter(
+            m_pControllerManager->getControllerLearningEventFilter());
+    pWidget->Init();
+    return pWidget;
+}
+
 QWidget* LegacySkinParser::parseEffectChainName(const QDomElement& node) {
     WEffectChain* pEffectChain = new WEffectChain(m_pParent, m_pEffectsManager);
     setupLabelWidget(node, pEffectChain);

src/skin/legacy/legacyskinparser.h

@@ -101,6 +101,7 @@ class LegacySkinParser : public QObject, public SkinParser {
     QWidget* parseEffectPushButton(const QDomElement& node);
     QWidget* parseEffectSelector(const QDomElement& node);
     QWidget* parseHotcueButton(const QDomElement& node);
+    QWidget* parsePlayButton(const QDomElement& node);
 
     // Legacy pre-1.12.0 skin support.
     QWidget* parseBackground(const QDomElement& node, QWidget* pOuterWidget, QWidget* pInnerWidget);

src/skin/legacy/tooltips.cpp

@@ -534,8 +534,13 @@ void Tooltips::addStandardTooltips() {
     // Currently used for samplers
     add("play_start")
             << tr("Play/Pause")
-            << QString("%1: %2").arg(leftClick, tr("Starts playing from the beginning of the track."))
-            << QString("%1: %2").arg(rightClick, tr("Jumps to the beginning of the track and stops."));
+            << QString("%1: %2").arg(leftClick,
+                       tr("Starts playing from the beginning of the track."))
+            << QString("%1: %2").arg(rightClick,
+                       tr("Jumps to the beginning of the track and stops."))
+            << " " // add linebreak, '\n' would result in two linebreaks
+            << tr("Drag a Hotcue button here to continue playing after "
+                  "releasing the Hotcue.");
 
     QString whilePlaying = tr("(while playing)");
     QString whileStopped = tr("(while stopped)");
@@ -552,7 +557,10 @@ void Tooltips::addStandardTooltips() {
             << tr("Play/Pause")
             << QString("%1: %2").arg(leftClick, tr("Plays or pauses the track."))
             << QString("%1 %2: %3").arg(leftClick, whilePreviewing, latchingPlay)
-            << QString("%1: %2").arg(rightClick, cueSet);
+            << QString("%1: %2").arg(rightClick, cueSet)
+            << " " // add linebreak, '\n' would result in two linebreaks
+            << tr("Drag a Hotcue button here to continue playing after "
+                  "releasing the Hotcue.");
 
     // Currently used for minimal decks
     add("play_cue_default")
@@ -561,7 +569,10 @@ void Tooltips::addStandardTooltips() {
             << QString("%1 %2: %3").arg(rightClick, whilePlaying, cueWhilePlaying)
             << QString("%1 %2: %3").arg(rightClick, whileStopped, cueWhileStopped)
             << cueHint
-            << quantizeSnap;
+            << quantizeSnap
+            << " " // add linebreak, '\n' would result in two linebreaks
+            << tr("Drag a Hotcue button here to continue playing after "
+                  "releasing the Hotcue.");
     add("cue_default_cue_gotoandstop")
             << tr("Cue")
             << QString("%1 %2: %3").arg(leftClick, whilePlaying, cueWhilePlaying)
@@ -703,8 +714,10 @@ void Tooltips::addStandardTooltips() {
                   << tr("Drag this button onto another Hotcue button to move it "
                         "there (change its index). If the other hotcue is set, "
                         "the two are swapped.")
+                  << tr("Drag this button onto a Play button while previewing "
+                        "to continue playback after release.")
                   << tr("Dragging with Shift key pressed will not start previewing "
-                        "the hotcue");
+                        "the hotcue.");
 
     // Status displays and toggle buttons
     add("toggle_recording")

src/widget/hotcuedrag.cpp

@@ -1,9 +1,7 @@
 #include <widget/hotcuedrag.h>
 
 #include <QDragEnterEvent>
-#include <QMimeData>
 #include <QMouseEvent>
-#include <QString>
 
 #include "mixer/playerinfo.h"
 #include "track/track.h"

src/widget/hotcuedrag.h

@@ -52,7 +52,7 @@ template<typename T>
 bool isValidHotcueDragOrDropEvent(T* pEvent,
         QObject* pTarget,
         const QString& group,
-        int ignoreHotcueIndex,
+        int ignoreHotcueIndex = Cue::kNoHotCue,
         HotcueDragInfo* pDragData = nullptr);
 
 } // namespace hotcuedrag

src/widget/wplaybutton.cpp

@@ -0,0 +1,46 @@
+#include "widget/wplaybutton.h"
+
+#include <QMouseEvent>
+
+#include "control/controlobject.h"
+#include "moc_wplaybutton.cpp"
+#include "widget/hotcuedrag.h"
+
+using namespace mixxx::hotcuedrag;
+
+WPlayButton::WPlayButton(QWidget* pParent, const QString& group)
+        : WPushButton(pParent),
+          m_group(group) {
+    setAcceptDrops(true);
+}
+
+void WPlayButton::dragEnterEvent(QDragEnterEvent* pEvent) {
+    if (isValidHotcueDragOrDropEvent<QDragEnterEvent>(
+                pEvent,
+                this,
+                m_group)) {
+        pEvent->acceptProposedAction();
+    } else {
+        pEvent->ignore();
+    }
+}
+
+void WPlayButton::dropEvent(QDropEvent* pEvent) {
+    // Enable 'play' if we drop a hotcue here while we're
+    // previewing it but NOT playing.
+    // If not previewing this is no-op.
+    if (ControlObject::get(ConfigKey(m_group, QStringLiteral("play_latched"))) <= 0 &&
+            isValidHotcueDragOrDropEvent<QDropEvent>(
+                    pEvent,
+                    this,
+                    m_group)) {
+        // This seems counterintuitive but it's the same action that
+        // allows to latch `play` with keyboard or controllers while
+        // previewing a hotcue.
+        // See EngineBuffer::slotControlPlayRequest()
+        ControlObject::set(ConfigKey(m_group, QStringLiteral("play")), 0.0);
+        pEvent->accept();
+    } else {
+        pEvent->ignore();
+    }
+}

src/widget/wplaybutton.h

@@ -0,0 +1,17 @@
+#pragma once
+
+#include "widget/wpushbutton.h"
+
+struct HotcueDragInfo;
+
+class WPlayButton : public WPushButton {
+    Q_OBJECT
+  public:
+    WPlayButton(QWidget* pParent, const QString& group);
+
+  private:
+    void dragEnterEvent(QDragEnterEvent* pEvent) override;
+    void dropEvent(QDropEvent* pEvent) override;
+
+    QString m_group;
+};