UI: Add option to snap to vertical/horizontal center

Allows users to snap sources to the horizontal or vertical centers of
the screen.  Off by default.

Closes jp9000/obs-studio#528

obs/data/locale/en-US.ini

@@ -357,6 +357,7 @@ Basic.Settings.General.WarnBeforeStartingStream="Show confirmation dialog when s
 Basic.Settings.General.WarnBeforeStoppingStream="Show confirmation dialog when stopping streams"
 Basic.Settings.General.Snapping="Source Alignment Snapping"
 Basic.Settings.General.ScreenSnapping="Snap Sources to edge of screen"
+Basic.Settings.General.CenterSnapping="Snap Sources to horizontal and vertical center"
 Basic.Settings.General.SnapDistance="Snap Sensitivity"
 
 # basic mode 'stream' settings

obs/forms/OBSBasicSettings.ui

@@ -233,6 +233,16 @@
               </property>
              </widget>
             </item>
+            <item row="4" column="1">
+             <widget class="QCheckBox" name="centerSnapping">
+              <property name="text">
+               <string>Basic.Settings.General.CenterSnapping</string>
+              </property>
+              <property name="checked">
+               <bool>true</bool>
+              </property>
+             </widget>
+            </item>
             <item row="1" column="1">
              <widget class="QDoubleSpinBox" name="snapDistance">
               <property name="decimals">
@@ -3616,6 +3626,22 @@
      <x>476</x>
      <y>202</y>
     </hint>
+    <hint type="destinationlabel">
+     <x>515</x>
+     <y>277</y>
+    </hint>
+   </hints>
+  </connection>
+  <connection>
+   <sender>snappingEnabled</sender>
+   <signal>toggled(bool)</signal>
+   <receiver>centerSnapping</receiver>
+   <slot>setEnabled(bool)</slot>
+   <hints>
+    <hint type="sourcelabel">
+     <x>557</x>
+     <y>207</y>
+    </hint>
     <hint type="destinationlabel">
      <x>777</x>
      <y>206</y>

obs/obs-app.cpp

@@ -343,6 +343,8 @@ bool OBSApp::InitGlobalConfigDefaults()
 			"SnappingEnabled", true);
 	config_set_default_bool(globalConfig, "BasicWindow",
 			"ScreenSnapping", true);
+	config_set_default_bool(globalConfig, "BasicWindow",
+			"CenterSnapping", false);
 	config_set_default_double(globalConfig, "BasicWindow",
 			"SnapDistance", 10.0);
 

obs/window-basic-preview.cpp

@@ -147,9 +147,13 @@ vec3 OBSBasicPreview::GetSnapOffset(const vec3 &tl, const vec3 &br)
 
 	const bool screenSnap = config_get_bool(GetGlobalConfig(),
 			"BasicWindow", "ScreenSnapping");
+	const bool centerSnap = config_get_bool(GetGlobalConfig(),
+			"BasicWindow", "CenterSnapping");
 
 	const float clampDist = config_get_double(GetGlobalConfig(),
 			"BasicWindow", "SnapDistance") / main->previewScale;
+	const float centerX = br.x - (br.x - tl.x) / 2.0f;
+	const float centerY = br.y - (br.y - tl.y) / 2.0f;
 
 	// Left screen edge.
 	if (screenSnap &&
@@ -160,6 +164,11 @@ vec3 OBSBasicPreview::GetSnapOffset(const vec3 &tl, const vec3 &br)
 	    fabsf(clampOffset.x) < EPSILON &&
 	    fabsf(screenSize.x - br.x) < clampDist)
 		clampOffset.x = screenSize.x - br.x;
+	// Horizontal center.
+	if (centerSnap &&
+	    fabsf(screenSize.x - (br.x - tl.x)) > clampDist &&
+	    fabsf(screenSize.x / 2.0f - centerX) < clampDist)
+		clampOffset.x = screenSize.x / 2.0f - centerX;
 
 	// Top screen edge.
 	if (screenSnap &&
@@ -170,6 +179,11 @@ vec3 OBSBasicPreview::GetSnapOffset(const vec3 &tl, const vec3 &br)
 	    fabsf(clampOffset.y) < EPSILON &&
 	    fabsf(screenSize.y - br.y) < clampDist)
 		clampOffset.y = screenSize.y - br.y;
+	// Vertical center.
+	if (centerSnap &&
+	    fabsf(screenSize.y - (br.y - tl.y)) > clampDist &&
+	    fabsf(screenSize.y / 2.0f - centerY) < clampDist)
+		clampOffset.y = screenSize.y / 2.0f - centerY;
 
 	return clampOffset;
 }

obs/window-basic-settings.cpp

@@ -268,6 +268,7 @@ OBSBasicSettings::OBSBasicSettings(QWidget *parent)
 	HookWidget(ui->warnBeforeStreamStop, CHECK_CHANGED,  GENERAL_CHANGED);
 	HookWidget(ui->snappingEnabled,      CHECK_CHANGED,  GENERAL_CHANGED);
 	HookWidget(ui->screenSnapping,       CHECK_CHANGED,  GENERAL_CHANGED);
+	HookWidget(ui->centerSnapping,       CHECK_CHANGED,  GENERAL_CHANGED);
 	HookWidget(ui->snapDistance,         SCROLL_CHANGED, GENERAL_CHANGED);
 	HookWidget(ui->outputMode,           COMBO_CHANGED,  OUTPUTS_CHANGED);
 	HookWidget(ui->streamType,           COMBO_CHANGED,  STREAM1_CHANGED);
@@ -774,6 +775,10 @@ void OBSBasicSettings::LoadGeneralSettings()
 			"BasicWindow", "ScreenSnapping");
 	ui->screenSnapping->setChecked(screenSnapping);
 
+	bool centerSnapping = config_get_bool(GetGlobalConfig(),
+			"BasicWindow", "CenterSnapping");
+	ui->centerSnapping->setChecked(centerSnapping);
+
 	double snapDistance = config_get_double(GetGlobalConfig(),
 			"BasicWindow", "SnapDistance");
 	ui->snapDistance->setValue(snapDistance);
@@ -2062,6 +2067,10 @@ void OBSBasicSettings::SaveGeneralSettings()
 		config_set_bool(GetGlobalConfig(), "BasicWindow",
 				"ScreenSnapping",
 				ui->screenSnapping->isChecked());
+	if (WidgetChanged(ui->centerSnapping))
+		config_set_bool(GetGlobalConfig(), "BasicWindow",
+				"CenterSnapping",
+				ui->centerSnapping->isChecked());
 	if (WidgetChanged(ui->snapDistance))
 		config_set_double(GetGlobalConfig(), "BasicWindow",
 				"SnapDistance",