platforms/x11: Always set swap interval to 1

With the new compositing scheduling, we want the screen to be redrawn as
close as possible to the next vblank. Furthermore, compositing is no
longer driven by a timer. This change removes the NoSwapEncourage swap
strategy as it doesn't make sense now, in addition to that it just does
not work on Wayland.

kcmkwin/kwincompositing/compositing.ui

@@ -227,11 +227,6 @@ Alternatively, you might want to use the XRender backend instead.</string>
    </item>
    <item row="12" column="1">
     <widget class="QComboBox" name="kcfg_glPreferBufferSwap">
-     <item>
-      <property name="text">
-       <string>Never</string>
-      </property>
-     </item>
      <item>
       <property name="text">
        <string>Automatic</string>

kcmkwin/kwincompositing/kwincompositing_setting.kcfg

@@ -45,7 +45,6 @@
        <entry name="glPreferBufferSwap" key="GLPreferBufferSwap" type="Enum">
            <default>AutoSwapStrategy</default>
            <choices>
-               <choice name="NoSwapEncourage" value="n" />
                <choice name="AutoSwapStrategy" value="a" />
                <choice name="ExtendDamage" value="e" />
                <choice name="PaintFullScreen" value="p" />

kcmkwin/kwincompositing/main.cpp

@@ -130,15 +130,15 @@ void KWinCompositingKCM::init()
     // tearing prevention
     connect(m_form.kcfg_glPreferBufferSwap, currentIndexChangedSignal, this,
         [this](int index) {
-            if (index == 2) {
+            if (index == 1) {
                 // only when cheap - tearing
                 m_form.tearingWarning->setText(i18n("\"Only when cheap\" only prevents tearing for full screen changes like a video."));
                 m_form.tearingWarning->animatedShow();
-            } else if (index == 3) {
+            } else if (index == 2) {
                 // full screen repaints
                 m_form.tearingWarning->setText(i18n("\"Full screen repaints\" can cause performance problems."));
                 m_form.tearingWarning->animatedShow();
-            } else if (index == 4) {
+            } else if (index == 3) {
                 // re-use screen content
                 m_form.tearingWarning->setText(i18n("\"Re-use screen content\" causes severe performance problems on MESA drivers."));
                 m_form.tearingWarning->animatedShow();

kconf_update/CMakeLists.txt

@@ -6,6 +6,8 @@ install(PROGRAMS kwin-5.18-move-animspeed.py
         DESTINATION ${KDE_INSTALL_KCONFUPDATEDIR})
 install(PROGRAMS kwin-5.21-desktop-grid-click-behavior.py
         DESTINATION ${KDE_INSTALL_KCONFUPDATEDIR})
+install(PROGRAMS kwin-5.21-no-swap-encourage.py
+        DESTINATION ${KDE_INSTALL_KCONFUPDATEDIR})
 
 install(FILES kwinrules.upd
         DESTINATION ${KDE_INSTALL_KCONFUPDATEDIR})

kconf_update/kwin-5.21-no-swap-encourage.py

@@ -0,0 +1,11 @@
+#!/usr/bin/env python3
+
+import fileinput
+
+for line in fileinput.input():
+    if not line.startswith("GLPreferBufferSwap="):
+        continue
+    value = line[len("GLPreferBufferSwap="):].strip()
+    if value != "n":
+        continue
+    print("# DELETE GLPreferBufferSwap") # will use the default swap strategy

kconf_update/kwin.upd

@@ -43,3 +43,9 @@ Id=desktop-grid-click-behavior
 File=kwinrc
 Group=Effect-DesktopGrid
 Script=kwin-5.21-desktop-grid-click-behavior.py,python3
+
+# Remove GLPreferBufferSwap if it has a value of "n"
+Id=no-swap-encourage
+File=kwinrc
+Group=Compositing
+File=kwin-5.21-no-swap-encourage.py,python3

options.cpp

@@ -896,7 +896,7 @@ void Options::reloadCompositingSettings(bool force)
     if (!s.isEmpty())
         c = s.at(0).toLatin1();
     if (c != 'a' && c != 'c' && c != 'p' && c != 'e')
-        c = 0;
+        c = Options::defaultGlPreferBufferSwap();
     setGlPreferBufferSwap(c);
 
     m_xrenderSmoothScale = config.readEntry("XRenderSmoothScale", false);

options.h

@@ -590,7 +590,7 @@ public:
         return m_glPlatformInterface;
     }
 
-    enum GlSwapStrategy { NoSwapEncourage = 0, CopyFrontBuffer = 'c', PaintFullScreen = 'p', ExtendDamage = 'e', AutoSwapStrategy = 'a' };
+    enum GlSwapStrategy { CopyFrontBuffer = 'c', PaintFullScreen = 'p', ExtendDamage = 'e', AutoSwapStrategy = 'a' };
     Q_ENUM(GlSwapStrategy)
     GlSwapStrategy glPreferBufferSwap() const {
         return m_glPreferBufferSwap;

plugins/platforms/x11/common/eglonxbackend.cpp

@@ -102,20 +102,15 @@ void EglOnXBackend::init()
     if (surfaceHasSubPost) {
         qCDebug(KWIN_CORE) << "EGL implementation and surface support eglPostSubBufferNV, let's use it";
 
-        if (options->glPreferBufferSwap() != Options::NoSwapEncourage) {
+        // check if swap interval 1 is supported
-            // check if swap interval 1 is supported
+        EGLint val;
-            EGLint val;
+        eglGetConfigAttrib(eglDisplay(), config(), EGL_MAX_SWAP_INTERVAL, &val);
-            eglGetConfigAttrib(eglDisplay(), config(), EGL_MAX_SWAP_INTERVAL, &val);
+        if (val >= 1) {
-            if (val >= 1) {
+            if (eglSwapInterval(eglDisplay(), 1)) {
-                if (eglSwapInterval(eglDisplay(), 1)) {
+                qCDebug(KWIN_CORE) << "Enabled v-sync";
-                    qCDebug(KWIN_CORE) << "Enabled v-sync";
-                }
-            } else {
-                qCWarning(KWIN_CORE) << "Cannot enable v-sync as max. swap interval is" << val;
             }
         } else {
-            // disable v-sync
+            qCWarning(KWIN_CORE) << "Cannot enable v-sync as max. swap interval is" << val;
-            eglSwapInterval(eglDisplay(), 0);
         }
     } else {
         /* In the GLX backend, we fall back to using glCopyPixels if we have no extension providing support for partial screen updates.

plugins/platforms/x11/standalone/glxbackend.cpp

@@ -224,17 +224,12 @@ void GlxBackend::init()
         m_haveINTELSwapEvent = false;
     }
 
-    const bool wantSync = options->glPreferBufferSwap() != Options::NoSwapEncourage;
+    if (haveSwapInterval) {
-    if (wantSync && glXIsDirect(display(), ctx)) {
+        setSwapInterval(1);
-        if (haveSwapInterval) { // glXSwapInterval is preferred being more reliable
-            setSwapInterval(1);
-        } else {
-            qCWarning(KWIN_X11STANDALONE) << "glSwapInterval is unsupported";
-        }
     } else {
-        // disable v-sync (if possible)
+        qCWarning(KWIN_X11STANDALONE) << "glSwapInterval is unsupported";
-        setSwapInterval(0);
     }
+
     if (glPlatform->isVirtualBox()) {
         // VirtualBox does not support glxQueryDrawable
         // this should actually be in kwinglutils_funcs, but QueryDrawable seems not to be provided by an extension