From b48cefdbc39df81615e54f922539bd30766ac396 Mon Sep 17 00:00:00 2001
From: Simon Rettberg
Date: Thu, 20 Oct 2022 15:08:26 +0200
Subject: Introduce --fb again

No idea why it was removed, it seems to work great. :>
---
 src/loginrpc.cpp | 51 ++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 48 insertions(+), 3 deletions(-)

diff --git a/src/loginrpc.cpp b/src/loginrpc.cpp
index 3d6092b..353d824 100644
--- a/src/loginrpc.cpp
+++ b/src/loginrpc.cpp
@@ -8,6 +8,8 @@
 #include <QProcess>
 #include <QRegularExpression>
 
+static int doFbOnly(int x, int y, const QStringList &allOutputs);
+
 static int setMode(const QString &virtOut, const QString &name, const QStringList &allOutputs);
 
 static int sizeDiff(const QSize &a, const QSize &b)
@@ -184,6 +186,12 @@ void LoginRpc::handleCommandV1(const QString &command)
                     ret = setMode(bestConMode.output, bestConMode.modeName, allOutputs);
                     bestConMode.modeName.clear();
                 }
+            } else {
+                if (ret != 0) {
+                    // Do the --fb thing - we had that before and there was a problem, but I don't remember what it
+                    // was, and initial testing seems fine!? Not taking notes FTW!
+                    ret = doFbOnly(x, y, allOutputs);
+                }
             }
             // Either -1 if we didn't have a virtual one, or != 0 if xrandr setting failed
             // Now as fallback, try enabling a disconnected output only
@@ -192,7 +200,7 @@ void LoginRpc::handleCommandV1(const QString &command)
                 QRegularExpression re("\\d+$");
                 QString dis;
                 int used[10] = {};
-                for (QString c : connectedOutputs) {
+                for (const auto & c : connectedOutputs) {
                     auto m = re.match(c);
                     if (m.hasMatch()) {
                         int i = m.captured().toInt();
@@ -201,7 +209,7 @@ void LoginRpc::handleCommandV1(const QString &command)
                         }
                     }
                 }
-                for (QString c : disconnectedOutputs) {
+                for (const auto & c : disconnectedOutputs) {
                     auto m = re.match(c);
                     if (m.hasMatch()) {
                         int i = m.captured().toInt();
@@ -220,6 +228,9 @@ void LoginRpc::handleCommandV1(const QString &command)
                 p.kill();
                 ret = setMode(dis, name, allOutputs);
             }
+            if (lowResFallback && ret != 0) {
+                ret = doFbOnly(x, y, allOutputs);
+            }
             // Try this stuff again in case --newmode succeeded but --addmode now didn't (NVIDIA)
             if (ret != 0 && !bestDisconMode.modeName.isEmpty()) {
                 qDebug() << "Ret" << ret << "- Trying to enable best disconnected screen (2)";
@@ -247,12 +258,46 @@ void LoginRpc::handleCommandV1(const QString &command)
     emit loginRequest(lines[0], lines[1], lines[2]);
 }
 
+static int doFbOnly(int x, int y, const QStringList &allOutputs)
+{
+    QStringList setMode(QStringLiteral("--verbose"));
+    QProcess p;
+    p.setProcessChannelMode(QProcess::ForwardedChannels);
+    for (const auto &output : allOutputs) {
+        setMode << "--output" << output << "--off";
+    }
+    setMode << "--fb" << QString("%1x%2").arg(x).arg(y);
+    // Set all outputs
+    qDebug() << setMode;
+    p.start("xrandr", setMode);
+    p.waitForFinished(2000);
+    int ret = p.exitCode();
+    p.kill();
+    if (ret != 0)
+        return ret;
+    p.setProcessChannelMode(QProcess::MergedChannels);
+    p.start("xrandr", QStringList("--current"));
+    p.waitForFinished(1000);
+    p.kill();
+    QString xrandrOutput = QString::fromLocal8Bit(p.readAll());
+    QRegularExpression re("current (\\d+) x (\\d+),", QRegularExpression::MultilineOption);
+    QRegularExpressionMatch m = re.match(xrandrOutput);
+    if (!m.hasMatch()) {
+        qDebug() << "Could not query current screen size after setting --fb";
+    } else {
+        if (m.captured(1).toInt() == x && m.captured(2).toInt() == y)
+            return 0;
+        qDebug() << "Screen size after --fb is not" << x << "x" << y << "but" << m.captured();
+    }
+    return -1;
+}
+
 static int setMode(const QString &virtOut, const QString &name, const QStringList &allOutputs)
 {
     QStringList setMode(QStringLiteral("--verbose"));
     QProcess p;
     p.setProcessChannelMode(QProcess::ForwardedChannels);
-    for (auto output : allOutputs) {
+    for (const auto & output : allOutputs) {
         if (output == virtOut)
             continue; // Skip self
         setMode << "--output" << output << "--off";
-- 
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