ui: auto scaling on resolution below 1920 x 1080 (#22842)

* ui: resizable on PC by mouse drag

* Revert "ui: resizable on PC by mouse drag"

This reverts commit 56aa8254a2.

* ui: auto scaling on resolution below 1920 x 1080

special case when on PC and screen resolution is exactly 1920 x 1080,
we don't use fixed-sized window to account for taskbar/menubar area

* Update qt_window.cc

set maximum window size

* keep SCALE

Co-authored-by: Willem Melching <willem.melching@gmail.com>

selfdrive/ui/qt/qt_window.cc

@@ -1,11 +1,16 @@
 #include "selfdrive/ui/qt/qt_window.h"
 
 void setMainWindow(QWidget *w) {
-  const bool wide = (QGuiApplication::primaryScreen()->size().width() >= WIDE_WIDTH) ^
-                    (getenv("INVERT_WIDTH") != NULL);
-  const float scale = util::getenv("SCALE", 1.0f);
-
-  w->setFixedSize(QSize(wide ? WIDE_WIDTH : 1920, 1080) * scale);
+  const QSize sz = QGuiApplication::primaryScreen()->size();
+  if (Hardware::PC() && sz.width() <= 1920 && sz.height() <= 1080 && getenv("SCALE") == nullptr) {
+    w->setMinimumSize(QSize(640, 480)); // allow resize smaller than fullscreen
+    w->setMaximumSize(QSize(2160, 1080));
+    w->resize(sz);
+  } else {
+    const float scale = util::getenv("SCALE", 1.0f);
+    const bool wide = (sz.width() >= WIDE_WIDTH) ^ (getenv("INVERT_WIDTH") != NULL);
+    w->setFixedSize(QSize(wide ? WIDE_WIDTH : 1920, 1080) * scale);
+  }
   w->show();
 
 #ifdef QCOM2