More gtk-webview high-dpi setup tweaks

Signed-off-by: falkTX <falktx@falktx.com>

Author: falkTX

distrho/extra/WebViewImpl.cpp

@@ -1114,6 +1114,33 @@ static bool gtk3(Display* const display,
     webkit_web_view_run_javascript_t webkit_web_view_run_javascript = reinterpret_cast<webkit_web_view_run_javascript_t>(dlsym(nullptr, "webkit_web_view_run_javascript"));
     DISTRHO_SAFE_ASSERT_RETURN(webkit_web_view_evaluate_javascript != nullptr || webkit_web_view_run_javascript != nullptr, false);
 
+    // get desktop scale factor, gtk dpi scaling needs to be based on this one
+    XrmInitialize();
+
+    double desktopScaleFactor = 1.0;
+    if (char* const rms = XResourceManagerString(display))
+    {
+        if (const XrmDatabase db = XrmGetStringDatabase(rms))
+        {
+            char* type = nullptr;
+            XrmValue value = {};
+
+            if (XrmGetResource(db, "Xft.dpi", "Xft.Dpi", &type, &value)
+                && type != nullptr
+                && std::strcmp(type, "String") == 0
+                && value.addr != nullptr)
+            {
+                char*        end    = nullptr;
+                const double xftDpi = std::strtod(value.addr, &end);
+                if (xftDpi > 0.0 && xftDpi < HUGE_VAL)
+                    desktopScaleFactor = xftDpi / 96.0;
+            }
+
+            XrmDestroyDatabase(db);
+        }
+    }
+
+    // gtk3 does not support fractional scaling, so we round to next integer if fmod >= 0.75
     const int gdkScale = std::fmod(scaleFactor, 1.0) >= 0.75
                        ? static_cast<int>(scaleFactor + 0.5)
                        : static_cast<int>(scaleFactor);
@@ -1124,13 +1151,23 @@ static bool gtk3(Display* const display,
         std::snprintf(scale, 7, "%d", gdkScale);
         setenv("GDK_SCALE", scale, 1);
 
-        std::snprintf(scale, 7, "%.2f", (1.0 / scaleFactor) * 1.2);
-        setenv("GDK_DPI_SCALE", scale, 1);
+        if (gdkScale > scaleFactor)
+        {
+            std::snprintf(scale, 7, "%.2f", 0.5 + ((0.25 - gdkScale + scaleFactor) / 0.25 * 0.0835));
+            setenv("GDK_DPI_SCALE", scale, 1);
+        }
+        else
+        {
+            std::snprintf(scale, 7, "%.2f", 1.0 / scaleFactor);
+            setenv("GDK_DPI_SCALE", scale, 1);
+        }
     }
-    else if (scaleFactor > 1.0)
+    else
     {
+        setenv("GDK_SCALE", "1", 1);
+
         char scale[8] = {};
-        std::snprintf(scale, 7, "%.2f", (1.0 / scaleFactor) * 1.4);
+        std::snprintf(scale, 7, "%.2f", (1.0 / desktopScaleFactor) * scaleFactor);
         setenv("GDK_DPI_SCALE", scale, 1);
     }
 
@@ -1148,7 +1185,7 @@ static bool gtk3(Display* const display,
     DISTRHO_SAFE_ASSERT_RETURN(window != nullptr, false);
 
     gtk_window_set_default_size(GTK_WINDOW(window), width / gdkScale, height / gdkScale);
-    gtk_window_move(GTK_WINDOW(window), x, y);
+    gtk_window_move(GTK_WINDOW(window), x / gdkScale, y / gdkScale);
 
     WebKitSettings* const settings = webkit_settings_new();
     DISTRHO_SAFE_ASSERT_RETURN(settings != nullptr, false);