From bc2acdd060bf6a10fbe1fa87a0035bd7fa68c260 Mon Sep 17 00:00:00 2001
From: "Jeffrey C. Ollie" <jeff@ocjtech.us>
Date: Sun, 23 Feb 2025 10:59:59 -0600
Subject: [PATCH] gtk: ensure that the content scale is always positive

Fixes #5927

This doesn't fix the underlying reason that GTK sometimes reports
content scales as negative. If GTK reports a negative scale, we ignore
that and use 1.0 for the scale.
---
 src/apprt/gtk/Surface.zig | 35 ++++++++++++++++++++++++-----------
 1 file changed, 24 insertions(+), 11 deletions(-)

diff --git a/src/apprt/gtk/Surface.zig b/src/apprt/gtk/Surface.zig
index 3c94989c2..e25375d98 100644
--- a/src/apprt/gtk/Surface.zig
+++ b/src/apprt/gtk/Surface.zig
@@ -847,28 +847,41 @@ pub fn shouldClose(self: *const Surface) bool {
 }
 
 pub fn getContentScale(self: *const Surface) !apprt.ContentScale {
-    // Future: detect GTK version 4.12+ and use gdk_surface_get_scale so we
-    // can support fractional scaling.
-    const gtk_scale: f32 = @floatFromInt(c.gtk_widget_get_scale_factor(@ptrCast(self.gl_area)));
+    const gtk_scale: f32 = scale: {
+        const widget: *gtk.Widget = @ptrCast(@alignCast(self.gl_area));
+        // Future: detect GTK version 4.12+ and use gdk_surface_get_scale so we
+        // can support fractional scaling.
+        const scale = widget.getScaleFactor();
+        if (scale < 0) {
+            log.warn("gtk_widget_get_scale_factor returned a negative number: {d:.3}", .{scale});
+            break :scale 1.0;
+        }
+        break :scale @floatFromInt(scale);
+    };
 
     // Also scale using font-specific DPI, which is often exposed to the user
     // via DE accessibility settings (see https://docs.gtk.org/gtk4/class.Settings.html).
     const xft_dpi_scale = xft_scale: {
         // gtk-xft-dpi is font DPI multiplied by 1024. See
         // https://docs.gtk.org/gtk4/property.Settings.gtk-xft-dpi.html
-        const settings = c.gtk_settings_get_default();
+        const settings = gtk.Settings.getDefault() orelse break :xft_scale 1.0;
+        var value = std.mem.zeroes(gobject.Value);
+        defer value.unset();
+        _ = value.init(gobject.ext.typeFor(c_int));
+        settings.as(gobject.Object).getProperty("gtk-xft-dpi", &value);
+        const gtk_xft_dpi = value.getInt();
 
-        var value: c.GValue = std.mem.zeroes(c.GValue);
-        defer c.g_value_unset(&value);
-        _ = c.g_value_init(&value, c.G_TYPE_INT);
-        c.g_object_get_property(@ptrCast(@alignCast(settings)), "gtk-xft-dpi", &value);
-        const gtk_xft_dpi = c.g_value_get_int(&value);
+        // ensure that the scale is never negative
+        if (gtk_xft_dpi < 0) {
+            log.warn("gtk-xft-dpi setting was negative: {d:.3}", .{gtk_xft_dpi});
+            break :xft_scale 1.0;
+        }
 
         // As noted above gtk-xft-dpi is multiplied by 1024, so we divide by
         // 1024, then divide by the default value (96) to derive a scale. Note
         // gtk-xft-dpi can be fractional, so we use floating point math here.
-        const xft_dpi: f32 = @as(f32, @floatFromInt(gtk_xft_dpi)) / 1024;
-        break :xft_scale xft_dpi / 96;
+        const xft_dpi: f32 = @as(f32, @floatFromInt(gtk_xft_dpi)) / 1024.0;
+        break :xft_scale xft_dpi / 96.0;
     };
 
     const scale = gtk_scale * xft_dpi_scale;