gui: on GTK 3 with no font DPI set, magpie gives GDK one before the first webview, so the window and panel no longer collapse (#1371, haoxianhan)

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This empty commit holds the message for 2018882e, which was pushed with
another session's davsync commit message by mistake (a reused scratch
file). 2018882e changes only docs/subsystems/gui-shell.md,
internal/gui/app.go and internal/gui/fontdpi_* (+ testdata probe); it
contains no davsync change.

GDK's unset font resolution is -1. WebKitGTK 2.54's GTK 3 settings
reader (SystemSettingsManagerProxy::xftDPI) multiplies it by 1024
unchecked, and every page laid out at a negative width with a
9000000px body font: the window showed its text one word per line.

fontDPI queues a G_PRIORITY_HIGH idle just before app.Run. Wails makes
its GtkApplication (and so initialises GTK, with its program name set)
inside Run and makes each window from a default-idle-priority callback,
so the check runs on the main thread after GTK's own start and before
the first webview, without initialising GTK earlier than Wails does.
A positive DPI (the user's own) is left alone. An unset one takes
gtk-xft-dpi, or 96, times a valid GDK_DPI_SCALE, as GTK does for a
positive gtk-xft-dpi. GTK 4 builds, macOS and Windows are unchanged.

Run, in Docker (Debian 13 arm64, GTK 3.24.49, WebKitGTK 2.54.0, Xvfb):
- testdata/fontdpi_probe.c without the guard at DPI -1: viewport
  -40320, font 9000000 (the reporter's literal values); with it: DPI 96,
  viewport 420, font 16.
- TestFontDPIUnset (-tags gtk3): 4 cases pass (unset -> 96, unset with
  GDK_DPI_SCALE 1.25 -> 120, bad scale -> 96, a user's 144 kept). With
  the guard returning early it FAILs: "font DPI -1, want 96", "page laid
  out at viewport -40320, body font 9e+06px".
- The real magpie binary (-tags gtk3, `magpie gui`, an LD_PRELOAD that
  leaves GDK's DPI at -1 after gtk_application_new): without fontDPI()
  both webviews are made at -1, the main page measures viewport -57600,
  font 9000000px, and the screenshot shows the one-word column; with it
  both are made at 96, viewport 600, font 13px, normal layout.
- go vet -tags gtk3 ./internal/gui; go vet ./...; GOOS=linux go vet
  -tags nogui ./...; GOOS=windows go vet ./...; go build; GOOS=linux go
  build -tags nogui; GOOS=windows go build; go test -tags nogui
  ./internal/gui; gofmt -l: clean.

Not run: a real Wayland compositor (the reporter's Niri) or WebKitGTK
2.54.1 exactly; the unset DPI was injected, not natural. The test skips
without a display, so CI only compiles it.

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yetone committed 2026-10-09 12:10:30 +08:00

1 parent 2018882e47

commit b86001d432

gui: on GTK 3 with no font DPI set, magpie gives GDK one before the first webview, so the window and panel no longer collapse (#1371, haoxianhan)

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