Display component

Implemented: Symbian::Display exports ReadPrimaryDisplayGeometry() in <symbian/api/display/display.h> and a resident control panel in <symbian/api/display/resident_panel.h>.

Motivation and modernization

The original HAL returns individual integer attributes. The adapter combines the two required pixel dimensions into one DisplayGeometry value and keeps physical twip dimensions as independent std::optional<int> values. This prevents one failed attribute from silently becoming zero or a guessed DPI. absl::StatusOr rejects nonpositive pixel geometry. The type describes HAL geometry only: a Window Server layout may differ after rotation.

Ownership and cost

native_display.cc contains the legacy HAL include; public code sees ordinary C++ values. Four small synchronous HAL reads need no Window Server connection, heap buffer or long-lived session. Results are not cached because a display profile can change. A caller that cannot tolerate those calls on an event thread can run the query on a worker.

Choose an initial grid density

Link Symbian::Display. Use the primary width to choose an initial thumbnail column count; confirm the actual client rectangle with Window Server when the window opens or its size changes.

#include <algorithm>

#include "symbian/api/display/display.h"

absl::StatusOr<int> InitialThumbnailColumns() {
  auto screen = symbian::api::display::ReadPrimaryDisplayGeometry();
  if (!screen.ok()) {
    return screen.status();
  }
  return std::clamp(screen->width_pixels / 160, 1, 3);
}

This uses pixel geometry rather than inventing a DPI from missing twip fields.

Resident control panel

RunResidentPanel creates a minimal Window Server view for a manually started background service. The app supplies a UID, caption, short uppercase labels, and a property identity; the SDK owns the window session, rendering, and foreground signal. BACK lowers the panel while the service keeps running. STOP sets the shared atomic stop flag; the service then signals its active loop. A second app launch may call RequestResidentPanelForeground to bring the existing view back. Run the panel on a separate guest thread so the service thread can continue accepting connections. This is a small built-in UI, with a limited bitmap alphabet and fixed layout, rather than a general widget kit. An optional heading_provider supplies a static label for changing service state. The panel calls it on the Window Server thread and checks for a new label on its existing wake timer, redrawing only after a change. Return immutable strings that remain valid until the panel closes; share the state with a worker through an atomic value.

Restrictions

The geometry query is a snapshot. It does not subscribe to orientation or size-change notifications and does not enumerate multiple screens.

For an application window, use the Window Server counter or the Symbian Qt button. The Qt example requires guest Qt 4.8.1 and uses raster graphics and Plastique in the emulator; the host emulator's desktop Qt libraries do not supply guest widgets.