Per-monitor HiDPI

Mixed-DPI setups are the norm: a 4K external monitor next to a 1080p laptop, fractional scaling on Linux, Retina mirrored to non-Retina on macOS. The Tao backend tracks each window's current output and reconfigures its render surface every time the scale changes — Compose stays in Dp, the GPU rasterises at the right pixel density.

TL;DR

• Each window has its own scale factor; Tao updates it when the window moves between monitors.
• Compose Dp values stay logical — Skiko rasterises at the per-window pixel density.
• Works on macOS (Retina + display arrangement), Windows (Per-Monitor V2 DPI awareness), Linux Wayland (wp_fractional_scale_v1).
• For X11 sessions, see the linux-hidpi module.

Install

Bundled with decorated-window-tao. No extra opt-in.

How it works

When you open a DecoratedWindow on Tao, the backend queries the active output for its scale factor and configures the Skiko surface accordingly — CAMetalLayer.contentsScale on macOS, the swapchain colour space on Windows, EGL buffer scale on Wayland. The native window receives WindowEvent::ScaleFactorChanged whenever the user drags between displays, plugs in an external monitor, or changes the system scale. Tao forwards that to the ComposeScene, which propagates a new LocalDensity to your composables.

The practical consequence: a Modifier.size(48.dp) is 48 dp on a 1.0 monitor (48 device pixels), 96 dp on a 2.0 monitor (96 device pixels), 72 dp on a 1.5 fractional Wayland output. Your UI doesn't change — only the rasterised output does.

import androidx.compose.runtime.*
import androidx.compose.ui.platform.LocalDensity

@Composable
fun ShowDensity() {
    val density = LocalDensity.current
    Text("Scale: ${density.density}x · font scale: ${density.fontScale}")
}

Differences vs linux-hidpi

linux-hidpi is an X11/AWT helper: it reads the system scale from GSettings / Xft.dpi and applies it to JVM properties before the AWT toolkit boots. It's a single global scale, set once at startup. Use it when you ship the AWT-based JBR / JNI backends on X11 sessions.

The Tao backend doesn't need that helper — it observes per-window scale changes at runtime. When you migrate from JBR to Tao on Linux, you can drop the linux-hidpi dependency.

Reference

• LocalDensity.current — Compose density for the current window.
• Platform.isWayland — distinguishes Wayland (fractional scale supported) from X11.
• WindowState — keep window sizes in Dp, never in pixels.

Notes

• On Windows 10 1607+, Tao declares Per-Monitor V2 DPI awareness via the manifest. The Nucleus Gradle plugin handles the manifest for packaged builds.
• On macOS, Retina backing stores are automatic — no opt-in.
• Fractional scaling on KDE Plasma works on both X11 and Wayland in Tao, but Wayland gives you per-monitor accuracy.