winit/src/platform_impl/windows/dpi.rs

#![allow(non_snake_case, unused_unsafe)]

use std::mem;
use std::os::raw::c_void;
use std::sync::{Once, ONCE_INIT};

use winapi::shared::minwindef::{BOOL, UINT, FALSE};
use winapi::shared::windef::{
    DPI_AWARENESS_CONTEXT,
    DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE,
    HMONITOR,
    HWND,
};
use winapi::shared::winerror::S_OK;
use winapi::um::libloaderapi::{GetProcAddress, LoadLibraryA};
use winapi::um::shellscalingapi::{
    MDT_EFFECTIVE_DPI,
    MONITOR_DPI_TYPE,
    PROCESS_DPI_AWARENESS,
    PROCESS_PER_MONITOR_DPI_AWARE,
};
use winapi::um::wingdi::{GetDeviceCaps, LOGPIXELSX};
use winapi::um::winnt::{HRESULT, LPCSTR};
use winapi::um::winuser::{self, MONITOR_DEFAULTTONEAREST};

const DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2: DPI_AWARENESS_CONTEXT = -4isize as _;

type SetProcessDPIAware = unsafe extern "system" fn () -> BOOL;
type SetProcessDpiAwareness = unsafe extern "system" fn (
    value: PROCESS_DPI_AWARENESS,
) -> HRESULT;
type SetProcessDpiAwarenessContext = unsafe extern "system" fn (
    value: DPI_AWARENESS_CONTEXT,
) -> BOOL;
type GetDpiForWindow = unsafe extern "system" fn (hwnd: HWND) -> UINT;
type GetDpiForMonitor = unsafe extern "system" fn (
    hmonitor: HMONITOR,
    dpi_type: MONITOR_DPI_TYPE,
    dpi_x: *mut UINT,
    dpi_y: *mut UINT,
) -> HRESULT;
type EnableNonClientDpiScaling = unsafe extern "system" fn (hwnd: HWND) -> BOOL;

// Helper function to dynamically load function pointer.
// `library` and `function` must be zero-terminated.
fn get_function_impl(library: &str, function: &str) -> Option<*const c_void> {
    assert_eq!(library.chars().last(), Some('\0'));
    assert_eq!(function.chars().last(), Some('\0'));

    // Library names we will use are ASCII so we can use the A version to avoid string conversion.
    let module = unsafe { LoadLibraryA(library.as_ptr() as LPCSTR) };
    if module.is_null() {
        return None;
    }

    let function_ptr = unsafe { GetProcAddress(module, function.as_ptr() as LPCSTR) };
    if function_ptr.is_null() {
        return None;
    }

    Some(function_ptr as _)
}

macro_rules! get_function {
    ($lib:expr, $func:ident) => {
        get_function_impl(concat!($lib, '\0'), concat!(stringify!($func), '\0'))
            .map(|f| unsafe { mem::transmute::<*const _, $func>(f) })
    }
}

lazy_static! {
    static ref GET_DPI_FOR_WINDOW: Option<GetDpiForWindow> = get_function!(
        "user32.dll",
        GetDpiForWindow
    );
    static ref GET_DPI_FOR_MONITOR: Option<GetDpiForMonitor> = get_function!(
        "shcore.dll",
        GetDpiForMonitor
    );
    static ref ENABLE_NON_CLIENT_DPI_SCALING: Option<EnableNonClientDpiScaling> = get_function!(
        "user32.dll",
        EnableNonClientDpiScaling
    );
}

pub fn become_dpi_aware(enable: bool) {
    if !enable { return; }
    static ENABLE_DPI_AWARENESS: Once = ONCE_INIT;
    ENABLE_DPI_AWARENESS.call_once(|| { unsafe {
        if let Some(SetProcessDpiAwarenessContext) = get_function!(
            "user32.dll",
            SetProcessDpiAwarenessContext
        ) {
            // We are on Windows 10 Anniversary Update (1607) or later.
            if SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2)
            == FALSE {
                // V2 only works with Windows 10 Creators Update (1703). Try using the older
                // V1 if we can't set V2.
                SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE);
            }
        } else if let Some(SetProcessDpiAwareness) = get_function!(
            "shcore.dll",
            SetProcessDpiAwareness
        ) {
            // We are on Windows 8.1 or later.
            SetProcessDpiAwareness(PROCESS_PER_MONITOR_DPI_AWARE);
        } else if let Some(SetProcessDPIAware) = get_function!(
            "user32.dll",
            SetProcessDPIAware
        ) {
            // We are on Vista or later.
            SetProcessDPIAware();
        }
    } });
}

pub fn enable_non_client_dpi_scaling(hwnd: HWND) {
    unsafe {
        if let Some(EnableNonClientDpiScaling) = *ENABLE_NON_CLIENT_DPI_SCALING {
            EnableNonClientDpiScaling(hwnd);
        }
    }
}

pub fn get_monitor_dpi(hmonitor: HMONITOR) -> Option<u32> {
    unsafe {
        if let Some(GetDpiForMonitor) = *GET_DPI_FOR_MONITOR {
            // We are on Windows 8.1 or later.
            let mut dpi_x = 0;
            let mut dpi_y = 0;
            if GetDpiForMonitor(hmonitor, MDT_EFFECTIVE_DPI, &mut dpi_x, &mut dpi_y) == S_OK {
                // MSDN says that "the values of *dpiX and *dpiY are identical. You only need to
                // record one of the values to determine the DPI and respond appropriately".
                // https://msdn.microsoft.com/en-us/library/windows/desktop/dn280510(v=vs.85).aspx
                return Some(dpi_x as u32)
            }
        }
    }
    None
}

pub const BASE_DPI: u32 = 96;
pub fn dpi_to_scale_factor(dpi: u32) -> f64 {
    dpi as f64 / BASE_DPI as f64
}

pub unsafe fn get_hwnd_dpi(hwnd: HWND) -> u32 {
    let hdc = winuser::GetDC(hwnd);
    if hdc.is_null() {
        panic!("[winit] `GetDC` returned null!");
    }
    if let Some(GetDpiForWindow) = *GET_DPI_FOR_WINDOW {
        // We are on Windows 10 Anniversary Update (1607) or later.
        match GetDpiForWindow(hwnd) {
            0 => BASE_DPI, // 0 is returned if hwnd is invalid
            dpi => dpi as u32,
        }
    } else if let Some(GetDpiForMonitor) = *GET_DPI_FOR_MONITOR {
        // We are on Windows 8.1 or later.
        let monitor = winuser::MonitorFromWindow(hwnd, MONITOR_DEFAULTTONEAREST);
        if monitor.is_null() {
            return BASE_DPI;
        }

        let mut dpi_x = 0;
        let mut dpi_y = 0;
        if GetDpiForMonitor(monitor, MDT_EFFECTIVE_DPI, &mut dpi_x, &mut dpi_y) == S_OK {
            dpi_x as u32
        } else {
            BASE_DPI
        }
    } else {
        // We are on Vista or later.
        if winuser::IsProcessDPIAware() != FALSE {
            // If the process is DPI aware, then scaling must be handled by the application using
            // this DPI value.
            GetDeviceCaps(hdc, LOGPIXELSX) as u32
        } else {
            // If the process is DPI unaware, then scaling is performed by the OS; we thus return
            // 96 (scale factor 1.0) to prevent the window from being re-scaled by both the
            // application and the WM.
            BASE_DPI
        }
    }
}

pub fn get_hwnd_scale_factor(hwnd: HWND) -> f64 {
    dpi_to_scale_factor(unsafe { get_hwnd_dpi(hwnd) })
}