DPI for everyone (#548)

src/platform/windows/dpi.rs

@@ -0,0 +1,196 @@
+#![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,
+    HDC,
+    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_window_dpi(hwnd: HWND, hdc: HDC) -> u32 {
+    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
+        }
+    }
+}
+
+// Use this when you have both the HWND and HDC on hand (i.e. window methods)
+pub fn get_window_scale_factor(hwnd: HWND, hdc: HDC) -> f64 {
+    dpi_to_scale_factor(unsafe { get_window_dpi(hwnd, hdc) })
+}
+
+// Use this when you only have the HWND (i.e. event handling)
+pub fn get_hwnd_scale_factor(hwnd: HWND) -> f64 {
+    let hdc = unsafe { winuser::GetDC(hwnd) };
+    if hdc.is_null() {
+        panic!("[winit] `GetDC` returned null!");
+    }
+    unsafe { get_window_scale_factor(hwnd, hdc) }
+}