Transparent background for tooltips, dropdowns etc.

druid-shell/src/platform/gtk/window.rs

@@ -116,6 +116,7 @@ pub(crate) struct WindowBuilder {
     min_size: Option<Size>,
     resizable: bool,
     show_titlebar: bool,
+    transparent: bool,
 }
 
 #[derive(Clone)]
@@ -137,6 +138,7 @@ pub(crate) struct WindowState {
     window: ApplicationWindow,
     scale: Cell<Scale>,
     area: Cell<ScaledArea>,
+    is_transparent: Cell<bool>,
     /// Used to determine whether to honor close requests from the system: we inhibit them unless
     /// this is true, and this gets set to true when our client requests a close.
     closing: Cell<bool>,
@@ -180,6 +182,7 @@ impl WindowBuilder {
             min_size: None,
             resizable: true,
             show_titlebar: true,
+            transparent: false,
         }
     }
 
@@ -203,6 +206,10 @@ impl WindowBuilder {
         self.show_titlebar = show_titlebar;
     }
 
+    pub fn set_transparent(&mut self, transparent: bool) {
+        self.transparent = transparent;
+    }
+
     pub fn set_position(&mut self, position: Point) {
         self.position = Some(position);
     }
@@ -232,7 +239,16 @@ impl WindowBuilder {
 
         window.set_title(&self.title);
         window.set_resizable(self.resizable);
+        window.set_app_paintable(true);
         window.set_decorated(self.show_titlebar);
+        let mut can_transparent = false;
+        if self.transparent {
+            if let Some(screen) = window.get_screen() {
+                let visual = screen.get_rgba_visual();
+                can_transparent = visual.is_some();
+                window.set_visual(visual.as_ref());
+            }
+        }
 
         // Get the scale factor based on the GTK reported DPI
         let scale_factor =
@@ -254,6 +270,7 @@ impl WindowBuilder {
             window,
             scale: Cell::new(scale),
             area: Cell::new(area),
+            is_transparent: Cell::new(self.transparent & can_transparent),
             closing: Cell::new(false),
             drawing_area,
             surface: RefCell::new(None),
@@ -409,6 +426,19 @@ impl WindowBuilder {
             Inhibit(false)
         }));
 
+        win_state.drawing_area.connect_screen_changed(
+            clone!(handle => move |widget, _prev_screen| {
+                if let Some(state) = handle.state.upgrade() {
+
+                    if let Some(screen) = widget.get_screen(){
+                        let visual = screen.get_rgba_visual();
+                        state.is_transparent.set(visual.is_some());
+                        widget.set_visual(visual.as_ref());
+                    }
+                }
+            }),
+        );
+
         win_state.drawing_area.connect_button_press_event(clone!(handle => move |_widget, event| {
             if let Some(state) = handle.state.upgrade() {
                 state.with_handler(|handler| {
@@ -712,7 +742,11 @@ impl WindowState {
             *surface = None;
 
             if let Some(w) = self.drawing_area.get_window() {
-                *surface = w.create_similar_surface(cairo::Content::Color, width, height);
+                if self.is_transparent.get() {
+                    *surface = w.create_similar_surface(cairo::Content::ColorAlpha, width, height);
+                } else {
+                    *surface = w.create_similar_surface(cairo::Content::Color, width, height);
+                }
                 if surface.is_none() {
                     return Err(anyhow!("create_similar_surface failed"));
                 }

druid-shell/src/platform/mac/window.rs

@@ -24,8 +24,8 @@ use std::time::Instant;
 
 use block::ConcreteBlock;
 use cocoa::appkit::{
-    CGFloat, NSApp, NSApplication, NSAutoresizingMaskOptions, NSBackingStoreBuffered, NSEvent,
-    NSView, NSViewHeightSizable, NSViewWidthSizable, NSWindow, NSWindowStyleMask,
+    CGFloat, NSApp, NSApplication, NSAutoresizingMaskOptions, NSBackingStoreBuffered, NSColor,
+    NSEvent, NSView, NSViewHeightSizable, NSViewWidthSizable, NSWindow, NSWindowStyleMask,
 };
 use cocoa::base::{id, nil, BOOL, NO, YES};
 use cocoa::foundation::{
@@ -119,6 +119,7 @@ pub(crate) struct WindowBuilder {
     window_state: Option<WindowState>,
     resizable: bool,
     show_titlebar: bool,
+    transparent: bool,
 }
 
 #[derive(Clone)]
@@ -170,6 +171,7 @@ impl WindowBuilder {
             window_state: None,
             resizable: true,
             show_titlebar: true,
+            transparent: false,
         }
     }
 
@@ -193,6 +195,10 @@ impl WindowBuilder {
         self.show_titlebar = show_titlebar;
     }
 
+    pub fn set_transparent(&mut self, transparent: bool) {
+        self.transparent = transparent;
+    }
+
     pub fn set_level(&mut self, level: WindowLevel) {
         self.level = Some(level);
     }
@@ -246,6 +252,11 @@ impl WindowBuilder {
                 window.setContentMinSize_(size);
             }
 
+            if self.transparent {
+                window.setOpaque_(NO);
+                window.setBackgroundColor_(NSColor::clearColor(nil));
+            }
+
             window.setTitle_(make_nsstring(&self.title));
 
             let (view, idle_queue) = make_view(self.handler.expect("view"));

druid-shell/src/platform/web/window.rs

@@ -357,6 +357,10 @@ impl WindowBuilder {
         // Ignored
     }
 
+    pub fn set_transparent(&mut self, _transparent: bool) {
+        // Ignored
+    }
+
     pub fn set_position(&mut self, _position: Point) {
         // Ignored
     }

druid-shell/src/platform/windows/paint.rs

@@ -46,6 +46,7 @@ pub(crate) unsafe fn create_render_target_dxgi(
     d2d_factory: &D2DFactory,
     swap_chain: *mut IDXGISwapChain1,
     scale: Scale,
+    transparent: bool,
 ) -> Result<DxgiSurfaceRenderTarget, Error> {
     let mut buffer: *mut IDXGISurface = null_mut();
     as_result((*swap_chain).GetBuffer(
@@ -57,7 +58,11 @@ pub(crate) unsafe fn create_render_target_dxgi(
         _type: D2D1_RENDER_TARGET_TYPE_DEFAULT,
         pixelFormat: D2D1_PIXEL_FORMAT {
             format: DXGI_FORMAT_B8G8R8A8_UNORM,
-            alphaMode: D2D1_ALPHA_MODE_IGNORE,
+            alphaMode: if transparent {
+                D2D1_ALPHA_MODE_PREMULTIPLIED
+            } else {
+                D2D1_ALPHA_MODE_IGNORE
+            },
         },
         dpiX: (scale.x() * SCALE_TARGET_DPI) as f32,
         dpiY: (scale.y() * SCALE_TARGET_DPI) as f32,

druid-shell/src/platform/windows/util.rs

@@ -24,6 +24,9 @@ use std::ptr;
 use std::slice;
 
 use lazy_static::lazy_static;
+use winapi::ctypes::c_void;
+use winapi::shared::dxgi::IDXGIDevice;
+use winapi::shared::guiddef::REFIID;
 use winapi::shared::minwindef::{BOOL, HMODULE, UINT};
 use winapi::shared::ntdef::{HRESULT, LPWSTR};
 use winapi::shared::windef::{HMONITOR, HWND, RECT};
@@ -147,6 +150,11 @@ type GetSystemMetricsForDpi =
 // from shcore.dll
 type GetDpiForMonitor = unsafe extern "system" fn(HMONITOR, MONITOR_DPI_TYPE, *mut UINT, *mut UINT);
 type SetProcessDpiAwareness = unsafe extern "system" fn(PROCESS_DPI_AWARENESS) -> HRESULT;
+type DCompositionCreateDevice = unsafe extern "system" fn(
+    dxgiDevice: *const IDXGIDevice,
+    iid: REFIID,
+    dcompositionDevice: *mut *mut c_void,
+) -> HRESULT;
 
 #[allow(non_snake_case)] // For member fields
 pub struct OptionalFunctions {
@@ -156,6 +164,7 @@ pub struct OptionalFunctions {
     pub GetDpiForMonitor: Option<GetDpiForMonitor>,
     pub SetProcessDpiAwareness: Option<SetProcessDpiAwareness>,
     pub GetSystemMetricsForDpi: Option<GetSystemMetricsForDpi>,
+    pub DCompositionCreateDevice: Option<DCompositionCreateDevice>,
 }
 
 #[allow(non_snake_case)] // For local variables
@@ -201,13 +210,15 @@ fn load_optional_functions() -> OptionalFunctions {
 
     let shcore = load_library("shcore.dll");
     let user32 = load_library("user32.dll");
+    let dcomp = load_library("dcomp.dll");
 
     let mut GetDpiForSystem = None;
     let mut GetDpiForMonitor = None;
     let mut GetDpiForWindow = None;
     let mut SetProcessDpiAwarenessContext = None;
     let mut SetProcessDpiAwareness = None;
     let mut GetSystemMetricsForDpi = None;
+    let mut DCompositionCreateDevice = None;
 
     if shcore.is_null() {
         tracing::info!("No shcore.dll");
@@ -225,13 +236,20 @@ fn load_optional_functions() -> OptionalFunctions {
         load_function!(user32, GetSystemMetricsForDpi, "10");
     }
 
+    if dcomp.is_null() {
+        tracing::info!("No dcomp.dll");
+    } else {
+        load_function!(dcomp, DCompositionCreateDevice, "8.1");
+    }
+
     OptionalFunctions {
         GetDpiForSystem,
         GetDpiForWindow,
         SetProcessDpiAwarenessContext,
         GetDpiForMonitor,
         SetProcessDpiAwareness,
         GetSystemMetricsForDpi,
+        DCompositionCreateDevice,
     }
 }