macOS: Implement NSTextInputClient (#518)

Fixes #263

src/platform/macos/util.rs

@@ -0,0 +1,38 @@
+use cocoa::appkit::NSWindowStyleMask;
+use cocoa::base::{class, id, nil};
+use cocoa::foundation::{NSRect, NSUInteger};
+use core_graphics::display::CGDisplay;
+
+use platform::platform::ffi;
+use platform::platform::window::IdRef;
+
+pub const EMPTY_RANGE: ffi::NSRange = ffi::NSRange {
+    location: ffi::NSNotFound as NSUInteger,
+    length: 0,
+};
+
+// For consistency with other platforms, this will...
+// 1. translate the bottom-left window corner into the top-left window corner
+// 2. translate the coordinate from a bottom-left origin coordinate system to a top-left one
+pub fn bottom_left_to_top_left(rect: NSRect) -> i32 {
+    (CGDisplay::main().pixels_high() as f64 - (rect.origin.y + rect.size.height)) as _
+}
+
+pub unsafe fn set_style_mask(window: id, view: id, mask: NSWindowStyleMask) {
+    use cocoa::appkit::NSWindow;
+    window.setStyleMask_(mask);
+    // If we don't do this, key handling will break. Therefore, never call `setStyleMask` directly!
+    window.makeFirstResponder_(view);
+}
+
+pub unsafe fn create_input_context(view: id) -> IdRef {
+    let input_context: id = msg_send![class("NSTextInputContext"), alloc];
+    let input_context: id = msg_send![input_context, initWithClient:view];
+    IdRef::new(input_context)
+}
+
+#[allow(dead_code)]
+pub unsafe fn open_emoji_picker() {
+    let app: id = msg_send![class("NSApplication"), sharedApplication];
+    let _: () = msg_send![app, orderFrontCharacterPalette:nil];
+}