Fix transparency on X11 (#2006)

* find transparent in x11

* remove debug hooks

* update changelog

* polish and failed to find visual warning

CHANGELOG.md

@@ -1,5 +1,6 @@
 # Unreleased
 
+- On X11, select an appropriate visual for transparency if is requested
 - On Wayland and X11, fix diagonal window resize cursor orientation.
 - On macOS, drop the event callback before exiting.
 - On Android, implement `Window::request_redraw`

src/platform_impl/linux/x11/window.rs

@@ -8,6 +8,7 @@ use std::{
  ptr, slice,
  sync::Arc,
 };
+use x11_dl::xlib::TrueColor;
 
 use libc;
 use mio_misc::channel::Sender;
@@ -180,13 +181,40 @@ impl UnownedWindow {
  };
 
  // creating
+ let (visual, depth) = match pl_attribs.visual_infos {
+ Some(vi) => (vi.visual, vi.depth),
+ None if window_attrs.transparent == true => {
+ // Find a suitable visual
+ let mut vinfo = MaybeUninit::uninit();
+ let vinfo_initialized = unsafe {
+ (xconn.xlib.XMatchVisualInfo)(
+ xconn.display,
+ screen_id,
+ 32,
+ TrueColor,
+ vinfo.as_mut_ptr(),
+ ) != 0
+ };
+ if vinfo_initialized {
+ let vinfo = unsafe { vinfo.assume_init() };
+ (vinfo.visual, vinfo.depth)
+ } else {
+ debug!("Could not set transparency, because XMatchVisualInfo returned zero for the required parameters");
+ (ffi::CopyFromParent as *mut ffi::Visual, ffi::CopyFromParent)
+ }
+ }
+ _ => (ffi::CopyFromParent as *mut ffi::Visual, ffi::CopyFromParent),
+ };
+
  let mut set_win_attr = {
  let mut swa: ffi::XSetWindowAttributes = unsafe { mem::zeroed() };
  swa.colormap = if let Some(vi) = pl_attribs.visual_infos {
  unsafe {
  let visual = vi.visual;
  (xconn.xlib.XCreateColormap)(xconn.display, root, visual, ffi::AllocNone)
  }
+ } else if window_attrs.transparent {
+ unsafe { (xconn.xlib.XCreateColormap)(xconn.display, root, visual, ffi::AllocNone) }
  } else {
  0
  };
@@ -220,23 +248,9 @@ impl UnownedWindow {
  dimensions.0 as c_uint,
  dimensions.1 as c_uint,
  0,
- match pl_attribs.visual_infos {
- Some(vi) => vi.depth,
- None => ffi::CopyFromParent,
- },
+ depth,
  ffi::InputOutput as c_uint,
- // TODO: If window wants transparency and `visual_infos` is None,
- // we need to find our own visual which has an `alphaMask` which
- // is > 0, like we do in glutin.
- //
- // It is non obvious which masks, if any, we should pass to
- // `XGetVisualInfo`. winit doesn't receive any info about what
- // properties the user wants. Users should consider choosing the
- // visual themselves as glutin does.
- match pl_attribs.visual_infos {
- Some(vi) => vi.visual,
- None => ffi::CopyFromParent as *mut ffi::Visual,
- },
+ visual,
  window_attributes,
  &mut set_win_attr,
  )