Three live bug reports after a restart: icon drag, lock cursor, lock box

All three reported directly after the owner restarted into today's build.

Desktop icons could not be dragged at all in single-click mode. The press
handler opened the icon immediately when general.desktop_icon_single_click
was on, so the branch that starts a drag was unreachable and an icon could
never be moved. Deciding activation on press cannot distinguish a click from
the first instant of a drag. Every press on an icon now starts a potential
drag and release decides which it was, using a 4px movement threshold that
latches once exceeded. Double-click mode goes through the same path, so both
modes now drag identically.

The lock screen drew no cursor. The cursor push in the udev render loop sits
inside `if !locked`, and a locked head renders only the lock element list, so
nothing drew a pointer - and on a bare TTY nothing else does. The on-screen
keyboard's clicks were being handled correctly the whole time
(native_lock_click); they simply could not be aimed. The pointer is now
prepended to the lock element list, above the UI it is used to click.

The password field's opaque panel is gone. New LockConfig::box_opacity,
default 0.0: no fill, no border, no rounded rectangle, just the dots and
status text over the blurred background. Raising it restores the panel at
that opacity for anyone who wants a solid field. Drawing text on a
transparent surface needed a new blit_glyph_over: the existing blit_glyph
blends against one flat opaque colour and writes alpha 255, which would have
turned every glyph into a block of the assumed background - the same box
with its middle removed.

VERIFICATION STATUS, stated plainly: all three are code-complete and the
suite passes, but none is confirmed on screen. The nested backend's capture
pass does not draw the desktop icon grid (a gap already recorded in
winit/capture.rs), so the icon drag cannot be checked by screenshot there,
and aiming blind is what this project's own rules forbid. The two lock
changes were not visually checked either.

515 tests pass, clippy clean.

1 files changed, 25 insertions, 6 deletions

diff --git a/crates/wayland/src/native_lock.rs b/crates/wayland/src/native_lock.rs
index 14c4f21..96e4ac9 100644
--- a/crates/wayland/src/native_lock.rs
+++ b/crates/wayland/src/native_lock.rs
@@ -780,14 +780,22 @@ fn render_header_box(native: &NativeLock, theme: &srdwm_core::LockConfig) -> (Ve
 /// `rgb_to_bgra`), promoted to `pub(crate)` there rather than duplicated
 /// here.
 fn render_ui_box(native: &NativeLock, theme: &srdwm_core::LockConfig) -> (Vec<u8>, (i32, i32)) {
-    use crate::decoration::{blit_glyph, find_system_font, rgb_to_bgra, round_bottom_corners, round_top_corners, FONT_PIXELS, TEXT_LEFT_PADDING};
+    use crate::decoration::{blit_glyph_over, find_system_font, rgb_to_bgra, round_bottom_corners, round_top_corners, FONT_PIXELS, TEXT_LEFT_PADDING};
 
     const WIDTH: usize = 340;
     const HEIGHT: usize = 120;
     let mut buf = vec![0u8; WIDTH * HEIGHT * 4];
-    let bg = rgb_to_bgra(theme.box_bg, 255);
-    for px in buf.chunks_exact_mut(4) {
-        px.copy_from_slice(&bg);
+    // `box_opacity` 0 (the default) leaves the buffer fully transparent, so
+    // the dots and status text sit straight on the blurred background with
+    // no panel behind them at all - see `LockConfig::box_opacity`. Above
+    // 0 the panel comes back at that opacity, border and rounded corners
+    // included, exactly as it used to look at 1.0.
+    let panel_alpha = (theme.box_opacity.clamp(0.0, 1.0) * 255.0).round() as u8;
+    if panel_alpha > 0 {
+        let bg = rgb_to_bgra(theme.box_bg, panel_alpha);
+        for px in buf.chunks_exact_mut(4) {
+            px.copy_from_slice(&bg);
+        }
     }
 
     let font = find_system_font();
@@ -814,7 +822,7 @@ fn render_ui_box(native: &NativeLock, theme: &srdwm_core::LockConfig) -> (Vec<u8
             if metrics.width > 0 && metrics.height > 0 {
                 let glyph_x = pen_x + metrics.xmin as f32;
                 let glyph_y = y - metrics.height as f32 - metrics.ymin as f32;
-                blit_glyph(&mut buf, WIDTH, HEIGHT, glyph_x.round() as i32, glyph_y.round() as i32, &metrics, &coverage, theme.box_bg, color);
+                blit_glyph_over(&mut buf, WIDTH, HEIGHT, glyph_x.round() as i32, glyph_y.round() as i32, &metrics, &coverage, color);
             }
             pen_x += metrics.advance_width;
         }
@@ -827,7 +835,11 @@ fn render_ui_box(native: &NativeLock, theme: &srdwm_core::LockConfig) -> (Vec<u8
     // (GNOME, macOS): dimmer than the real text colour, never mistakable
     // for an actual password once one is entered.
     if native.password.is_empty() && !native.show_error {
-        let placeholder = crate::decoration::mix_rgb(theme.text_color, theme.box_bg, 0.5);
+        // Dimmed toward the panel colour when there is a panel, and toward
+        // plain black otherwise - mixing toward a background that is not
+        // actually drawn would tint the placeholder for no visible reason.
+        let toward = if panel_alpha > 0 { theme.box_bg } else { (0, 0, 0) };
+        let placeholder = crate::decoration::mix_rgb(theme.text_color, toward, 0.5);
         draw_line_centered("Enter Password", 65.0, placeholder);
     } else {
         let dots: String = std::iter::repeat_n(theme.dot_char, native.password.chars().count()).collect();
@@ -850,6 +862,13 @@ fn render_ui_box(native: &NativeLock, theme: &srdwm_core::LockConfig) -> (Vec<u8
     // this box's size read as a thin, easy-to-miss hairline rather than a
     // deliberate frame around the box.
     const BORDER: usize = 2;
+    // Border and corner rounding belong to the panel: with no panel there
+    // is nothing to frame, and a floating rounded outline around bare text
+    // is the "horrendus box" with its middle removed rather than the box
+    // gone.
+    if panel_alpha == 0 {
+        return (buf, (WIDTH as i32, HEIGHT as i32));
+    }
     let border_px = rgb_to_bgra(theme.box_border, 255);
     for t in 0..BORDER {
         for x in 0..WIDTH {