core: button: add HeldPressed and HeldLockedPressed modifier state

The Held state is for modifier that should be off when the corresponding
key is released. If the user presses the modifier key and a normal key,
it would be in this state. The modifier would continue to be active when
the user moves to a different key part (a cancel, e.g. from Fn to Alt)
afterwards. To fix this, add the HeldPressed and HeldLockedPressed
states that reset to the Released state when cancelled.

src/core/button.rs

@@ -29,7 +29,8 @@ use std::time::Instant;
  * modifier would apply to any other key press until it is released, pressed and
  * released again.
  * Finally, it could be held down while another key is being pressed, going
- * Pressed -> Held (or Locked -> HeldLocked) to apply until it is released.
+ * Pressed -> HeldPressed (or Locked -> HeldLockedPressed) to apply until it is
+ * released.
  *
  * When latched, it could go Latched -> Released when any key
  * (including itself) is released.
@@ -44,10 +45,12 @@ use std::time::Instant;
 pub enum ModState {
     Released,
     Pressed,
+    HeldPressed,
     Latched,
     Held,
     Locked,
     HeldLocked,
+    HeldLockedPressed,
 }
 
 #[derive(PartialEq)]
@@ -245,10 +248,10 @@ impl<D: Display, K: Keyboard> Button<D, K> {
             for modifier in 1..=MODIFIERS_MAX {
                 self.update_modifier(modifier,
                                      ModState::Pressed,
-                                     ModState::Held);
+                                     ModState::HeldPressed);
                 self.update_modifier(modifier,
                                      ModState::Locked,
-                                     ModState::HeldLocked);
+                                     ModState::HeldLockedPressed);
             }
         }
 
@@ -359,6 +362,20 @@ impl<D: Display, K: Keyboard> Button<D, K> {
                 draw = draw + DrawOperation::Labels;
             }
 
+            let changed = self.update_modifier(modifier,
+                                               ModState::HeldPressed,
+                                               ModState::Released);
+            if changed && Layout::is_label_modifier(modifier) {
+                draw = draw + DrawOperation::Labels;
+            }
+
+            let changed = self.update_modifier(modifier,
+                                               ModState::HeldLockedPressed,
+                                               ModState::Released);
+            if changed && Layout::is_label_modifier(modifier) {
+                draw = draw + DrawOperation::Labels;
+            }
+
             self.update_modifier(modifier,
                                  ModState::Held,
                                  ModState::Latched);
@@ -440,6 +457,20 @@ impl<D: Display, K: Keyboard> Button<D, K> {
             if changed && Layout::is_label_modifier(modifier) {
                 draw = draw + DrawOperation::Labels;
             }
+
+            let changed = self.update_modifier(modifier,
+                                               ModState::HeldPressed,
+                                               ModState::Released);
+            if changed && Layout::is_label_modifier(modifier) {
+                draw = draw + DrawOperation::Labels;
+            }
+
+            let changed = self.update_modifier(modifier,
+                                               ModState::HeldLockedPressed,
+                                               ModState::Released);
+            if changed && Layout::is_label_modifier(modifier) {
+                draw = draw + DrawOperation::Labels;
+            }
         } else {
             for modifier in 1..=MODIFIERS_MAX {
                 let changed = self.update_modifier(modifier,