Big Cursor State Refactor

This makes a few major changes:

  - cursor style on terminal is single source of stylistic truth
  - cursor style is split between style and style request
  - cursor blinking is handled by the renderer thread
  - cursor style/visibility is no longer stored as persistent state on
    renderers
  - cursor style computation is extracted to be shared by all renderers
  - mode 12 "cursor_blinking" is now source of truth on whether blinking
    is enabled or not
  - CSI q and mode 12 are synced like xterm

src/renderer/cursor.zig

@@ -1,19 +1,52 @@
+const std = @import("std");
 const terminal = @import("../terminal/main.zig");
+const State = @import("State.zig");
 
 /// Available cursor styles for drawing that renderers must support.
+/// This is a superset of terminal cursor styles since the renderer supports
+/// some additional cursor states such as the hollow block.
 pub const CursorStyle = enum {
-    box,
-    box_hollow,
+    block,
+    block_hollow,
     bar,
 
     /// Create a cursor style from the terminal style request.
-    pub fn fromTerminal(style: terminal.CursorStyle) ?CursorStyle {
+    pub fn fromTerminal(style: terminal.Cursor.Style) ?CursorStyle {
         return switch (style) {
-            .blinking_block, .steady_block => .box,
-            .blinking_bar, .steady_bar => .bar,
-            .blinking_underline, .steady_underline => null, // TODO
-            .default => .box,
-            else => null,
+            .bar => .bar,
+            .block => .block,
+            .underline => null, // TODO
         };
     }
 };
+
+/// Returns the cursor style to use for the current render state or null
+/// if a cursor should not be rendered at all.
+pub fn cursorStyle(
+    state: *State,
+    focused: bool,
+    blink_visible: bool,
+) ?CursorStyle {
+    // The cursor is only at the bottom of the viewport. If we aren't
+    // at the bottom, we never render the cursor.
+    if (!state.terminal.screen.viewportIsBottom()) return null;
+
+    // If we are in preedit, then we always show the cursor
+    if (state.preedit != null) return .block;
+
+    // If the cursor is explicitly not visible by terminal mode, then false.
+    if (!state.terminal.modes.get(.cursor_visible)) return null;
+
+    // If we're not focused, our cursor is always visible so that
+    // we can show the hollow box.
+    if (!focused) return .block_hollow;
+
+    // If the cursor is blinking and our blink state is not visible,
+    // then we don't show the cursor.
+    if (state.terminal.modes.get(.cursor_blinking) and !blink_visible) {
+        return null;
+    }
+
+    // Otherwise, we use whatever the terminal wants.
+    return CursorStyle.fromTerminal(state.terminal.screen.cursor.style);
+}