wayland: keyboard: Cache text input parameters.

Some applications (and embarrassingly, testime is one of them) call
SDL_StartTextInput() or SDL_SetTextInputRect() every frame. On KDE/KWin
with fcitx5, this causes there to be several preedit events every frame
(particularly given some of the workarounds in Wayland_StartTextInput),
which slows testime down to an unusable crawl.

Instead, make SDL_StartTextInput() a no-op if text input is already
enabled, and cache the input rect, only changing it when the new rect is
actually different.

With these changes, we only get preedit events (and hence
SDL_TEXTEDITING events) when the preedit string actually changes. This
matches the behaviour under XWayland, and works very smoothly.

src/video/wayland/SDL_waylandkeyboard.c

@@ -61,6 +61,10 @@ Wayland_StartTextInput(_THIS)
         if (input != NULL && input->text_input) {
             const SDL_Rect *rect = &input->text_input->cursor_rect;
 
+            /* Don't re-enable if we're already enabled. */
+            if (input->text_input->is_enabled)
+                return;
+
             /* For some reason this has to be done twice, it appears to be a
              * bug in mutter? Maybe?
              * -flibit
@@ -83,6 +87,7 @@ Wayland_StartTextInput(_THIS)
                                                        rect->h);
             }
             zwp_text_input_v3_commit(input->text_input->text_input);
+            input->text_input->is_enabled = SDL_TRUE;
         }
     }
 }
@@ -97,6 +102,7 @@ Wayland_StopTextInput(_THIS)
         if (input != NULL && input->text_input) {
             zwp_text_input_v3_disable(input->text_input->text_input);
             zwp_text_input_v3_commit(input->text_input->text_input);
+            input->text_input->is_enabled = SDL_FALSE;
         }
     }
 
@@ -120,13 +126,16 @@ Wayland_SetTextInputRect(_THIS, const SDL_Rect *rect)
     if (driverdata->text_input_manager) {
         struct SDL_WaylandInput *input = driverdata->input;
         if (input != NULL && input->text_input) {
-            SDL_copyp(&input->text_input->cursor_rect, rect);
-            zwp_text_input_v3_set_cursor_rectangle(input->text_input->text_input,
-                                                   rect->x,
-                                                   rect->y,
-                                                   rect->w,
-                                                   rect->h);
-            zwp_text_input_v3_commit(input->text_input->text_input);
+            if (!SDL_RectEquals(rect, &input->text_input->cursor_rect))
+            {
+                SDL_copyp(&input->text_input->cursor_rect, rect);
+                zwp_text_input_v3_set_cursor_rectangle(input->text_input->text_input,
+                                                       rect->x,
+                                                       rect->y,
+                                                       rect->w,
+                                                       rect->h);
+                zwp_text_input_v3_commit(input->text_input->text_input);
+            }
         }
     }
 

src/video/wayland/SDL_waylandkeyboard.h

@@ -28,6 +28,7 @@ typedef struct SDL_WaylandTextInput
     struct zwp_text_input_v3 *text_input;
     SDL_Rect cursor_rect;
     SDL_bool has_preedit;
+    SDL_bool is_enabled;
 } SDL_WaylandTextInput;
 
 extern int Wayland_InitKeyboard(_THIS);