Allow the user to control the draw strategy during OS window resizes

Changed the default to scaled which matches current macOS behavior.
Fixes #1591

docs/changelog.rst

@@ -34,8 +34,9 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
 - Allow specifying a value of ``none`` for the :opt:`selection_foreground`
   which will cause kitty to not change text color in selections (:iss:`1358`)
 
-- Make live resizing of OS windows smoother and show the size in cells
-  while the resize is in progress.
+- Make live resizing of OS windows smoother and add an option
+  :opt:`resize_draw_strategy` to control what is drawn while a
+  resize is in progress.
 
 - macOS: Improve handling of IME extended input. Compose characters
   are now highlighted and the IME panel moves along with the text

kitty/child-monitor.c

@@ -684,14 +684,14 @@ render(double now) {
             continue;
         }
         make_os_window_context_current(w);
-        if (w->live_resize.in_progress) {
+        if (OPT(resize_draw_strategy) != RESIZE_DRAW_SCALED && w->live_resize.in_progress) {
             blank_os_window(w);
-            draw_resizing_text(w);
+            if (OPT(resize_draw_strategy) == RESIZE_DRAW_SIZE) draw_resizing_text(w);
             swap_window_buffers(w);
             if (USE_RENDER_FRAMES) request_frame_render(w);
             continue;
         }
-        bool needs_render = w->is_damaged;
+        bool needs_render = w->is_damaged || w->live_resize.in_progress;
         if (w->viewport_size_dirty) {
             w->clear_count = 0;
             update_surface_size(w->viewport_width, w->viewport_height, w->offscreen_texture_id);

kitty/config_data.py

@@ -609,6 +609,20 @@ def to_layout_names(raw):
 resize event is received. On platforms such as macOS, where the
 operating system sends event corresponding to the start and end
 of a resize, this number is ignored.'''))
+
+
+def resize_draw_strategy(x):
+    cmap = {'scale': 0, 'blank': 1, 'size': 2}
+    return cmap.get(x.lower(), 0)
+
+
+o('resize_draw_strategy', 'scale', option_type=resize_draw_strategy, long_text=_('''
+Choose how kitty draws a window while a resize is in progress. A
+value of :code:`scale` means draw the current window contents scaled.
+A value of :code:`blank` means draw a blank window.
+A value of :code:`size` means show the window size in cells.
+'''))
+
 # }}}
 
 g('tabbar')   # {{{

kitty/state.c

@@ -410,6 +410,7 @@ PYWRAP1(set_options) {
     S(macos_thicken_font, PyFloat_AsDouble);
     S(tab_bar_min_tabs, PyLong_AsUnsignedLong);
     S(disable_ligatures, PyLong_AsLong);
+    S(resize_draw_strategy, PyLong_AsLong);
 
     GA(tab_bar_style);
     global_state.tab_bar_hidden = PyUnicode_CompareWithASCIIString(ret, "hidden") == 0 ? true: false;

kitty/state.h

@@ -11,6 +11,7 @@
 #define OPT(name) global_state.opts.name
 
 typedef enum { LEFT_EDGE, TOP_EDGE, RIGHT_EDGE, BOTTOM_EDGE } Edge;
+typedef enum { RESIZE_DRAW_SCALED, RESIZE_DRAW_BLANK, RESIZE_DRAW_SIZE } ResizeDrawStrategy;
 
 typedef struct {
     double visual_bell_duration, cursor_blink_interval, cursor_stop_blinking_after, mouse_hide_wait, click_interval, wheel_scroll_multiplier, touch_scroll_multiplier;
@@ -36,6 +37,7 @@ typedef struct {
     Edge tab_bar_edge;
     unsigned long tab_bar_min_tabs;
     DisableLigature disable_ligatures;
+    ResizeDrawStrategy resize_draw_strategy;
     bool sync_to_monitor;
     bool close_on_child_death;
     bool window_alert_on_bell;