Revert "Enable syncing of redraws to monitor refresh rate"

This reverts commit 6a51096304.
Turns out that dynamically changing the swap interval causes bad flicker
when rendering on X11 in a fullscreen window (or more generally, when
only a single X11 window is visible).

README.asciidoc

@@ -348,15 +348,6 @@ glyph in video RAM so that font rendering is not a bottleneck.  Interaction
 with child programs takes place in a separate thread from rendering, to improve
 smoothness.
 
-kitty goes to great lengths to reduce latency. In order to minimize latency,
-kitty dynamically decides whether to sync updates to the monitor refresh rate
-or not. When doing latency sensitive activities such as typing or selecting
-with the mouse, kitty does not sync to the monitor refresh rate, as that limits
-latency to a minimum of `17ms` for common monitors. However, when
-scrolling or making other large scale changes to the screen, kitty syncs to the
-monitor refresh rate, to avoid
-link:https://en.wikipedia.org/wiki/Screen_tearing[screen tearing].
-
 There are two parameters you can tune to adjust the performance. ``repaint_delay``
 and ``input_delay``. These control the artificial delays introduced into the
 render loop to reduce CPU usage. See the link:kitty/kitty.conf[config file] for details.

kitty/child-monitor.c

@@ -605,7 +605,6 @@ render_os_window(OSWindow *os_window, double now, unsigned int active_window_id)
     Tab *tab = os_window->tabs + os_window->active_tab;
     BorderRects *br = &tab->border_rects;
     draw_borders(br->vao_idx, br->num_border_rects, br->rect_buf, br->is_dirty, os_window->viewport_width, os_window->viewport_height);
-    bool needs_vsync = false;
     if (TD.screen && os_window->num_tabs > 1) draw_cells(TD.vao_idx, 0, TD.xstart, TD.ystart, TD.dx, TD.dy, TD.screen, os_window, true);
     for (unsigned int i = 0; i < tab->num_windows; i++) {
         Window *w = tab->windows + i;
@@ -619,11 +618,9 @@ render_os_window(OSWindow *os_window, double now, unsigned int active_window_id)
                 double bell_left = global_state.opts.visual_bell_duration - (now - WD.screen->start_visual_bell_at);
                 set_maximum_wait(bell_left);
             }
-            if (!needs_vsync && (WD.screen->render_activity.large_change || WD.screen->render_activity.chars_written > 100)) needs_vsync = true;
-            WD.screen->render_activity.large_change = false; WD.screen->render_activity.chars_written = 0;
         }
     }
-    swap_window_buffers(os_window, needs_vsync);
+    swap_window_buffers(os_window);
     br->is_dirty = false;
     os_window->last_active_tab = os_window->active_tab; os_window->last_num_tabs = os_window->num_tabs; os_window->last_active_window_id = active_window_id;
     os_window->focused_at_last_render = os_window->is_focused;

kitty/glfw.c

@@ -626,11 +626,7 @@ hide_mouse(OSWindow *w) {
 }
 
 void
-swap_window_buffers(OSWindow *w, bool needs_vsync) {
+swap_window_buffers(OSWindow *w) {
-    if (needs_vsync != w->vsync_enabled) {
-        glfwSwapInterval(needs_vsync ? 1 : 0);
-        w->vsync_enabled = needs_vsync;
-    }
     glfwSwapBuffers(w->handle);
 }
 
@@ -743,7 +739,7 @@ os_window_swap_buffers(PyObject UNUSED *self, PyObject *args) {
     for (size_t i = 0; i < global_state.num_os_windows; i++) {
         OSWindow *w = global_state.os_windows + i;
         if (w->id == os_window_id) {
-            swap_window_buffers(w, false); Py_RETURN_NONE;
+            swap_window_buffers(w); Py_RETURN_NONE;
         }
     }
     PyErr_SetString(PyExc_ValueError, "no such OSWindow");

kitty/screen.c

@@ -123,7 +123,6 @@ screen_reset(Screen *self) {
     init_tabstops(self->alt_tabstops, self->columns);
     cursor_reset(self->cursor);
     self->is_dirty = true;
-    self->render_activity.large_change = true;
     screen_cursor_position(self, 1, 1);
     set_dynamic_color(self, 110, NULL);
     set_dynamic_color(self, 111, NULL);
@@ -203,7 +202,6 @@ screen_resize(Screen *self, unsigned int lines, unsigned int columns) {
         self->cursor->y = num_content_lines;
         if (self->cursor->y >= self->lines) { self->cursor->y = self->lines - 1; screen_index(self); }
     }
-    self->render_activity.large_change = true;
     return true;
 }
 
@@ -356,7 +354,6 @@ screen_draw(Screen *self, uint32_t och) {
         line_right_shift(self->linebuf->line, self->cursor->x, char_width);
     }
     line_set_char(self->linebuf->line, self->cursor->x, ch, char_width, self->cursor, false);
-    self->render_activity.chars_written += 1;
     self->cursor->x++;
     if (char_width == 2) {
         line_set_char(self->linebuf->line, self->cursor->x, 0, 0, self->cursor, true);
@@ -491,7 +488,6 @@ screen_toggle_screen_buffer(Screen *self) {
     }
     screen_history_scroll(self, SCROLL_FULL, false);
     self->is_dirty = true;
-    self->render_activity.large_change = true;
 }
 
 void screen_normal_keypad_mode(Screen UNUSED *self) {} // Not implemented as this is handled by the GUI
@@ -728,8 +724,7 @@ screen_cursor_to_column(Screen *self, unsigned int column) {
         self->history_line_added_count++; \
     } \
     linebuf_clear_line(self->linebuf, bottom); \
-    self->is_dirty = true; \
+    self->is_dirty = true;
-    self->render_activity.large_change = true;
 
 void
 screen_index(Screen *self) {
@@ -754,8 +749,7 @@ screen_scroll(Screen *self, unsigned int count) {
     linebuf_reverse_index(self->linebuf, top, bottom); \
     linebuf_clear_line(self->linebuf, top); \
     INDEX_GRAPHICS(1) \
-    self->is_dirty = true; \
+    self->is_dirty = true;
-    self->render_activity.large_change = true;
 
 void
 screen_reverse_index(Screen *self) {
@@ -980,7 +974,6 @@ screen_erase_in_display(Screen *self, unsigned int how, bool private) {
             linebuf_mark_line_dirty(self->linebuf, i);
         }
         self->is_dirty = true;
-        self->render_activity.large_change = true;
     }
     if (how != 2) {
         screen_erase_in_line(self, how, private);
@@ -990,7 +983,6 @@ screen_erase_in_display(Screen *self, unsigned int how, bool private) {
         if (self->scrolled_by != 0) {
             self->scrolled_by = 0;
             self->scroll_changed = true;
-            self->render_activity.large_change = true;
         }
     }
 }
@@ -1002,7 +994,6 @@ screen_insert_lines(Screen *self, unsigned int count) {
     if (top <= self->cursor->y && self->cursor->y <= bottom) {
         linebuf_insert_lines(self->linebuf, count, self->cursor->y, bottom);
         self->is_dirty = true;
-        self->render_activity.large_change = true;
         screen_carriage_return(self);
     }
 }
@@ -1014,7 +1005,6 @@ screen_delete_lines(Screen *self, unsigned int count) {
     if (top <= self->cursor->y && self->cursor->y <= bottom) {
         linebuf_delete_lines(self->linebuf, count, self->cursor->y, bottom);
         self->is_dirty = true;
-        self->render_activity.large_change = true;
         screen_carriage_return(self);
     }
 }
@@ -1712,7 +1702,6 @@ screen_history_scroll(Screen *self, int amt, bool upwards) {
     if (new_scroll != self->scrolled_by) {
         self->scrolled_by = new_scroll;
         self->scroll_changed = true;
-        self->render_activity.large_change = true;
         return true;
     }
     return false;

kitty/screen.h

@@ -51,12 +51,6 @@ typedef struct {
 } SavemodesBuffer;
 
 
-typedef struct {
-    bool large_change;
-    unsigned int chars_written;
-} RenderActivitity;
-
-
 typedef struct {
     PyObject_HEAD
 
@@ -90,7 +84,6 @@ typedef struct {
     pthread_mutex_t read_buf_lock, write_buf_lock;
 
     CursorRenderInfo cursor_render_info;
-    RenderActivitity render_activity;
 
 } Screen;
 

kitty/state.h

@@ -114,7 +114,6 @@ typedef struct {
     bool is_damaged;
     uint32_t offscreen_texture_id;
     unsigned int clear_count;
-    bool vsync_enabled;
 } OSWindow;
 
 
@@ -157,7 +156,7 @@ bool should_os_window_be_rendered(OSWindow* w);
 void set_dpi_from_os_window(OSWindow *w);
 void wakeup_main_loop();
 void event_loop_wait(double timeout);
-void swap_window_buffers(OSWindow *w, bool);
+void swap_window_buffers(OSWindow *w);
 void make_window_context_current(OSWindow *w);
 void hide_mouse(OSWindow *w);
 void destroy_os_window(OSWindow *w);