Automatically adjust cell height when DPI changes

DPI changes are detected as a change in the ration of the window size to
the framebuffer size. I dont know how reliable that is. Possiblly Fix #77

kitty/boss.py

@@ -11,8 +11,8 @@ from .constants import appname, set_boss, wakeup
 from .fast_data_types import (
     ChildMonitor, create_os_window, current_os_window, destroy_global_data,
     destroy_sprite_map, get_clipboard_string, glfw_post_empty_event,
-    layout_sprite_map, mark_os_window_for_close, show_window,
-    toggle_fullscreen, viewport_for_window
+    layout_sprite_map, mark_os_window_for_close, set_dpi_from_os_window,
+    show_window, toggle_fullscreen, viewport_for_window
 )
 from .fonts.render import prerender, resize_fonts, set_font_family
 from .keys import get_shortcut
@@ -162,10 +162,16 @@ class Boss:
         if tm is not None:
             tm.activate_tab_at(x)
 
-    def on_window_resize(self, os_window_id, w, h):
+    def on_window_resize(self, os_window_id, w, h, dpi_changed):
         tm = self.os_window_map.get(os_window_id)
         if tm is not None:
-            tm.resize()
+            if dpi_changed:
+                if set_dpi_from_os_window(os_window_id):
+                    self.on_dpi_change(os_window_id)
+                else:
+                    tm.resize()
+            else:
+                tm.resize()
 
     def increase_font_size(self):
         self.change_font_size(
@@ -182,10 +188,9 @@ class Boss:
     def restore_font_size(self):
         self.change_font_size(self.opts.font_size)
 
-    def change_font_size(self, new_size):
-        if new_size == self.current_font_size:
-            return
-        self.current_font_size = new_size
+    def _change_font_size(self, new_size=None):
+        if new_size is not None:
+            self.current_font_size = new_size
         old_cell_width, old_cell_height = viewport_for_window()[-2:]
         windows = tuple(filter(None, self.window_id_map.values()))
         resize_fonts(self.current_font_size)
@@ -199,6 +204,14 @@ class Boss:
             tm.refresh_sprite_positions()
         glfw_post_empty_event()
 
+    def change_font_size(self, new_size):
+        if new_size == self.current_font_size:
+            return
+        self._change_font_size(new_size)
+
+    def on_dpi_change(self, os_window_id):
+        self._change_font_size()
+
     @property
     def active_tab_manager(self):
         os_window_id = current_os_window()

kitty/glfw.c

@@ -21,12 +21,14 @@ update_os_window_viewport(OSWindow *window, bool notify_boss) {
     int w, h;
     glfwGetFramebufferSize(window->handle, &window->viewport_width, &window->viewport_height);
     glfwGetWindowSize(window->handle, &w, &h);
+    double xr = window->viewport_x_ratio, yr = window->viewport_y_ratio;
     window->viewport_x_ratio = (double)window->viewport_width / (double)w;
     window->viewport_y_ratio = (double)window->viewport_height / (double)h;
+    bool dpi_changed = (xr != 0.0 && xr != window->viewport_x_ratio) || (yr != 0.0 && yr != window->viewport_y_ratio);
     window->viewport_size_dirty = true;
     window->has_pending_resizes = false;
     if (notify_boss) {
-        call_boss(on_window_resize, "Kii", window->id, window->viewport_width, window->viewport_height);
+        call_boss(on_window_resize, "KiiO", window->id, window->viewport_width, window->viewport_height, dpi_changed ? Py_True : Py_False);
     }
     window->last_resize_at = monotonic();
 }
@@ -246,8 +248,8 @@ current_monitor(GLFWwindow *window) {
 }
 
 
-static inline void
-set_dpi_from_window(OSWindow *w) {
+void
+set_dpi_from_os_window(OSWindow *w) {
     GLFWmonitor *monitor = NULL;
     if (w) { monitor = current_monitor(w->handle); }
     if (monitor == NULL) monitor = glfwGetPrimaryMonitor();
@@ -315,7 +317,7 @@ create_os_window(PyObject UNUSED *self, PyObject *args) {
     current_os_window_ctx = glfw_window;
     glfwSwapInterval(swap_interval);  // a value of 1 makes mouse selection laggy
     if (is_first_window) {
-        set_dpi_from_window(NULL);
+        set_dpi_from_os_window(NULL);
         gl_init();
         PyObject *ret = PyObject_CallFunction(load_programs, "i", glfwGetWindowAttrib(glfw_window, GLFW_TRANSPARENT_FRAMEBUFFER));
         if (ret == NULL) return NULL;

kitty/state.c

@@ -373,6 +373,15 @@ PYWRAP1(viewport_for_window) {
     return Py_BuildValue("iiII", 400, 400, global_state.cell_width, global_state.cell_height);
 }
 
+PYWRAP1(set_dpi_from_os_window) {
+    id_type os_window_id = PyLong_AsUnsignedLongLong(args);
+    WITH_OS_WINDOW(os_window_id)
+        set_dpi_from_os_window(os_window);
+        Py_RETURN_TRUE;
+    END_WITH_OS_WINDOW
+    Py_RETURN_FALSE;
+}
+
 PYWRAP1(mark_os_window_for_close) {
     id_type os_window_id;
     int yes = 1;
@@ -476,6 +485,7 @@ static PyMethodDef module_methods[] = {
     MW(set_logical_dpi, METH_VARARGS),
     MW(pt_to_px, METH_O),
     MW(pt_to_px_ceil, METH_O),
+    MW(set_dpi_from_os_window, METH_O),
     MW(add_tab, METH_O),
     MW(add_window, METH_VARARGS),
     MW(update_window_title, METH_VARARGS),

kitty/state.h

@@ -146,6 +146,7 @@ void mark_os_window_for_close(OSWindow* w, bool yes);
 void update_os_window_viewport(OSWindow *window, bool);
 bool should_os_window_close(OSWindow* w);
 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);