When dragging to select with the mouse "grab" the mouse so that if it strays into neighboring windows, the selection is still updated

Fixes #624

docs/changelog.rst

@@ -12,6 +12,9 @@ Changelog
 - Fix triple-click to select line not working when the entire line is filled
   (:iss:`703`)
 
+- When dragging to select with the mouse "grab" the mouse so that if it strays
+  into neighboring windows, the selection is still updated (:pull:`624`)
+
 
 0.11.2 [2018-07-01]
 ------------------------------

kitty/glfw.c

@@ -202,6 +202,7 @@ push_focus_history(OSWindow *w) {
 
 static void
 window_focus_callback(GLFWwindow *w, int focused) {
+    global_state.active_drag_in_window = 0;
     if (!set_callback_window(w)) return;
     global_state.callback_os_window->is_focused = focused ? true : false;
     if (focused) {

kitty/mouse.c

@@ -119,6 +119,8 @@ contains_mouse(Window *w, OSWindow *os_window) {
     return (w->visible && window_left(w, os_window) <= x && x <= window_right(w, os_window) && window_top(w, os_window) <= y && y <= window_bottom(w, os_window));
 }
 
+static bool clamp_to_window = false;
+
 static inline bool
 cell_for_pos(Window *w, unsigned int *x, unsigned int *y, OSWindow *os_window) {
     WindowGeometry *g = &w->geometry;
@@ -128,6 +130,10 @@ cell_for_pos(Window *w, unsigned int *x, unsigned int *y, OSWindow *os_window) {
     double mouse_x = global_state.callback_os_window->mouse_x;
     double mouse_y = global_state.callback_os_window->mouse_y;
     double left = window_left(w, os_window), top = window_top(w, os_window), right = window_right(w, os_window), bottom = window_bottom(w, os_window);
+    if (clamp_to_window) {
+        mouse_x = MIN(MAX(mouse_x, left), right);
+        mouse_y = MIN(MAX(mouse_y, top), bottom);
+    }
     if (mouse_x < left || mouse_y < top || mouse_x > right || mouse_y > bottom) return false;
     if (mouse_x >= g->right) qx = screen->columns - 1;
     else if (mouse_x >= g->left) qx = (unsigned int)((double)(mouse_x - g->left) / os_window->fonts_data->cell_width);
@@ -147,10 +153,14 @@ update_drag(bool from_button, Window *w, bool is_release, int modifiers) {
     Screen *screen = w->render_data.screen;
     if (from_button) {
         if (is_release) {
+            global_state.active_drag_in_window = 0;
             if (screen->selection.in_progress)
                 screen_update_selection(screen, w->mouse_cell_x, w->mouse_cell_y, true);
         }
-        else screen_start_selection(screen, w->mouse_cell_x, w->mouse_cell_y, modifiers == (int)OPT(rectangle_select_modifiers) || modifiers == ((int)OPT(rectangle_select_modifiers) | GLFW_MOD_SHIFT), EXTEND_CELL);
+        else {
+            global_state.active_drag_in_window = w->id;
+            screen_start_selection(screen, w->mouse_cell_x, w->mouse_cell_y, modifiers == (int)OPT(rectangle_select_modifiers) || modifiers == ((int)OPT(rectangle_select_modifiers) | GLFW_MOD_SHIFT), EXTEND_CELL);
+        }
     } else if (screen->selection.in_progress) {
         screen_update_selection(screen, w->mouse_cell_x, w->mouse_cell_y, false);
     }
@@ -372,6 +382,16 @@ mouse_in_region(Region *r) {
 	return true;
 }
 
+static inline Window*
+window_for_id(id_type window_id) {
+    Tab *t = global_state.callback_os_window->tabs + global_state.callback_os_window->active_tab;
+    for (unsigned int i = 0; i < t->num_windows; i++) {
+        Window *w = t->windows + i;
+        if (w->id == window_id) return w;
+    }
+    return NULL;
+}
+
 static inline Window*
 window_for_event(unsigned int *window_idx, bool *in_tab_bar) {
     Region central, tab_bar;
@@ -405,7 +425,21 @@ mouse_event(int button, int modifiers) {
     MouseShape old_cursor = mouse_cursor_shape;
     bool in_tab_bar;
     unsigned int window_idx = 0;
-    Window *w = window_for_event(&window_idx, &in_tab_bar);
+    Window *w = NULL;
+    if (button == -1 && global_state.active_drag_in_window) {  // drag move
+        w = window_for_id(global_state.active_drag_in_window);
+        if (w) {
+            for (int i = 0; i < GLFW_MOUSE_BUTTON_5; i++) { if (global_state.callback_os_window->mouse_button_pressed[i]) { button = i; break; } }
+            if (button == GLFW_MOUSE_BUTTON_LEFT) {
+                clamp_to_window = true;
+                handle_move_event(w, button, modifiers, window_idx);
+                clamp_to_window = false;
+                return;
+            }
+        }
+
+    }
+    w = window_for_event(&window_idx, &in_tab_bar);
     if (in_tab_bar) {
         mouse_cursor_shape = HAND;
         handle_tab_bar_mouse(button, modifiers);

kitty/state.h

@@ -141,6 +141,7 @@ typedef struct {
     bool in_sequence_mode;
     double font_sz_in_pts;
     struct { double x, y; } default_dpi;
+    id_type active_drag_in_window;
 } GlobalState;
 
 extern GlobalState global_state;