dialog system: add a side-by-side alignment feature.

This will let us put two controls side by side (e.g. in disjoint
columns of a multi-col layout) and indicate that instead of the
default behaviour of aligning their top edges, their centreline (or,
even better if available, font baseline) should be aligned.

NFC: nothing uses this yet.

dialog.c

@@ -221,6 +221,7 @@ static union control *ctrl_new(struct controlset *s, int type,
     c->generic.handler = handler;
     c->generic.context = context;
     c->generic.label = NULL;
+    c->generic.align_next_to = NULL;
     return c;
 }
 

dialog.h

@@ -113,7 +113,8 @@ typedef void (*handler_fn)(union control *ctrl, dlgparam *dp,
         int column; \
         handler_fn handler; \
         intorptr context; \
-        intorptr helpctx
+        intorptr helpctx; \
+        union control *align_next_to
 
 union control {
     /*
@@ -179,6 +180,18 @@ union control {
          * to ensure it brings up the right piece of help text.
          */
         intorptr helpctx;
+        /*
+         * Setting this to non-NULL coerces two controls to have their
+         * y-coordinates adjusted so that they can sit alongside each
+         * other and look nicely aligned, even if they're different
+         * heights.
+         *
+         * Set this field on the _second_ control of the pair (in
+         * terms of order in the data structure), so that when it's
+         * instantiated, the first one is already there to be referred
+         * to.
+         */
+        union control *align_next_to;
     } generic;
     struct {
         STANDARD_PREFIX;

unix/gtkdlg.c

@@ -2491,6 +2491,28 @@ GtkWidget *layout_ctrls(
                     COLUMN_SPAN(ctrl->generic.column));
         if (left)
             columns_force_left_align(cols, w);
+        if (ctrl->generic.align_next_to) {
+            /*
+             * Implement align_next_to by simply forcing the two
+             * controls to have the same height of size allocation. At
+             * least for the controls we're currently doing this with,
+             * the GTK layout system will automatically vertically
+             * centre each control within its allocation, which will
+             * get the two controls aligned alongside each other
+             * reasonably well.
+             */
+            struct uctrl *uc2 = dlg_find_byctrl(
+                dp, ctrl->generic.align_next_to);
+            assert(uc2);
+            columns_force_same_height(cols, w, uc2->toplevel);
+
+#if GTK_CHECK_VERSION(3, 10, 0)
+            /* Slightly nicer to align baselines than just vertically
+             * centring, where the option is available */
+            gtk_widget_set_valign(w, GTK_ALIGN_BASELINE);
+            gtk_widget_set_valign(uc2->toplevel, GTK_ALIGN_BASELINE);
+#endif
+        }
         gtk_widget_show(w);
 
         uc->toplevel = w;

windows/winctrls.c

@@ -1325,6 +1325,28 @@ struct winctrl *winctrl_findbyindex(struct winctrls *wc, int index)
     return index234(wc->byid, index);
 }
 
+static void move_windows(HWND hwnd, int base_id, int num_ids, LONG dy)
+{
+    if (!dy)
+        return;
+    for (int i = 0; i < num_ids; i++) {
+        HWND win = GetDlgItem(hwnd, base_id + i);
+
+        RECT rect;
+        if (!GetWindowRect(win, &rect))
+            continue;
+
+        POINT p;
+        p.x = rect.left;
+        p.y = rect.top + dy;
+        if (!ScreenToClient(hwnd, &p))
+            continue;
+
+        SetWindowPos(win, NULL, p.x, p.y, 0, 0,
+                     SWP_NOACTIVATE | SWP_NOSIZE | SWP_NOZORDER);
+    }
+}
+
 void winctrl_layout(struct dlgparam *dp, struct winctrls *wc,
                     struct ctlpos *cp, struct controlset *s, int *id)
 {
@@ -1340,7 +1362,7 @@ void winctrl_layout(struct dlgparam *dp, struct winctrls *wc,
     char shortcuts[MAX_SHORTCUTS_PER_CTRL];
     int nshortcuts;
     char *escaped;
-    int i, actual_base_id, base_id, num_ids;
+    int i, actual_base_id, base_id, num_ids, align_id_relative;
     void *data;
 
     base_id = *id;
@@ -1349,7 +1371,7 @@ void winctrl_layout(struct dlgparam *dp, struct winctrls *wc,
     if (s->boxname && *s->boxname) {
         struct winctrl *c = snew(struct winctrl);
         c->ctrl = NULL;
-        c->base_id = base_id;
+        c->base_id = c->align_id = base_id;
         c->num_ids = 1;
         c->data = NULL;
         memset(c->shortcuts, NO_SHORTCUT, lenof(c->shortcuts));
@@ -1362,7 +1384,7 @@ void winctrl_layout(struct dlgparam *dp, struct winctrls *wc,
     if (!s->boxname && s->boxtitle) {
         struct winctrl *c = snew(struct winctrl);
         c->ctrl = NULL;
-        c->base_id = base_id;
+        c->base_id = c->align_id = base_id;
         c->num_ids = 1;
         c->data = dupstr(s->boxtitle);
         memset(c->shortcuts, NO_SHORTCUT, lenof(c->shortcuts));
@@ -1491,6 +1513,11 @@ void winctrl_layout(struct dlgparam *dp, struct winctrls *wc,
         /* Almost all controls start at base_id. */
         actual_base_id = base_id;
 
+        /* For vertical alignment purposes, the most relevant control
+         * in a group is usually the last one. But that can be
+         * overridden occasionally. */
+        align_id_relative = -1;
+
         /*
          * Now we're ready to actually create the control, by
          * switching on its type.
@@ -1659,6 +1686,10 @@ void winctrl_layout(struct dlgparam *dp, struct winctrls *wc,
             unreachable("bad control type in winctrl_layout");
         }
 
+        /* Translate the original align_id_relative of -1 into n-1 */
+        if (align_id_relative < 0)
+            align_id_relative += num_ids;
+
         /*
          * Create a `struct winctrl' for this control, and advance
          * the dialog ID counter, if it's actually been created
@@ -1669,6 +1700,7 @@ void winctrl_layout(struct dlgparam *dp, struct winctrls *wc,
 
             c->ctrl = ctrl;
             c->base_id = actual_base_id;
+            c->align_id = c->base_id + align_id_relative;
             c->num_ids = num_ids;
             c->data = data;
             memcpy(c->shortcuts, shortcuts, sizeof(shortcuts));
@@ -1676,6 +1708,31 @@ void winctrl_layout(struct dlgparam *dp, struct winctrls *wc,
             winctrl_add_shortcuts(dp, c);
             if (actual_base_id == base_id)
                 base_id += num_ids;
+
+            if (ctrl->generic.align_next_to) {
+                /*
+                 * Implement align_next_to by looking at the y extents
+                 * of the two controls now that both are created, and
+                 * moving one or the other downwards so that they're
+                 * centred on a common horizontal line.
+                 */
+                struct winctrl *c2 = winctrl_findbyctrl(
+                    wc, ctrl->generic.align_next_to);
+                HWND win1 = GetDlgItem(pos.hwnd, c->align_id);
+                HWND win2 = GetDlgItem(pos.hwnd, c2->align_id);
+                RECT rect1, rect2;
+                if (win1 && win2 &&
+                    GetWindowRect(win1, &rect1) &&
+                    GetWindowRect(win2, &rect2)) {
+                    LONG top = (rect1.top < rect2.top ? rect1.top : rect2.top);
+                    LONG bottom = (rect1.bottom > rect2.bottom ?
+                                   rect1.bottom : rect2.bottom);
+                    move_windows(pos.hwnd, c->base_id, c->num_ids,
+                                 (top + bottom - rect1.top - rect1.bottom)/2);
+                    move_windows(pos.hwnd, c2->base_id, c2->num_ids,
+                                 (top + bottom - rect2.top - rect2.bottom)/2);
+                }
+            }
         } else {
             sfree(data);
         }

windows/winstuff.h

@@ -491,6 +491,12 @@ struct winctrl {
      */
     int base_id;
     int num_ids;
+    /*
+     * For vertical alignment, the id of a particular representative
+     * control that has the y-extent of the sensible part of the
+     * control.
+     */
+    int align_id;
     /*
      * Remember what keyboard shortcuts were used by this control,
      * so that when we remove it again we can take them out of the