feature: add resize-by-cells option to constrain window sizes...

...to multiples of the cell size, and preserve grid size when changing
fonts or display scales in floating windows.

CHANGELOG.md

@@ -54,6 +54,8 @@
 
 * Unicode input mode now accepts input from the numpad as well,
   numlock is ignored.
+* A new `resize-by-cells` option, enabled by default, allows the size
+  of floating windows to be constrained to multiples of the cell size.
 
 
 ### Changed
@@ -68,6 +70,8 @@
 * Kitty keyboard protocol: updated behavior of modifiers bits during
   modifier key events, to match the (new [#6913][kitty-6913]) behavior
   in kitty >= 0.32.0 ([#1561][1561]).
+* When changing font sizes or display scales in floating windows, the
+  window will be resized as needed to preserve the same grid size.
 
 [1526]: https://codeberg.org/dnkl/foot/issues/1526
 [1528]: https://codeberg.org/dnkl/foot/issues/1528

config.c

@@ -921,6 +921,9 @@ parse_section_main(struct context *ctx)
     else if (streq(key, "resize-delay-ms"))
         return value_to_uint16(ctx, 10, &conf->resize_delay_ms);
 
+    else if (streq(key, "resize-by-cells"))
+        return value_to_bool(ctx, &conf->resize_by_cells);
+
     else if (streq(key, "bold-text-in-bright")) {
         if (streq(value, "palette-based")) {
             conf->bold_in_bright.enabled = true;
@@ -2990,6 +2993,7 @@ config_load(struct config *conf, const char *conf_path,
         },
         .pad_x = 0,
         .pad_y = 0,
+        .resize_by_cells = true,
         .resize_delay_ms = 100,
         .bold_in_bright = {
             .enabled = false,

config.h

@@ -128,6 +128,9 @@ struct config {
     unsigned pad_x;
     unsigned pad_y;
     bool center;
+
+    bool resize_by_cells;
+
     uint16_t resize_delay_ms;
 
     struct {

doc/foot.ini.5.scd

@@ -252,6 +252,21 @@ empty string to be set, but it must be quoted: *KEY=""*)
 	
 	Default: _100_.
 
+*resize-by-cells*
+	Boolean.
+
+	When set to *yes*, the window size will be constrained to multiples
+	of the cell size (plus any configured padding). When set to *no*,
+	the window size will be unconstrained, and padding may be adjusted
+	as necessary to accommodate window sizes that are not multiples of
+	the cell size.
+
+	This option only applies to floating windows. Sizes of maxmized, tiled
+	or fullscreen windows will not be constrained to multiples of the cell
+	size.
+
+	Default: _yes_
+
 *initial-window-size-pixels*
 	Initial window width and height in _pixels_ (subject to output
 	scaling), in the form _WIDTHxHEIGHT_. The height _includes_ the

render.c

@@ -3912,9 +3912,25 @@ send_dimensions_to_client(struct terminal *term)
     }
 }
 
+static void
+set_size_from_grid(struct terminal *term, int *width, int *height, int cols, int rows)
+{
+    /* Nominal grid dimensions */
+    *width = cols * term->cell_width;
+    *height = rows * term->cell_height;
+
+    /* Include any configured padding */
+    *width += 2 * term->conf->pad_x * term->scale;
+    *height += 2 * term->conf->pad_y * term->scale;
+
+    /* Round to multiples of scale */
+    *width = round(term->scale * round(*width / term->scale));
+    *height = round(term->scale * round(*height / term->scale));
+}
+
 /* Move to terminal.c? */
-static bool
-maybe_resize(struct terminal *term, int width, int height, bool force)
+bool
+render_resize(struct terminal *term, int width, int height, uint8_t opts)
 {
     if (term->shutdown.in_progress)
         return false;
@@ -3925,21 +3941,29 @@ maybe_resize(struct terminal *term, int width, int height, bool force)
     if (term->cell_width == 0 && term->cell_height == 0)
         return false;
 
+    const bool is_floating =
+        !term->window->is_maximized &&
+        !term->window->is_fullscreen &&
+        !term->window->is_tiled;
+
+    /* Convert logical size to physical size */
     const float scale = term->scale;
     width = round(width * scale);
     height = round(height * scale);
 
+    /* If the grid should be kept, the size should be overridden */
+    if (is_floating && (opts & RESIZE_KEEP_GRID)) {
+        set_size_from_grid(term, &width, &height, term->cols, term->rows);
+    }
+
     if (width == 0 && height == 0) {
-        /*
-         * The compositor is letting us choose the size
-         *
-         * If we have a "last" used size - use that. Otherwise, use
-         * the size from the user configuration.
-         */
+        /* The compositor is letting us choose the size */
         if (term->stashed_width != 0 && term->stashed_height != 0) {
+            /* If a default size is requested, prefer the "last used" size */
             width = term->stashed_width;
             height = term->stashed_height;
         } else {
+            /* Otherwise, use a user-configured size */
             switch (term->conf->size.type) {
             case CONF_SIZE_PX:
                 width = term->conf->size.width;
@@ -3959,15 +3983,8 @@ maybe_resize(struct terminal *term, int width, int height, bool force)
                 break;
 
             case CONF_SIZE_CELLS:
-                width = term->conf->size.width * term->cell_width;
-                height = term->conf->size.height * term->cell_height;
-
-                width += 2 * term->conf->pad_x * scale;
-                height += 2 * term->conf->pad_y * scale;
-
-                /* Ensure width/height is a valid multiple of scale */
-                width = roundf(scale * roundf(width / scale));
-                height = roundf(scale * roundf(height / scale));
+                set_size_from_grid(term, &width, &height,
+                                   term->conf->size.width, term->conf->size.height);
                 break;
             }
         }
@@ -3990,8 +4007,25 @@ maybe_resize(struct terminal *term, int width, int height, bool force)
     const int pad_x = min(max_pad_x, scale * term->conf->pad_x);
     const int pad_y = min(max_pad_y, scale * term->conf->pad_y);
 
-    if (!force && width == term->width && height == term->height && scale == term->scale)
+    if (is_floating &&
+        (opts & RESIZE_BY_CELLS) &&
+        term->conf->resize_by_cells)
+    {
+        /* If resizing in cell increments, restrict the width and height */
+        width = ((width - 2 * pad_x) / term->cell_width) * term->cell_width + 2 * pad_x;
+        width = max(min_width, roundf(scale * roundf(width / scale)));
+
+        height = ((height - 2 * pad_y) / term->cell_height) * term->cell_height + 2 * pad_y;
+        height = max(min_height, roundf(scale * roundf(height / scale)));
+    }
+
+    if (!(opts & RESIZE_FORCE) &&
+        width == term->width &&
+        height == term->height &&
+        scale == term->scale)
+    {
         return false;
+    }
 
     /* Cancel an application initiated "Synchronized Update" */
     term_disable_app_sync_updates(term);
@@ -4225,10 +4259,7 @@ damage_view:
     /* Signal TIOCSWINSZ */
     send_dimensions_to_client(term);
 
-    if (!term->window->is_maximized &&
-        !term->window->is_fullscreen &&
-        !term->window->is_tiled)
-    {
+    if (is_floating) {
         /* Stash current size, to enable us to restore it when we're
          * being un-maximized/fullscreened/tiled */
         term->stashed_width = term->width;
@@ -4291,18 +4322,6 @@ damage_view:
     return true;
 }
 
-bool
-render_resize(struct terminal *term, int width, int height)
-{
-    return maybe_resize(term, width, height, false);
-}
-
-bool
-render_resize_force(struct terminal *term, int width, int height)
-{
-    return maybe_resize(term, width, height, true);
-}
-
 static void xcursor_callback(
     void *data, struct wl_callback *wl_callback, uint32_t callback_data);
 static const struct wl_callback_listener xcursor_listener = {

render.h

@@ -10,8 +10,15 @@ struct renderer;
 struct renderer *render_init(struct fdm *fdm, struct wayland *wayl);
 void render_destroy(struct renderer *renderer);
 
-bool render_resize(struct terminal *term, int width, int height);
-bool render_resize_force(struct terminal *term, int width, int height);
+enum resize_options {
+    RESIZE_NORMAL = 0,
+    RESIZE_FORCE = 1 << 0,
+    RESIZE_BY_CELLS = 1 << 1,
+    RESIZE_KEEP_GRID = 1 << 2,
+};
+
+bool render_resize(
+    struct terminal *term, int width, int height, uint8_t resize_options);
 
 void render_refresh(struct terminal *term);
 void render_refresh_csd(struct terminal *term);

terminal.c

@@ -784,10 +784,11 @@ term_set_fonts(struct terminal *term, struct fcft_font *fonts[static 4],
      * render_resize() after this function */
     if (resize_grid) {
         /* Use force, since cell-width/height may have changed */
-        render_resize_force(
+        render_resize(
             term,
             (int)roundf(term->width / term->scale),
-            (int)roundf(term->height / term->scale));
+            (int)roundf(term->height / term->scale),
+            RESIZE_FORCE | RESIZE_KEEP_GRID);
     }
     return true;
 }

wayland.c

@@ -392,8 +392,6 @@ static void
 update_term_for_output_change(struct terminal *term)
 {
     const float old_scale = term->scale;
-    const float logical_width = term->width / term->scale;
-    const float logical_height = term->height / term->scale;
 
     /* Note: order matters! term_update_scale() must come first */
     bool scale_updated = term_update_scale(term);
@@ -402,24 +400,37 @@ update_term_for_output_change(struct terminal *term)
 
     csd_reload_font(term->window, old_scale);
 
+    uint8_t resize_opts = RESIZE_KEEP_GRID;
+
     if (fonts_updated) {
         /*
          * If the fonts have been updated, the cell dimensions have
          * changed. This requires a “forced” resize, since the surface
          * buffer dimensions may not have been updated (in which case
-         * render_size() normally shortcuts and returns early).
+         * render_resize() normally shortcuts and returns early).
          */
-        render_resize_force(term, (int)roundf(logical_width), (int)roundf(logical_height));
+        resize_opts |= RESIZE_FORCE;
+    } else if (!scale_updated) {
+        /* No need to resize if neither scale nor fonts have changed */
+        return;
+    } else if (term->conf->dpi_aware) {
+        /*
+	 * If fonts are sized according to DPI, it is possible for the cell
+	 * size to remain the same when display scale changes. This will not
+	 * change the surface buffer dimensions, but will change the logical
+	 * size of the window. To ensure that the compositor is made aware of
+	 * the proper logical size, force a resize rather than allowing
+	 * render_resize() to shortcut the notification if the buffer
+	 * dimensions remain the same.
+	 */
+        resize_opts |= RESIZE_FORCE;
     }
 
-    else if (scale_updated) {
-        /*
-         * A scale update means the surface buffer dimensions have
-         * been updated, even though the window logical dimensions
-         * haven’t changed.
-         */
-        render_resize(term, (int)roundf(logical_width), (int)roundf(logical_height));
-    }
+    render_resize(
+        term,
+        (int)roundf(term->width / term->scale),
+        (int)roundf(term->height / term->scale),
+        resize_opts);
 }
 
 static void
@@ -976,6 +987,8 @@ xdg_surface_configure(void *data, struct xdg_surface *xdg_surface,
 
     xdg_surface_ack_configure(xdg_surface, serial);
 
+    enum resize_options opts = RESIZE_BY_CELLS;
+
 #if 1
     /*
      * TODO: decide if we should do the last “forced” call when ending
@@ -989,13 +1002,12 @@ xdg_surface_configure(void *data, struct xdg_surface *xdg_surface,
      * Note: if we also disable content centering while resizing, then
      * the last, forced, resize *is* necessary.
      */
-    bool resized = was_resizing && !win->is_resizing
-        ? render_resize_force(term, new_width, new_height)
-        : render_resize(term, new_width, new_height);
-#else
-    bool resized = render_resize(term, new_width, new_height);
+    if (was_resizing && !win->is_resizing)
+        opts |= RESIZE_FORCE;
 #endif
 
+    bool resized = render_resize(term, new_width, new_height, opts);
+
     if (win->configure.is_activated)
         term_visual_focus_in(term);
     else