Add screen magnifier

This adds a screen magnifier which can be controlled with the
`ZoomIn` / `ZoomOut` and `ToggleMagnify` actions.

It scales up part of the rendered framebuffer so the magnification
may end up looking blurry depending on the magnification scale.

PR #1774

docs/labwc-actions.5.scd

@@ -264,6 +264,18 @@ Actions are used in menus and keyboard/mouse bindings.
 	decorations (including those for which the server-side titlebar has been
 	hidden) are not eligible for shading.
 
+*<action name="ToggleMagnify">*
+	Toggle the screen magnifier on or off at the last magnification level
+	used.
+
+*<action name="ZoomIn">*++
+*<action name="ZoomOut">*
+	Increase or decrease the magnification level for the screen magnifier.
+	If the magnifier is currently off, ZoomIn will enable it at the lowest
+	magnification, equal to (1 + the magnifier increment set in the theme).
+	If the magnifier is on and at the lowest magnification, ZoomOut will
+	turn it off.
+
 *<action name="None" />*
 	If used as the only action for a binding: clear an earlier defined
 	binding.

docs/labwc-config.5.scd

@@ -909,6 +909,39 @@ situation.
 	option has been exposed for unusual use-cases. It is equivalent to
 	Openbox's `<hideDelay>`. Default is 250 ms.
 
+## MAGNIFIER
+
+```
+<magnifier>
+  <width>400</width>
+  <height>400</height>
+  <initScale>2</initScale>
+  <increment>0.2</increment>
+  <useFilter>true</useFilter>
+</magnifier>
+```
+
+*<magnifier><width>*
+	Width of magnifier window in pixels. Default is 400.
+	Set to -1 to use fullscreen magnifier.
+
+*<magnifier><height>*
+	Height of magnifier window in pixels. Default is 400.
+	Set to -1 to use fullscreen magnifier.
+
+*<magnifier><initScale>*
+	Initial number of times by which magnified image is scaled. Value
+	is the default at boot; can be modified at run-time in a keyboard
+	or mouse binding by calling 'ZoomIn' or 'ZoomOut'. Default is x2.0.
+
+*<magnifier><increment>*
+	Step by which magnification changes on each call to 'ZoomIn' or
+	'ZoomOut'. Default is 0.2.
+
+*<magnifier><useFilter>* [yes|no|default]
+	Whether to apply a bilinear filter to the magnified image, or
+	just to use nearest-neighbour. Default is true - bilinear filtered.
+
 ## ENVIRONMENT VARIABLES
 
 *XCURSOR_THEME* and *XCURSOR_SIZE* are supported to set cursor theme

docs/labwc-theme.5.scd

@@ -277,6 +277,12 @@ elements are not listed here, but are supported.
 	*window.inactive.border.color*. This is obsolete, but supported for
 	backward compatibility as some themes still contain it.
 
+*magnifier.border.width*
+	Width of magnifier window border in pixels. Default is 1.
+
+*magnifier.border.color*
+	Color of the magnfier window border. Default is #ff0000 (red).
+
 # BUTTONS
 
 The images used for the titlebar icons are referred to as buttons.

docs/rc.xml.all

@@ -589,4 +589,23 @@
   <menu>
     <ignoreButtonReleasePeriod>250</ignoreButtonReleasePeriod>
   </menu>
+
+  <!--
+    Magnifier settings
+    'width' sets the width in pixels of the magnifier window.
+    'height' sets the height in pixels of the magnifier window.
+    'initScale' sets the initial magnification factor at boot.
+    'increment' sets the amount by which the magnification factor
+      changes when 'ZoomIn' or 'ZoomOut' are called.
+    'useFilter' sets whether to use a bilinear filter on the magnified
+      output or simply to take nearest pixel.
+  -->
+  <magnifier>
+    <width>400</width>
+    <height>400</height>
+    <initScale>2.0</initScale>
+    <increment>0.2</increment>
+    <useFilter>true</useFilter>
+  </magnifier>
+
 </labwc_config>

include/config/rcxml.h

@@ -140,6 +140,13 @@ struct rcxml {
 
 	/* Menu */
 	unsigned int menu_ignore_button_release_period;
+
+	/* Magnifier */
+	int mag_width;
+	int mag_height;
+	float mag_scale;
+	float mag_increment;
+	bool mag_filter;
 };
 
 extern struct rcxml rc;

include/magnifier.h

@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef LABWC_MAGNIFIER_H
+#define LABWC_MAGNIFIER_H
+
+#include <stdbool.h>
+#include <wayland-server-core.h>
+
+struct server;
+struct output;
+
+enum magnify_dir {
+	MAGNIFY_INCREASE,
+	MAGNIFY_DECREASE
+};
+
+void magnify_toggle(struct server *server);
+void magnify_set_scale(struct server *server, enum magnify_dir dir);
+bool output_wants_magnification(struct output *output);
+void magnify(struct output *output, struct wlr_buffer *output_buffer,
+	struct wlr_box *damage);
+bool is_magnify_on(void);
+
+#endif /* LABWC_MAGNIFIER_H */

include/theme.h

@@ -139,6 +139,10 @@ struct theme {
 
 	/* not set in rc.xml/themerc, but derived from font & padding_height */
 	int osd_window_switcher_item_height;
+
+	/* magnifier */
+	float mag_border_color[4];
+	int mag_border_width;
 };
 
 struct server;

src/action.c

@@ -15,6 +15,7 @@
 #include "common/string-helpers.h"
 #include "debug.h"
 #include "labwc.h"
+#include "magnifier.h"
 #include "menu/menu.h"
 #include "osd.h"
 #include "output-virtual.h"
@@ -110,6 +111,9 @@ enum action_type {
 	ACTION_TYPE_SHADE,
 	ACTION_TYPE_UNSHADE,
 	ACTION_TYPE_TOGGLE_SHADE,
+	ACTION_TYPE_TOGGLE_MAGNIFY,
+	ACTION_TYPE_ZOOM_IN,
+	ACTION_TYPE_ZOOM_OUT
 };
 
 const char *action_names[] = {
@@ -163,6 +167,9 @@ const char *action_names[] = {
 	"Shade",
 	"Unshade",
 	"ToggleShade",
+	"ToggleMagnify",
+	"ZoomIn",
+	"ZoomOut",
 	NULL
 };
 
@@ -1046,6 +1053,15 @@ actions_run(struct view *activator, struct server *server,
 				view_set_shade(view, false);
 			}
 			break;
+		case ACTION_TYPE_TOGGLE_MAGNIFY:
+			magnify_toggle(server);
+			break;
+		case ACTION_TYPE_ZOOM_IN:
+			magnify_set_scale(server, MAGNIFY_INCREASE);
+			break;
+		case ACTION_TYPE_ZOOM_OUT:
+			magnify_set_scale(server, MAGNIFY_DECREASE);
+			break;
 		case ACTION_TYPE_INVALID:
 			wlr_log(WLR_ERROR, "Not executing unknown action");
 			break;

src/common/scene-helpers.c

@@ -5,6 +5,7 @@
 #include <wlr/types/wlr_scene.h>
 #include <wlr/util/log.h>
 #include "common/scene-helpers.h"
+#include "magnifier.h"
 
 struct wlr_surface *
 lab_wlr_surface_from_node(struct wlr_scene_node *node)
@@ -44,16 +45,29 @@ lab_wlr_scene_output_commit(struct wlr_scene_output *scene_output)
 	assert(scene_output);
 	struct wlr_output *wlr_output = scene_output->output;
 	struct wlr_output_state *state = &wlr_output->pending;
+	struct output *output = wlr_output->data;
+	bool wants_magnification = output_wants_magnification(output);
+	static bool last_mag = false;
 
 	if (!wlr_output->needs_frame && !pixman_region32_not_empty(
-			&scene_output->damage_ring.current)) {
+			&scene_output->damage_ring.current) && !wants_magnification
+			&& last_mag != is_magnify_on()) {
 		return false;
 	}
+
+	last_mag = is_magnify_on();
+
 	if (!wlr_scene_output_build_state(scene_output, state, NULL)) {
 		wlr_log(WLR_ERROR, "Failed to build output state for %s",
 			wlr_output->name);
 		return false;
 	}
+
+	struct wlr_box additional_damage = {0};
+	if (state->buffer && is_magnify_on()) {
+		magnify(output, state->buffer, &additional_damage);
+	}
+
 	if (!wlr_output_commit(wlr_output)) {
 		wlr_log(WLR_INFO, "Failed to commit output %s",
 			wlr_output->name);
@@ -66,5 +80,9 @@ lab_wlr_scene_output_commit(struct wlr_scene_output *scene_output)
 	 * again.
 	 */
 	wlr_damage_ring_rotate(&scene_output->damage_ring);
+
+	if (!wlr_box_empty(&additional_damage)) {
+		wlr_damage_ring_add_box(&scene_output->damage_ring, &additional_damage);
+	}
 	return true;
 }

src/config/rcxml.c

@@ -1036,6 +1036,16 @@ entry(xmlNode *node, char *nodename, char *content)
 		}
 	} else if (!strcasecmp(nodename, "ignoreButtonReleasePeriod.menu")) {
 		rc.menu_ignore_button_release_period = atoi(content);
+	} else if (!strcasecmp(nodename, "width.magnifier")) {
+		rc.mag_width = atoi(content);
+	} else if (!strcasecmp(nodename, "height.magnifier")) {
+		rc.mag_height = atoi(content);
+	} else if (!strcasecmp(nodename, "initScale.magnifier")) {
+		set_float(content, &rc.mag_scale);
+	} else if (!strcasecmp(nodename, "increment.magnifier")) {
+		set_float(content, &rc.mag_increment);
+	} else if (!strcasecmp(nodename, "useFilter.magnifier")) {
+		set_bool(content, &rc.mag_filter);
 	}
 }
 
@@ -1242,6 +1252,12 @@ rcxml_init(void)
 	rc.workspace_config.min_nr_workspaces = 1;
 
 	rc.menu_ignore_button_release_period = 250;
+
+	rc.mag_width = 400;
+	rc.mag_height = 400;
+	rc.mag_scale = 2.0;
+	rc.mag_increment = 0.2;
+	rc.mag_filter = true;
 }
 
 static void
@@ -1468,6 +1484,10 @@ post_processing(void)
 		wlr_log(WLR_INFO, "load default window switcher fields");
 		load_default_window_switcher_fields();
 	}
+
+	if (rc.mag_scale <= 0.0) {
+		rc.mag_scale = 1.0;
+	}
 }
 
 static void

src/magnifier.c

@@ -0,0 +1,302 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <assert.h>
+#include <wlr/types/wlr_output.h>
+#include "magnifier.h"
+#include "labwc.h"
+#include "theme.h"
+#include "common/macros.h"
+
+bool magnify_on;
+double mag_scale = 0.0;
+
+#define CLAMP(in, lower, upper) MAX(MIN(in, upper), lower)
+
+void
+magnify(struct output *output, struct wlr_buffer *output_buffer, struct wlr_box *damage)
+{
+	int width, height;
+	double x, y;
+	struct wlr_box border_box, dst_box;
+	struct wlr_fbox src_box;
+	bool fullscreen = false;
+
+	/* Reuse a single scratch buffer */
+	static struct wlr_buffer *tmp_buffer = NULL;
+	static struct wlr_texture *tmp_texture = NULL;
+
+	/* TODO: This looks way too complicated to just get the used format */
+	struct wlr_drm_format wlr_drm_format = {0};
+	struct wlr_shm_attributes shm_attribs = {0};
+	struct wlr_dmabuf_attributes dma_attribs = {0};
+	if (wlr_buffer_get_dmabuf(output_buffer, &dma_attribs)) {
+		wlr_drm_format.format = dma_attribs.format;
+		wlr_drm_format.len = 1;
+		wlr_drm_format.modifiers = &dma_attribs.modifier;
+	} else if (wlr_buffer_get_shm(output_buffer, &shm_attribs)) {
+		wlr_drm_format.format = shm_attribs.format;
+	} else {
+		wlr_log(WLR_ERROR, "Failed to read buffer format");
+		return;
+	}
+
+	/* Fetch scale-adjusted cursor coordinates */
+	struct server *server = output->server;
+	struct theme *theme = server->theme;
+	struct wlr_cursor *cursor = server->seat.cursor;
+	double ox = cursor->x;
+	double oy = cursor->y;
+	wlr_output_layout_output_coords(server->output_layout, output->wlr_output, &ox, &oy);
+	ox *= output->wlr_output->scale;
+	oy *= output->wlr_output->scale;
+	if (rc.mag_width == -1 || rc.mag_height == -1) {
+		fullscreen = true;
+	}
+	if ((ox < 0 || oy < 0 || ox >= output_buffer->width || oy >= output_buffer->height)
+		&& fullscreen) {
+		return;
+	}
+
+	if (mag_scale == 0.0) {
+		mag_scale = rc.mag_scale;
+	}
+	if (mag_scale == 0.0) {
+		mag_scale = 1.0;
+	}
+
+	if (fullscreen) {
+		width = output_buffer->width;
+		height = output_buffer->height;
+		x = 0;
+		y = 0;
+	} else {
+		width = rc.mag_width + 1;
+		height = rc.mag_height + 1;
+		x = ox - (rc.mag_width / 2.0);
+		y = oy - (rc.mag_height / 2.0);
+	}
+	double cropped_width = width;
+	double cropped_height = height;
+	double dst_x = 0;
+	double dst_y = 0;
+
+	/* Ensure everything is kept within output boundaries */
+	if (x < 0) {
+		cropped_width += x;
+		dst_x = x * -1;
+		x = 0;
+	}
+	if (y < 0) {
+		cropped_height += y;
+		dst_y = y * -1;
+		y = 0;
+	}
+	cropped_width = MIN(cropped_width, (double)output_buffer->width - x);
+	cropped_height = MIN(cropped_height, (double)output_buffer->height - y);
+
+	/* (Re)create the temporary buffer if required */
+	if (tmp_buffer && (tmp_buffer->width != width || tmp_buffer->height != height)) {
+		wlr_log(WLR_DEBUG, "tmp buffer size changed, dropping");
+		assert(tmp_texture);
+		wlr_texture_destroy(tmp_texture);
+		wlr_buffer_drop(tmp_buffer);
+		tmp_buffer = NULL;
+		tmp_texture = NULL;
+	}
+	if (!tmp_buffer) {
+		tmp_buffer = wlr_allocator_create_buffer(
+			server->allocator, width, height, &wlr_drm_format);
+	}
+	if (!tmp_buffer) {
+		wlr_log(WLR_ERROR, "Failed to allocate temporary magnifier buffer");
+		return;
+	}
+
+	/* Paste the magnified result back into the output buffer */
+	if (!tmp_texture) {
+		tmp_texture = wlr_texture_from_buffer(server->renderer, tmp_buffer);
+	}
+	if (!tmp_texture) {
+		wlr_log(WLR_ERROR, "Failed to allocate temporary texture");
+		wlr_buffer_drop(tmp_buffer);
+		tmp_buffer = NULL;
+		return;
+	}
+
+	/* Extract source region into temporary buffer */
+
+	struct wlr_render_pass *tmp_render_pass = wlr_renderer_begin_buffer_pass(
+		server->renderer, tmp_buffer, NULL);
+
+	wlr_buffer_lock(output_buffer);
+	struct wlr_texture *output_texture = wlr_texture_from_buffer(
+		server->renderer, output_buffer);
+	if (!output_texture) {
+		goto cleanup;
+	}
+
+	struct wlr_render_texture_options opts = {
+		.texture = output_texture,
+		.src_box = (struct wlr_fbox) {
+			x, y, cropped_width, cropped_height },
+		.dst_box = (struct wlr_box) {
+			dst_x, dst_y, cropped_width, cropped_height },
+		.alpha = NULL,
+	};
+	wlr_render_pass_add_texture(tmp_render_pass, &opts);
+	if (!wlr_render_pass_submit(tmp_render_pass)) {
+		wlr_log(WLR_ERROR, "Failed to extract magnifier source region");
+		wlr_texture_destroy(output_texture);
+		goto cleanup;
+	}
+	wlr_texture_destroy(output_texture);
+
+	/* Render to the output buffer itself */
+	tmp_render_pass = wlr_renderer_begin_buffer_pass(
+		server->renderer, output_buffer, NULL);
+
+	/* Borders */
+	if (fullscreen) {
+		border_box.x = 0;
+		border_box.y = 0;
+		border_box.width = width;
+		border_box.height = height;
+	} else {
+		border_box.x = ox - (width / 2 + theme->mag_border_width);
+		border_box.y = oy - (height / 2 + theme->mag_border_width);
+		border_box.width = (width + theme->mag_border_width * 2);
+		border_box.height = (height + theme->mag_border_width * 2);
+		struct wlr_render_rect_options bg_opts = {
+			.box = border_box,
+			.color = (struct wlr_render_color) {
+				.r = theme->mag_border_color[0],
+				.g = theme->mag_border_color[1],
+				.b = theme->mag_border_color[2],
+				.a = theme->mag_border_color[3]
+			},
+			.clip = NULL,
+		};
+		wlr_render_pass_add_rect(tmp_render_pass, &bg_opts);
+	}
+
+	src_box.width = width / mag_scale;
+	src_box.height = height / mag_scale;
+	dst_box.width = width;
+	dst_box.height = height;
+
+	if (fullscreen) {
+		src_box.x = CLAMP(ox - (ox / mag_scale), 0.0,
+			width * (mag_scale - 1.0) / mag_scale);
+		src_box.y = CLAMP(oy - (oy / mag_scale), 0.0,
+			height * (mag_scale - 1.0) / mag_scale);
+		dst_box.x = 0;
+		dst_box.y = 0;
+	} else {
+		src_box.x = width * (mag_scale - 1.0) / (2.0 * mag_scale);
+		src_box.y = height * (mag_scale - 1.0) / (2.0 * mag_scale);
+		dst_box.x = ox - (width / 2);
+		dst_box.y = oy - (height / 2);
+	}
+
+	opts = (struct wlr_render_texture_options) {
+		.texture = tmp_texture,
+		.src_box = src_box,
+		.dst_box = dst_box,
+		.alpha = NULL,
+		.clip = NULL,
+		.filter_mode = rc.mag_filter ? WLR_SCALE_FILTER_BILINEAR
+			: WLR_SCALE_FILTER_NEAREST,
+	};
+	wlr_render_pass_add_texture(tmp_render_pass, &opts);
+	if (!wlr_render_pass_submit(tmp_render_pass)) {
+		wlr_log(WLR_ERROR, "Failed to submit render pass");
+		goto cleanup;
+	}
+
+	/* And finally mark the extra damage */
+	*damage = border_box;
+	damage->width += 1;
+	damage->height += 1;
+
+cleanup:
+	wlr_buffer_unlock(output_buffer);
+}
+
+bool
+output_wants_magnification(struct output *output)
+{
+	static double x = -1;
+	static double y = -1;
+	struct wlr_cursor *cursor = output->server->seat.cursor;
+	if (!magnify_on) {
+		x = -1;
+		y = -1;
+		return false;
+	}
+	if (cursor->x == x && cursor->y == y) {
+		return false;
+	}
+	x = cursor->x;
+	y = cursor->y;
+	return output_nearest_to_cursor(output->server) == output;
+}
+
+/*
+ * Toggles magnification on and off
+ */
+
+void
+magnify_toggle(struct server *server)
+{
+	struct output *output = output_nearest_to_cursor(server);
+
+	if (magnify_on) {
+		magnify_on = false;
+	} else {
+		magnify_on = true;
+	}
+
+	if (output) {
+		wlr_output_schedule_frame(output->wlr_output);
+	}
+}
+
+/*
+ * Increases and decreases magnification scale
+ */
+
+void
+magnify_set_scale(struct server *server, enum magnify_dir dir)
+{
+	struct output *output = output_nearest_to_cursor(server);
+
+	if (dir == MAGNIFY_INCREASE) {
+		if (magnify_on) {
+			mag_scale += rc.mag_increment;
+		} else {
+			magnify_on = true;
+			mag_scale = 1.0 + rc.mag_increment;
+		}
+	} else {
+		if (magnify_on && mag_scale > 1.0 + rc.mag_increment) {
+			mag_scale -= rc.mag_increment;
+		} else {
+			magnify_on = false;
+		}
+	}
+
+	if (output) {
+		wlr_output_schedule_frame(output->wlr_output);
+	}
+}
+
+/*
+ * Report whether magnification is enabled
+ */
+
+bool
+is_magnify_on(void)
+{
+	return magnify_on;
+}
+

src/meson.build

@@ -9,6 +9,7 @@ labwc_sources = files(
   'idle.c',
   'interactive.c',
   'layers.c',
+  'magnifier.c',
   'main.c',
   'node.c',
   'osd.c',

src/theme.c

@@ -571,6 +571,10 @@ theme_builtin(struct theme *theme, struct server *server)
 	memset(theme->snapping_overlay_edge.border_color, 0,
 		sizeof(theme->snapping_overlay_edge.border_color));
 	theme->snapping_overlay_edge.border_color[0][0] = FLT_MIN;
+
+	/* magnifier */
+	parse_hexstr("#ff0000", theme->mag_border_color);
+	theme->mag_border_width = 1;
 }
 
 static void
@@ -826,6 +830,13 @@ entry(struct theme *theme, const char *key, const char *value)
 	if (match_glob(key, "snapping.overlay.edge.border.color")) {
 		parse_hexstrs(value, theme->snapping_overlay_edge.border_color);
 	}
+
+	if (match_glob(key, "magnifier.border.width")) {
+		theme->mag_border_width = atoi(value);
+	}
+	if (match_glob(key, "magnifier.border.color")) {
+		parse_hexstr(value, theme->mag_border_color);
+	}
 }
 
 static void