improve zooming feature with logarithmic scale

Zooming now uses a logarithmic scale, and the events for zooming
in/out gravitate to powers of 2, such as 50%, 100%, 200%, etc.

The option `--zoom-step` has been changed to represent the number
of zoom steps between powers of 2, with the default being 3 steps.

Author: myQwil

man/feh.pre

@@ -1003,12 +1003,12 @@ zoom the image like the
 .Cm --bg-fill
 mode.
 .
-.It Cm --zoom-step Ar percent
+.It Cm --zoom-step Ar index
 .
-Zoom images in and out by
-.Ar percent
-.Pq default: 25
-when using the zoom keys and buttons.
+Zoom images in and out by a factor of the nth root
+.Pq Ar index
+of 2 when using the zoom keys and buttons. The default is the 3rd root,
+which means that there will be 3 steps between powers of 2.
 .
 .El
 .

src/events.c

@@ -40,6 +40,8 @@ fehkey *feh_str_to_kb(char *action);
 
 feh_event_handler *ev_handler[LASTEvent];
 
+static const double zoom_rate = M_LN2 / 128.0;
+
 static void feh_event_handle_ButtonPress(XEvent * ev);
 static void feh_event_handle_ButtonRelease(XEvent * ev);
 static void feh_event_handle_LeaveNotify(XEvent * ev);
@@ -242,29 +244,31 @@ static void feh_event_handle_ButtonPress(XEvent * ev)
 		D(("click offset is %d,%d\n", ev->xbutton.x, ev->xbutton.y));
 		winwid->click_offset_x = ev->xbutton.x;
 		winwid->click_offset_y = ev->xbutton.y;
-		winwid->old_zoom = winwid->zoom;
+		winwid->old_step = round(log(winwid->zoom) / zoom_rate);
 
 		/* required to adjust the image position in zoom mode */
 		winwid->im_click_offset_x = (winwid->click_offset_x
-				- winwid->im_x) / winwid->old_zoom;
+				- winwid->im_x) / winwid->zoom;
 		winwid->im_click_offset_y = (winwid->click_offset_y
-				- winwid->im_y) / winwid->old_zoom;
+				- winwid->im_y) / winwid->zoom;
 
 	} else if (feh_is_bb(EVENT_zoom_in, button, state)) {
 		D(("Zoom_In Button Press event\n"));
 		D(("click offset is %d,%d\n", ev->xbutton.x, ev->xbutton.y));
+		if (winwid->zoom >= ZOOM_MAX || opt.step_rate <= 0)
+			return;
+
 		winwid->click_offset_x = ev->xbutton.x;
 		winwid->click_offset_y = ev->xbutton.y;
-		winwid->old_zoom = winwid->zoom;
 
 		/* required to adjust the image position in zoom mode */
 		winwid->im_click_offset_x = (winwid->click_offset_x
-				- winwid->im_x) / winwid->old_zoom;
+				- winwid->im_x) / winwid->zoom;
 		winwid->im_click_offset_y = (winwid->click_offset_y
-				- winwid->im_y) / winwid->old_zoom;
+				- winwid->im_y) / winwid->zoom;
 
 		/* copied from zoom_in, keyevents.c */
-		winwid->zoom = winwid->zoom * opt.zoom_rate;
+		winwid->zoom = exp(++winwid->zoom_step * opt.step_rate);
 
 		if (winwid->zoom > ZOOM_MAX)
 			winwid->zoom = ZOOM_MAX;
@@ -281,18 +285,20 @@ static void feh_event_handle_ButtonPress(XEvent * ev)
 	} else if (feh_is_bb(EVENT_zoom_out, button, state)) {
 		D(("Zoom_Out Button Press event\n"));
 		D(("click offset is %d,%d\n", ev->xbutton.x, ev->xbutton.y));
+		if (winwid->zoom <= ZOOM_MIN || opt.step_rate <= 0)
+			return;
+
 		winwid->click_offset_x = ev->xbutton.x;
 		winwid->click_offset_y = ev->xbutton.y;
-		winwid->old_zoom = winwid->zoom;
 
 		/* required to adjust the image position in zoom mode */
 		winwid->im_click_offset_x = (winwid->click_offset_x
-				- winwid->im_x) / winwid->old_zoom;
+				- winwid->im_x) / winwid->zoom;
 		winwid->im_click_offset_y = (winwid->click_offset_y
-				- winwid->im_y) / winwid->old_zoom;
+				- winwid->im_y) / winwid->zoom;
 
 		/* copied from zoom_out, keyevents.c */
-		winwid->zoom = winwid->zoom / opt.zoom_rate;
+		winwid->zoom = exp(--winwid->zoom_step * opt.step_rate);
 
 		if (winwid->zoom < ZOOM_MIN)
 			winwid->zoom = ZOOM_MIN;
@@ -400,11 +406,16 @@ static void feh_event_handle_ButtonRelease(XEvent * ev)
 		opt.mode = MODE_NORMAL;
 		winwid->mode = MODE_NORMAL;
 
-		if ((feh_is_bb(EVENT_zoom, button, state))
-				&& (ev->xbutton.x == winwid->click_offset_x)
-				&& (ev->xbutton.y == winwid->click_offset_y)) {
-			winwid->zoom = 1.0;
-			winwidget_center_image(winwid);
+		if ((feh_is_bb(EVENT_zoom, button, state))) {
+			if ((ev->xbutton.x == winwid->click_offset_x)
+					&& (ev->xbutton.y == winwid->click_offset_y)) {
+				winwid->zoom = 1.0;
+				winwid->zoom_step = 0;
+				winwidget_center_image(winwid);
+			} else {
+				winwid->zoom_step = round(log(winwid->zoom) / opt.step_rate);
+				winwidget_sanitise_offsets(winwid);
+			}
 		} else
 			winwidget_sanitise_offsets(winwid);
 
@@ -543,14 +554,8 @@ static void feh_event_handle_MotionNotify(XEvent * ev)
 
 		winwid = winwidget_get_from_window(ev->xmotion.window);
 		if (winwid) {
-			if (ev->xmotion.x > winwid->click_offset_x)
-				winwid->zoom = winwid->old_zoom + (
-						((double) ev->xmotion.x - (double) winwid->click_offset_x)
-						/ 128.0);
-			else
-				winwid->zoom = winwid->old_zoom - (
-						((double) winwid->click_offset_x - (double) ev->xmotion.x)
-						/ 128.0);
+			int step = winwid->old_step + ev->xmotion.x - winwid->click_offset_x;
+			winwid->zoom = exp(step * zoom_rate);
 
 			if (winwid->zoom < ZOOM_MIN)
 				winwid->zoom = ZOOM_MIN;

src/keyevents.c

@@ -602,35 +602,42 @@ void feh_event_handle_generic(winwidget winwid, unsigned int state, KeySym keysy
 		feh_event_invoke_action(winwid, 9);
 	}
 	else if (feh_is_kp(EVENT_zoom_in, state, keysym, button)) {
-		winwid->old_zoom = winwid->zoom;
-		winwid->zoom = winwid->zoom * opt.zoom_rate;
+		if (winwid->zoom >= ZOOM_MAX || opt.step_rate <= 0)
+			return;
+
+		double old_zoom = winwid->zoom;
+		winwid->zoom = exp(++winwid->zoom_step * opt.step_rate);
 
 		if (winwid->zoom > ZOOM_MAX)
 			winwid->zoom = ZOOM_MAX;
 
 		winwid->im_x = (winwid->w / 2) - (((winwid->w / 2) - winwid->im_x) /
-			winwid->old_zoom * winwid->zoom);
+			old_zoom * winwid->zoom);
 		winwid->im_y = (winwid->h / 2) - (((winwid->h / 2) - winwid->im_y) /
-			winwid->old_zoom * winwid->zoom);
+			old_zoom * winwid->zoom);
 		winwidget_sanitise_offsets(winwid);
 		winwidget_render_image(winwid, 0, 0);
 	}
 	else if (feh_is_kp(EVENT_zoom_out, state, keysym, button)) {
-		winwid->old_zoom = winwid->zoom;
-		winwid->zoom = winwid->zoom / opt.zoom_rate;
+		if (winwid->zoom <= ZOOM_MIN || opt.step_rate <= 0)
+			return;
+
+		double old_zoom = winwid->zoom;
+		winwid->zoom = exp(--winwid->zoom_step * opt.step_rate);
 
 		if (winwid->zoom < ZOOM_MIN)
 			winwid->zoom = ZOOM_MIN;
 
 		winwid->im_x = (winwid->w / 2) - (((winwid->w / 2) - winwid->im_x) /
-			winwid->old_zoom * winwid->zoom);
+			old_zoom * winwid->zoom);
 		winwid->im_y = (winwid->h / 2) - (((winwid->h / 2) - winwid->im_y) /
-			winwid->old_zoom * winwid->zoom);
+			old_zoom * winwid->zoom);
 		winwidget_sanitise_offsets(winwid);
 		winwidget_render_image(winwid, 0, 0);
 	}
 	else if (feh_is_kp(EVENT_zoom_default, state, keysym, button)) {
 		winwid->zoom = 1.0;
+		winwid->zoom_step = 0;
 		winwidget_center_image(winwid);
 		winwidget_render_image(winwid, 0, 0);
 	}

src/options.c

@@ -63,7 +63,7 @@ void init_parse_options(int argc, char **argv)
 	opt.font = NULL;
 	opt.max_height = opt.max_width = UINT_MAX;
 
-	opt.zoom_rate = 1.25;
+	opt.step_rate = M_LN2 / 3.0;
 
 	opt.start_list_at = NULL;
 	opt.jump_on_resort = 1;
@@ -848,12 +848,11 @@ static void feh_parse_option_array(int argc, char **argv, int finalrun)
 			opt.x11_windowid = strtol(optarg, NULL, 0);
 			break;
 		case OPTION_zoom_step:
-			opt.zoom_rate = atof(optarg);
-			if ((opt.zoom_rate <= 0)) {
-				weprintf("Zooming disabled due to --zoom-step=%f", opt.zoom_rate);
-				opt.zoom_rate = 1.0;
+			opt.step_rate = atof(optarg);
+			if ((opt.step_rate <= 0)) {
+				weprintf("Zooming disabled due to --zoom-step=%f", opt.step_rate);
 			} else {
-				opt.zoom_rate = 1 + ((float)opt.zoom_rate / 100);
+				opt.step_rate = M_LN2 / opt.step_rate;
 			}
 			break;
 		default:

src/options.h

@@ -127,7 +127,7 @@ struct __fehoptions {
 	int offset_y;
 	int default_zoom;
 	int zoom_mode;
-	double zoom_rate;
+	double step_rate;
 	unsigned char adjust_reload;
 	int xinerama_index;
 	char *x11_class;

src/winwidget.c

@@ -77,7 +77,8 @@ static winwidget winwidget_allocate(void)
 	ret->im_x = 0;
 	ret->im_y = 0;
 	ret->zoom = 1.0;
-	ret->old_zoom = 1.0;
+	ret->zoom_step = 0;
+	ret->old_step = 0;
 
 	ret->click_offset_x = 0;
 	ret->click_offset_y = 0;
@@ -494,6 +495,8 @@ void winwidget_render_image(winwidget winwid, int resize, int force_alias)
 				&& (!opt.default_zoom || required_zoom < winwid->zoom))
 			winwid->zoom = required_zoom;
 
+		winwid->zoom_step = round(log(winwid->zoom) / opt.step_rate);
+
 		if (opt.offset_flags & XValue) {
 			if (opt.offset_flags & XNegative) {
 				winwid->im_x = winwid->w - (winwid->im_w * winwid->zoom) - opt.offset_x;
@@ -1065,20 +1068,20 @@ void feh_debug_print_winwid(winwidget w)
 	       "h = %d\n" "im_w = %d\n" "im_h = %d\n" "im_angle = %f\n"
 	       "type = %d\n" "had_resize = %d\n" "im = %p\n" "GC = %p\n"
 	       "pixmap = %ld\n" "name = %s\n" "file = %p\n" "mode = %d\n"
-	       "im_x = %d\n" "im_y = %d\n" "zoom = %f\n" "old_zoom = %f\n"
-	       "click_offset_x = %d\n" "click_offset_y = %d\n"
+	       "im_x = %d\n" "im_y = %d\n" "zoom = %f\n" "zoom_step = %d\n"
+	       "old_step = %d" "click_offset_x = %d\n" "click_offset_y = %d\n"
 	       "has_rotated = %d\n", (void *)w, w->win, w->w, w->h, w->im_w,
 	       w->im_h, w->im_angle, w->type, w->had_resize, w->im, (void *)w->gc,
 	       w->bg_pmap, w->name, (void *)w->file, w->mode, w->im_x, w->im_y,
-	       w->zoom, w->old_zoom, w->click_offset_x, w->click_offset_y,
+	       w->zoom, w->zoom_step, w->old_step, w->click_offset_x, w->click_offset_y,
 	       w->has_rotated);
 }
 
 void winwidget_reset_image(winwidget winwid)
 {
 	if (!opt.keep_zoom_vp) {
 		winwid->zoom = 1.0;
-		winwid->old_zoom = 1.0;
+		winwid->zoom_step = 0;
 		winwid->im_x = 0;
 		winwid->im_y = 0;
 	}

src/winwidget.h

@@ -107,7 +107,8 @@ struct __winwidget {
 	 * all the way up to INT_MAX (eww)
 	 */
 	double zoom;
-	double old_zoom;
+	int zoom_step;
+	int old_step;
 
 	int click_offset_x;
 	int click_offset_y;