From 5beb01373db64cd9458a4c6ac9488f4918383b13 Mon Sep 17 00:00:00 2001
From: Sunny <github@darkowlzz.space>
Date: Mon, 23 Mar 2026 23:48:03 +0000
Subject: [PATCH] Add smooth scroll support in GthImageViewer

Enabling smooth scroll support in image viewer allows touch pad (on
laptops) to zoom-in/zoom-out and change image without a mouse with
a wheel.

The zoom and image change scenarios are handled differently. Since
smooth/non-discrete change in zoom level is preferable, the scroll delta
is directly used to change the zoom level. But in case of image change,
directly applying even a tiny scroll delta change +/- can result in
quick and large jump in image change. A small threshold is introduced to
reject tiny scroll delta which may result in unintended image change.
This still allows large jumps in image change using scroll above the
threshold.
---
 pix/gth-browser.c      | 26 ++++++++++++++++++++++++--
 pix/gth-image-viewer.c | 16 ++++++++++++++++
 2 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/pix/gth-browser.c b/pix/gth-browser.c
index 822f657e..5570126b 100644
--- a/pix/gth-browser.c
+++ b/pix/gth-browser.c
@@ -6009,13 +6009,35 @@ gth_browser_viewer_scroll_event_cb (GthBrowser     *browser,
 	if (event->state & GDK_CONTROL_MASK)
 		return FALSE;
 
-	if ((event->direction != GDK_SCROLL_UP) && (event->direction != GDK_SCROLL_DOWN))
+	if ((event->direction != GDK_SCROLL_UP) && (event->direction != GDK_SCROLL_DOWN)
+		&& (event->direction != GDK_SCROLL_SMOOTH))
 		return FALSE;
 
 	handled = FALSE;
 	switch (browser->priv->scroll_action) {
 	case GTH_SCROLL_ACTION_CHANGE_FILE:
-		if (event->direction == GDK_SCROLL_UP)
+		if (event->direction == GDK_SCROLL_SMOOTH)
+		{
+			gdouble y_delta;
+			if (gdk_event_get_scroll_deltas ((GdkEvent *)event, NULL, &y_delta))
+			{
+				/* Introduce a small threshold that must be crossed to trigger
+				 * the action. This helps cancel out short touch scroll movements
+				 * which may be unintended. */
+				if (fabs(y_delta) < 0.5)
+				{
+					handled = FALSE;
+					break;
+				}
+				if (y_delta > 0)
+					gth_browser_show_next_image (browser, FALSE, FALSE);
+				else
+					gth_browser_show_prev_image (browser, FALSE, FALSE);
+				handled = TRUE;
+			}
+			break;
+		}
+		else if (event->direction == GDK_SCROLL_UP)
 			gth_browser_show_prev_image (browser, FALSE, FALSE);
 		else
 			gth_browser_show_next_image (browser, FALSE, FALSE);
diff --git a/pix/gth-image-viewer.c b/pix/gth-image-viewer.c
index 7bcafb08..be7bf984 100644
--- a/pix/gth-image-viewer.c
+++ b/pix/gth-image-viewer.c
@@ -427,6 +427,7 @@ gth_image_viewer_realize (GtkWidget *widget)
 				  | GDK_POINTER_MOTION_HINT_MASK
 				  | GDK_BUTTON_MOTION_MASK
 				  | GDK_SCROLL_MASK
+				  | GDK_SMOOTH_SCROLL_MASK
 				  | GDK_STRUCTURE_MASK);
 	attributes_mask = GDK_WA_X | GDK_WA_Y | GDK_WA_VISUAL | GDK_WA_WMCLASS;
 	window = gdk_window_new (gtk_widget_get_parent_window (widget),
@@ -2188,6 +2189,21 @@ gth_image_viewer_zoom_from_scroll (GthImageViewer *self,
 		gtk_widget_queue_resize (GTK_WIDGET (self));
 		handled = TRUE;
 		break;
+	case GDK_SCROLL_SMOOTH:
+		gdouble y_delta;
+		if (gdk_event_get_scroll_deltas ((GdkEvent *)event, NULL, &y_delta))
+		{
+			if (y_delta < 0)
+				new_zoom_level = get_prev_zoom (self->priv->zoom_level);
+			else if (y_delta > 0)
+				new_zoom_level = get_next_zoom (self->priv->zoom_level);
+			else
+				break;
+			set_zoom_centered_at (self, new_zoom_level, FALSE, (int) event->x, (int) event->y);
+			gtk_widget_queue_resize (GTK_WIDGET (self));
+			handled = TRUE;
+		}
+		break;
 
 	default:
 		break;