From 0aec12b3576e93f8387992de73bca99ab6e50d2f Mon Sep 17 00:00:00 2001
From: Oleg Oshmyan <chortos@inbox.lv>
Date: Sat, 17 Oct 2020 02:38:49 +0300
Subject: Fix Scroll effects with rectangle \clip/\iclip

---
 libass/ass_parse.c  |  4 ++--
 libass/ass_render.c | 12 ++++++++++--
 libass/ass_render.h |  1 +
 3 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/libass/ass_parse.c b/libass/ass_parse.c
index 920b035..4134987 100644
--- a/libass/ass_parse.c
+++ b/libass/ass_parse.c
@@ -943,8 +943,8 @@ void apply_transition_effects(ASS_Renderer *render_priv, ASS_Event *event)
             y0 = v[1];
             y1 = v[0];
         }
-        render_priv->state.clip_y0 = y0;
-        render_priv->state.clip_y1 = y1;
+        render_priv->state.scroll_y0 = y0;
+        render_priv->state.scroll_y1 = y1;
         render_priv->state.evt_type |= EVENT_VSCROLL;
         render_priv->state.detect_collisions = 0;
     }
diff --git a/libass/ass_render.c b/libass/ass_render.c
index 272a1e8..b00f22a 100644
--- a/libass/ass_render.c
+++ b/libass/ass_render.c
@@ -2687,13 +2687,13 @@ ass_render_event(ASS_Renderer *render_priv, ASS_Event *event,
         if (render_priv->state.scroll_direction == SCROLL_TB)
             device_y =
                 y2scr(render_priv,
-                      render_priv->state.clip_y0 +
+                      render_priv->state.scroll_y0 +
                       render_priv->state.scroll_shift) -
                 bbox.y_max;
         else if (render_priv->state.scroll_direction == SCROLL_BT)
             device_y =
                 y2scr(render_priv,
-                      render_priv->state.clip_y1 -
+                      render_priv->state.scroll_y1 -
                       render_priv->state.scroll_shift) -
                 bbox.y_min;
     } else if (!(render_priv->state.evt_type & EVENT_POSITIONED)) {
@@ -2760,6 +2760,14 @@ ass_render_event(ASS_Renderer *render_priv, ASS_Event *event,
         render_priv->state.clip_y1 = render_priv->settings.frame_height;
     }
 
+    if (render_priv->state.evt_type & EVENT_VSCROLL) {
+        double y0 = y2scr_pos(render_priv, render_priv->state.scroll_y0);
+        double y1 = y2scr_pos(render_priv, render_priv->state.scroll_y1);
+
+        render_priv->state.clip_y0 = FFMAX(render_priv->state.clip_y0, y0);
+        render_priv->state.clip_y1 = FFMIN(render_priv->state.clip_y1, y1);
+    }
+
     calculate_rotation_params(render_priv, &bbox, device_x, device_y);
 
     render_and_combine_glyphs(render_priv, device_x, device_y);
diff --git a/libass/ass_render.h b/libass/ass_render.h
index 22d7230..4714dfa 100644
--- a/libass/ass_render.h
+++ b/libass/ass_render.h
@@ -261,6 +261,7 @@ typedef struct {
         SCROLL_BT
     } scroll_direction;         // for EVENT_HSCROLL, EVENT_VSCROLL
     int scroll_shift;
+    int scroll_y0, scroll_y1;
 
     // face properties
     char *family;
-- 
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