From: Oleg Oshmyan <chortos@inbox.lv>
Date: Fri, 22 May 2015 23:35:21 +0000 (+0300)
Subject: Apply fade only when the fade alpha is positive (like VSFilter)
X-Git-Tag: 0.12.3~11
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=3bbd058c6d5c8b953fd80658ae696a16ff928896;p=libass

Apply fade only when the fade alpha is positive (like VSFilter)
---

diff --git a/libass/ass_parse.c b/libass/ass_parse.c
index 1d97a31..63bce2b 100644
--- a/libass/ass_parse.c
+++ b/libass/ass_parse.c
@@ -207,11 +207,11 @@ inline uint32_t mult_alpha(uint32_t a, uint32_t b)
  * \brief Calculate alpha value by piecewise linear function
  * Used for \fad, \fade implementation.
  */
-static unsigned
+static int
 interpolate_alpha(long long now, long long t1, long long t2, long long t3,
-                  long long t4, unsigned a1, unsigned a2, unsigned a3)
+                  long long t4, int a1, int a2, int a3)
 {
-    unsigned a;
+    int a;
     double cf;
 
     if (now < t1) {
diff --git a/libass/ass_render.c b/libass/ass_render.c
index 18ddea4..f471c81 100644
--- a/libass/ass_render.c
+++ b/libass/ass_render.c
@@ -1950,8 +1950,10 @@ static int parse_events(ASS_Renderer *render_priv, ASS_Event *event)
         info->font = render_priv->state.font;
         for (i = 0; i < 4; ++i) {
             uint32_t clr = render_priv->state.c[i];
-            change_alpha(&clr,
-                         mult_alpha(_a(clr), render_priv->state.fade), 1.);
+            // VSFilter compatibility: apply fade only when it's positive
+            if (render_priv->state.fade > 0)
+                change_alpha(&clr,
+                             mult_alpha(_a(clr), render_priv->state.fade), 1.);
             info->c[i] = clr;
         }
 
diff --git a/libass/ass_render.h b/libass/ass_render.h
index b8333cd..2136049 100644
--- a/libass/ass_render.h
+++ b/libass/ass_render.h
@@ -240,7 +240,7 @@ typedef struct {
     int clip_x0, clip_y0, clip_x1, clip_y1;
     char clip_mode;             // 1 = iclip
     char detect_collisions;
-    uint32_t fade;              // alpha from \fad
+    int fade;                   // alpha from \fad
     char be;                    // blur edges
     double blur;                // gaussian blur
     double shadow_x;