From dbc439e41a1aaa17e237ccf058c75ea8975bc79b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ale=C5=A1=20Jelov=C4=8Dan?= <frogstomp>
Date: Tue, 17 May 2022 15:56:20 +0200
Subject: Fix unreported: GPencil Time offset modifier Reverse only plays 2
 times

This patch fixes long standing issue of reverse mode only performing loop 2 times and then stops displaying.

Differential revision: https://developer.blender.org/D14921
---
 .../gpencil_modifiers/intern/MOD_gpenciltime.c     | 68 +++++++---------------
 1 file changed, 20 insertions(+), 48 deletions(-)

(limited to 'source/blender/gpencil_modifiers')

diff --git a/source/blender/gpencil_modifiers/intern/MOD_gpenciltime.c b/source/blender/gpencil_modifiers/intern/MOD_gpenciltime.c
index bf2e9a86817..c576cfbe525 100644
--- a/source/blender/gpencil_modifiers/intern/MOD_gpenciltime.c
+++ b/source/blender/gpencil_modifiers/intern/MOD_gpenciltime.c
@@ -58,18 +58,19 @@ static int remapTime(struct GpencilModifierData *md,
   const bool invpass = mmd->flag & GP_TIME_INVERT_LAYERPASS;
   int sfra = custom ? mmd->sfra : scene->r.sfra;
   int efra = custom ? mmd->efra : scene->r.efra;
+  int offset = mmd->offset;
+  int nfra = 0;
   CLAMP_MIN(sfra, 0);
   CLAMP_MIN(efra, 0);
 
+  if (offset < 0) {
+    offset = abs(efra - sfra + offset + 1);
+  }
   /* Avoid inverse ranges. */
-  if (efra < sfra) {
+  if (efra <= sfra) {
     return cfra;
   }
 
-  const int time_range = efra - sfra + 1;
-  int offset = mmd->offset;
-  int segments = 0;
-
   /* omit if filter by layer */
   if (mmd->layername[0] != '\0') {
     if (invgpl == false) {
@@ -97,60 +98,31 @@ static int remapTime(struct GpencilModifierData *md,
     }
   }
 
-  /* if fix mode, return predefined frame number */
-  if (mmd->mode == GP_TIME_MODE_FIX) {
-    return offset;
-  }
-
-  /* invert current frame number */
-  if (mmd->mode == GP_TIME_MODE_REVERSE) {
-    cfra = efra - cfra + sfra;
-  }
-
   /* apply frame scale */
   cfra *= mmd->frame_scale;
 
-  /* verify offset never is greater than frame range */
-  if (abs(offset) > time_range) {
-    offset = offset - ((offset / time_range) * time_range);
+  /* if fix mode, return predefined frame number */
+  if (mmd->mode == GP_TIME_MODE_FIX) {
+    return offset;
   }
 
-  /* verify not outside range if loop is disabled */
-  if ((mmd->flag & GP_TIME_KEEP_LOOP) == 0) {
-    if (cfra + offset < sfra) {
-      return sfra;
+  if (mmd->mode == GP_TIME_MODE_NORMAL) {
+    if ((mmd->flag & GP_TIME_KEEP_LOOP) == 0) {
+      nfra = cfra + sfra + offset - 1 < efra ? cfra + sfra + offset - 1 : efra;
     }
-    if (cfra + offset > efra) {
-      return efra;
+    else {
+      nfra = (offset + cfra - 1) % (efra - sfra + 1) + sfra;
     }
   }
-
-  /* check frames before start */
-  if (cfra < sfra) {
-    segments = ((cfra + sfra) / time_range);
-    cfra = cfra + (segments * time_range);
-  }
-
-  /* check frames after end */
-  if (cfra > efra) {
-    segments = ((cfra - sfra) / time_range);
-    cfra = cfra - (segments * time_range);
-  }
-
-  if (mmd->flag & GP_TIME_KEEP_LOOP) {
-    const int nfra = cfra + offset;
-
-    /* if the sum of the cfra is out scene frame range, recalc */
-    if (cfra + offset < sfra) {
-      const int delta = abs(sfra - nfra);
-      return efra - delta + 1;
+  if (mmd->mode == GP_TIME_MODE_REVERSE) {
+    if ((mmd->flag & GP_TIME_KEEP_LOOP) == 0) {
+      nfra = efra - cfra - offset > sfra ? efra - cfra - offset + 1 : sfra;
     }
-    if (cfra + offset > efra) {
-      return nfra - efra + sfra - 1;
+    else {
+      nfra = (efra + 1 - (cfra + offset - 1) % (efra - sfra + 1)) - 1;
     }
   }
-
-  return cfra + offset;
+  return nfra;
 }
 
 static void panel_draw(const bContext *UNUSED(C), Panel *panel)
-- 
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