From 6213f3da599e7dab091b20bd3cf6f12a97a7bf03 Mon Sep 17 00:00:00 2001
From: brunoherbelin <bruno.herbelin@gmail.com>
Date: Fri, 28 Aug 2020 22:29:20 +0200
Subject: [PATCH] Fixed interpolation alpha in timeline

---
 Timeline.cpp | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/Timeline.cpp b/Timeline.cpp
index 95d9b04..b993417 100644
--- a/Timeline.cpp
+++ b/Timeline.cpp
@@ -1,6 +1,6 @@
 
 #include <algorithm>
-
+#include <cmath>
 
 #include "defines.h"
 #include "Log.h"
@@ -194,14 +194,13 @@ void Timeline::clearGaps()
 
 float Timeline::fadingAt(const GstClockTime t)
 {
-    GstClockTime modulo = t % step_;
-    GstClockTime keyframe = t - modulo;
-    size_t keyframe_index = CLAMP( (MAX_TIMELINE_ARRAY * keyframe) / timing_.end, 0, MAX_TIMELINE_ARRAY-1);
+    double true_index = (static_cast<double>(MAX_TIMELINE_ARRAY) * static_cast<double>(t)) / static_cast<double>(timing_.end);
+    double previous_index = floor(true_index);
+    float percent = static_cast<float>(true_index - previous_index);
+    size_t keyframe_index = CLAMP( static_cast<size_t>(previous_index), 0, MAX_TIMELINE_ARRAY-1);
     size_t keyframe_next_index = CLAMP( keyframe_index+1, 0, MAX_TIMELINE_ARRAY-1);
-
-    float interpol = static_cast<float>( static_cast<double>(modulo) / static_cast<double>(step_) );
     float v = fadingArray_[keyframe_index];
-    v += interpol * (fadingArray_[keyframe_next_index] - fadingArray_[keyframe_index]);
+    v += percent * (fadingArray_[keyframe_next_index] - fadingArray_[keyframe_index]);
 
     return v;
 }