From a97c1d7ee0a483876ffb8a062dd9648dfad02bd7 Mon Sep 17 00:00:00 2001
From: attila <attila@juce.com>
Date: Wed, 14 Dec 2022 18:27:10 +0100
Subject: [PATCH] ARAPluginDemo:  Use crossfade in the EditorRenderer to avoid
 clicks

---
 examples/Plugins/ARAPluginDemo.h | 78 ++++++++++++++++++++++++++++++--
 1 file changed, 73 insertions(+), 5 deletions(-)

diff --git a/examples/Plugins/ARAPluginDemo.h b/examples/Plugins/ARAPluginDemo.h
index 2abc297ec4..ded495d4cc 100644
--- a/examples/Plugins/ARAPluginDemo.h
+++ b/examples/Plugins/ARAPluginDemo.h
@@ -117,6 +117,18 @@ private:
     SpinLock processingFlag;
 };
 
+static void crossfade (const float* sourceA,
+                       const float* sourceB,
+                       float aProportionAtStart,
+                       float aProportionAtFinish,
+                       float* destinationBuffer,
+                       int numSamples)
+{
+    AudioBuffer<float> destination { &destinationBuffer, 1, numSamples };
+    destination.copyFromWithRamp (0, 0, sourceA, numSamples, aProportionAtStart, aProportionAtFinish);
+    destination.addFromWithRamp (0, 0, sourceB, numSamples, 1.0f - aProportionAtStart, 1.0f - aProportionAtFinish);
+}
+
 class Looper
 {
 public:
@@ -138,28 +150,60 @@ public:
         }
 
         const auto numChannelsToCopy = std::min (inputBuffer->getNumChannels(), buffer.getNumChannels());
+        const auto actualCrossfadeLengthSamples = std::min (loopRange.getLength() / 2, (int64) desiredCrossfadeLengthSamples);
 
         for (auto samplesCopied = 0; samplesCopied < buffer.getNumSamples();)
         {
-            const auto numSamplesToCopy =
-                std::min (buffer.getNumSamples() - samplesCopied, (int) (loopRange.getEnd() - pos));
+            const auto [needsCrossfade, samplePosOfNextCrossfadeTransition] = [&]() -> std::pair<bool, int64>
+            {
+                if (const auto endOfFadeIn = loopRange.getStart() + actualCrossfadeLengthSamples; pos < endOfFadeIn)
+                    return { true, endOfFadeIn };
+
+                return { false, loopRange.getEnd() - actualCrossfadeLengthSamples };
+            }();
+
+            const auto samplesToNextCrossfadeTransition = samplePosOfNextCrossfadeTransition - pos;
+            const auto numSamplesToCopy = std::min (buffer.getNumSamples() - samplesCopied,
+                                                    (int) samplesToNextCrossfadeTransition);
+
+            const auto getFadeInGainAtPos = [this, actualCrossfadeLengthSamples] (auto p)
+            {
+                return jmap ((float) p, (float) loopRange.getStart(), (float) loopRange.getStart() + (float) actualCrossfadeLengthSamples - 1.0f, 0.0f, 1.0f);
+            };
 
             for (int i = 0; i < numChannelsToCopy; ++i)
             {
-                buffer.copyFrom (i, samplesCopied, *inputBuffer, i, (int) pos, numSamplesToCopy);
+                if (needsCrossfade)
+                {
+                    const auto overlapStart = loopRange.getEnd() - actualCrossfadeLengthSamples
+                                              + (pos - loopRange.getStart());
+
+                    crossfade (inputBuffer->getReadPointer (i, (int) pos),
+                               inputBuffer->getReadPointer (i, (int) overlapStart),
+                               getFadeInGainAtPos (pos),
+                               getFadeInGainAtPos (pos + numSamplesToCopy),
+                               buffer.getWritePointer (i, samplesCopied),
+                               numSamplesToCopy);
+                }
+                else
+                {
+                    buffer.copyFrom (i, samplesCopied, *inputBuffer, i, (int) pos, numSamplesToCopy);
+                }
             }
 
             samplesCopied += numSamplesToCopy;
             pos += numSamplesToCopy;
 
-            jassert (pos <= loopRange.getEnd());
+            jassert (pos <= loopRange.getEnd() - actualCrossfadeLengthSamples);
 
-            if (pos == loopRange.getEnd())
+            if (pos == loopRange.getEnd() - actualCrossfadeLengthSamples)
                 pos = loopRange.getStart();
         }
     }
 
 private:
+    static constexpr int desiredCrossfadeLengthSamples = 50;
+
     const AudioBuffer<float>* inputBuffer;
     Range<int64> loopRange;
     int64 pos;
@@ -510,8 +554,21 @@ public:
             if (! locked)
                 return true;
 
+            const auto fadeOutIfNecessary = [this, &buffer]
+            {
+                if (std::exchange (wasPreviewing, false))
+                {
+                    previewLooper.writeInto (buffer);
+                    const auto fadeOutStart = std::max (0, buffer.getNumSamples() - 50);
+                    buffer.applyGainRamp (fadeOutStart, buffer.getNumSamples() - fadeOutStart, 1.0f, 0.0f);
+                }
+            };
+
             if (positionInfo.getIsPlaying())
+            {
+                fadeOutIfNecessary();
                 return true;
+            }
 
             if (const auto previewedRegion = previewState->previewedRegion.load())
             {
@@ -565,9 +622,19 @@ public:
                     else
                     {
                         previewLooper.writeInto (buffer);
+
+                        if (! std::exchange (wasPreviewing, true))
+                        {
+                            const auto fadeInLength = std::min (50, buffer.getNumSamples());
+                            buffer.applyGainRamp (0, fadeInLength, 0.0f, 1.0f);
+                        }
                     }
                 }
             }
+            else
+            {
+                fadeOutIfNecessary();
+            }
 
             return true;
         });
@@ -599,6 +666,7 @@ private:
     double lastPreviewTime = 0.0;
     ARAPlaybackRegion* lastPlaybackRegion = nullptr;
     bool lastPreviewDimmed = false;
+    bool wasPreviewing = false;
     std::unique_ptr<AudioBuffer<float>> previewBuffer;
     Looper previewLooper;