public static byte[] GetTempoEnvelope(int[] groove, int groovePadMode, bool palSource)
{
// Look in the cache first.
var key = new CachedTempoEnvelopeKey()
{
groove = groove, groovePadMode = groovePadMode, palSource = palSource
};
if (cachedTempoEnvelopes.TryGetValue(key, out var env))
{
return(env);
}
// Otherwise build.
var dstFactor = palSource ? 6 : 5;
var srcFactor = palSource ? 5 : 6;
var noteLength = Utils.Min(groove);
var grooveNumFrames = Utils.Sum(groove);
var grooveRepeatCount = 1;
// Repeat the groove until we have something perfectly divisible by 6 (5 on PAL).
while ((grooveNumFrames % srcFactor) != 0)
{
grooveNumFrames += Utils.Sum(groove);
grooveRepeatCount++;
}
// Figure out how many frames that is on the playback machine.
var adaptedNumFrames = grooveNumFrames / srcFactor * dstFactor;
// Mark some frames as "important", this will typically be the first
// and last frame of the note. This will preserve the attack and
// 1-frame silence between notes.
var importantFrames = new bool[grooveNumFrames];
var frameIndex = 0;
for (int i = 0; i < grooveRepeatCount; i++)
{
for (int j = 0; j < groove.Length; j++)
{
if (groove[j] == noteLength)
{
importantFrames[frameIndex] = true;
importantFrames[frameIndex + noteLength - 1] = true;
}
else
{
if (groovePadMode != GroovePaddingType.Beginning || noteLength == 1)
{
importantFrames[frameIndex] = true;
}
else
{
importantFrames[frameIndex + 1] = true;
}
if (groovePadMode != GroovePaddingType.End || noteLength == 1)
{
importantFrames[frameIndex + noteLength] = true;
}
else
{
importantFrames[frameIndex + noteLength - 1] = true;
}
}
frameIndex += groove[j];
}
}
#if FALSE
var numSkipFrames = palSource ? adaptedNumFrames - grooveNumFrames : grooveNumFrames - adaptedNumFrames;
var bestScore = int.MaxValue;
var bestOffset = -1;
for (int i = 0; i < srcFactor; i++)
{
var score = 0;
frameIndex = i;
for (int j = 0; j < numSkipFrames; j++)
{
if (importantFrames[frameIndex])
{
score++;
}
frameIndex += srcFactor;
}
if (score < bestScore)
{
bestScore = score;
bestOffset = i;
}
}
#else
// Start by distributing the skip (or double) frames evenly.
var numSkipFrames = palSource ? adaptedNumFrames - grooveNumFrames : grooveNumFrames - adaptedNumFrames;
var skipFrames = new bool[grooveNumFrames];
frameIndex = srcFactor / 2;
for (int i = 0; i < numSkipFrames; i++)
{
skipFrames[frameIndex] = true;
frameIndex += srcFactor;
}
int GetFrameCost(int idx)
{
if (!skipFrames[idx])
{
return(0);
}
var cost = 0;
// Penalize important frames
if (importantFrames[idx])
{
cost += srcFactor;
}
// Look right for another skipped frame.
for (int i = 1; i < srcFactor; i++)
{
var nextIdx = idx + i;
if (nextIdx >= skipFrames.Length)
{
nextIdx -= skipFrames.Length;
}
if (skipFrames[nextIdx])
{
// The closer we are, the higher the cost.
cost += (srcFactor - i);
break;
}
}
// Look left for another skipped frame.
for (int i = 1; i < srcFactor; i++)
{
var prevIdx = idx - i;
if (prevIdx < 0)
{
prevIdx += skipFrames.Length;
}
// The closer we are, the higher the cost.
if (skipFrames[prevIdx])
{
cost += (srcFactor - i);
break;
}
}
return(cost);
}
var frameCosts = new int[grooveNumFrames];
// Optimize.
for (int i = 0; i < 100; i++)
{
// Update costs.
var maxCost = -10;
var maxCostIndex = -1;
var totalCost = 0;
for (int j = 0; j < frameCosts.Length; j++)
{
var cost = GetFrameCost(j);
frameCosts[j] = cost;
totalCost += cost;
if (cost > maxCost)
{
maxCost = cost;
maxCostIndex = j;
}
}
if (maxCost == 0)
{
break;
}
var currentFrameCost = GetFrameCost(maxCostIndex);
// Try to optimize the most expensive frame by moving it to the left.
if (maxCostIndex > 0 && !skipFrames[maxCostIndex - 1] && !importantFrames[maxCostIndex - 1])
{
Utils.Swap(ref skipFrames[maxCostIndex], ref skipFrames[maxCostIndex - 1]);
if (GetFrameCost(maxCostIndex - 1) < currentFrameCost)
{
continue;
}
Utils.Swap(ref skipFrames[maxCostIndex], ref skipFrames[maxCostIndex - 1]);
}
// Try to optimize the most expensive frame by moving it to the right.
if (maxCostIndex < skipFrames.Length - 1 && !skipFrames[maxCostIndex + 1] && !importantFrames[maxCostIndex + 1])
{
Utils.Swap(ref skipFrames[maxCostIndex], ref skipFrames[maxCostIndex + 1]);
if (GetFrameCost(maxCostIndex + 1) < currentFrameCost)
{
continue;
}
Utils.Swap(ref skipFrames[maxCostIndex], ref skipFrames[maxCostIndex + 1]);
}
break;
}
#endif
// Build the actual envelope.
var lastFrameIndex = -1;
var firstFrameIndex = -1;
var envelope = new List <byte>();
var sum = 0;
for (int i = 0; i < skipFrames.Length; i++)
{
if (skipFrames[i])
{
var frameDelta = i - lastFrameIndex;
envelope.Add((byte)(frameDelta + (palSource ? 1 : -1)));
sum += frameDelta;
lastFrameIndex = i;
if (firstFrameIndex < 0)
{
firstFrameIndex = i;
}
}
}
if (palSource)
{
envelope[0]--;
}
var remainingFrames = skipFrames.Length - sum;
if (remainingFrames != 0)
{
envelope.Add((byte)(remainingFrames + firstFrameIndex + 1 + (palSource ? 1 : -1)));
}
envelope.Add(0x80);
env = envelope.ToArray();
cachedTempoEnvelopes[key] = env;
return(env);
}