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Reveal pacing: switch to predicted-arrival algorithm

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Adds the V2 reveal-pacing simulator and switches the live pacing
controller from the EWMA inter-arrival approach to a predicted-arrival
algorithm.
This commit is contained in:
isaac 2026-05-20 00:32:08 +08:00
parent e06e154396
commit cea2846249
2 changed files with 495 additions and 40 deletions
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62
submodules/TelegramUI/Components/Chat/ChatMessageTextBubbleContentNode/Sources/ChatMessageTextBubbleContentNode.swift
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@ -121,20 +121,21 @@ public class ChatMessageTextBubbleContentNode: ChatMessageBubbleContentNode {
private var isSummaryApplied = false
private final class TextRevealController {
private static let headroomTime: Double = 0.4
private static let responseTime: Double = 0.3
private static let velocityTau: Double = 0.15
private static let rateEwmaAlpha: Double = 0.4
private static let initialInputRate: Double = 40.0
private static let minInterArrival: Double = 0.05
private static let velocityTau: Double = 0.12
private static let gapEwmaAlpha: Double = 0.4
private static let initialGap: Double = 0.5
private static let stallFloor: Double = 0.10
private static let finalizeTime: Double = 0.3
private static let frameDtCap: Double = 0.05
private static let initialInputRate: Double = 40.0
private(set) var revealedCount: Double
private var velocity: Double = 0.0
private var inputRate: Double = TextRevealController.initialInputRate
private var avgInterArrival: Double = TextRevealController.initialGap
private var lastSampleTime: Double?
private var lastSampleLength: Int?
private var predictedNextArrivalTime: Double?
private var chunkCount: Int = 0
private(set) var latestLength: Int
private(set) var isFinalizing: Bool = false
private var lastFrameTime: Double?
@ -149,42 +150,33 @@ public class ChatMessageTextBubbleContentNode: ChatMessageBubbleContentNode {
}
func observeUpdate(latestLength: Int, at now: Double) {
let prevLength = self.lastSampleLength
let prevTime = self.lastSampleTime
let prevRate = self.inputRate
if let lastLen = self.lastSampleLength {
if latestLength > lastLen {
if let lastTime = self.lastSampleTime {
let dt = max(now - lastTime, TextRevealController.minInterArrival)
let sampleRate = Double(latestLength - lastLen) / dt
self.inputRate = TextRevealController.rateEwmaAlpha * sampleRate
+ (1.0 - TextRevealController.rateEwmaAlpha) * self.inputRate
let interArrival = max(now - lastTime, 0.001)
self.avgInterArrival = TextRevealController.gapEwmaAlpha * interArrival
+ (1.0 - TextRevealController.gapEwmaAlpha) * self.avgInterArrival
}
self.lastSampleTime = now
self.lastSampleLength = latestLength
self.predictedNextArrivalTime = now + self.avgInterArrival
self.chunkCount += 1
} else if latestLength < lastLen {
self.lastSampleLength = latestLength
}
} else {
self.lastSampleTime = now
self.lastSampleLength = latestLength
self.predictedNextArrivalTime = now + self.avgInterArrival
self.chunkCount += 1
}
self.latestLength = latestLength
if self.revealedCount > Double(latestLength) {
self.revealedCount = Double(latestLength)
}
let dtStr: String
if let pt = prevTime {
dtStr = String(format: "%.3f", now - pt)
} else {
dtStr = "n/a"
}
let prevLenStr = prevLength.map { "\($0)" } ?? "nil"
print("[reveal] observeUpdate prev=\(prevLenStr) new=\(latestLength) dt=\(dtStr)s rate=\(String(format: "%.1f", prevRate))→\(String(format: "%.1f", self.inputRate)) revealed=\(String(format: "%.1f", self.revealedCount))")
}
func finalize(finalLength: Int) {
print("[reveal] finalize finalLen=\(finalLength) revealed=\(String(format: "%.1f", self.revealedCount)) lag=\(String(format: "%.1f", Double(finalLength) - self.revealedCount)) inputRate=\(String(format: "%.1f", self.inputRate)) v=\(String(format: "%.1f", self.velocity))")
self.latestLength = finalLength
self.isFinalizing = true
if self.revealedCount > Double(finalLength) {
@ -198,22 +190,20 @@ public class ChatMessageTextBubbleContentNode: ChatMessageBubbleContentNode {
let targetVelocity: Double
if self.isFinalizing {
targetVelocity = max(self.velocity, lag / TextRevealController.finalizeTime)
} else if self.chunkCount < 2 {
targetVelocity = lag > 0.0 ? TextRevealController.initialInputRate : 0.0
} else if let predNext = self.predictedNextArrivalTime {
let timeToNext = max(TextRevealController.stallFloor, predNext - now)
targetVelocity = lag / timeToNext
} else {
let targetLag = self.inputRate * TextRevealController.headroomTime
let excess = max(0.0, lag - targetLag)
targetVelocity = self.inputRate + excess / TextRevealController.responseTime
targetVelocity = lag > 0.0 ? TextRevealController.initialInputRate : 0.0
}
let smoothing = min(1.0, dt / TextRevealController.velocityTau)
let prevIntCount = Int(self.revealedCount)
self.velocity += (targetVelocity - self.velocity) * smoothing
self.revealedCount = min(Double(self.latestLength), self.revealedCount + self.velocity * dt)
self.lastFrameTime = now
let newIntCount = Int(self.revealedCount)
let isComplete = self.isFinalizing && self.revealedCount >= Double(self.latestLength)
if newIntCount != prevIntCount || isComplete {
print("[reveal] tick \(prevIntCount)→\(newIntCount)/\(self.latestLength) v=\(String(format: "%.1f", self.velocity)) target=\(String(format: "%.1f", targetVelocity)) lag=\(String(format: "%.1f", lag)) inputRate=\(String(format: "%.1f", self.inputRate)) dt=\(String(format: "%.4f", dt))s\(self.isFinalizing ? " FIN" : "")\(isComplete ? " COMPLETE" : "")")
}
return (newIntCount, isComplete)
return (Int(self.revealedCount), isComplete)
}
}
@ -1246,16 +1236,13 @@ public class ChatMessageTextBubbleContentNode: ChatMessageBubbleContentNode {
private func updateTextRevealAnimation(previousGlyphCount: Int, hasDraft: Bool, hadDraft: Bool) {
let toCount = self.textNode.textNode.cachedLayout?.attributedString?.length ?? 0
let now = CACurrentMediaTime()
print("[reveal] updateTextRevealAnimation prevGlyph=\(previousGlyphCount) toCount=\(toCount) hasDraft=\(hasDraft) hadDraft=\(hadDraft) hasController=\(self.textRevealController != nil)")
if hasDraft, let controller = self.textRevealController, controller.isFinalizing {
print("[reveal] reset controller (re-entering draft after finalize)")
self.textRevealController = nil
self.textRevealLink = nil
}
if self.textRevealController == nil && (hasDraft || hadDraft) {
print("[reveal] create controller initialRevealed=\(previousGlyphCount) initialLength=\(toCount)")
self.textRevealController = TextRevealController(initialRevealedCount: previousGlyphCount, initialLength: toCount)
}
@ -1270,7 +1257,6 @@ public class ChatMessageTextBubbleContentNode: ChatMessageBubbleContentNode {
}
if controller.isFinalizing && controller.revealedCount >= Double(controller.latestLength) {
print("[reveal] teardown (already complete after finalize)")
self.textRevealController = nil
self.textRevealLink = nil
self.textNode.textNode.updateRevealCharacterCount(count: nil, animated: false)
@ -1278,26 +1264,22 @@ public class ChatMessageTextBubbleContentNode: ChatMessageBubbleContentNode {
}
if self.textRevealLink == nil {
print("[reveal] arm display link")
self.textRevealLink = SharedDisplayLinkDriver.shared.add { [weak self] _ in
guard let self else {
return
}
guard let item = self.item else {
print("[reveal] teardown (item is nil from link callback)")
self.textRevealController = nil
self.textRevealLink = nil
return
}
guard let controller = self.textRevealController else {
print("[reveal] teardown (controller is nil from link callback)")
self.textRevealLink = nil
return
}
let now = CACurrentMediaTime()
let (revealedGlyphCount, isComplete) = controller.tick(now: now)
if isComplete {
print("[reveal] teardown (complete from link callback)")
self.textRevealController = nil
self.textRevealLink = nil