fix jittery behavior in SwiftUI live view in analogy to 858c157

by moving new sample count tracking inside of WaveformDrawer

Author: dmrschmidt

DSWaveformImage/DSWaveformImage/Common/WaveformImageDrawer.swift

@@ -15,6 +15,9 @@ public class WaveformImageDrawer: ObservableObject {
     /// Makes sure we always look at the same samples while animating
     private var lastOffset: Int = 0
 
+    /// Keep track of how many samples we are adding each draw cycle
+    private var lastSampleCount: Int = 0
+
 #if compiler(>=5.5) && canImport(_Concurrency)
     /// Async analyzes the provided audio and renders a UIImage of the waveform data calculated by the analyzer.
     public func waveformImage(fromAudioAt audioAssetURL: URL,
@@ -69,12 +72,18 @@ extension WaveformImageDrawer {
     ///
     /// Samples need to be normalized within interval `(0...1)`.
     /// Ensure context size & scale match with the configuration's size & scale.
-    func draw(waveform samples: [Float], newSampleCount: Int, on context: CGContext, with configuration: Waveform.Configuration) {
+    func draw(waveform samples: [Float], on context: CGContext, with configuration: Waveform.Configuration) {
         guard samples.count > 0 || shouldDrawSilencePadding else {
             return
         }
 
         let samplesNeeded = Int(configuration.size.width * configuration.scale)
+
+        let newSampleCount: Int = lastSampleCount > samples.count
+            ? samples.count // this implies that we have reset drawing an are starting over
+            : samples.count - lastSampleCount
+
+        lastSampleCount = samples.count
 
         // Reset the cumulative lastOffset when new drawing begins
         if samples.count == newSampleCount {

DSWaveformImage/DSWaveformImage/SwiftUI/WaveformLiveCanvas.swift

@@ -9,7 +9,6 @@ public struct WaveformLiveCanvas: View {
     @Binding public var shouldDrawSilencePadding: Bool
 
     @StateObject private var waveformDrawer = WaveformImageDrawer()
-    @State private var lastNewSampleCount: Int = 0
 
     public init(
         samples: Binding<[Float]>,
@@ -19,21 +18,17 @@ public struct WaveformLiveCanvas: View {
         _samples = samples
         _configuration = configuration
         _shouldDrawSilencePadding = shouldDrawSilencePadding
-        lastNewSampleCount = samples.count
     }
 
     public var body: some View {
         Canvas(rendersAsynchronously: true) { context, size in
             context.withCGContext { cgContext in
-                waveformDrawer.draw(waveform: samples, newSampleCount: lastNewSampleCount, on: cgContext, with: configuration.with(size: size))
+                waveformDrawer.draw(waveform: samples, on: cgContext, with: configuration.with(size: size))
             }
         }
         .onAppear {
             waveformDrawer.shouldDrawSilencePadding = shouldDrawSilencePadding
         }
-        .onChange(of: samples) { [samples] newValue in
-            lastNewSampleCount = max(0, newValue.count - samples.count)
-        }
         .onChange(of: shouldDrawSilencePadding) { newValue in
             waveformDrawer.shouldDrawSilencePadding = newValue
         }

DSWaveformImage/DSWaveformImage/UIKit/WaveformLiveView.swift

@@ -73,8 +73,6 @@ public class WaveformLiveView: UIView {
 class WaveformLiveLayer: CALayer {
     @NSManaged var samples: [Float]
 
-    private var lastNewSampleCount: Int = 0
-
     var configuration = WaveformLiveView.defaultConfiguration {
         didSet { contentsScale = configuration.scale }
     }
@@ -99,19 +97,15 @@ class WaveformLiveLayer: CALayer {
         super.draw(in: context)
 
         UIGraphicsPushContext(context)
-        waveformDrawer.draw(waveform: samples, newSampleCount: lastNewSampleCount, on: context, with: configuration.with(size: bounds.size))
+        waveformDrawer.draw(waveform: samples, on: context, with: configuration.with(size: bounds.size))
         UIGraphicsPopContext()
-        
-        lastNewSampleCount = 0
     }
 
     func add(_ newSamples: [Float]) {
-        lastNewSampleCount += newSamples.count
         samples += newSamples
     }
 
     func reset() {
-        lastNewSampleCount = 0
         samples = []
     }
 }