From a56b089bb28b75323349718d324beed81eee047f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Rapha=C3=ABl=20Forment?= <raphael.forment@gmail.com>
Date: Sun, 12 Oct 2025 11:47:31 +0200
Subject: [PATCH] Region processing

---
 src/App.svelte                            |  83 +++++++++-
 src/lib/audio/utils/AudioEdit.ts          | 193 ++++++++++++++++++++++
 src/lib/components/WaveformDisplay.svelte | 160 +++++++++++++++++-
 3 files changed, 429 insertions(+), 7 deletions(-)
 create mode 100644 src/lib/audio/utils/AudioEdit.ts

diff --git a/src/App.svelte b/src/App.svelte
index d3d9d27..6acf357 100644
--- a/src/App.svelte
+++ b/src/App.svelte
@@ -10,6 +10,7 @@
   import { AudioService } from "./lib/audio/services/AudioService";
   import { downloadWAV } from "./lib/audio/utils/WAVEncoder";
   import { loadVolume, saveVolume, loadDuration, saveDuration, loadPitchLockEnabled, savePitchLockEnabled, loadPitchLockFrequency, savePitchLockFrequency } from "./lib/utils/settings";
+  import { cropAudio, cutAudio, processSelection } from "./lib/audio/utils/AudioEdit";
   import { generateRandomColor } from "./lib/utils/colors";
   import { getRandomProcessor } from "./lib/audio/processors/registry";
   import type { AudioProcessor } from "./lib/audio/processors/AudioProcessor";
@@ -39,6 +40,8 @@
   let pitchLockFrequency = $state(loadPitchLockFrequency());
   let pitchLockInput = $state(formatFrequency(loadPitchLockFrequency()));
   let pitchLockInputValid = $state(true);
+  let selectionStart = $state<number | null>(null);
+  let selectionEnd = $state<number | null>(null);
 
   const showDuration = $derived(engineType !== 'sample');
   const showRandomButton = $derived(engineType === 'generative');
@@ -47,6 +50,8 @@
   const showMutateButton = $derived(engineType === 'generative' && !isProcessed && currentBuffer);
   const showPitchLock = $derived(engineType === 'generative');
   const pitchLock = $derived<PitchLock>({ enabled: pitchLockEnabled, frequency: pitchLockFrequency });
+  const hasSelection = $derived(selectionStart !== null && selectionEnd !== null && currentBuffer !== null);
+  const showEditButtons = $derived(hasSelection);
 
   $effect(() => {
     audioService.setVolume(volume);
@@ -89,13 +94,20 @@
     onVolumeIncrease: (large) => {
       volume = Math.min(1, volume + (large ? 0.2 : 0.05));
     },
-    onEscape: () => showModal && closeModal(),
+    onEscape: () => {
+      if (hasSelection) {
+        clearSelection();
+      } else if (showModal) {
+        closeModal();
+      }
+    },
   });
 
   function generateRandom() {
     currentParams = engine.randomParams(pitchLock);
     waveformColor = generateRandomColor();
     isProcessed = false;
+    clearSelection();
     regenerateBuffer();
   }
 
@@ -154,9 +166,26 @@
   async function applyProcessor(processor: AudioProcessor) {
     if (!currentBuffer) return;
 
-    const leftChannel = currentBuffer.getChannelData(0);
-    const rightChannel = currentBuffer.getChannelData(1);
-    const [processedLeft, processedRight] = await processor.process(leftChannel, rightChannel);
+    let processedLeft: Float32Array;
+    let processedRight: Float32Array;
+
+    if (hasSelection) {
+      const start = Math.min(selectionStart!, selectionEnd!);
+      const end = Math.max(selectionStart!, selectionEnd!);
+      const sampleRate = audioService.getSampleRate();
+
+      [processedLeft, processedRight] = await processSelection(
+        currentBuffer,
+        start,
+        end,
+        processor,
+        sampleRate
+      );
+    } else {
+      const leftChannel = currentBuffer.getChannelData(0);
+      const rightChannel = currentBuffer.getChannelData(1);
+      [processedLeft, processedRight] = await processor.process(leftChannel, rightChannel);
+    }
 
     currentBuffer = audioService.createAudioBuffer([processedLeft, processedRight]);
     isProcessed = true;
@@ -169,6 +198,7 @@
     currentBuffer = null;
     currentParams = null;
     isProcessed = false;
+    clearSelection();
 
     if (engineType === 'generative') {
       generateRandom();
@@ -256,6 +286,44 @@
     showProcessorPopup = false;
   }
 
+  function handleSelectionChange(start: number | null, end: number | null) {
+    selectionStart = start;
+    selectionEnd = end;
+  }
+
+  function clearSelection() {
+    selectionStart = null;
+    selectionEnd = null;
+  }
+
+  function cropSelection() {
+    if (!currentBuffer || selectionStart === null || selectionEnd === null) return;
+
+    const start = Math.min(selectionStart, selectionEnd);
+    const end = Math.max(selectionStart, selectionEnd);
+
+    const sampleRate = audioService.getSampleRate();
+    const [newLeft, newRight] = cropAudio(currentBuffer, start, end, sampleRate);
+
+    currentBuffer = audioService.createAudioBuffer([newLeft, newRight]);
+    clearSelection();
+    audioService.play(currentBuffer);
+  }
+
+  function cutSelection() {
+    if (!currentBuffer || selectionStart === null || selectionEnd === null) return;
+
+    const start = Math.min(selectionStart, selectionEnd);
+    const end = Math.max(selectionStart, selectionEnd);
+
+    const sampleRate = audioService.getSampleRate();
+    const [newLeft, newRight] = cutAudio(currentBuffer, start, end, sampleRate);
+
+    currentBuffer = audioService.createAudioBuffer([newLeft, newRight]);
+    clearSelection();
+    audioService.play(currentBuffer);
+  }
+
   async function closeModal() {
     showModal = false;
     await audioService.initialize();
@@ -375,6 +443,9 @@
           buffer={currentBuffer}
           color={waveformColor}
           {playbackPosition}
+          {selectionStart}
+          {selectionEnd}
+          onselectionchange={handleSelectionChange}
           onclick={replaySound}
         />
       {/if}
@@ -391,6 +462,10 @@
         {#if showMutateButton}
           <button onclick={mutate}>Mutate (M)</button>
         {/if}
+        {#if showEditButtons}
+          <button onclick={cropSelection}>Crop</button>
+          <button onclick={cutSelection}>Cut</button>
+        {/if}
         {#if currentBuffer}
           <div
             class="process-button-container"
diff --git a/src/lib/audio/utils/AudioEdit.ts b/src/lib/audio/utils/AudioEdit.ts
new file mode 100644
index 0000000..e1ce5fa
--- /dev/null
+++ b/src/lib/audio/utils/AudioEdit.ts
@@ -0,0 +1,193 @@
+import type { AudioProcessor } from "../processors/AudioProcessor";
+
+const CROSSFADE_SAMPLES = 256;
+
+/**
+ * Apply equal-power crossfade between two regions
+ */
+function applyCrossfade(
+  samples: Float32Array,
+  fadeOutStart: number,
+  fadeOutEnd: number,
+  fadeInStart: number,
+  fadeInEnd: number
+): void {
+  const fadeLength = Math.min(fadeOutEnd - fadeOutStart, fadeInEnd - fadeInStart);
+
+  for (let i = 0; i < fadeLength; i++) {
+    const t = i / fadeLength;
+    const fadeOutGain = Math.cos(t * Math.PI * 0.5);
+    const fadeInGain = Math.sin(t * Math.PI * 0.5);
+
+    const fadeOutIdx = fadeOutStart + i;
+    const fadeInIdx = fadeInStart + i;
+
+    if (fadeOutIdx < samples.length && fadeInIdx < samples.length) {
+      const fadeOutSample = samples[fadeOutIdx] * fadeOutGain;
+      const fadeInSample = samples[fadeInIdx] * fadeInGain;
+      samples[fadeOutIdx] = fadeOutSample + fadeInSample;
+    }
+  }
+}
+
+/**
+ * Extract a portion of the audio buffer (crop to selection)
+ */
+export function cropAudio(
+  buffer: AudioBuffer,
+  startSample: number,
+  endSample: number,
+  sampleRate: number
+): [Float32Array, Float32Array] {
+  const start = Math.max(0, Math.floor(startSample));
+  const end = Math.min(buffer.length, Math.ceil(endSample));
+  const length = end - start;
+
+  const leftChannel = buffer.getChannelData(0);
+  const rightChannel = buffer.getChannelData(1);
+
+  const newLeft = new Float32Array(length);
+  const newRight = new Float32Array(length);
+
+  for (let i = 0; i < length; i++) {
+    newLeft[i] = leftChannel[start + i];
+    newRight[i] = rightChannel[start + i];
+  }
+
+  return [newLeft, newRight];
+}
+
+/**
+ * Remove a portion of the audio buffer (cut with crossfade)
+ */
+export function cutAudio(
+  buffer: AudioBuffer,
+  startSample: number,
+  endSample: number,
+  sampleRate: number
+): [Float32Array, Float32Array] {
+  const start = Math.max(0, Math.floor(startSample));
+  const end = Math.min(buffer.length, Math.ceil(endSample));
+
+  const leftChannel = buffer.getChannelData(0);
+  const rightChannel = buffer.getChannelData(1);
+
+  const beforeLength = start;
+  const afterLength = buffer.length - end;
+  const newLength = beforeLength + afterLength;
+
+  const newLeft = new Float32Array(newLength);
+  const newRight = new Float32Array(newLength);
+
+  for (let i = 0; i < beforeLength; i++) {
+    newLeft[i] = leftChannel[i];
+    newRight[i] = rightChannel[i];
+  }
+
+  for (let i = 0; i < afterLength; i++) {
+    newLeft[beforeLength + i] = leftChannel[end + i];
+    newRight[beforeLength + i] = rightChannel[end + i];
+  }
+
+  const crossfadeLength = Math.min(CROSSFADE_SAMPLES, beforeLength, afterLength);
+  if (crossfadeLength > 0 && beforeLength > 0 && afterLength > 0) {
+    const crossfadeStart = beforeLength - crossfadeLength;
+
+    for (let i = 0; i < crossfadeLength; i++) {
+      const t = i / crossfadeLength;
+      const fadeOutGain = Math.cos(t * Math.PI * 0.5);
+      const fadeInGain = Math.sin(t * Math.PI * 0.5);
+
+      const idx = crossfadeStart + i;
+      const beforeSample = newLeft[idx];
+      const afterSample = newLeft[beforeLength + i];
+      newLeft[idx] = beforeSample * fadeOutGain + afterSample * fadeInGain;
+
+      const beforeSampleR = newRight[idx];
+      const afterSampleR = newRight[beforeLength + i];
+      newRight[idx] = beforeSampleR * fadeOutGain + afterSampleR * fadeInGain;
+    }
+
+    for (let i = crossfadeLength; i < afterLength; i++) {
+      newLeft[beforeLength - crossfadeLength + i] = newLeft[beforeLength + i];
+      newRight[beforeLength - crossfadeLength + i] = newRight[beforeLength + i];
+    }
+
+    const finalLength = beforeLength - crossfadeLength + afterLength;
+    return [
+      newLeft.slice(0, finalLength),
+      newRight.slice(0, finalLength)
+    ];
+  }
+
+  return [newLeft, newRight];
+}
+
+/**
+ * Process only a selected region of the audio with crossfades at boundaries
+ */
+export async function processSelection(
+  buffer: AudioBuffer,
+  startSample: number,
+  endSample: number,
+  processor: AudioProcessor,
+  sampleRate: number
+): Promise<[Float32Array, Float32Array]> {
+  const start = Math.max(0, Math.floor(startSample));
+  const end = Math.min(buffer.length, Math.ceil(endSample));
+  const selectionLength = end - start;
+
+  const leftChannel = buffer.getChannelData(0);
+  const rightChannel = buffer.getChannelData(1);
+
+  const selectedLeft = new Float32Array(selectionLength);
+  const selectedRight = new Float32Array(selectionLength);
+
+  for (let i = 0; i < selectionLength; i++) {
+    selectedLeft[i] = leftChannel[start + i];
+    selectedRight[i] = rightChannel[start + i];
+  }
+
+  const [processedLeft, processedRight] = await processor.process(selectedLeft, selectedRight);
+
+  const newLeft = new Float32Array(buffer.length);
+  const newRight = new Float32Array(buffer.length);
+
+  for (let i = 0; i < buffer.length; i++) {
+    newLeft[i] = leftChannel[i];
+    newRight[i] = rightChannel[i];
+  }
+
+  for (let i = 0; i < processedLeft.length; i++) {
+    newLeft[start + i] = processedLeft[i];
+    newRight[start + i] = processedRight[i];
+  }
+
+  const maxCrossfade = Math.floor(selectionLength / 4);
+  const crossfadeLength = Math.min(CROSSFADE_SAMPLES, start, buffer.length - end, maxCrossfade);
+
+  if (crossfadeLength > 0) {
+    for (let i = 0; i < crossfadeLength; i++) {
+      const t = i / crossfadeLength;
+      const unprocessedGain = Math.cos(t * Math.PI * 0.5);
+      const processedGain = Math.sin(t * Math.PI * 0.5);
+
+      const startIdx = start + i;
+      newLeft[startIdx] = leftChannel[startIdx] * unprocessedGain + processedLeft[i] * processedGain;
+      newRight[startIdx] = rightChannel[startIdx] * unprocessedGain + processedRight[i] * processedGain;
+    }
+
+    for (let i = 0; i < crossfadeLength; i++) {
+      const t = i / crossfadeLength;
+      const processedGain = Math.cos(t * Math.PI * 0.5);
+      const unprocessedGain = Math.sin(t * Math.PI * 0.5);
+
+      const endIdx = end - crossfadeLength + i;
+      const processedIdx = processedLeft.length - crossfadeLength + i;
+      newLeft[endIdx] = processedLeft[processedIdx] * processedGain + leftChannel[endIdx] * unprocessedGain;
+      newRight[endIdx] = processedRight[processedIdx] * processedGain + rightChannel[endIdx] * unprocessedGain;
+    }
+  }
+
+  return [newLeft, newRight];
+}
diff --git a/src/lib/components/WaveformDisplay.svelte b/src/lib/components/WaveformDisplay.svelte
index 6efdbbc..c763423 100644
--- a/src/lib/components/WaveformDisplay.svelte
+++ b/src/lib/components/WaveformDisplay.svelte
@@ -5,11 +5,26 @@
     buffer: AudioBuffer | null;
     color?: string;
     playbackPosition?: number;
+    selectionStart?: number | null;
+    selectionEnd?: number | null;
+    onselectionchange?: (start: number | null, end: number | null) => void;
     onclick?: () => void;
   }
 
-  let { buffer, color = '#646cff', playbackPosition = 0, onclick }: Props = $props();
+  let {
+    buffer,
+    color = '#646cff',
+    playbackPosition = 0,
+    selectionStart = null,
+    selectionEnd = null,
+    onselectionchange,
+    onclick
+  }: Props = $props();
+
   let canvas: HTMLCanvasElement;
+  let isDragging = $state(false);
+  let dragStartX = $state(0);
+  let hasMoved = $state(false);
 
   onMount(() => {
     const resizeObserver = new ResizeObserver(() => {
@@ -28,6 +43,8 @@
     buffer;
     color;
     playbackPosition;
+    selectionStart;
+    selectionEnd;
     draw();
   });
 
@@ -37,12 +54,120 @@
     canvas.height = parent.clientHeight;
   }
 
-  function handleClick() {
+  function handleClick(event: MouseEvent) {
+    if (hasMoved) return;
+
+    const rect = canvas.getBoundingClientRect();
+    const x = event.clientX - rect.left;
+
+    if (buffer && selectionStart !== null && selectionEnd !== null) {
+      const selStart = Math.min(selectionStart, selectionEnd);
+      const selEnd = Math.max(selectionStart, selectionEnd);
+      const width = canvas.width;
+      const startX = (selStart / buffer.length) * width;
+      const endX = (selEnd / buffer.length) * width;
+
+      if (x < startX || x > endX) {
+        if (onselectionchange) {
+          onselectionchange(null, null);
+        }
+        return;
+      }
+    }
+
     if (onclick) {
       onclick();
     }
   }
 
+  function handleMouseDown(event: MouseEvent) {
+    if (!buffer) return;
+
+    isDragging = true;
+    hasMoved = false;
+    const rect = canvas.getBoundingClientRect();
+    dragStartX = event.clientX - rect.left;
+
+    const sample = Math.floor((dragStartX / canvas.width) * buffer.length);
+    if (onselectionchange) {
+      onselectionchange(sample, sample);
+    }
+  }
+
+  function handleMouseMove(event: MouseEvent) {
+    if (!isDragging || !buffer) return;
+
+    const rect = canvas.getBoundingClientRect();
+    const currentX = event.clientX - rect.left;
+    const clampedX = Math.max(0, Math.min(canvas.width, currentX));
+
+    if (Math.abs(clampedX - dragStartX) > 2) {
+      hasMoved = true;
+    }
+
+    const endSample = Math.floor((clampedX / canvas.width) * buffer.length);
+
+    if (onselectionchange && selectionStart !== null) {
+      onselectionchange(selectionStart, endSample);
+    }
+  }
+
+  function handleMouseUp() {
+    if (isDragging && selectionStart !== null && selectionEnd !== null) {
+      if (Math.abs(selectionEnd - selectionStart) < buffer!.sampleRate * 0.01) {
+        if (onselectionchange) {
+          onselectionchange(null, null);
+        }
+      }
+    }
+    isDragging = false;
+  }
+
+  function handleTouchStart(event: TouchEvent) {
+    if (!buffer || event.touches.length !== 1) return;
+
+    event.preventDefault();
+    isDragging = true;
+    hasMoved = false;
+    const rect = canvas.getBoundingClientRect();
+    dragStartX = event.touches[0].clientX - rect.left;
+
+    const sample = Math.floor((dragStartX / canvas.width) * buffer.length);
+    if (onselectionchange) {
+      onselectionchange(sample, sample);
+    }
+  }
+
+  function handleTouchMove(event: TouchEvent) {
+    if (!isDragging || !buffer || event.touches.length !== 1) return;
+
+    event.preventDefault();
+    const rect = canvas.getBoundingClientRect();
+    const currentX = event.touches[0].clientX - rect.left;
+    const clampedX = Math.max(0, Math.min(canvas.width, currentX));
+
+    if (Math.abs(clampedX - dragStartX) > 2) {
+      hasMoved = true;
+    }
+
+    const endSample = Math.floor((clampedX / canvas.width) * buffer.length);
+
+    if (onselectionchange && selectionStart !== null) {
+      onselectionchange(selectionStart, endSample);
+    }
+  }
+
+  function handleTouchEnd() {
+    if (isDragging && selectionStart !== null && selectionEnd !== null) {
+      if (Math.abs(selectionEnd - selectionStart) < buffer!.sampleRate * 0.01) {
+        if (onselectionchange) {
+          onselectionchange(null, null);
+        }
+      }
+    }
+    isDragging = false;
+  }
+
   function draw() {
     if (!canvas) return;
 
@@ -102,6 +227,25 @@
       }
     }
 
+    if (buffer && selectionStart !== null && selectionEnd !== null) {
+      const selStart = Math.min(selectionStart, selectionEnd);
+      const selEnd = Math.max(selectionStart, selectionEnd);
+      const startX = (selStart / buffer.length) * width;
+      const endX = (selEnd / buffer.length) * width;
+
+      ctx.fillStyle = 'rgba(100, 108, 255, 0.2)';
+      ctx.fillRect(startX, 0, endX - startX, height);
+
+      ctx.strokeStyle = 'rgba(100, 108, 255, 0.8)';
+      ctx.lineWidth = 2;
+      ctx.beginPath();
+      ctx.moveTo(startX, 0);
+      ctx.lineTo(startX, height);
+      ctx.moveTo(endX, 0);
+      ctx.lineTo(endX, height);
+      ctx.stroke();
+    }
+
     if (playbackPosition >= 0 && buffer) {
       const duration = buffer.length / buffer.sampleRate;
       const x = (playbackPosition / duration) * width;
@@ -116,7 +260,17 @@
   }
 </script>
 
-<canvas bind:this={canvas} onclick={handleClick} style="cursor: pointer;"></canvas>
+<svelte:window onmouseup={handleMouseUp} ontouchend={handleTouchEnd} />
+
+<canvas
+  bind:this={canvas}
+  onclick={handleClick}
+  onmousedown={handleMouseDown}
+  onmousemove={handleMouseMove}
+  ontouchstart={handleTouchStart}
+  ontouchmove={handleTouchMove}
+  style="cursor: {isDragging ? 'text' : 'pointer'}; touch-action: none;"
+></canvas>
 
 <style>
   canvas {