fix: verify scale adjust footprint shrink

lib/canvas/generate-image.ts

@@ -170,6 +170,8 @@ const SCALE_ADJUST_DIFF_SAMPLE_SIZE = 112;
 const SCALE_ADJUST_FALLBACK_MASK_DISTANCE_THRESHOLD = 42;
 const SCALE_ADJUST_FALLBACK_MASK_LUMA_GAP = 18;
 const SCALE_ADJUST_FALLBACK_INPAINT_ITERATIONS = 180;
+const SCALE_ADJUST_SHRINK_OUTSIDE_FOOTPRINT_MAX_RATIO = 0.72;
+const SCALE_ADJUST_SHRINK_MIN_SOURCE_OUTSIDE_PIXELS = 60;
 
 const SUPPORTED_CANVAS_PROVIDER_TYPES = new Set([
   "gemini",
@@ -815,6 +817,109 @@ function isScaleAdjustOutsidePixelChanged(params: {
   );
 }
 
+async function getScaleAdjustFootprintChangeStats(params: {
+  generatedBuffer: Buffer;
+  sourceBuffer: Buffer;
+  sourceWidth: number;
+  sourceHeight: number;
+  verification: CanvasScaleAdjustVerificationConfig;
+}) {
+  const { generatedBuffer, sourceBuffer, sourceHeight, sourceWidth, verification } =
+    params;
+  const normalizeToRaw = (buffer: Buffer) =>
+    sharp(buffer, { failOn: "none" })
+      .rotate()
+      .resize(sourceWidth, sourceHeight, {
+        fit: "cover",
+        position: "center",
+      })
+      .removeAlpha()
+      .toColorspace("srgb")
+      .raw()
+      .toBuffer();
+  const [sourceRaw, generatedRaw] = await Promise.all([
+    normalizeToRaw(sourceBuffer),
+    normalizeToRaw(generatedBuffer),
+  ]);
+  const shrinkStats: Array<{
+    generatedOutsidePixels: number;
+    outsideRatio: number;
+    passed: boolean;
+    regionIndex: number;
+    sourceOutsidePixels: number;
+  }> = [];
+
+  for (const [index, region] of verification.regions.entries()) {
+    const targetRegion =
+      verification.targetRegions?.[index] ||
+      (typeof verification.scalePercent === "number"
+        ? scaleRegionAroundCenter(region, verification.scalePercent)
+        : null);
+    if (!targetRegion) continue;
+    const widthFactor = region.width > 0 ? targetRegion.width / region.width : 1;
+    const heightFactor = region.height > 0 ? targetRegion.height / region.height : 1;
+    const isShrink = widthFactor < 0.92 || heightFactor < 0.92;
+    if (!isShrink) continue;
+
+    const sourceBox = rectToPixelBox({
+      height: sourceHeight,
+      region,
+      width: sourceWidth,
+    });
+    const targetBox = rectToPixelBox({
+      height: sourceHeight,
+      region: targetRegion,
+      width: sourceWidth,
+    });
+    const sourceMask = buildScaleAdjustFallbackSubjectMask({
+      box: sourceBox,
+      raw: sourceRaw,
+      width: sourceWidth,
+    });
+    const generatedMask = buildScaleAdjustFallbackSubjectMask({
+      box: sourceBox,
+      raw: generatedRaw,
+      width: sourceWidth,
+    });
+    let sourceOutsidePixels = 0;
+    let generatedOutsidePixels = 0;
+    for (let localY = 0; localY < sourceBox.height; localY += 1) {
+      const y = sourceBox.top + localY;
+      for (let localX = 0; localX < sourceBox.width; localX += 1) {
+        const x = sourceBox.left + localX;
+        const insideTarget =
+          x >= targetBox.left &&
+          x < targetBox.left + targetBox.width &&
+          y >= targetBox.top &&
+          y < targetBox.top + targetBox.height;
+        if (insideTarget) continue;
+        const maskIndex = localY * sourceBox.width + localX;
+        if (sourceMask[maskIndex] > 0) sourceOutsidePixels += 1;
+        if (generatedMask[maskIndex] > 0) generatedOutsidePixels += 1;
+      }
+    }
+    const outsideRatio =
+      sourceOutsidePixels > 0 ? generatedOutsidePixels / sourceOutsidePixels : 0;
+    const passed =
+      sourceOutsidePixels < SCALE_ADJUST_SHRINK_MIN_SOURCE_OUTSIDE_PIXELS ||
+      outsideRatio <= SCALE_ADJUST_SHRINK_OUTSIDE_FOOTPRINT_MAX_RATIO;
+    shrinkStats.push({
+      generatedOutsidePixels,
+      outsideRatio,
+      passed,
+      regionIndex: index,
+      sourceOutsidePixels,
+    });
+  }
+
+  return {
+    failedRegionCount: shrinkStats.filter((item) => !item.passed).length,
+    passed: shrinkStats.every((item) => item.passed),
+    shrinkRegionCount: shrinkStats.length,
+    shrinkStats,
+  };
+}
+
 async function loadScaleAdjustSourceImage(
   verification: CanvasScaleAdjustVerificationConfig
 ) {
@@ -1038,6 +1143,7 @@ async function applyScaleAdjustVerificationToImages(params: {
     changedInside: boolean;
     cleanedImage?: ParsedImage;
     diffScores: number[];
+    footprintStats: Awaited<ReturnType<typeof getScaleAdjustFootprintChangeStats>>;
     image: ParsedImage;
     index: number;
     outsideChanged: boolean;
@@ -1050,7 +1156,13 @@ async function applyScaleAdjustVerificationToImages(params: {
     const generatedUrl = image.originalUrl || image.thumbnailUrl;
     const generatedBuffer = await fetchImageBufferFromUrl(generatedUrl);
     const changeRegions = getScaleAdjustEffectiveChangeRegions(verification);
-    const [diffScores, changeDiffScores, outsideDiffScores, outsidePixelStats] = await Promise.all([
+    const [
+      diffScores,
+      changeDiffScores,
+      outsideDiffScores,
+      outsidePixelStats,
+      footprintStats,
+    ] = await Promise.all([
       getScaleAdjustDiffScores({
         generatedBuffer,
         regions: verification.regions,
@@ -1079,10 +1191,18 @@ async function applyScaleAdjustVerificationToImages(params: {
         sourceWidth: sourceImage.sourceWidth,
         verification,
       }),
+      getScaleAdjustFootprintChangeStats({
+        generatedBuffer,
+        sourceBuffer: sourceImage.sourceBuffer,
+        sourceHeight: sourceImage.sourceHeight,
+        sourceWidth: sourceImage.sourceWidth,
+        verification,
+      }),
     ]);
-    const changedInside = changeDiffScores.some(
+    const visuallyChangedInside = changeDiffScores.some(
       (score) => score >= SCALE_ADJUST_VISUAL_DIFF_THRESHOLD
     );
+    const changedInside = visuallyChangedInside && footprintStats.passed;
     const outsideChanged =
       isScaleAdjustOutsideChanged(outsideDiffScores) ||
       isScaleAdjustOutsidePixelChanged(outsidePixelStats);
@@ -1090,6 +1210,18 @@ async function applyScaleAdjustVerificationToImages(params: {
     console.info("[Canvas Generate Image] Scale adjust result guard:", {
       debugLabel,
       changedInside,
+      footprintChanged: footprintStats.passed,
+      footprintStats: {
+        failedRegionCount: footprintStats.failedRegionCount,
+        shrinkRegionCount: footprintStats.shrinkRegionCount,
+        shrinkStats: footprintStats.shrinkStats.map((item) => ({
+          generatedOutsidePixels: item.generatedOutsidePixels,
+          outsideRatio: Number(item.outsideRatio.toFixed(3)),
+          passed: item.passed,
+          regionIndex: item.regionIndex,
+          sourceOutsidePixels: item.sourceOutsidePixels,
+        })),
+      },
       imageIndex: index,
       outsideChanged,
       outsideDiffScores: outsideDiffScores.map((score) => Number(score.toFixed(2))),
@@ -1120,6 +1252,18 @@ async function applyScaleAdjustVerificationToImages(params: {
         imageIndex: index,
         reasons: guardWarnings,
         changedInside,
+        footprintChanged: footprintStats.passed,
+        footprintStats: {
+          failedRegionCount: footprintStats.failedRegionCount,
+          shrinkRegionCount: footprintStats.shrinkRegionCount,
+          shrinkStats: footprintStats.shrinkStats.map((item) => ({
+            generatedOutsidePixels: item.generatedOutsidePixels,
+            outsideRatio: Number(item.outsideRatio.toFixed(3)),
+            passed: item.passed,
+            regionIndex: item.regionIndex,
+            sourceOutsidePixels: item.sourceOutsidePixels,
+          })),
+        },
         outsideChanged,
         outsideDiffScores: outsideDiffScores.map((score) => Number(score.toFixed(2))),
         outsidePixelStats: {
@@ -1155,6 +1299,7 @@ async function applyScaleAdjustVerificationToImages(params: {
           changedInside,
           cleanedImage,
           diffScores,
+          footprintStats,
           image,
           index,
           outsideChanged,
@@ -1176,6 +1321,7 @@ async function applyScaleAdjustVerificationToImages(params: {
       changedInside,
       cleanedImage,
       diffScores,
+      footprintStats,
       image,
       index,
       outsideChanged,