feat(realtime-canvas): auto-crop and zoom sketch before i2i

components/canvas/RealtimeCanvasDialog.tsx

@@ -108,14 +108,166 @@ async function canvasToJpegDataUri(
   canvas: HTMLCanvasElement,
   maxInputResolution: number,
   jpegQuality: number,
-  backgroundColor: string
+  backgroundColor: string,
+  options?: {
+    autoCrop?: boolean;
+  }
 ) {
+  const parseColor = (rawColor: string) => {
+    const tempCanvas = document.createElement("canvas");
+    tempCanvas.width = 1;
+    tempCanvas.height = 1;
+    const tempCtx = tempCanvas.getContext("2d");
+    if (!tempCtx) {
+      return { r: 255, g: 255, b: 255 };
+    }
+
+    tempCtx.fillStyle = rawColor;
+    const normalized = String(tempCtx.fillStyle || "").trim().toLowerCase();
+    if (normalized.startsWith("#")) {
+      const hex = normalized.slice(1);
+      if (hex.length === 3) {
+        return {
+          r: Number.parseInt(hex[0] + hex[0], 16),
+          g: Number.parseInt(hex[1] + hex[1], 16),
+          b: Number.parseInt(hex[2] + hex[2], 16),
+        };
+      }
+      if (hex.length >= 6) {
+        return {
+          r: Number.parseInt(hex.slice(0, 2), 16),
+          g: Number.parseInt(hex.slice(2, 4), 16),
+          b: Number.parseInt(hex.slice(4, 6), 16),
+        };
+      }
+    }
+
+    const rgbMatch = normalized.match(/^rgba?\((\d+),\s*(\d+),\s*(\d+)/);
+    if (rgbMatch) {
+      return {
+        r: Number(rgbMatch[1]),
+        g: Number(rgbMatch[2]),
+        b: Number(rgbMatch[3]),
+      };
+    }
+
+    return { r: 255, g: 255, b: 255 };
+  };
+
+  const findForegroundBox = () => {
+    const sourceCtx = canvas.getContext("2d", { willReadFrequently: true });
+    if (!sourceCtx) return null;
+    const { width, height } = canvas;
+    const imageData = sourceCtx.getImageData(0, 0, width, height);
+    const data = imageData.data;
+    const rowCounts = new Uint32Array(height);
+    const colCounts = new Uint32Array(width);
+    const bg = parseColor(backgroundColor);
+    const tolerance = 16;
+
+    let minX = width;
+    let minY = height;
+    let maxX = -1;
+    let maxY = -1;
+    let foregroundPixels = 0;
+
+    for (let y = 0; y < height; y += 1) {
+      for (let x = 0; x < width; x += 1) {
+        const offset = (y * width + x) * 4;
+        const alpha = data[offset + 3];
+        if (alpha < 16) continue;
+        const dr = Math.abs(data[offset] - bg.r);
+        const dg = Math.abs(data[offset + 1] - bg.g);
+        const db = Math.abs(data[offset + 2] - bg.b);
+        const isForeground = dr > tolerance || dg > tolerance || db > tolerance;
+        if (!isForeground) continue;
+
+        foregroundPixels += 1;
+        rowCounts[y] += 1;
+        colCounts[x] += 1;
+        if (x < minX) minX = x;
+        if (x > maxX) maxX = x;
+        if (y < minY) minY = y;
+        if (y > maxY) maxY = y;
+      }
+    }
+
+    if (foregroundPixels <= 0 || maxX < minX || maxY < minY) {
+      return null;
+    }
+
+    const trimPixels = Math.max(0, Math.floor(foregroundPixels * 0.01));
+    if (trimPixels > 0) {
+      let cumulative = 0;
+      for (let x = minX; x <= maxX; x += 1) {
+        cumulative += colCounts[x];
+        if (cumulative > trimPixels) {
+          minX = x;
+          break;
+        }
+      }
+
+      cumulative = 0;
+      for (let x = maxX; x >= minX; x -= 1) {
+        cumulative += colCounts[x];
+        if (cumulative > trimPixels) {
+          maxX = x;
+          break;
+        }
+      }
+
+      cumulative = 0;
+      for (let y = minY; y <= maxY; y += 1) {
+        cumulative += rowCounts[y];
+        if (cumulative > trimPixels) {
+          minY = y;
+          break;
+        }
+      }
+
+      cumulative = 0;
+      for (let y = maxY; y >= minY; y -= 1) {
+        cumulative += rowCounts[y];
+        if (cumulative > trimPixels) {
+          maxY = y;
+          break;
+        }
+      }
+    }
+
+    const boxWidth = Math.max(1, maxX - minX + 1);
+    const boxHeight = Math.max(1, maxY - minY + 1);
+    const padding = Math.max(20, Math.floor(Math.max(boxWidth, boxHeight) * 0.24));
+    const x = Math.max(0, minX - padding);
+    const y = Math.max(0, minY - padding);
+    const right = Math.min(width, maxX + 1 + padding);
+    const bottom = Math.min(height, maxY + 1 + padding);
+
+    return {
+      x,
+      y,
+      width: Math.max(1, right - x),
+      height: Math.max(1, bottom - y),
+    };
+  };
+
   const sourceWidth = canvas.width;
   const sourceHeight = canvas.height;
-  const longestSide = Math.max(sourceWidth, sourceHeight);
+  const cropBox = options?.autoCrop ? findForegroundBox() : null;
+  const drawSourceX = cropBox?.x || 0;
+  const drawSourceY = cropBox?.y || 0;
+  const drawSourceWidth = cropBox?.width || sourceWidth;
+  const drawSourceHeight = cropBox?.height || sourceHeight;
+
+  const autoCropEnabled = Boolean(options?.autoCrop && cropBox);
+  const longestSide = Math.max(drawSourceWidth, drawSourceHeight);
   const scale = longestSide > maxInputResolution ? maxInputResolution / longestSide : 1;
-  const exportWidth = Math.max(1, Math.round(sourceWidth * scale));
-  const exportHeight = Math.max(1, Math.round(sourceHeight * scale));
+  const exportWidth = autoCropEnabled
+    ? Math.max(512, maxInputResolution)
+    : Math.max(1, Math.round(drawSourceWidth * scale));
+  const exportHeight = autoCropEnabled
+    ? Math.max(512, maxInputResolution)
+    : Math.max(1, Math.round(drawSourceHeight * scale));
 
   const exportCanvas = document.createElement("canvas");
   exportCanvas.width = exportWidth;
@@ -127,7 +279,37 @@ async function canvasToJpegDataUri(
 
   exportCtx.fillStyle = backgroundColor;
   exportCtx.fillRect(0, 0, exportWidth, exportHeight);
-  exportCtx.drawImage(canvas, 0, 0, exportWidth, exportHeight);
+
+  if (autoCropEnabled) {
+    const fitScale = Math.min((exportWidth * 0.88) / drawSourceWidth, (exportHeight * 0.88) / drawSourceHeight);
+    const targetWidth = Math.max(1, Math.round(drawSourceWidth * fitScale));
+    const targetHeight = Math.max(1, Math.round(drawSourceHeight * fitScale));
+    const targetX = Math.round((exportWidth - targetWidth) / 2);
+    const targetY = Math.round((exportHeight - targetHeight) / 2);
+    exportCtx.drawImage(
+      canvas,
+      drawSourceX,
+      drawSourceY,
+      drawSourceWidth,
+      drawSourceHeight,
+      targetX,
+      targetY,
+      targetWidth,
+      targetHeight
+    );
+  } else {
+    exportCtx.drawImage(
+      canvas,
+      drawSourceX,
+      drawSourceY,
+      drawSourceWidth,
+      drawSourceHeight,
+      0,
+      0,
+      exportWidth,
+      exportHeight
+    );
+  }
 
   const blob = await new Promise<Blob | null>((resolve) => {
     exportCanvas.toBlob(resolve, "image/jpeg", jpegQuality);
@@ -276,7 +458,8 @@ export function RealtimeCanvasDialog({
           canvas,
           config.image.maxInputResolution,
           config.image.jpegQuality,
-          canvasBackgroundRef.current
+          canvasBackgroundRef.current,
+          { autoCrop: true }
         );
 
         const activeConnection = connectionRef.current;