Add draggable preview and keep 30 histories

app/page.tsx

@@ -156,8 +156,18 @@ export default function Home() {
   const fileInputRef = useRef<HTMLInputElement | null>(null);
   const cropCanvasRef = useRef<HTMLCanvasElement | null>(null);
   const canvasRef = useRef<HTMLCanvasElement | null>(null);
+  const patternStageRef = useRef<HTMLDivElement | null>(null);
   const cropPreviewRef = useRef<HTMLDivElement | null>(null);
   const cropDragRef = useRef<{ pointerId: number; x: number; y: number; cropX: number; cropY: number } | null>(null);
+  const patternDragRef = useRef<{
+    pointerId: number;
+    x: number;
+    y: number;
+    scrollLeft: number;
+    scrollTop: number;
+    moved: boolean;
+  } | null>(null);
+  const suppressCanvasClickRef = useRef(false);
 
   useEffect(() => {
     const saved = localStorage.getItem("bead-pattern-history");
@@ -362,7 +372,50 @@ export default function Home() {
     });
   };
 
+  const handlePatternPointerDown = (event: React.PointerEvent<HTMLCanvasElement>) => {
+    if (event.button !== 0) return;
+    const stage = patternStageRef.current;
+    if (!stage) return;
+    stage.setPointerCapture(event.pointerId);
+    patternDragRef.current = {
+      pointerId: event.pointerId,
+      x: event.clientX,
+      y: event.clientY,
+      scrollLeft: stage.scrollLeft,
+      scrollTop: stage.scrollTop,
+      moved: false,
+    };
+  };
+
+  const handlePatternPointerMove = (event: React.PointerEvent<HTMLCanvasElement>) => {
+    const stage = patternStageRef.current;
+    const drag = patternDragRef.current;
+    if (!stage || !drag || drag.pointerId !== event.pointerId) return;
+    const deltaX = event.clientX - drag.x;
+    const deltaY = event.clientY - drag.y;
+    if (!drag.moved && Math.hypot(deltaX, deltaY) < 5) return;
+    drag.moved = true;
+    stage.classList.add("is-dragging");
+    stage.scrollLeft = drag.scrollLeft - deltaX;
+    stage.scrollTop = drag.scrollTop - deltaY;
+    setHoveredPixel(null);
+  };
+
+  const handlePatternPointerUp = (event: React.PointerEvent<HTMLCanvasElement>) => {
+    const stage = patternStageRef.current;
+    const drag = patternDragRef.current;
+    if (!drag || drag.pointerId !== event.pointerId) return;
+    suppressCanvasClickRef.current = drag.moved;
+    patternDragRef.current = null;
+    stage?.classList.remove("is-dragging");
+    if (stage?.hasPointerCapture(event.pointerId)) stage.releasePointerCapture(event.pointerId);
+  };
+
   const handleCanvasClick = (event: React.MouseEvent<HTMLCanvasElement>) => {
+    if (suppressCanvasClickRef.current) {
+      suppressCanvasClickRef.current = false;
+      return;
+    }
     const canvas = canvasRef.current;
     if (!canvas) return;
     const rect = canvas.getBoundingClientRect();
@@ -499,9 +552,22 @@ export default function Home() {
             </div>
           </div>
 
-          <div className="canvas-stage">
+          <div
+            className="canvas-stage"
+            ref={patternStageRef}
+          >
             <div className="canvas-wrap">
-              <canvas ref={canvasRef} onClick={handleCanvasClick} onMouseMove={handleCanvasMove} onMouseLeave={() => setHoveredPixel(null)} aria-label="转换后的拼豆像素图，点击格子可选择颜色" />
+              <canvas
+                ref={canvasRef}
+                onPointerDown={handlePatternPointerDown}
+                onPointerMove={handlePatternPointerMove}
+                onPointerUp={handlePatternPointerUp}
+                onPointerCancel={handlePatternPointerUp}
+                onClick={handleCanvasClick}
+                onMouseMove={handleCanvasMove}
+                onMouseLeave={() => setHoveredPixel(null)}
+                aria-label="转换后的拼豆像素图，可拖动查看，轻点格子选择颜色"
+              />
               {hoveredPixel && <div className="pixel-tooltip" style={{ left: hoveredPixel.left, top: hoveredPixel.top }}>
                 <span className="tooltip-swatch" style={{ backgroundColor: hoveredPixel.color.hex }} />
                 <strong>第 {hoveredPixel.row} 行 · 第 {hoveredPixel.column} 列</strong>