修复手机签名时坐标偏移的问题，确保画布尺寸与显示尺寸一致

certificate.html

@@ -774,6 +774,9 @@
       // 初始化主画布
       canvas = document.getElementById('signatureCanvas');
       if (canvas) {
+        // 确保画布的实际尺寸与显示尺寸一致
+        resizeCanvas(canvas);
+        
         ctx = canvas.getContext('2d');
         ctx.strokeStyle = '#000';
         ctx.lineWidth = 2;
@@ -786,6 +789,12 @@
       
       // 初始化弹窗画布
       initModalSignatureCanvas();
+      
+      // 监听窗口大小变化，重新调整画布尺寸
+      window.addEventListener('resize', function() {
+        if (canvas) resizeCanvas(canvas);
+        if (modalCanvas) resizeCanvas(modalCanvas);
+      });
     }
     
     // 初始化弹窗签名画布
@@ -793,6 +802,9 @@
       modalCanvas = document.getElementById('signatureModalCanvas');
       if (!modalCanvas) return;
       
+      // 确保画布的实际尺寸与显示尺寸一致
+      resizeCanvas(modalCanvas);
+      
       modalCtx = modalCanvas.getContext('2d');
       modalCtx.strokeStyle = '#000';
       modalCtx.lineWidth = 3; // 弹窗中使用更粗的线条
@@ -814,15 +826,25 @@
       modalCanvas.addEventListener('touchend', stopModalDrawing);
     }
     
+    // 调整画布尺寸，确保实际尺寸与显示尺寸一致
+    function resizeCanvas(canvas) {
+      const rect = canvas.getBoundingClientRect();
+      canvas.width = rect.width;
+      canvas.height = rect.height;
+    }
+    
     // 打开签名弹窗
     function openSignatureModal() {
       const modal = document.getElementById('signatureModal');
       if (modal) {
         modal.classList.add('show');
-        // 清除弹窗画布
-        clearModalSignature();
-        // 添加点击外部区域关闭弹窗的事件
+        // 等待弹窗完全显示后调整画布尺寸
         setTimeout(() => {
+          if (modalCanvas) {
+            resizeCanvas(modalCanvas);
+            clearModalSignature();
+          }
+          // 添加点击外部区域关闭弹窗的事件
           modal.addEventListener('click', handleModalClick);
         }, 100);
       }