如何打印A4尺寸页面？A4面板打印图片居中异常问题求助

我编写了用于打印带图片的A4尺寸面板的代码，目前面板可按A4尺寸打印，但图片仅在纸张居中显示，未适配A4面板。

以下是我的代码：

private void btn_print_Click(object sender, EventArgs e) {
  PrintDocument pd = new PrintDocument();
  pd.PrintPage += new PrintPageEventHandler(PrintPage);
  PrintDialog printDialog = new PrintDialog();
  printDialog.Document = pd;
  if (printDialog.ShowDialog() == DialogResult.OK) {
    pd.Print();
  }
}

private void PrintPage(object sender, PrintPageEventArgs e) {
  Graphics g = e.Graphics;
  Rectangle marginBounds = e.MarginBounds;

  // Calculate the aspect ratio of the image
  float aspectRatio = (float) panel1.BackgroundImage.Width / panel1.BackgroundImage.Height;

  // Calculate the target width and height for A4 size
  int targetWidth = marginBounds.Width;
  int targetHeight = (int)(targetWidth / aspectRatio);

  // Check if the height exceeds the printable area height
  if (targetHeight > marginBounds.Height) {
    targetHeight = marginBounds.Height;
    targetWidth = (int)(targetHeight * aspectRatio);
  }

  // Calculate the position to center the image
  int x = marginBounds.Left + (marginBounds.Width - targetWidth) / 2;
  int y = marginBounds.Top + (marginBounds.Height - targetHeight) / 2;

  // Draw the image on the print page graphics
  g.DrawImage(panel1.BackgroundImage, x, y, targetWidth, targetHeight);
}

问题排查与修复 #

你的代码逻辑是保持图片原比例居中显示，因此会出现图片无法铺满A4面板的情况。若要让图片完全适配A4可打印区域，可根据需求选择以下两种修改方式：

方式1：拉伸图片铺满整个可打印区域（忽略原比例） #

直接使用可打印区域的宽高绘制图片，无需计算比例：

private void PrintPage(object sender, PrintPageEventArgs e) {
  Graphics g = e.Graphics;
  Rectangle marginBounds = e.MarginBounds;
  // 直接用可打印区域尺寸绘制图片
  g.DrawImage(panel1.BackgroundImage, marginBounds);
}

方式2：按比例铺满（裁剪超出部分） #

若要保持图片比例并铺满A4区域，需计算覆盖整个区域的尺寸，再裁剪超出部分：

private void PrintPage(object sender, PrintPageEventArgs e) {
  Graphics g = e.Graphics;
  Rectangle marginBounds = e.MarginBounds;
  Image img = panel1.BackgroundImage;

  float imgRatio = (float)img.Width / img.Height;
  float areaRatio = (float)marginBounds.Width / marginBounds.Height;

  int drawWidth, drawHeight;
  int x = marginBounds.Left, y = marginBounds.Top;

  if (imgRatio > areaRatio) {
    // 图片更宽，按高度铺满，裁剪左右
    drawHeight = marginBounds.Height;
    drawWidth = (int)(drawHeight * imgRatio);
    x -= (drawWidth - marginBounds.Width) / 2;
  } else {
    // 图片更高，按宽度铺满，裁剪上下
    drawWidth = marginBounds.Width;
    drawHeight = (int)(drawWidth / imgRatio);
    y -= (drawHeight - marginBounds.Height) / 2;
  }

  // 绘制图片，超出可打印区域的部分会被自动裁剪
  g.DrawImage(img, x, y, drawWidth, drawHeight);
}

额外注意点 #

• 若需要去掉打印边距，可将MarginBounds替换为e.PageBounds（对应整个纸张区域）。
• 可通过g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;设置图形插值模式，提升拉伸后图片的清晰度。

内容的提问来源于stack exchange，提问作者Gihan Sanjeewa