VB2022实现位图无拉伸缩放至A4尺寸打印的代码咨询

问题说明 #

现有代码能将Panel中的内容生成为位图并打印到A4纸，但位图会被强制拉伸填充A4区域，导致原有形状变形。需要修改代码，实现位图等比例放大/缩小，完整适配A4纸且保持长宽比。

原始代码 #

Public Class Form1

    Private Sub PrintDocument1_PrintPage(sender As Object, e As Printing.PrintPageEventArgs) Handles PrintDocument1.PrintPage

        Dim margX As Single = e.PageSettings.HardMarginX
        Dim margY As Single = e.PageSettings.HardMarginY
        Dim adjustToA4 As New Rectangle(e.PageBounds.Left - margX, e.PageBounds.Top - margY, e.PageBounds.Width, e.PageBounds.Height)


        Dim dm As New Bitmap(Panel2.Width, Panel2.Height)
        Panel2.DrawToBitmap(dm, New Rectangle(0, 0, Panel2.Width, Panel2.Height))

        e.Graphics.DrawImage(dm, adjustToA4)

    End Sub

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click

        PrintPreviewDialog1.Document = PrintDocument1
        PrintPreviewDialog1.ShowDialog()

    End Sub

End Class

修改后的代码（等比例适配） #

Public Class Form1

    Private Sub PrintDocument1_PrintPage(sender As Object, e As Printing.PrintPageEventArgs) Handles PrintDocument1.PrintPage
        ' 获取打印区域（去除硬边距）
        Dim margX As Single = e.PageSettings.HardMarginX
        Dim margY As Single = e.PageSettings.HardMarginY
        Dim printArea As New RectangleF(e.PageBounds.Left - margX, e.PageBounds.Top - margY, e.PageBounds.Width, e.PageBounds.Height)

        ' 将Panel内容转换为位图
        Dim panelBitmap As New Bitmap(Panel2.Width, Panel2.Height)
        Panel2.DrawToBitmap(panelBitmap, New Rectangle(0, 0, Panel2.Width, Panel2.Height))

        ' 计算等比例缩放比例
        Dim scaleWidth As Single = printArea.Width / panelBitmap.Width
        Dim scaleHeight As Single = printArea.Height / panelBitmap.Height
        Dim scaleFactor As Single = Math.Min(scaleWidth, scaleHeight) ' 取较小比例，保证完整显示

        ' 计算缩放后的位图尺寸
        Dim newWidth As Single = panelBitmap.Width * scaleFactor
        Dim newHeight As Single = panelBitmap.Height * scaleFactor

        ' 计算居中位置（让位图在A4纸中间显示）
        Dim posX As Single = printArea.Left + (printArea.Width - newWidth) / 2
        Dim posY As Single = printArea.Top + (printArea.Height - newHeight) / 2

        ' 绘制等比例缩放后的位图
        e.Graphics.DrawImage(panelBitmap, posX, posY, newWidth, newHeight)

        ' 释放位图资源
        panelBitmap.Dispose()
    End Sub

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        PrintPreviewDialog1.Document = PrintDocument1
        PrintPreviewDialog1.ShowDialog()
    End Sub

End Class

关键说明 #

• 比例计算：分别计算位图宽高与打印区域宽高的比例，取较小值作为缩放因子，保证位图完整放入A4区域，不会超出边界
• 居中处理：通过计算打印区域与缩放后位图的尺寸差，让位图在A4纸上居中显示，视觉效果更合理
• 资源释放：手动调用Dispose()释放位图资源，避免内存泄漏

内容的提问来源于stack exchange，提问作者zeak