VB6下通过ESC/POS模式向POS打印机输出位图的技术问询

一、位图是否需要转换？ #

必须转换。ESC/POS打印机不支持直接打印标准位图文件，需要将其转换为单色（1位）点阵数据，并按打印机的打印宽度（常见为384点、203点等）做字节对齐处理，最终封装成ESC/POS指令能识别的格式才能发送打印。

二、如何转换并打印？ #

1. 核心转换流程 #

• 加载位图：用VB6自带的LoadPicture加载BMP文件，通过Windows GDI API提取像素数据。
• 转为单色：将彩色/灰度位图按阈值转为黑白单色（黑为打印点，白为空白），生成1位深度的点阵。
• 行数据对齐：按打印机每行点数拆分点阵，每行数据需对齐到字节边界（8个像素为1字节）。
• 封装ESC/POS指令：用ESC *系列指令包裹转换后的点阵数据，发送至打印机端口。

2. VB6 示例代码 #

Private Declare Function GetDIBits Lib "gdi32" (ByVal hDC As Long, ByVal hBitmap As Long, ByVal nStartScan As Long, ByVal nNumScans As Long, lpBits As Any, lpBI As BITMAPINFO, ByVal wUsage As Long) As Long
Private Declare Function CreateCompatibleDC Lib "gdi32" (ByVal hDC As Long) As Long
Private Declare Function SelectObject Lib "gdi32" (ByVal hDC As Long, ByVal hObject As Long) As Long
Private Declare Function DeleteDC Lib "gdi32" (ByVal hDC As Long) As Long
Private Declare Function GetObject Lib "gdi32" Alias "GetObjectA" (ByVal hObject As Long, ByVal nCount As Long, lpObject As Any) As Long

Private Type BITMAP
    bmType As Long
    bmWidth As Long
    bmHeight As Long
    bmWidthBytes As Long
    bmPlanes As Integer
    bmBitsPixel As Integer
    bmBits As Long
End Type

Private Type BITMAPINFOHEADER
    biSize As Long
    biWidth As Long
    biHeight As Long
    biPlanes As Integer
    biBitCount As Integer
    biCompression As Long
    biSizeImage As Long
    biXPelsPerMeter As Long
    biYPelsPerMeter As Long
    biClrUsed As Long
    biClrImportant As Long
End Type

Private Type BITMAPINFO
    bmiHeader As BITMAPINFOHEADER
    bmiColors(1) As Long
End Type

Sub PrintESCposBitmap(printerPort As String, bmpPath As String)
    Dim hBmp As StdPicture, bmpInfo As BITMAP
    Dim hDC As Long, hOldBmp As Long
    Dim bmi As BITMAPINFO, bits() As Byte
    Dim escCmd As String, bytePerRow As Long, printerDotWidth As Integer
    Dim y As Long, x As Long, bitIdx As Integer, currByte As Byte
    
    ' 80mm热敏打印机对应384点宽度，58mm对应203点，按需修改
    printerDotWidth = 384
    bytePerRow = printerDotWidth \ 8 ' 每行对应字节数
    
    ' 加载位图并获取基础信息
    Set hBmp = LoadPicture(bmpPath)
    GetObject hBmp, Len(bmpInfo), bmpInfo
    
    ' 初始化单色位图信息结构
    With bmi.bmiHeader
        .biSize = Len(bmi.bmiHeader)
        .biWidth = printerDotWidth
        .biHeight = bmpInfo.bmHeight
        .biPlanes = 1
        .biBitCount = 1 ' 强制转为单色
        .biCompression = 0
        .biSizeImage = bytePerRow * .biHeight
    End With
    
    ' 创建兼容DC并获取单色点阵数据
    hDC = CreateCompatibleDC(0)
    hOldBmp = SelectObject(hDC, hBmp)
    ReDim bits(1 To bmi.bmiHeader.biSizeImage)
    GetDIBits hDC, hBmp, 0, bmi.bmiHeader.biHeight, bits(1), bmi, 0
    
    ' 构建ESC/POS位图打印指令（24点密度模式）
    escCmd = Chr$(27) & "*" & Chr$(33)
    ' 追加宽度的低字节、高字节
    escCmd = escCmd & Chr$(printerDotWidth Mod 256) & Chr$(printerDotWidth \ 256)
    ' 追加高度的低字节、高字节
    escCmd = escCmd & Chr$(bmi.bmiHeader.biHeight Mod 256) & Chr$(bmi.bmiHeader.biHeight \ 256)
    
    ' 反转行顺序（GetDIBits返回的点阵是倒序的）并拼接字节数据
    For y = bmi.bmiHeader.biHeight To 1 Step -1
        currByte = 0
        bitIdx = 7
        For x = 1 To printerDotWidth
            ' 判断当前像素是否为黑色（单色位图中0为黑）
            If Not (bits((y - 1) * bytePerRow + (x - 1) \ 8 + 1) And (128 \ ((x - 1) Mod 8))) Then
                currByte = currByte Or (2 ^ bitIdx)
            End If
            bitIdx = bitIdx - 1
            If bitIdx < 0 Then
                escCmd = escCmd & Chr$(currByte)
                currByte = 0
                bitIdx = 7
            End If
        Next x
        ' 补全行末剩余的字节
        If bitIdx <> 7 Then escCmd = escCmd & Chr$(currByte)
    Next y
    
    ' 发送指令到打印机端口
    Open printerPort For Binary As #1
        Put #1, , escCmd
        Put #1, , Chr$(10) ' 换行
    Close #1
    
    ' 清理资源
    SelectObject hDC, hOldBmp
    DeleteDC hDC
End Sub

3. 注意事项 #

• 打印机宽度适配：不同机型的打印宽度不同，需先确认打印机的点宽度（可查厂商手册），修改printerDotWidth参数。
• 位图缩放：如果原位图宽度超过打印机宽度，需提前用StretchBlt API做缩放处理，避免打印内容被截断。
• 指令密度调整：示例用的是24点密度（Chr$(33)），如果需要更浅的打印效果，可替换为8点密度（Chr$(32)）。

三、参考资料 #

• 打印机厂商的ESC/POS指令手册：比如爱普生、佳博等品牌的官方文档，会详细说明ESC *指令的参数格式、不同密度模式的差异。
• VB6 GDI API文档：重点了解GetDIBits、CreateCompatibleDC等API的使用，用于提取和转换位图像素数据。

内容的提问来源于stack exchange，提问作者DKKABG