目前有許多軟件都采用了類似于“電視字幕”的滾動字幕的形式(如電子小說閱讀器以及諸如Winamp的“關于”界面等)。在VB中通常用一個Timer控件來控制文本的滾動速度，但是它的缺點就是跳躍感太強，效果不好。本文將介紹在VB中通過API函數DrawText來實現文本的平滑滾動。
函數說明
該函數的用法如下：
Declare Function DrawText Lib "user32" Alias "DrawTextA" (ByVal hdc As Long, ByVal lpStr As String, ByVal nCount As Long, lpRect As RECT, ByVal wFormat As Long) As Long
其作用是將文本描繪到指定的矩形中返回值Long：描繪文字的高度
參數類型及說明
hdc：欲在其中顯示文字的一個設備場景的句柄；
lpStr：欲描繪的文本字串；
nCount：欲描繪的字符數量。如果要描繪整個字串(直到空終止符)，則可將這個參數設為-1；
lpRect：指定用于繪圖的一個格式化矩形(采用邏輯坐標)；
wFormat：一個標志位數組，決定了以何種形式執行繪圖。
程序實現
進入VB，在默認窗體FORM1上放一個Picture控件“Picmain”，一個命令按鈕“Command1”，然后輸入如下代碼：
Option Explicit
Private Declare Function DrawText Lib "user32" Alias "DrawTextA" (ByVal hdc As Long, ByVal lpStr As String, ByVal nCount As Long, lpRect As RECT, ByVal wFormat As Long) As Long
Private Declare Function GetTickCount Lib "kernel32" () As Long
Const DT_BOTTOM As Long = &&H8
Const DT_CALCRECT As Long = &&H400
Const DT_CENTER As Long = &&H1
Const DT_WORDBREAK As Long = &&H10
Private Type RECT
Left As Long
Top As Long
Right As Long
Bottom As Long
End Type
Const ScrollText As String = "滾動字幕示例" && vbCrLf && vbCrLf && vbCrLf && "作者:姜衛東" && vbCrLf && _ vbCrLf && "地址：黑龍江省農業經濟學校" && vbCrLf && vbCrLf && "有問題請給我來信!!!" && vbCrLf && "E-MAIL:hyjs@yeah.net" && vbCrLf && vbCrLf && vbCrLf && "謝謝使用"
Dim isend As Boolean
Private Sub Command1_Click()
If isend = False Then
isend = True
Else
isend = False
frmAbout.Refresh
scrollme
End If
End Sub
Private Sub Form_Activate()
scrollme
End Sub
Private Sub Form_Load()
picmain.ForeColor = vbGreen
picmain.FontSize = 14
End Sub
Private Sub scrollme()
Dim LastFrameTime As Long
'設置時間間隔,即滾動速度
Const IntervalTime As Long = 10
Dim rt As Long
Dim DrawingRect As RECT
'設置所畫矩形的左邊位置。
Dim tmpX As Long, tmpY As Long
Dim RectHeight As Long
'顯示窗體
frmAbout.Refresh
'獲得所畫矩形的尺寸
rt = DrawText(picmain.hdc, ScrollText, -1, DrawingRect, DT_CALCRECT)
If rt = 0 Then
MsgBox "出錯", vbExclamation
isend = True
Else
'設置矩形的位置
DrawingRect.Top = picmain.ScaleHeight
DrawingRect.Left = 0
DrawingRect.Right = picmain.ScaleWidth
'設置矩形的高度
RectHeight = DrawingRect.Bottom
DrawingRect.Bottom = DrawingRect.Bottom + picmain.ScaleHeight
End If
Do While Not isend
If GetTickCount() - LastFrameTime > IntervalTime Then
picmain.Cls
DrawText picmain.hdc, ScrollText, -1, DrawingRect, DT_CENTER Or DT_WORDBREAK
DrawingRect.Top = DrawingRect.Top - 1
DrawingRect.Bottom = DrawingRect.Bottom - 1
'控制文本的循環滾動
If DrawingRect.Top < -(RectHeight) Then
DrawingRect.Top = picmain.ScaleHeight
DrawingRect.Bottom = RectHeight + picmain.ScaleHeight
End If
picmain.Refresh
LastFrameTime = GetTickCount()
End If
DoEvents
Loop
Set frmAbout = Nothing
End Sub
Private Sub Form_Unload(Cancel As Integer)
isend = True
End Sub Sub
以上程序在Windows+VB6.0中文企業版中運行通過。
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