用VB编程让文本滚动更平滑
姜卫东、华云
目前有许多软件都采用了类似于“电视字幕”的滚动字幕的形式(如电子小说阅读器以及诸如Winamp的“关于”界面等)。在VB中通常用一个Timer控件来控制文本的滚动速度，但是它的缺点就是跳跃感太强，效果不好。本文将介绍在VB中通过API函数DrawText来实现文本的平滑滚动。
函数说明
该函数的用法如下：
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
其作用是将文本描绘到指定的矩形中返回值Long：描绘文字的高度
参数类型及说明
hdc：欲在其中显示文字的一个设备场景的句柄；
lpStr：欲描绘的文本字串；
nCount：欲描绘的字符数量。如果要描绘整个字串(直到空终止符)，则可将这个参数设为-1；
lpRect：指定用于绘图的一个格式化矩形(采用逻辑坐标)；
wFormat：一个标志位数组，决定了以何种形式执行绘图。
程序实现
进入VB，在默认窗体FORM1上放一个Picture控件“Picmain”，一个命令按钮“Command1”，然后输入如下代码：
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 = "滚动字幕示例" && vbCrLf && vbCrLf && vbCrLf && "作者:姜卫东" && vbCrLf && _ vbCrLf && "地址：黑龙江省农业经济学校" && vbCrLf && vbCrLf && "有问题请给我来信!!!" && vbCrLf && "E-MAIL:hyjs@yeah.net" && vbCrLf && vbCrLf && vbCrLf && "谢谢使用"
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
’设置时间间隔,即滚动速度
Const IntervalTime As Long = 10
Dim rt As Long
Dim DrawingRect As RECT
’设置所画矩形的左边位置。
Dim tmpX As Long, tmpY As Long
Dim RectHeight As Long
’显示窗体
frmAbout.Refresh
’获得所画矩形的尺寸
rt = DrawText(picmain.hdc, ScrollText, -1, DrawingRect, DT_CALCRECT)
If rt = 0 Then
MsgBox "出错", vbExclamation
isend = True
Else
’设置矩形的位置
DrawingRect.Top = picmain.ScaleHeight
DrawingRect.Left = 0
DrawingRect.Right = picmain.ScaleWidth
’设置矩形的高度
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
’控制文本的循环滚动
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中文企业版中运行通过。
