用多媒體庫 Bass.dll 播放 mp3 [9] - 繪制波形圖

　本例效果圖:

　　代碼文件:unit Unit1;
interface
uses
　Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
　Dialogs, StdCtrls, ExtCtrls, ComCtrls;
type
　TForm1 = class(TForm)
　　OpenDialog1: TOpenDialog;
　　PaintBox1: TPaintBox;
　　Button1: TButton;
　　Button2: TButton;
　　Button3: TButton;
　　ColorBox1: TColorBox;
　　ColorBox2: TColorBox;
　　procedure FormCreate(Sender: TObject);
　　procedure Button1Click(Sender: TObject);
　　procedure Button2Click(Sender: TObject);
　　procedure Button3Click(Sender: TObject);
　　procedure ColorBox1Change(Sender: TObject);
　　procedure ColorBox2Change(Sender: TObject);
　　procedure FormDestroy(Sender: TObject);
　　procedure PaintBox1Paint(Sender: TObject);
　private
　　procedure Draw;
　end;
var
　Form1: TForm1;
implementation
{$R *.dfm}
uses Bass;
var
　hs: HSTREAM;　{流句柄}
　Data: array of Cardinal;
　bit: TBitmap;
procedure TForm1.FormCreate(Sender: TObject);
begin
　bit := TBitmap.Create;
　PaintBox1.Align := alTop;
　ColorBox1.Selected := clBlack;
　ColorBox2.Selected := clLime;
　if HiWord(BASS_GetVersion) <> BASSVERSION then
　　MessageBox(0, '"Bass.dll" 文件版本不合適! ', nil, MB_ICONERROR);
　if not BASS_Init(-1, 44100, 0, 0, nil) then ShowMessage('初始化錯誤');
end;
{打開}
procedure TForm1.Button1Click(Sender: TObject);
var
　Mp3Path: AnsiString;
　i: Cardinal;
　time: Double;
　hs2: HSTREAM;
begin
　BASS_StreamFree(hs);
　OpenDialog1.Filter := 'Mp3 文件(*.mp3)|*.mp3|Wav 文件(*.wav)|*wav';
　if OpenDialog1.Execute then
　　Mp3Path := AnsiString(OpenDialog1.FileName);
　hs := BASS_StreamCreateFile(False, PAnsiChar(Mp3Path), 0, 0, 0);
　if hs < BASS_ERROR_ENDED then
　　Text := '打開失敗'
　else begin
　　Text := string(Mp3Path);
　　bit.Free;
　　bit := TBitmap.Create;
　　PaintBox1.Repaint;
　　{下面幾行不好理解}
　　{重新建立文件流 hs2, 最後的參數是: BASS_STREAM_DECODE, 這樣可以提前讀取波形數據}
　　hs2 := BASS_StreamCreateFile(False, PAnsiChar(Mp3Path), 0, 0, BASS_STREAM_DECODE);
　　{用 BASS_ChannelGetLevel 獲取峰值時, 是以 20ms 為一個單位的; 先獲取總時間}
　　time := BASS_ChannelBytes2Seconds(hs2, BASS_ChannelGetLength(hs, BASS_POS_BYTE));
　　{time * 1000 div 20 + 1 是可以獲取的總的峰值數據, 也是數組需要的大小}
　　SetLength(Data, Trunc(time * 50 + 1));
　　{遍歷峰值數據填充數組}
　　for i := 0 to Length(Data) - 1 do Data[i] := BASS_ChannelGetLevel(hs2);
　　{hs2 此時已完成使命, 釋放它}
　　BASS_StreamFree(hs2);
　　{調用繪制過程}
　　Draw;
　end;
end;
{播放}
procedure TForm1.Button2Click(Sender: TObject);
begin
　BASS_ChannelPlay(hs, False);
end;
{暫停}
procedure TForm1.Button3Click(Sender: TObject);
begin
　BASS_ChannelPause(hs);
end;
{背景色}
procedure TForm1.ColorBox1Change(Sender: TObject);
begin
　Draw;
end;
{前景色}
procedure TForm1.ColorBox2Change(Sender: TObject);
begin
　Draw;
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
　BASS_Free;
　bit.Free;
end;
{刷新}
procedure TForm1.PaintBox1Paint(Sender: TObject);
begin
　PaintBox1.Canvas.StretchDraw(Bounds(0, 0, PaintBox1.Width, PaintBox1.Height), bit);
end;
{繪制波形圖}
procedure TForm1.Draw;
var
　i,ch: Integer;
　L,R: SmallInt;
begin
　bit.Width := Length(Data);
　bit.Height := PaintBox1.Height;
　ch := bit.Height div 2;
　bit.Canvas.Brush.Color := ColorBox1.Selected;
　bit.Canvas.FillRect(Bounds(0, 0, bit.Width, bit.Height));
　bit.Canvas.Pen.Color := ColorBox2.Selected;
　for i := 0 to Length(Data) - 1 do
　begin
　　L := LoWord(Data[i]);
　　R := HiWord(Data[i]);
　　bit.Canvas.MoveTo(i, ch - Trunc(L/32768*ch));
　　bit.Canvas.LineTo(i, ch + Trunc(R/32768*ch));
　end;
　PaintBox1.Repaint;
end;
end.窗體文件:object Form1: TForm1
　Left = 222
　Top = 114
　Caption = 'Form1'
　ClIEntHeight = 173
　ClIEntWidth = 504
　Color = clBtnFace
　Font.Charset = DEFAULT_CHARSET
　Font.Color = clWindowText
　Font.Height = -11
　Font.Name = 'Tahoma'
　Font.Style = []
　OldCreateOrder = False
　Position = poDesigned
　OnCreate = FormCreate
　OnDestroy = FormDestroy
　PixelsPerInch = 96
　TextHeight = 13
　object PaintBox1: TPaintBox
　　Left = 40
　　Top = 0
　　Width = 105
　　Height = 131
　　OnPaint = PaintBox1Paint
　end
　object Button1: TButton
　　Left = 8
　　Top = 137
　　Width = 75
　　Height = 25
　　Caption = #25171#24320
　　TabOrder = 0
　　OnClick = Button1Click
　end
　object Button2: TButton
　　Left = 89
　　Top = 137
　　Width = 75
　　Height = 25
　　Caption = #25773#25918
　　TabOrder = 1
　　OnClick = Button2Click
　end
　object Button3: TButton
　　Left = 170
　　Top = 137
　　Width = 75
　　Height = 25
　　Caption = #26242#20572
　　TabOrder = 2
　　OnClick = Button3Click
　end
　object ColorBox1: TColorBox
　　Left = 315
　　Top = 139
　　Width = 85
　　Height = 22
　　ItemHeight = 16
　　TabOrder = 3
　　OnChange = ColorBox1Change
　end
　object ColorBox2: TColorBox
　　Left = 406
　　Top = 139
　　Width = 90
　　Height = 22
　　ItemHeight = 16
　　TabOrder = 4
　　OnChange = ColorBox2Change
　end
　object OpenDialog1: TOpenDialog
　　Left = 192
　　Top = 32
　end