Originally published in Computer World Daily:
http://www.ccw.com.cn/htm/app/aprog/01_1_12_4.asp
Delphi data compression processing
Cai Jian
Mailto: chaijian@21cn.com
Borland's RAD Development Tools Delphi 5.0 serves as a mainstream development tool on a Windows platform, its visualized development environment and object-oriented programming have attracted countless developers. However, some programmers often compress a large amount of data while the actual development process is often compressed, and has to find some highly efficient compression algorithms or to find third-party controls on the Internet to implement compression. Does Delphi do not provide this feature? In fact, Delphi's programming designer has long been considering this, providing Zlib.Pas and ZlibConst.Pas two unit files to solve data compression issues, achieving a high data compression ratio. These two files are saved in the Delphi 5.0 installation disc / info / extras / zlib directory, in addition, the OBJ file referenced by the Zlib.PAS unit is saved in the INFO / Extras / Zlib / ObJ directory. Below will be described herein as an example to describe how this feature is used as an example.
Solutions
First capture the image of the current entire screen with a screen copy, then save it as a BMP file format in memory. When compressed, the original image is compressed and saved as a custom file format using the TcompressionStream object; decompressing the compressed image, reducing the image file of the BMP format using the TDeCompressionStream object.
Implementation
Create a new project file, reference Zlib.PAS in the interface part of the main unit, and place two buttons button1, button2 on the main form, write the corresponding procedure call code in their OnClick event.
Some program source code is as follows:
Unit unit1;
Interface
Uses
Windows, Messages, Sysutils, Classes, Graphics, Controls, Forms, Dialogs, Stdctrls, Zlib
Type
TFORM1 = Class (TFORM)
Button1: tbutton;
Button2: tbutton;
Procedure Button1Click (Sender: TOBJECT);
Procedure Button2Click (Sender: TOBJECT);
Private
{Private Declarations}
public
{Public declarations}
END;
VAR
FORM1: TFORM1;
IMPLEMentation
{$ R * .dfm}
1. Capture full screen image
Procedure getScreen (var bmp: tbitmap);
VAR
DC: HDC;
Mycanvas: tcanvas;
MYRECT: TRECT;
Begin
DC: = getwindowdc (0);
Mycanvas: = tcanvas.create;
Try
Mycanvas.handle: = DC;
MyRect: = Rect (0, 0, Screen.width, Screen.Height);
// The image is 24-bit true color, or it can be adjusted according to actual needs.
Bmp.pixelformat: = pf24bit;
Bmp.width: = myRect.right;
Bmp.height: = myRect.bottom;
// Capture the entire screen image
Bmp.canvas.copyRect (MyRect, Mycanvas, MyRect); Finally
Mycanvas.handle: = 0;
Mycanvas.free;
ReleaseDC (0, DC);
END;
END;
2. Compressed image
Procedure CompressBitmap (Var CompressedStream; Const CompressionLevel: TcompressionLevel);
VAR
SourceStream: TcompressionStream;
Deststream: TMemoryStream DESTSTREAM
Count: integer;
Begin
// Get the original size of the image stream
Count: = compressedStream.size;
Deststream: = TMEMORYSTREAM.CREATE;
SourceStream: = TcompressionStream.create
CompressionLevel, DeststReam;
Try
The original image stream is saved in // SourceStream
CompressedStream.saveTostream (SourceStream);
/ / Compress the original image stream, and the compressed image stream is saved in DestStream
SourceStream.Free;
CompressedStream.clear;
// Write the size of the original image
CompressedStream.writebuffer (Count, Sizeof
COUNT);
// Write a compressed image stream
CompressedStream.copyFrom (Deststream, 0);
Finally
Deststream.free;
END;
END;
3. Restore is compressed image
Procedure UncompressBitmap (Const CompressedStream; var bmp: tbitmap);
VAR
SourceStream: TDECompRessionsTream;
Deststream: TMemoryStream DESTSTREAM
Buffer: pchar;
Count: integer;
Begin
/ / Read the size of the original image from the compressed image stream
CompressedStream.Readbuffer (Count, Sizeof (count);
/ / According to the size of the image size, allocate memory blocks to be read.
GetMem (buffer, count);
Deststream: = TMEMORYSTREAM.CREATE;
SourceStream: = TDecompressionStream.create (CompressedStream);
Try
/ / The compressed image is compressed and then stored in the buffer memory block.
SourceStream.Readbuffer (buffer ^, count);
// Save the original image stream to the DestStream stream
Deststream.writebuffer (buffer ^, count);
DestStream.position: = 0; // Reset stream pointer
// Load the original image stream from the DestStream stream
Bmp.LoadFromstream (Deststream);
Finally
FreeMem (buffer);
Deststream.free;
END;
END;
4. Compressed button onclick event
Procedure TFORM1.BUTTON1CLICK (Sender: TOBJECT);
VAR
BMP: TBITMAP;
CompressedStream: TMemoryStream;
Begin
BMP: = tbitmap.create; compressedStream: = tmemorystream.create;
Try
// Capture the current screen, save the image to GetScreen (BMP) in the BMP object;
// Save the image in the BMP object to the memory stream
Bmp.savetostream (CompressedStream);
// Compress the original image stream according to the default compression ratio
CompressBitmap (CompressedStream, CLDEFAULT);
// Save the image stream after the compression as a file in a custom format
CompressedStream.savetofile ('c: /cj.dat');
Finally
Bmp.free;
CompressedStream.Free;
END;
END;
5. Unzip button onclick event
Procedure TFORM1.BUTTON2CLICK (Sender: TOBJECT);
VAR
CompressedStream: TfileStream;
BMP: TBITMAP;
Begin
BMP: = Tbitmap.create;
// Open a custom compressed format file with a read-only mode of the file stream
CompressedStream: = TFileStream.create ('c: /cj.dat', fmopenread);
Try
// Unzip the compressed image stream
UncompressBitmap (CompressedStream, BMP);
// Restore the original image stream into the specified BMP file
Bmp.savetofile ('c: /cj.bmp');
Finally
Bmp.free;
CompressedStream.Free;
END;
END;
In addition, the TcompressionStream object also provides the CompressionRate property, which is used to describe the compression ratio after compression of the original data, and the onprogress event is triggered during the compression and decompression process, and the developer can write the progress in the event. Code.
The above code is transferred in Delphi 5.0.
