Two ways to access private variables of a class

When loading BMP images with image, it is traditionally scanline, canvas.pixel, or API functions to use the pixel values of a certain point.

Since image can draw a BMP image, the BMP should contain the pixel value of this bitmap. To look for. I found it, sure.

Tbitmap's parent class is tgraphic,

  Tbitmap = Class (tgraphic)  private    fimage:tbitmapimage;    Fcanvas:tcanvas;    Fignorepalette:boolean;    Fmaskbitsvalid:boolean;    Fmaskvalid:boolean;    Ftransparentcolor:tcolor;    Ftransparentmode:ttransparentmode;    Falphaformat:talphaformat;    Procedure changing (sender:tobject);    Procedure Copyimage (Ahandle:hbitmap; Apalette:hpalette; dib:tdibsection);    Procedure dibneeded;    Procedure Freecontext;    function Getcanvas:tcanvas;

Tgraphic's first private variable is fimage, fimage:tbitmapimage;

View Tbitmapimage

  Tbitmapimage = Class (Tsharedimage)  private    fhandle:hbitmap;     DDB or DIB handle, used for drawing    fmaskhandle:hbitmap;//DDB handle    Fpalette:hpalette;    Fdibhandle:hbitmap;  DIB handle corresponding to Tdibsection    fdib:tdibsection;    Fsavestream:tmemorystream; Save original RLE stream until image is modified    Fhalftone:boolean;   Fpalette is halftone; Don ' t write to file{$IF DEFINED (CLR)}    fimageformat:timageformat;{ $ELSE}    Fos2format:boolean;  Write BMP file header, color table in OS/2 format{$IFEND}  protected    procedure freehandle; override;  Public    destructor Destroy; override;{ $IF DEFINED (CLR)}    function Gethashcode:integer; override;{ $IFEND}  end;

Fdib:tdibsection, that's what I need.

Type  pdibsection = ^tdibsection;  {$EXTERNALSYM Tagdibsection}  tagdibsection = packed record    dsbm:tbitmap;    Dsbmih:tbitmapinfoheader;    DSBITFIELDS:ARRAY[0..2] of DWORD;    Dshsection:thandle;    Dsoffset:dword;  End;  Tdibsection = tagdibsection;  {$EXTERNALSYM Dibsection}  Dibsection = tagdibsection;

Dsbm:tbitmap; Contains the pixel value. View Tbitmap.

  Pbitmap = ^tbitmap;  {$EXTERNALSYM Tagbitmap}  Tagbitmap = packed record    bmtype:longint;    Bmwidth:longint;    Bmheight:longint;    Bmwidthbytes:longint;    Bmplanes:word;    Bmbitspixel:word;    Bmbits:pointer;  End;  Tbitmap = Tagbitmap;  {$EXTERNALSYM BITMAP}  BITMAP = Tagbitmap;

Bmbits:pointer contains the pixel value of the bitmap.

How do I get this value?

This involves the question of how to get the private variables of the class

First step: Get Fimage, get the private variable method of the class one

The Ignorepalette property of Tbitmap is public and we can access it. Fignorepalette = Ignorepalette, indicating that we can find the Fignorepalette address through Ignorepalette, on the two

It's Fimage's address.

  Fimage: = Pointer (@srcbmp. Ignorepalette);  Dec (fimage, SizeOf (Tcanvas)-2);

Second step: Get Fdib, get the private variable method of class two

The Tbitmapimage class does not have any export functions, and the method is useless.

directly with the address.

fimage^ contains the memory start address of the Tbitmapimage class

fimage^ + 4 * 4 + 8 is Fdib's address.

Fdib: = Pointer (fimage^ + 24);

Good, you can access the private variables arbitrarily.

Two ways to access private variables of a class