delphi - Can I somehow "instrument" Graphics.TBitmapCanvas with overriden GetPixel/SetPixel methods, which are specific to TBitmap's canvas? -


as know, working tbitmap's pixels (bitmap.canvas.pixels[x,y]) slow in out-of-box vcl. has been caused getter , setter of pixels property inherited tcanvas, encapsulates general wingdi dc object , not specific memdc of bitmap.

for dib section-based bitmaps (bmdib) well-known workaround exists, not see way integrate proper getter/setter in vcl tbitmap class (besides direct modification of library code, proven real pain in stern when comes compiling against different vcl versions).

please advise if there hackish way reach tbitmapcanvas class , inject overriden methods it.

i'm sure done more elegantly, here's ask implemented using class helper crack private members:

unit bitmapcanvascracker;  interface  uses   sysutils, windows, graphics;  implementation  procedure fail; begin   raise eassertionfailed.create('fixup failed.'); end;  procedure patchcode(address: pointer; const newcode; size: integer); var   oldprotect: dword; begin   if not virtualprotect(address, size, page_execute_readwrite, oldprotect) begin     fail;   end;   move(newcode, address^, size);   flushinstructioncache(getcurrentprocess, nil, 0);   if not virtualprotect(address, size, oldprotect, @oldprotect) begin     fail;   end; end;  type   pinstruction = ^tinstruction;   tinstruction = packed record     opcode: byte;     offset: integer;   end;  procedure redirectprocedure(oldaddress, newaddress: pointer); var   newcode: tinstruction; begin   newcode.opcode := $e9;//jump relative   newcode.offset := nativeint(newaddress)-nativeint(oldaddress)-sizeof(newcode);   patchcode(oldaddress, newcode, sizeof(newcode)); end;  type   tbitmapcanvas = class(tcanvas)     // need implement class   end;  type   tbitmaphelper = class helper tbitmap     function newgetcanvas: tcanvas;     class procedure patch;   end;  function tbitmaphelper.newgetcanvas: tcanvas; begin   if self.fcanvas = nil   begin     self.handleneeded;     if self.fcanvas = nil     begin       self.fcanvas := tbitmapcanvas.create;       self.fcanvas.onchange := self.changed;       self.fcanvas.onchanging := self.changing;     end;   end;   result := self.fcanvas; end;  class procedure tbitmaphelper.patch; begin   redirectprocedure(@tbitmap.getcanvas, @tbitmap.newgetcanvas); end;  initialization   tbitmap.patch;  end.

include unit in project , tbitmap class patched getcanvas method redirects newgetcanvas , allows implement own tcanvas subclass.

i don't think code work if using runtime packages sort out need use more capable hooking code.


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