Fast pixel access
lazarus / 39-Graphics

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user5 · 2019-11-28 13:00

In the code below lines 1 and 2 together do the same thing as line 3
except of course line 3 would be much slower if I used it in the code
instead of lines 1 and 2. Line 1 uses a raw image fast pixel access
method that is similar to BGRABitmap.
    Line 5 accesses pixels next to x and y and I was wondering if
anyone knows how I could use the fast pixel method to accomplish the
same thing but at a faster speed.
    Thanks and happy Thanksgiving morning!

    Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i for y :=
starty to (mybitmap.height - 1) do  begin   PixelPtr := PixelRowPtr; 
 for x := startx to (mybitmap.width - 1) do    begin     tempcolor :=
PixelPtr^; //line 1     tempcolor := SwapRedBlue(tempcolor); //line
2      tempcolor := mybitmap.canvas.pixels[x,y]; //line 3    
 newcolor := mybitmap.canvas.pixels[x + 1,y + 1]; //line 5    end; 
end;

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user5 · 2019-11-28 13:04

Oops. Line 5 should have been: newcolor := mybitmap.canvas.pixels[x +
1,y]; //to access the pixel next to x

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winni · 2019-11-28 14:44

Hi!

There is a page about fast direct pixel access in Lazarus with a lot
of examples:

https://wiki.freepascal.org/Fast_direct_pixel_access

No thanksgiving here tomorrow - just another Friday for Future.

Winni

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user5 · 2019-11-28 18:31

I checked out the page you mentioned and it led me to some other sites
but it seems like not enough information is provided. For example, I
found the following code but I can't get it to work. "colGreen" from
what I understand is supposed to be a TFPColor but the compiler
wouldn't let me define something like var newcolor:TFPColor. I put in
all the correct headers.

  Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.Button4Click(Sender: TObject);var  b: TBitmap;  t:
TLazIntfImage;begin  b := TBitmap.Create;  try   
b.LoadFromFile('test.bmp');    t := b.CreateIntfImage;     // Read
and/or write to the pixels    t.Colors[10,20] := colGreen; //This
won't compile.     b.LoadFromIntfImage(t);  finally    t.Free;   
b.Free;  end;end;

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wp · 2019-11-28 18:40

Just missing the "uses":

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i uses 
fpImage,        // colGreen, TFPColor  IntfGraphics;   //
TLazIntfImage

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user5 · 2019-11-28 18:48

You are absolutely correct. I was missing FPImage in the "uses"
clause. It's working now. The old slow pixel method took 7 seconds to
fill a 1053x655 image with the color red but the TLazIntfImage method
did it almost instantaneously. Wow! I wonder if there's anything even
faster. Thanks a lot.

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user5 · 2019-11-28 18:52

Does the TFPColor "colRed" equal "clRed" or do I need a conversion of
some kind?

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user5 · 2019-11-28 19:08

Okay... I found the conversion function which converts a TColor to a
TFPColor so that: newcolor := TColorToFPColor(tempcolor); newcolor is
a TFPColor and tempcolor is a TColor. I also found the function which
converts a TFPColor to a TColor. Thanks again for taking the time to
help me. I really appreciate it. This seems to be what I need.

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Soner · 2019-11-28 19:52

Don't forget, TBitmap has Scanline property now. As someone the
wikipage wrote, then tbitmap has not this property.
NOw, you can manipulate Tbitmap without TLazIntfImage faster.