"waterfall" image
lazarus / 39-Graphics

----------------------------------------------------------------------
Rik · 2018-10-22 13:54

Hello,

I want to create an image where the lines shift down once a second and
a new line is added at the top (behaves a bit like a waterfall).
With the code below in a timer it is easily done, but very slow (takes
about 100 ms on my computer).
It should be possible to to this much faster by  moving memory blocks
or using Bitmap.RawImage instead of Pixels[], but I can't figure out
how.

Thanks,  Rik

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 with
WaterfallImage do // = TImagebegin // this works, but very slow (100
ms)  try    Picture.Bitmap.BeginUpdate(True); // without this it even
takes 200 ms    for y:= Height-1 downto 1 do    begin      for x:= 0
to Width-1 do      begin        Canvas.Pixels[x,y]:=
Canvas.Pixels[x,y-1];      end;    end;    for x:= 0 to Width-1 do   
begin      Canvas.Pixels[x,0]:= NewLine[x];    end;  finally   
Picture.Bitmap.EndUpdate(False);  end;end;

----------------------------------------------------------------------
Leledumbo · 2018-10-23 09:11

Don't use TImage for animation, see
$(LazarusDir)/examples/lazintfimage for reference on how to manipulate
pixels fast.

----------------------------------------------------------------------
Handoko · 2018-10-23 09:37

Quote from: Rik on October 22, 2018, 03:54:59 pmIt should be possible
to to this much faster by  moving memory blocks or using
Bitmap.RawImage instead of Pixels[], but I can't figure out how.

Try using TImage.Picture.Bitmap.ScanLine. On my tests, it is much
faster than single pixel accessing.
You can find the example code here:
http://forum.lazarus.freepascal.org/index.php/topic,37242

I think you will be interested to know:
http://wiki.freepascal.org/Fast_direct_pixel_access

----------------------------------------------------------------------
Rik · 2018-10-23 12:12

lazintfimage is what I needed, thank you for the hint.

In case someone is interested, here the code adapted for lazintfimage
(takes less than 1 millisecond):

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 type 
TRGBTripleArray = array[0..32767] of TRGBTriple;  PRGBTripleArray =
^TRGBTripleArray;var  x,y: word;  r1,r2: PRGBTripleArray;  Img:
TLazIntfImage;begin  with WaterfallImage.Picture.Bitmap do  begin   
try      Img:= CreateIntfImage;      for y:= Img.Height-1 downto 1 do
// shift image 1 row down (waterfall)      begin        r1:=
Img.GetDataLineStart(y-1);        r2:= Img.GetDataLineStart(y);      
for x:=0 to Img.Width-1 do r2^[x]:= r1^[x];      end;     
LoadFromIntfImage(Img);      BeginUpdate(True);      for x:= 0 to
Width-1 do Canvas.Pixels[x,0]:= NewLine[x]; // add the new line at the
top    finally      EndUpdate(False);    end;  end;end; 
Regarding Bitmap.ScanLine: I thought this works only in Delphi, not in
Lazarus. But GetDataLineStart does pretty much the same.

----------------------------------------------------------------------
circular · 2018-10-25 09:34

Indeed it seems GetDataLineStart works fine. I wonder though, how much
time one cycle takes in total (image re-creation and display). Note
that for very  quick things in milliseconds, you need to run the
operation 15 times and then divide the resulting time by 15. Because
the time is measured by lumps of 15 ms so if it takes 12 ms you will
get either that it took 0 ms or 15 ms.

I wonder if you need to free the Img object.

In fact you could do a Move to copy one whole line at once:
Code: Delphi  [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:=
Img.Height-1 downto 1 do // shift image 1 row down (waterfall)   
move(Img.GetDataLineStart(y-1)^, Img.GetDataLineStart(y)^,
sizeof(TRGBTriple)*Img.Width );