Recent

Author Topic: Points on image drawn on another image not lining up.  (Read 319 times)

Coxy

  • New Member
  • *
  • Posts: 17
Points on image drawn on another image not lining up.
« on: November 20, 2020, 01:51:43 pm »
Hi,

I'm drawing an image, with a point highlighted, on an outer image using Canvas2D. If I draw the highlighted point on the outer image they don't line up. I can get them to line up if I use an offset of -0.75 pixels. Why are the coordinate systems of drawn image and outer image not aligned?

See example output for various offsets below.

Example Code

Code: Pascal  [Select][+][-]
  1. unit Unit1;
  2.  
  3. {$mode objfpc}{$H+}
  4.  
  5. interface
  6.  
  7. uses
  8.   Classes, SysUtils, Forms, Controls, Graphics, Dialogs, StdCtrls, BGRABitmap,
  9.   BGRABitmapTypes;
  10.  
  11. type
  12.  
  13.   { TForm1 }
  14.  
  15.   TForm1 = class(TForm)
  16.     procedure FormPaint(Sender: TObject);
  17.   private
  18.  
  19.   public
  20.  
  21.   end;
  22.  
  23. var
  24.   Form1: TForm1;
  25.  
  26. implementation
  27.  
  28. {$R *.lfm}
  29.  
  30. { TForm1 }
  31.  
  32. procedure TForm1.FormPaint(Sender: TObject);
  33. const
  34.   BoxSize = 4;
  35. var
  36.   Screen, Img : TBGRABitmap;
  37.   X,Y, RX, RY, Offset : single;
  38.   W, H : integer;
  39.   info : string;
  40. begin
  41.   W := 120;
  42.   H := 75;
  43.  
  44.   X := 100;
  45.   Y := 75;
  46.  
  47.   RX := 90;
  48.   RY := 65;
  49.  
  50.   Screen := TBGRABitmap.Create(1920,1080,BGRAWhite);
  51.   Img := TBGRABitmap.Create(w,h);
  52.  
  53.   Img.Fill(BGRA(200,200,40));
  54.  
  55.   // Draw point
  56.   Img.Canvas2D.fillStyle(BGRABlack);
  57.   Img.Canvas2D.fillRect(RX-BoxSize,RY-BoxSize,BoxSize*2,BoxSize*2);
  58.  
  59.   // Draw image on screen
  60.   Offset:=-0.75;                                                                          // <<<-------- Set desired offset
  61.   info := 'Offset='+FloatToStr(Offset);
  62.   Screen.Canvas2D.drawImage(Img,X+Offset,Y+Offset);
  63.  
  64.   // Draw point on screen
  65.   Screen.Canvas2D.fillStyle(BGRA(240,0,240));
  66.   Screen.Canvas2D.fillRect(X+RX-BoxSize,Y+RY-BoxSize,BoxSize*2,BoxSize*2);
  67.  
  68.  
  69.   Screen.TextOut(100,50,info,BGRABlack);
  70.   Screen.Draw(Canvas,0,0);
  71.  
  72.   Screen.SaveToFile('x:\Temp\image '+FloatToStr(Offset)+'.png');
  73.  
  74.   Img.Free;
  75.   Screen.Free;
  76. end;
  77.  
  78. end.
  79.  


I've tried various settings of pixelCenteredCoordinates, for drawn and outer image, having no effect as Canvas2D.drawImage does not use Canvas2D.FCanvasOffset but has a hard coded offset of PointF(0.5,0.5).


Lazarus:  2.0.10
FPC: 3.2.0
OS: Windows 10 Pro

Coxy

  • New Member
  • *
  • Posts: 17
Re: Points on image drawn on another image not lining up.
« Reply #1 on: November 21, 2020, 09:47:54 am »
Hi,

Here's another example, using lines, that better highlights the problem.

When running this code does anyone else experience this issue.

Code: Pascal  [Select][+][-]
  1. unit Unit1;
  2.  
  3. {$mode objfpc}{$H+}
  4.  
  5. interface
  6.  
  7. uses
  8.   Classes, SysUtils, Forms, Controls, Graphics, Dialogs, StdCtrls, BGRABitmap,
  9.   BGRABitmapTypes;
  10.  
  11. type
  12.  
  13.   { TForm1 }
  14.  
  15.   TForm1 = class(TForm)
  16.     procedure FormPaint(Sender: TObject);
  17.   private
  18.  
  19.   public
  20.  
  21.   end;
  22.  
  23. var
  24.   Form1: TForm1;
  25.  
  26. implementation
  27.  
  28. {$R *.lfm}
  29.  
  30. { TForm1 }
  31.  
  32. procedure TForm1.FormPaint(Sender: TObject);
  33. var
  34.   Screen, Img : TBGRABitmap;
  35.   X,Y, RX, RY, Offset, LineWidth : single;
  36.   W, H : integer;
  37.   info : string;
  38. begin
  39.   W := 120;
  40.   H := 75;
  41.  
  42.   X := 100;
  43.   Y := 75;
  44.  
  45.   RX := 90;
  46.   RY := 65;
  47.  
  48.   LineWidth:=4.0;
  49.  
  50.   Screen := TBGRABitmap.Create(1920,1080,BGRAWhite);
  51.   Img := TBGRABitmap.Create(w,h);
  52.  
  53.   Img.Fill(BGRA(200,200,40));
  54.  
  55.   // Draw Lines On Img
  56.   Img.Canvas2D.strokeStyle(BGRABlack);
  57.   Img.Canvas2D.lineWidth:=LineWidth;
  58.   Img.Canvas2D.beginPath;
  59.   Img.Canvas2D.moveTo(0,RY);
  60.   Img.Canvas2D.lineTo(w,RY);
  61.   Img.Canvas2D.moveTo(RX,0);
  62.   Img.Canvas2D.lineTo(RX,h);
  63.   Img.Canvas2D.stroke;
  64.  
  65.  
  66.   // Draw Lines On Screen which will be behind image
  67.   Screen.Canvas2D.fillStyle(BGRA(240,0,240));
  68.   Screen.Canvas2D.lineWidth:=LineWidth;
  69.   Screen.Canvas2D.beginPath;
  70.   Screen.Canvas2D.moveTo(0,RY+Y);
  71.   Screen.Canvas2D.lineTo(1920,RY+Y);
  72.   Screen.Canvas2D.moveTo(RX+X,0);
  73.   Screen.Canvas2D.lineTo(RX+X,1080);
  74.   Screen.Canvas2D.stroke;
  75.  
  76.   // Draw image on screen
  77.   Offset:=1;
  78.   info := 'Offset='+FloatToStr(Offset);
  79.   Screen.Canvas2D.drawImage(Img,X+Offset,Y+Offset);
  80.  
  81.   Screen.TextOut(100,50,info,BGRABlack);
  82.   Screen.Draw(Canvas,0,0);
  83.  
  84.   // Change to folder on your machine
  85.   Screen.SaveToFile('x:\Temp\image_lines '+FloatToStr(Offset)+'.png');
  86.  
  87.   Img.Free;
  88.   Screen.Free;
  89. end;
  90.  
  91. end.
  92.  

circular

  • Hero Member
  • *****
  • Posts: 3561
    • Personal webpage
Re: Points on image drawn on another image not lining up.
« Reply #2 on: November 21, 2020, 02:35:14 pm »
There is a bug here. I guess I have fixed it on dev branch.
https://github.com/bgrabitmap/bgrabitmap/tree/dev-bgrabitmap

Can you give it a try?
Conscience is the debugger of the mind

Coxy

  • New Member
  • *
  • Posts: 17
Re: Points on image drawn on another image not lining up.
« Reply #3 on: November 21, 2020, 03:01:44 pm »
Hi Circular,

Dev code from github resolved problem, see output below.

Not sure I used correct method for testing dev code, but my steps were,

1) rename "lazarus\2.0.10\Config\onlinepackagemanager\packages\bgrabitmap-master" to "bgrabitmap-master old"
2) created new folder "bgrabitmap-master" and copied in dev code
3) rebuilt and ran example code

If this method is bad practice please let me know correct way.

Thanks for the quick resolution.


circular

  • Hero Member
  • *****
  • Posts: 3561
    • Personal webpage
Re: Points on image drawn on another image not lining up.
« Reply #4 on: November 21, 2020, 04:14:40 pm »
Hi Coxy,

Thanks for testing.

Well the way you did works, though that may confuse a bit the package manager.

Normally, you can get the dev code in a folder of your choice, then open the package in this folder with Lazarus, and that switches to this version of the package.
Conscience is the debugger of the mind

Coxy

  • New Member
  • *
  • Posts: 17
Re: Points on image drawn on another image not lining up.
« Reply #5 on: November 21, 2020, 05:11:19 pm »
Thanks,

I'll try that in future.

I miss our development environment under VMS on DEC VAXs back in the early 90s, there you could define an environment variable to point to the root of multiple directory trees. When searching for a file relative to the path it would use the first one found while processing the path. So in a dev account you set the environment to one of three modes,

Live, path=LIVE_ROOT
Test, path=TEST_ROOT,LIVE_ROOT
Dev, path=DEV_ROOT,TEST_ROOT,LIVE_ROOT

It made life so much easier for bug tracing, regression testing and development. Wish they had that feature on Windows and Linux.

circular

  • Hero Member
  • *****
  • Posts: 3561
    • Personal webpage
Re: Points on image drawn on another image not lining up.
« Reply #6 on: November 21, 2020, 06:57:17 pm »
Interesting.

In Lazarus, one can change the paths depending on the compile mode. But I don't think this can affect packages.

There is not much flexibility with packages. For example another feature that would be great would be to use a GUI control package without having to recompile Lazarus.
Conscience is the debugger of the mind

winni

  • Hero Member
  • *****
  • Posts: 1992
Re: Points on image drawn on another image not lining up.
« Reply #7 on: November 23, 2020, 12:24:26 am »

I miss our development environment under VMS on DEC VAXs back in the early 90s, there you could define an environment variable to point to the root of multiple directory trees.

VMS was/is the "super dooper luxury" OS . And DEC was #2 in those days.
A lot of things which where default on VMS/VAX which are still "unknown" today.

Anway: After DEC was sold to Compaq a part of the VMS-Team build Windows NT -
The first (a little bit) "stable" Windows. So it is not a miracle why one of the very first implementations
of NT appeared on a DEC Alpha.

Another part of the VMS team founded Apollo.

Poor conclusion: LIke with cars: Only the main stream survives.
Quality does not matter.

Winni


trev

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 1046
  • Former Delphi 1-7, 10.2 User
Re: Points on image drawn on another image not lining up.
« Reply #8 on: November 23, 2020, 01:10:53 am »
Ah VAXen and VMS - my favourite things were the automated file system version control and DCL. Memories...
o Lazarus v2.1.0 r63871, FPC v3.3.1 r47164, macOS 10.14.6 (with sup update), Xcode 11.3.1
o Lazarus v2.1.0 r61574, FPC v3.3.1 r42318, FreeBSD 12.1 amd64 (VMware Fusion VM)
o FPC 3.0.4, FreeBSD 12.2-STABLE r365646 amd64
o Lazarus v2.1.0 r61574, FPC v3.0.4, Ubuntu 20.04 (Parallels VM)

Coxy

  • New Member
  • *
  • Posts: 17
Re: Points on image drawn on another image not lining up.
« Reply #9 on: November 23, 2020, 08:35:49 am »
I also heard some of the VMS team went to Microsoft to develop Windows NT.

There was also homage to HAL the computer system from movie "2001: A Space Odyssey", HAL is one letter back from IBM.

VMS is one letter back from W(indows)NT.

Doesn't make sense with numbered OS's, Windows 10 becomes Windows 9.

 

TinyPortal © 2005-2018