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gluUnProject and FreePascal

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BTierens

Betreff des Beitrags: gluUnProject and FreePascal

Verfasst: Fr Aug 13, 2004 17:51

DGL Member

Registriert: Fr Aug 13, 2004 17:43
Beiträge: 60
Wohnort: Belgien

Hi,

I'm using the FreePascal compiler (http://www.freepascal.org/). I have a tile based landscape with objects and now I want to know at wich tile/object the user clicks. First I use gluUnProject to get the 3D coordinates and then, I use a tree to know on wich tile/object the user clicks. But the gluUnProject function has strange output.
This is the code:

Code:

 
//************************************************************************************************
//Get the tile wich is selected
//************************************************************************************************
function GetOGLPos(X, Y: Integer): T3D_Point;
var
  viewport: TViewPortArray;
  modelview:  T16dArray;
  projection: T16dArray;
  winZ: Single;
  resPoint: T3D_Point;
begin
  glGetDoublev(GL_MODELVIEW_MATRIX, @modelview );
  glGetDoublev(GL_PROJECTION_MATRIX, @projection );
  glGetIntegerv(GL_VIEWPORT, @viewport );
 
  // In Delphi A Y Value Of 0 Returns An Unknown Value
  // I Discovered This While I Was Testing A Crosshair
  if(Y = 0) then Y := 1;
  glReadPixels(X,-Y,1,1,GL_DEPTH_COMPONENT,GL_FLOAT,@winZ);
  gluUnProject(X,viewport[4]-Y,winZ,modelview,projection,viewport,@resPoint[0],@resPoint[1],@resPoint[2]);
  writeLn(floatToStr(resPoint[0]) + ' , ' + floatToStr(resPoint[1]) + ' , ' + floatToStr(resPoint[2]));
  Result := resPoint;
end;
 

I got results like 0.01268 for x, 1085,36 for y and -0,099 for z. All my tiles are 1x1 and the result doesn't change to much. The y-value (1085,36) is much too high.
Does somebody knows what the problem is?

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Sascha Willems

Betreff des Beitrags:

Verfasst: Fr Aug 13, 2004 18:00

DGL Member

Registriert: Mo Sep 23, 2002 19:27
Beiträge: 5812
Programmiersprache: C++

How does T3D_Point look? You must declare the return values for gluUnproject as doubles, or else you will get bogus results. I guess there lies your problem, as your T3D_Point most likely consists of singles. So change that to doubles and try again.

_________________
www.SaschaWillems.de | GitHub | Twitter | GPU Datenbanken (Vulkan, GL, GLES)

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BTierens

Betreff des Beitrags:

Verfasst: Fr Aug 13, 2004 18:08

DGL Member

Registriert: Fr Aug 13, 2004 17:43
Beiträge: 60
Wohnort: Belgien

No, T3D_Point is an array of gldouble. I get the same result if I change gldouble by double.

Zitat:

T3D_Point = Array[0..2] of gldouble;

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Sascha Willems

Betreff des Beitrags:

Verfasst: Fr Aug 13, 2004 18:17

DGL Member

Registriert: Mo Sep 23, 2002 19:27
Beiträge: 5812
Programmiersprache: C++

I just saw this (didn't look close before my last post) :

Code:

glReadPixels(X,-Y,1,1,GL_DEPTH_COMPONENT,GL_FLOAT,@winZ);

The -Y is wrong in there, and should just be Y.

_________________
www.SaschaWillems.de | GitHub | Twitter | GPU Datenbanken (Vulkan, GL, GLES)

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BTierens

Betreff des Beitrags:

Verfasst: Fr Aug 13, 2004 18:26

DGL Member

Registriert: Fr Aug 13, 2004 17:43
Beiträge: 60
Wohnort: Belgien

Now I get other output but now, most of the times the y value is 2170779,42944. I based my code on Delphi code from http://nehe.gamedev.net/data/articles/article.asp?article=13 wich was based on C++ code on the same page.

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BTierens

Betreff des Beitrags:

Verfasst: Fr Aug 13, 2004 18:59

DGL Member

Registriert: Fr Aug 13, 2004 17:43
Beiträge: 60
Wohnort: Belgien

I changed the code a bit so the code is more similar to the C++ code.

Code:

 
function GetOGLPos(X, Y: integer): T3D_Point;
var
  viewport: TViewPortArray;
  modelview:  T16dArray;
  projection: T16dArray;
  winZ: single;
  resPoint: T3D_Point;
begin
  glGetDoublev(GL_MODELVIEW_MATRIX, @modelview );
  glGetDoublev(GL_PROJECTION_MATRIX, @projection );
  glGetIntegerv(GL_VIEWPORT, @viewport );
 
  // In Delphi A Y Value Of 0 Returns An Unknown Value
  // I Discovered This While I Was Testing A Crosshair
  if(Y = 0) then Y := 1;
  glReadPixels(X,round(viewport[3]-Y),1,1,GL_DEPTH_COMPONENT,GL_FLOAT,@winZ);
  gluUnProject(X,viewport[3]-Y,winZ,modelview,projection,viewport,@resPoint[0],@resPoint[1],@resPoint[2]);
  writeLn(floatToStr(resPoint[0]) + ' , ' + floatToStr(resPoint[1]) + ' , ' + floatToStr(resPoint[2]));
  Result := resPoint;
end;
 

I don't get values that are too high anymore but I don't think the values are correct. I've attached a screenshot to show the problem.

Dateianhänge:

Dateikommentar: You can see tree cursors with the value of the getOGLPos function. In the center, you see the size of one tile (1x1).

screenshot.jpg [ 82.99 KiB | 6184-mal betrachtet ]

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Sascha Willems

Betreff des Beitrags:

Verfasst: Fr Aug 13, 2004 20:11

DGL Member

Registriert: Mo Sep 23, 2002 19:27
Beiträge: 5812
Programmiersprache: C++

Code:

glReadPixels(X,round(viewport[3]-Y),1,1,GL_DEPTH_COMPONENT,GL_FLOAT,@winZ)

Why that? glReadPixels(X, Y, ...) should be correct. In opposition to gluUnproject, die Origin for glReadPixels lies in the upper/left corner, so you don't need to subtract Y from the bottom of the viewport.

_________________
www.SaschaWillems.de | GitHub | Twitter | GPU Datenbanken (Vulkan, GL, GLES)

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BTierens

Betreff des Beitrags:

Verfasst: Sa Aug 14, 2004 07:29

DGL Member

Registriert: Fr Aug 13, 2004 17:43
Beiträge: 60
Wohnort: Belgien

The reference page from msdn.microsoft.com says this:

Zitat:

x, y
The window coordinates of the first pixel that is read from the framebuffer. This location is the lower-left corner of a rectangular block of pixels.

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BTierens

Betreff des Beitrags:

Verfasst: Sa Aug 14, 2004 08:57

DGL Member

Registriert: Fr Aug 13, 2004 17:43
Beiträge: 60
Wohnort: Belgien

It seems to work now. Thanks for your help.

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Phobeus

Betreff des Beitrags:

Verfasst: Sa Aug 14, 2004 13:54

Fels i.d. Brandung

Registriert: Sa Mai 04, 2002 19:48
Beiträge: 3830
Wohnort: Tespe (nahe Hamburg)

btw: Interesting to see that someone is using freepascal for a project. Please feel free to keep us informed about the progress. I will be interested in

_________________
"Light travels faster than sound. This is why some people appear bright, before you can hear them speak..."

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BTierens

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Verfasst: Sa Aug 14, 2004 15:40

DGL Member

Registriert: Fr Aug 13, 2004 17:43
Beiträge: 60
Wohnort: Belgien

I will do that.

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