Re: [fpc-pascal] Calculating Pixels to represent 3D coordinates

[James Richters]

Thanks for the Tip!  I had no idea there was a single function that would 
return both sine and cosine.

-Original Message-
From: fpc-pascal  On Behalf Of Jean 
SUZINEAU
Sent: Friday, September 20, 2019 8:01 PM
To: fpc-pascal@lists.freepascal.org
Subject: Re: [fpc-pascal] Calculating Pixels to represent 3D coordinates

Tip: if you need Sin(A) and Cos(A), it can be faster to make a single call to 
SinCos instead of two separated calls to Sin and Cos:

https://www.freepascal.org/docs-html/rtl/math/sincos.html

It was efficient 20 years ago when I was developing a sky map software, may be 
the gain is negligible today.

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Re: [fpc-pascal] Calculating Pixels to represent 3D coordinates

[Jean SUZINEAU]

Tip: if you need Sin(A) and Cos(A), it can be faster to make a single 
call to SinCos instead of two separated calls to Sin and Cos:


https://www.freepascal.org/docs-html/rtl/math/sincos.html

It was efficient 20 years ago when I was developing a sky map software, 
may be the gain is negligible today.


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Re: [fpc-pascal] Calculating Pixels to represent 3D coordinates

[Thomas Young via fpc-pascal]

James, are you not applying the rotation universally to all coordinates? If so, 
you are better off pre-calculating your directional sines and cosines.
For example:
TH: REAL;   {ROTATIONS (in degrees) AROUND Z-AXIS BY theta, LEFTRIGHT-> turn 
its back to us}

PHI: REAL; {ROTATIONS (in degrees) AROUND X-AXIS BY phi, UPDOWN-> a nod}

PSI: REAL; {ROTATIONS (in degrees) AROUND Y-AXIS BY psi, SPIN-> a clock face}
P
STH: REAL;{SIN(TH * (PI / 180)), CONVERT DEGREES TO RADIANS}
CTH: REAL;{COS(TH * (PI / 180)), CONVERT DEGREES TO RADIANS}
STI: REAL;{SIN(PHI * (PI / 180)), CONVERT DEGREES TO RADIANS}
CTI: REAL;{COS(PHI * (PI / 180)), CONVERT DEGREES TO RADIANS}
STS: REAL;{SIN(PSI * (PI / 180)), CONVERT DEGREES TO RADIANS}
CTS: REAL;{COS(PSI * (PI / 180)), CONVERT DEGREES TO RADIANS}

Thomas Young
330-256-7064
Sent from my iPhone

> On Sep 19, 2019, at 12:38 PM, James Richters  
> wrote:
> 
> Thank you for the help and suggestions with this.  After playing with the 
> suggested formulas I was able to figure out how they work...  The solution to 
> this is probably somewhere but I ended up just doing it myself.
> 
> I realized that Thomas' formula 
> var H1 = (Y - X) * 0.86602 + ScreenOrgin_H; var V1 = (X + Y) * 0.5 - Z + 
> ScreenOrgin_V;
> was multipying by the cosine of 30 degrees for H1 and the Sine of 30 degrees 
> for V1 
> 
> and Gustavo's forumla was basically the same thing but multiplying by the 
> cosine and sine of 45 degrees...  
> 
> so I realized that all I really want to do has nothing to do with camera 
> angles, or projections or anythng else... I just strictly need do the 3D 
> rotations then just display the resulting X, and Y coordinate and ignore Z.   
> My original 2D representaion showing only X and Y is as if I am looking 
> perfectly straight down at it.. so I can't see the Z only lines, but after I 
> perform the 3D rotations now I can see the Z component as they end up being 
> represented on the X and Y axis but I still act like I am still looking 
> straight down at it, so I only plot X and Y.
> I checked the results of my formula against my CAD program everything looks 
> EXACTLY the same no matter how I change the rotations,  so this must be what 
> the CAD program is doing as well.
> 
> Here are the formula I came up with that allows me to adjust the 3 possible 
> rotations,  A - rotating around the X axis, B rotating around the Y axis, and 
> C rotating around the Z axis.
> 
> X1 - initial X coordinate
> Y1 - initial Y coordinate
> Z1 - initial Z coordinate
> X2 - output  X coordinate
> Y2 - output Y coordinate
> 
> //XY Rotation - only rotates X and Y around the Z axis (C Rotation)
>  XC_Point := ((CoSine(C_Angle) * (X1-XC_Center)) - (Sine(C_Angle) * 
> (Y1-YC_Center) )) + XC_Center;
>  YC_Point := ((CoSine(C_Angle) * (Y1-YC_Center)) + (Sine(C_Angle) * 
> (X1-XC_Center) )) + YC_Center;
>  ZC_Point :=Z1;
> 
> //XZ Rotation - only rotates X and Z around the Y axis (B Rotation)
>  XB_Point := ((CoSine(B_Angle) * (XC_Point-XB_Center)) + (Sine(B_Angle) * 
> (ZC_Point-ZB_Center) )) + XB_Center;
>  YB_Point := YC_Point;
>  ZB_Point :=  ((CoSine(B_Angle) * (ZC_Point-ZB_Center)) - (Sine(B_Angle) * 
> (XC_Point-XB_Center) )) + ZB_Center;
> 
> //YZ Rotation  - only rotates Y and Z around the X axis (A Rotation)
>  XA_Point := XB_Point;
>  YA_Point := ((CoSine(A_Angle) * (YB_Point-YA_Center)) - (Sine(A_Angle) * 
> (ZB_Point-ZA_Center) )) +@YA_Center;
>  ZA_Point := ((CoSine(A_Angle) * (XB_Point-XA_Center)) + (Sine(A_Angle) * 
> (ZB_Point-ZA_Center) )) + XA_Center; // useless to plot point, just for 
> information
> 
> X2 := Scale * XA_Point+X_Offset;
> Y2 := Scale * YA_Point+Y_Offset;
> 
> Notes:  
> 
> My fuctions CoSine and Sine convert the angle to radians from given degrees. 
> 
> I have my 0,0 located in the lower left hand corner, but PTC-Graph has it in 
> the upper left corner.. I used the above formula before the section that 
> takes care of getting it on the screen, I don't know if some adjustment would 
> be nessecary for use on direct screen coordinates... things might end up 
> upside down, or the rotations might need to be reversed by switching the + 
> and - between CoSine and Sine because of this.. 
> 
> 
> Thank you again for all the help and suggestions.  I also found the websites 
> and books on the subject very interesting as well.
> 
> James
> 
> 
> -Original Message-
> From: fpc-pascal  On Behalf Of 
> Thomas Young via fpc-pascal
> Sent: Tuesday, September 17, 2019 5:00 PM
> To: FPC-Pascal users discussions 
> Cc: Thomas Young 
> Subject: Re: [fpc-pascal] Calculating Pixels to represent 3D coordinates
> 
> This is an isometric projection I use:
> var H1 = (Y - X) * 0.8660

Re: [fpc-pascal] Calculating Pixels to represent 3D coordinates

[James Richters]

Thank you for the help and suggestions with this.  After playing with the 
suggested formulas I was able to figure out how they work...  The solution to 
this is probably somewhere but I ended up just doing it myself.

I realized that Thomas' formula 
var H1 = (Y - X) * 0.86602 + ScreenOrgin_H; var V1 = (X + Y) * 0.5 - Z + 
ScreenOrgin_V;
was multipying by the cosine of 30 degrees for H1 and the Sine of 30 degrees 
for V1 

and Gustavo's forumla was basically the same thing but multiplying by the 
cosine and sine of 45 degrees...  

so I realized that all I really want to do has nothing to do with camera 
angles, or projections or anythng else... I just strictly need do the 3D 
rotations then just display the resulting X, and Y coordinate and ignore Z. 
  My original 2D representaion showing only X and Y is as if I am looking 
perfectly straight down at it.. so I can't see the Z only lines, but after I 
perform the 3D rotations now I can see the Z component as they end up being 
represented on the X and Y axis but I still act like I am still looking 
straight down at it, so I only plot X and Y.
I checked the results of my formula against my CAD program everything looks 
EXACTLY the same no matter how I change the rotations,  so this must be what 
the CAD program is doing as well.

Here are the formula I came up with that allows me to adjust the 3 possible 
rotations,  A - rotating around the X axis, B rotating around the Y axis, and C 
rotating around the Z axis.

X1 - initial X coordinate
Y1 - initial Y coordinate
Z1 - initial Z coordinate
X2 - output  X coordinate
Y2 - output Y coordinate

//XY Rotation - only rotates X and Y around the Z axis (C Rotation)
  XC_Point := ((CoSine(C_Angle) * (X1-XC_Center)) - (Sine(C_Angle) * 
(Y1-YC_Center) )) + XC_Center;
  YC_Point := ((CoSine(C_Angle) * (Y1-YC_Center)) + (Sine(C_Angle) * 
(X1-XC_Center) )) + YC_Center;
  ZC_Point :=Z1;

//XZ Rotation - only rotates X and Z around the Y axis (B Rotation)
  XB_Point := ((CoSine(B_Angle) * (XC_Point-XB_Center)) + (Sine(B_Angle) * 
(ZC_Point-ZB_Center) )) + XB_Center;
  YB_Point := YC_Point;
  ZB_Point :=  ((CoSine(B_Angle) * (ZC_Point-ZB_Center)) - (Sine(B_Angle) * 
(XC_Point-XB_Center) )) + ZB_Center;

//YZ Rotation  - only rotates Y and Z around the X axis (A Rotation)
  XA_Point := XB_Point;
  YA_Point := ((CoSine(A_Angle) * (YB_Point-YA_Center)) - (Sine(A_Angle) * 
(ZB_Point-ZA_Center) )) +@YA_Center;
  ZA_Point := ((CoSine(A_Angle) * (XB_Point-XA_Center)) + (Sine(A_Angle) * 
(ZB_Point-ZA_Center) )) + XA_Center; // useless to plot point, just for 
information
  
X2 := Scale * XA_Point+X_Offset;
Y2 := Scale * YA_Point+Y_Offset;

Notes:  

My fuctions CoSine and Sine convert the angle to radians from given degrees. 

I have my 0,0 located in the lower left hand corner, but PTC-Graph has it in 
the upper left corner.. I used the above formula before the section that takes 
care of getting it on the screen, I don't know if some adjustment would be 
nessecary for use on direct screen coordinates... things might end up upside 
down, or the rotations might need to be reversed by switching the + and - 
between CoSine and Sine because of this.. 


Thank you again for all the help and suggestions.  I also found the websites 
and books on the subject very interesting as well.

James


-Original Message-
From: fpc-pascal  On Behalf Of Thomas 
Young via fpc-pascal
Sent: Tuesday, September 17, 2019 5:00 PM
To: FPC-Pascal users discussions 
Cc: Thomas Young 
Subject: Re: [fpc-pascal] Calculating Pixels to represent 3D coordinates

This is an isometric projection I use:
var H1 = (Y - X) * 0.86602 + ScreenOrgin_H; var V1 = (X + Y) * 0.5 - Z + 
ScreenOrgin_V;

Thomas Young
330-256-7064
Sent from my iPhone

> On Sep 17, 2019, at 4:53 PM, Gustavo Enrique Jimenez  
> wrote:
> 
> A simple transformation is:
> 
> P3D=(X,Y,Z)
> P2D=(x,y)
> 
> x=X+Y*0.707
> y=Y*0.707+Z
> 
> I did not tried it, but I think that this is the transformation that 
> you are looking for.
> 
> 
> Gustavo
> 
> El mar., 17 sept. 2019 a las 17:37, James Richters
> () escribió:
>> 
>>> What exactly are you trying to do? Usually if you’re doing 3D this all 
>>> happens on the GPU and you get back a color/depth buffer. Maybe you need to 
>>> know where a 2D coordinate is in 3D space?
>> 
>> What I'm trying to do is much simpler than rendering a 3D object..  All I'm 
>> trying to do is display a 3D line drawing or wireframe on the screen.  I 
>> don't need it to dynamically rotate or anything, and it doesn't need to show 
>> any surfaces, textures, lighting, reflections, or shadows, just give a 
>> representation of the XYZ points and lines connecting 2 pair of XYZ 
>> coordinates on the screen.   The purpose of this is to show a 3D 
>> representation of a CNC tool path including the Z movem

Re: [fpc-pascal] Calculating Pixels to represent 3D coordinates

[Thomas Young via fpc-pascal]

This is an isometric projection I use:
var H1 = (Y - X) * 0.86602 + ScreenOrgin_H;
var V1 = (X + Y) * 0.5 - Z + ScreenOrgin_V;

Thomas Young
330-256-7064
Sent from my iPhone

> On Sep 17, 2019, at 4:53 PM, Gustavo Enrique Jimenez  
> wrote:
> 
> A simple transformation is:
> 
> P3D=(X,Y,Z)
> P2D=(x,y)
> 
> x=X+Y*0.707
> y=Y*0.707+Z
> 
> I did not tried it, but I think that this is the transformation that
> you are looking for.
> 
> 
> Gustavo
> 
> El mar., 17 sept. 2019 a las 17:37, James Richters
> () escribió:
>> 
>>> What exactly are you trying to do? Usually if you’re doing 3D this all 
>>> happens on the GPU and you get back a color/depth buffer. Maybe you need to 
>>> know where a 2D coordinate is in 3D space?
>> 
>> What I'm trying to do is much simpler than rendering a 3D object..  All I'm 
>> trying to do is display a 3D line drawing or wireframe on the screen.  I 
>> don't need it to dynamically rotate or anything, and it doesn't need to show 
>> any surfaces, textures, lighting, reflections, or shadows, just give a 
>> representation of the XYZ points and lines connecting 2 pair of XYZ 
>> coordinates on the screen.   The purpose of this is to show a 3D 
>> representation of a CNC tool path including the Z movements.
>> 
>> James
>> ___
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Re: [fpc-pascal] Calculating Pixels to represent 3D coordinates

[Karoly Balogh (Charlie/SGR)]

Hi,

On Tue, 17 Sep 2019, James Richters wrote:

> What I'm trying to do is much simpler than rendering a 3D object..  All
> I'm trying to do is display a 3D line drawing or wireframe on the
> screen.  I don't need it to dynamically rotate or anything, and it
> doesn't need to show any surfaces, textures, lighting, reflections, or
> shadows, just give a representation of the XYZ points and lines
> connecting 2 pair of XYZ coordinates on the screen.  The purpose of this
> is to show a 3D representation of a CNC tool path including the Z
> movements.

Well, it all boils down to the projection you want to make while you
transform from your coordinates from 3D to 2D. For the most simple
"isometric" projection with no perspective, you just throw away one of the
XYZ coordinates, and use the other two - this will result in a simple
"camera" which views at your object from either the front (XY), side (YZ)
or from the top (XZ). (Actually, this also depends on wether in your
coordinate system Y or Z represents depth, 3D editors/engines don't even
agree on this one, the code below assumes "Z" is depth.)

For a simple "perspective" projection, you can use a simplistic formula,
something like:

{ untested pseudocode }
procedure perspective_vertex(const v: T3DVertex; ZCenter: single;
  out X, Y: single);
var
  rdist1: single;
begin
  zdist1:=1.0 / (v.z - zcenter);
  X:=(v.x * zcenter) * zdist1;
  Y:=(v.y * zcenter) * zdist1;
end;

This will put some sort of "perspective" on your 3D vertex, depending on
its Z coordinate. The ZCenter should be larger than the maximum dimension
of your object facing the "camera". Note that this formula is massively
simplified, but serves as the most simple perspective projection.

After this, you can use x/y coordinates to feed the wireframe drawer using
whatever drawing unit you see fit. You might need to do inc(x,width/2);
and inc(y,height/2); and/or multiply your values with a certain
scale-factor, depending on the size of your object, and how its
coordinates map to your 2D resolution.

All of the above methods assume that your object's 3D center resides at
the origo (center of the coordinate system). Anything more complicated
would require some proper matrices to be set up and calculate a full
series of model, view, and projection matrices, as others have already
mentioned, or would require pre-processing your 3D coordinates in a
certain way, so this simplistic formula can work.

Hope this helps,
--
Charlie

(Ps: actually, the FPC Packages contain two similar examples of a rotating
3D cube, for PalmOS and Atari, both written by me, to showcase the m68k
code generator and the units for these retro/niche OSes. They're at (SVN
trunk):

- packages/tosunits/examples/gemcube.pas
- packages/palmunits/examples/palmcube.pas

Showcased here (with video):
https://twitter.com/chainq/status/945010617672523777
https://twitter.com/chainq/status/948865605209387010

These show this most simplistic form of 3D calculation, and they also use
fixed point math, as that fit the only a few mhz fast 68000 CPUs in these
machines. But the basic algo and formula is the same with float and on
faster platforms. Now I'm quite tempted to make a ptc-graph version. :) )
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Re: [fpc-pascal] Calculating Pixels to represent 3D coordinates

[Wolf]

What you are trying to do is write a very simple CAD program. Have a 
look at this link 
, 
which gives the basic formulae and also Pascal routines to do it.


Wolf

On 18/09/19 2:10 AM, James Richters wrote:

I'm curious if Freepascal has any package available that would calculate X,Y 
screen pixels based on 3D  X,Y,Z  data at some given rotations.  I'm using 
Agg-Pas with PTC-Graph in a console application on Windows.   I'm not sure what 
the technical term is for figuring out what pixels are used to represent 3D 
coordinates on a 2D screen, but I'm hoping maybe there is something that just 
does the calculations that I can use in conjunction with Agg-Pas and PTC-Graph 
instead of moving to a complete graphics package.

James
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Re: [fpc-pascal] Calculating Pixels to represent 3D coordinates

[Gustavo Enrique Jimenez]

A simple transformation is:

P3D=(X,Y,Z)
P2D=(x,y)

x=X+Y*0.707
y=Y*0.707+Z

I did not tried it, but I think that this is the transformation that
you are looking for.


Gustavo

El mar., 17 sept. 2019 a las 17:37, James Richters
() escribió:
>
> >What exactly are you trying to do? Usually if you’re doing 3D this all 
> >happens on the GPU and you get back a color/depth buffer. Maybe you need to 
> >know where a 2D coordinate is in 3D space?
>
> What I'm trying to do is much simpler than rendering a 3D object..  All I'm 
> trying to do is display a 3D line drawing or wireframe on the screen.  I 
> don't need it to dynamically rotate or anything, and it doesn't need to show 
> any surfaces, textures, lighting, reflections, or shadows, just give a 
> representation of the XYZ points and lines connecting 2 pair of XYZ 
> coordinates on the screen.   The purpose of this is to show a 3D 
> representation of a CNC tool path including the Z movements.
>
> James
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Re: [fpc-pascal] Calculating Pixels to represent 3D coordinates

[James Richters]

>What exactly are you trying to do? Usually if you’re doing 3D this all happens 
>on the GPU and you get back a color/depth buffer. Maybe you need to know where 
>a 2D coordinate is in 3D space?

What I'm trying to do is much simpler than rendering a 3D object..  All I'm 
trying to do is display a 3D line drawing or wireframe on the screen.  I don't 
need it to dynamically rotate or anything, and it doesn't need to show any 
surfaces, textures, lighting, reflections, or shadows, just give a 
representation of the XYZ points and lines connecting 2 pair of XYZ coordinates 
on the screen.   The purpose of this is to show a 3D representation of a CNC 
tool path including the Z movements.   

James
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Re: [fpc-pascal] Calculating Pixels to represent 3D coordinates

[Ryan Joseph]

What exactly are you trying to do? Usually if you’re doing 3D this all happens 
on the GPU and you get back a color/depth buffer. Maybe you need to know where 
a 2D coordinate is in 3D space?

> On Sep 17, 2019, at 10:10 AM, James Richters  
> wrote:
> 
> I'm curious if Freepascal has any package available that would calculate X,Y 
> screen pixels based on 3D X,Y,Z  data at some given rotations.  I'm using 
> Agg-Pas with PTC-Graph in a console application on Windows.   I'm not sure 
> what the technical term is for figuring out what pixels are used to represent 
> 3D coordinates on a 2D screen, but I'm hoping maybe there is something that 
> just does the calculations that I can use in conjunction with Agg-Pas and 
> PTC-Graph instead of moving to a complete graphics package.

Regards,
Ryan Joseph

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Re: [fpc-pascal] Calculating Pixels to represent 3D coordinates

[Graeme Geldenhuys]

On 17/09/2019 3:10 pm, James Richters wrote:
> I'm not sure what the technical term is for figuring out what pixels
> are used to represent 3D coordinates on a 2D screen, but I'm hoping
> maybe there is something that just does the calculations that I can
> use

https://en.wikipedia.org/wiki/Ray_tracing_(graphics)

Regards,
  Graeme

-- 
fpGUI Toolkit - a cross-platform GUI toolkit using Free Pascal
http://fpgui.sourceforge.net/

My public PGP key:  http://tinyurl.com/graeme-pgp
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Re: [fpc-pascal] Calculating Pixels to represent 3D coordinates

[Sven Barth via fpc-pascal]

James Richters  schrieb am Di., 17. Sep.
2019, 16:15:

> I'm curious if Freepascal has any package available that would calculate
> X,Y screen pixels based on 3D  X,Y,Z  data at some given rotations.  I'm
> using Agg-Pas with PTC-Graph in a console application on Windows.   I'm not
> sure what the technical term is for figuring out what pixels are used to
> represent 3D coordinates on a 2D screen, but I'm hoping maybe there is
> something that just does the calculations that I can use in conjunction
> with Agg-Pas and PTC-Graph instead of moving to a complete graphics package.
>

You're essentially looking for a software renderer/rasterizer. Lookup
things like projection matrix and model view matrix.

You can also take a look at the "Ray Tracing in one weekend" books (
https://github.com/RayTracing/raytracing.github.io ) to get a feeling for
what's required.

In the end you might be better served to use a graphics package or at least
OpenGL.

Regards,
Sven

>
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