[DBP/DBC] vector reflection example

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Phaelax

DBPro Master

21

Years of Service

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Joined: 16th Apr 2003

Location: Metropia

Posted: 26th Jan 2008 04:46

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No tag specified because it's technically for both Pro and Classic.
I made this while working on a new tutorial and suddenly forgot how to do reflection. Just move the mouse around to see how a line is reflected off.

set display mode 1024,768,32
sync on

REM x1,y1 represents the point of impact on the surface(or plane) from the ray
x1 = screen width()/2
y1 = 200

do
   cls

rem reflection plane or surface
   ink rgb(0,255,0),0
   line 0,y1,screen width(),y1

rem control angle of incident with mouse
   x2 = mousex()
   y2 = mousey()

rem draw the incoming ray
   ink rgb(255,255,255),0
   line x1,y1,x2,y2

rem length of ray
   d# = sqrt((x2-x1)^2+(y2-y1)^2)

rem normalize(unit length of 1) the incoming ray's vector components to determine
   rem its normalized direction vector
   nx# = (x1-x2)/d#
   ny# = (y1-y2)/d#

rem calculate direction vector of reflected ray
   ax# = getReflectedComponent#(nx#, 0)
   ay# = getReflectedComponent#(ny#, 1)

rem draw the reflected ray
   ink rgb(255,0,0),0
   line x1,y1,x1+ax#*d#,y1+ay#*d#

sync
loop

REM 'a' is direction of incoming vector
REM 'n' is the normal of the surface the incoming vector hits
function getReflectedComponent#(a as float, n as float)
   a = a - 2*(a*n)*n
endfunction a

+ Code Snippet

REM ==================================|
REM Vector reflection example         |
REM By: Phaelax                       |
REM ==================================|
REM Reflection equation is:           |
REM B = A - 2(A.N)N                   |
REM where '.' represents dot product  |
REM ==================================|

set display mode 1024,768,32
sync on

REM x1,y1 represents the point of impact on the surface(or plane) from the ray
x1 = screen width()/2
y1 = 200

do
   cls

   rem reflection plane or surface
   ink rgb(0,255,0),0
   line 0,y1,screen width(),y1


   rem control angle of incident with mouse
   x2 = mousex()
   y2 = mousey()

   rem draw the incoming ray
   ink rgb(255,255,255),0
   line x1,y1,x2,y2

   rem length of ray
   d# = sqrt((x2-x1)^2+(y2-y1)^2)

   rem normalize(unit length of 1) the incoming ray's vector components to determine
   rem its normalized direction vector
   nx# = (x1-x2)/d#
   ny# = (y1-y2)/d#

   rem calculate direction vector of reflected ray
   ax# = getReflectedComponent#(nx#, 0)
   ay# = getReflectedComponent#(ny#, 1)

   rem draw the reflected ray
   ink rgb(255,0,0),0
   line x1,y1,x1+ax#*d#,y1+ay#*d#


   sync
loop


REM 'a' is direction of incoming vector
REM 'n' is the normal of the surface the incoming vector hits
function getReflectedComponent#(a as float, n as float)
   a = a - 2*(a*n)*n
endfunction a

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TDK

Retired Moderator

21

Years of Service

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Joined: 19th Nov 2002

Location: UK

Posted: 27th Jan 2008 07:18

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Altered topic title to prevent deletion by mod as it does state it works for both DBC and DBP in the message body.

It now matches all the other snippets which work with both.

TDK_Man

* TDK's Game Programming Forums - Open To All - DB & Team Request Boards *

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Libervurto

17

Years of Service

User Offline

Joined: 30th Jun 2006

Location: On Toast

Posted: 29th Jan 2008 21:24

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It needs a very slight modification to run in DBC

set display mode 1024,768,32
sync on

REM x1,y1 represents the point of impact on the surface(or plane) from the ray
x1 = screen width()/2
y1 = 200

do
   cls

rem reflection plane or surface
   ink rgb(0,255,0),0
   line 0,y1,screen width(),y1

rem control angle of incident with mouse
   x2 = mousex()
   y2 = mousey()

rem draw the incoming ray
   ink rgb(255,255,255),0
   line x1,y1,x2,y2

rem length of ray
   d# = sqrt((x2-x1)^2+(y2-y1)^2)

rem normalize(unit length of 1) the incoming ray's vector components to determine
   rem its normalized direction vector
   nx# = (x1-x2)/d#
   ny# = (y1-y2)/d#

rem calculate direction vector of reflected ray
   ax# = getReflectedComponent#(nx#, 0.)
   ay# = getReflectedComponent#(ny#, 1.)

rem draw the reflected ray
   ink rgb(255,0,0),0
   line x1,y1,x1+ax#*d#,y1+ay#*d#

sync
loop

REM 'a' is direction of incoming vector
REM 'n' is the normal of the surface the incoming vector hits
function getReflectedComponent#(a#, n#)
   a# = a# - 2*(a#*n#)*n#
endfunction a#

+ Code Snippet

REM ==================================|
REM Vector reflection example         |
REM By: Phaelax                       |
REM ==================================|
REM Reflection equation is:           |
REM B = A - 2(A.N)N                   |
REM where '.' represents dot product  |
REM ==================================|

set display mode 1024,768,32
sync on

REM x1,y1 represents the point of impact on the surface(or plane) from the ray
x1 = screen width()/2
y1 = 200

do
   cls

   rem reflection plane or surface
   ink rgb(0,255,0),0
   line 0,y1,screen width(),y1


   rem control angle of incident with mouse
   x2 = mousex()
   y2 = mousey()

   rem draw the incoming ray
   ink rgb(255,255,255),0
   line x1,y1,x2,y2

   rem length of ray
   d# = sqrt((x2-x1)^2+(y2-y1)^2)

   rem normalize(unit length of 1) the incoming ray's vector components to determine
   rem its normalized direction vector
   nx# = (x1-x2)/d#
   ny# = (y1-y2)/d#

   rem calculate direction vector of reflected ray
   ax# = getReflectedComponent#(nx#, 0.)
   ay# = getReflectedComponent#(ny#, 1.)

   rem draw the reflected ray
   ink rgb(255,0,0),0
   line x1,y1,x1+ax#*d#,y1+ay#*d#


   sync
loop


REM 'a' is direction of incoming vector
REM 'n' is the normal of the surface the incoming vector hits
function getReflectedComponent#(a#, n#)
   a# = a# - 2*(a#*n#)*n#
endfunction a#

The green line runs straight through the only dead pixel on my screen

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Phaelax

DBPro Master

21

Years of Service

User Offline

Joined: 16th Apr 2003

Location: Metropia

Posted: 17th Feb 2008 03:42

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I need to make a correction in the reflection equation.

a = a - 2*(a*n)*n

(a*n) is really suppose to be a dot product b. Here's the new code.

set display mode 1024,768,32
sync on

rem ray of incident
null = make vector2(1)
rem normal vector
null = make vector2(2)

rem the reflective plane/surface/line
px1 = 0
py1 = 400
px2 = screen width()
py2 = 200

REM x2,y2 represents the point of impact on the surface(or plane) from the ray
REM in this case, the center of the line
x2 = screen width()/2
y2 = 300

do
   cls

rem reflection plane or surface
   ink rgb(0,255,0),0
   line px1,py1,px2,py2

rem reflection surface's normal
   rem we divided by the length of the line so we can have normalized values
   d# = sqrt((px2-px1)^2+(py2-py1)^2)
   nx# = (py1-py2)/d#
   ny# = -(px1-px2)/d#

line x2,y2,x2+nx#*20,y2+ny#*20

rem control angle of incident with mouse
   x1 = mousex()
   y1 = mousey()

rem draw the incoming ray
   ink rgb(255,255,255),0
   line x1,y1,x2,y2

rem length of incoming ray
   d# = sqrt((x2-x1)^2+(y2-y1)^2)

rem calculate reflection vector
   ax# = (x2-x1)
   ay# = (y2-y1)
   set vector2 1,ax#, ay#
   set vector2 2, nx#,ny#
   r# = dot product vector2(1,2)
   ax# = ax# - 2*r#*nx#
   ay# = ay# - 2*r#*ny#

rem draw the reflected ray
   ink rgb(255,0,0),0
   line x2,y2,x2+ax#*d#,y2+ay#*d#

sync
loop

+ Code Snippet

REM ==================================|
REM Vector reflection example         |
REM By: Phaelax                       |
REM ==================================|
REM Reflection equation is:           |
REM B = A - 2(A.N)N                   |
REM where '.' represents dot product  |
REM ==================================|

set display mode 1024,768,32
sync on

rem ray of incident
null = make vector2(1)
rem normal vector
null = make vector2(2)


rem the reflective plane/surface/line
px1 = 0
py1 = 400
px2 = screen width()
py2 = 200

REM x2,y2 represents the point of impact on the surface(or plane) from the ray
REM in this case, the center of the line
x2 = screen width()/2
y2 = 300



do
   cls

   rem reflection plane or surface
   ink rgb(0,255,0),0
   line px1,py1,px2,py2

   rem reflection surface's normal
   rem we divided by the length of the line so we can have normalized values
   d# = sqrt((px2-px1)^2+(py2-py1)^2)
   nx# = (py1-py2)/d#
   ny# = -(px1-px2)/d#


   line x2,y2,x2+nx#*20,y2+ny#*20

   rem control angle of incident with mouse
   x1 = mousex()
   y1 = mousey()

   rem draw the incoming ray
   ink rgb(255,255,255),0
   line x1,y1,x2,y2

   rem length of incoming ray
   d# = sqrt((x2-x1)^2+(y2-y1)^2)

   rem calculate reflection vector
   ax# = (x2-x1)
   ay# = (y2-y1)
   set vector2 1,ax#, ay#
   set vector2 2, nx#,ny#
   r# = dot product vector2(1,2)
   ax# = ax# - 2*r#*nx#
   ay# = ay# - 2*r#*ny#


   rem draw the reflected ray
   ink rgb(255,0,0),0
   line x2,y2,x2+ax#*d#,y2+ay#*d#

   sync
loop

I didn't catch the bug right away because it doesn't present itself when the reflective surface is axis-aligned, as in what demo used.

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Code Snippets / [DBP/DBC] vector reflection example