getpixel( x , y ) ?

[bluatigro]

i looked but i can not find this :
how do i read a color from a pixel
ans what does this return ?

i only fond this :

COLORREF GetPixel(
 HDC hdc,
 int x,
 int y
);


[tenochtitlanuk]

No native way.
Since the structure of a 24bit bmp file is known, you can 'getbmp' of the chosen pixel and read the three colours. This works and is usable in JB too.
In LB we can read by using Windows functions.
Example below reads all the pixels of a screen and replaces them with their RGB colours rotated. I've used this a lot ( see my many web examples) but it is NOT fast!


nomainwin

WindowWidth  =500
WindowHeight =500

open "getpixel in Liberty BASIC" for graphics_nsb as #wg

#wg "trapclose quit"

handleg  =hwnd( #wg)
calldll  #user32, "GetDC", handleg as ulong, hDC as ulong

#wg "down ; fill 110 110 60 ; color 110 110 60"
#wg "backcolor 255 0 0 ; goto 150 150 ; circlefilled 100"
#wg "backcolor 0 255 0 ; goto 300 250 ; circlefilled 100"
#wg "backcolor 0 0 255 ; goto 150 350 ; circlefilled 100"

for x =1 to 500
   for y =1 to 500

       calldll #gdi32, "GetPixel", hDC as ulong, x as long, y as long, pixcol as ulong
           bl      = int(  pixcol /( 256*256))
           gr      = int( (pixcol -bl *256*256) / 256)
           re      = int(  pixcol -bl *256*256 -gr *256)
           grey    = int( ( bl +gr +re) /3 /32)    '   not eye-sensitivity adjusted
       #wg "color "; gr; " "; bl; " "; re
       #wg "set "; x; " "; y

       scan
   next y
next x

wait

sub quit h$
   close #h$
   callDll #user32, "ReleaseDC", handleg as ulong, hDC as ulong, result as ushort
   end
end sub


[tenochtitlanuk]

[Alyce Watson]

Nov 12, 2018 4:05:17 GMT -5 bluatigro said:

i looked but i can not find this :
how do i read a color from a pixel
ans what does this return ?

i only fond this :

COLORREF GetPixel(
 HDC hdc,
 int x,
 int y
);


It returns a long value, from which you can extract the RGB. Here's a snippet to extract the red, green and blue color values from a long value.

Get RGB

The following set of tutorials explain the HDC (handle to the device context) and how to use it.

API Graphics Tutorials