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Global DISPLAY_GAMMA.d, USER_GAMMA.d, result
#STANDARD_GAMMA = 2.2 ; DE-FACTO STANDARD
USER_GAMMA = #STANDARD_GAMMA
Global Dim iGammaRamp.w(3,255)

Procedure SetDisplayGamma()

DISPLAY_GAMMA.d = USER_GAMMA / #STANDARD_GAMMA

; If DISPLAY_GAMMA < 0.9 Or DISPLAY_GAMMA > 1.1
;   MessageRequester("Error", "Display gamma must be not less than 0.9 and not more than 1.1.")
;   End  
; EndIf

DISPLAY_GAMMA.d = 1/DISPLAY_GAMMA
For ct = 0 To 255
  iValue.d =  (Pow(ct, DISPLAY_GAMMA) * 257)
If iValue > 65535: iValue = 65535: EndIf
iGammaRamp(0,ct) = iValue
iGammaRamp(1,ct) = iGammaRamp(0,ct)
iGammaRamp(2,ct) = iGammaRamp(0,ct)
;GIVE R G AND B CHANNELS THE SAME GAMMA VALUE
Next

;REWRITE THE GAMMA TABLE
result = SetDeviceGammaRamp_(GetDC_(0),@iGammaRamp())
EndProcedure

Procedure DrawWindow()
SetDisplayGamma()
StartDrawing(WindowOutput(1)) 
For ct = 0 To 10
  Box((ct * 74)+25, 250, 75, 100, RGB(ct * 25, ct*25,ct*25))
Next

DrawText(160, 100, "Gamma = " + StrD(1/DISPLAY_GAMMA * #STANDARD_GAMMA, 2),#White)
; If result = #True
; DrawText(50, 100, "Success",#White)
; EndIf
StopDrawing()
EndProcedure

OpenWindow(1, 0, 0, 930, 500, "Gamma", #PB_Window_ScreenCentered | #PB_Window_SystemMenu)
TrackBarGadget(1, 50, 145, 300, 20, 199, 242)
SetGadgetState(1, 220)

DrawWindow()

Repeat
  event = WaitWindowEvent()
  
  If event = #PB_Event_CloseWindow:
    
    If USER_GAMMA <> 2.2
    message = MessageRequester("Restore gamma?", "Restore gamma to default (2.2)?", #PB_MessageRequester_YesNo)
    
    If message = #PB_MessageRequester_Yes: USER_GAMMA = 2.2: DrawWindow(): End: ;EndIf
  Else
    End  
  EndIf
Else
  End
EndIf

ElseIf event = #PB_Event_Gadget
    Select EventGadget()
      Case 1
        USER_GAMMA = GetGadgetState(1) / 100
        DrawWindow()

  EndSelect    
    
  ElseIf event = #PB_Event_Repaint: DrawWindow()
    
  EndIf
ForEver