Transition_Linear - ProGUI Reference Manual

Syntax

Value.d = Transition_Linear(t.d, b.d, c.d, d.d)

Description

Calculates an intermediate value using a simple linear transition. The value changes at a constant rate from the start value to the end value over the specified duration.

Parameters

t.d
The current elapsed time of the animation in milliseconds.

b.d
The starting value of the property being animated.

c.d
The total change in value (target value - starting value).

d.d
The total duration of the animation in milliseconds.

Return Value

Returns the linearly interpolated value (Double) at the current time `t`.

Remarks

This is the most basic transition, representing a constant speed with no acceleration or deceleration.

Example

IncludeFile "ProGUI_PB.pbi"

Structure MyAnimData
  TargetValue.d
  StartValue.d
  x.d
EndStructure

Procedure DrawHandler(Window, EventType, *EventData.PG_EventDraw, *UserData.MyAnimData)
  
    DrawClear(RGB(200, 200, 200), 1) ; Grey background

    ; Draw a box whose X position is animated
    DrawBox(*UserData\x, (*EventData\height / 2) - 25, 50, 50, RGB(0, 0, 255))
    
EndProcedure

Procedure AnimateHandler(Window, EventType, *EventData.PG_EventAnimate, *UserData.MyAnimData)
  
  Select *EventData\state
  
    Case #PG_Event_Animate_Start
      Debug "Animation started."
      
    Case #PG_Event_Animate_Update
      ; Calculate intermediate value using the linear transition
      *UserData\x = Transition_Linear(*EventData\currentTime, *UserData\StartValue, *UserData\TargetValue - *UserData\StartValue, *EventData\duration) 
      WindowRedraw(Window)
      
    Case #PG_Event_Animate_End
      Debug "Animation ended"
      ; Ensure final value is set exactly
      *UserData\x = *UserData\TargetValue
      WindowRedraw(Window)
      ; Optional: Restart or clean up
      ; FreeStructure(*UserData) 
  EndSelect
EndProcedure

StartProGUI()

MyWindow = CreateWindow(0, 0, 300, 200, "Transition_Linear Example")

If MyWindow
    
  ; Setup data for animation
  *AnimData.MyAnimData = AllocateStructure(MyAnimData)
  *AnimData\StartValue = 10 
  *AnimData\TargetValue = 200
    
  AddEventHandler(MyWindow, #PG_Event_Draw, @DrawHandler(), *AnimData)
  AddEventHandler(MyWindow, #PG_Event_Animate, @AnimateHandler(), *AnimData) 

  ; Start a 2-second animation
  AnimID = StartAnimation(MyWindow, #PG_Any, 2000)

  WindowShow(MyWindow, #True, #PG_Window_ScreenCentered)
  Repeat : Event = WaitWindowEvent() : Until Event = #PB_Event_CloseWindow
  
  StopAnimation(MyWindow, AnimID) 
  FreeStructure(*AnimData)
  
EndIf 

StopProGUI()

Supported OS

Windows, Linux