how to code---> undo/redo for graphics utilities ????????

could somemone help me ?
i'm coding a sprite app in basic (no vb) !
what's the better way to code multiple undo redo function ?


  • I never coded something like that but I have some ideas.

    1. Saving the data to temporary files, the simplest way but the most ressource wasting.

    2. Macro based. (look at History window in Adobe Photoshop)
    You must firsd define few basic types of actions that can be done, I will use 3 (set pixel, Resize X, Resize Y). Those info must be stored in an array (so there can be many of them and will automaticly have a unique ID), you also need a "curentg position" index to know how many of Undo/Redo the user have alraedy used
    ' Use it for boolean operations
    const true = -1
    const false = 0

    TYPE undMacroType
    Used As Integer ' Tell that this item is used, I use that type of information
    ' very often because it's very useful for advanced manipulations.
    ' In an advanced sprite edit it would be useful to have
    ' an option to delete some Undo info without deleting others
    Mode As Integer ' The type of action that was done

    const mode_SetPixel = 0, mode_ResizeX = 1, mode_ResizeY = 2

    dim shared MacPos As Integer

    Now you need to store informations about each of the macro. First (the simpler one) the SetPixel macro:
    TYPE SetPixelInfoType
    Used As Integer
    Owner As Integer ' the owner macro ID
    coordX As Integer
    coordY As Integer
    OldColor As Integer ' The color that was previously on that location
    NewColor As Integer ' The new color
    So far it was very easy, Now the Resize infos (I'm using it only to show you how to add more complicated actions to Undo and Redo).
    You can use type for that action without stupidly loosing memory because QB45, QB7.1 and VBDOS does not allow use of Dynamic arrays in TYPE structures.
    REM Use the following line to enable dynamic arrays without the use of COMMON declaration
    DIM SHARED macResize_Used() As Integer
    DIM SHARED macResize_Owner() As Integer
    DIM SHARED macResize_Type() As Integer
    const resize_type_Xp=0, resize_type_Xm = 1
    const resize_type_Yp=2, resize_type_Ym = 3
    DIM SHARED macResize_Width As Integer
    DIM SHARED macResize_Height As Integer
    DIM SHARED macResize_Pic() As Integer ' The pixel colors that was added
    ' The 'p' after X or Y means that the field was enlarge by Resize_Width/Height
    ' and the 'm' means that the size was decrement by Width/Height
    Remember that after an undo if an action is made you must destroy all avaible REDOs.

    Now you must declare an array for undMacroType and SetPixelInfoType
    DIM SHARED Macros() As undMacroType
    DIM SHARED macSetPixel() As SetPixelInfoType

    You need a routine that will allocate new macros
    Function AddUndo() as integer
    MacPos = MacPos + 1
    ' It will destroy all avaible REDOs, but you should change it so it
    ' to destroy all it's informations held somwhare else
    redim preserve Macros(MacPos) As undMacroType
    AddUndo = MacPos ' returns the ID
    End function

    I'm too tired to continue it today, it's 04:20 a.m. in Poland. I will finish it tomarow
  • Ok I have some time now to finish it since my Girlfriend is mad at me.

    Now the function SetPixel which is the base of all graphical operations:
    ' Image is an array of your picture data
    SUB SetPixel(x, y, col, mspi)
    dim oldcol As integer

    oldcol = Image(x,y)
    Image(x,y) = col
    macSetPixel(mspi).Used = true
    macSetPixel(mspi).CoordX = x
    macSetPixel(mspi).CoordY = y
    macSetPixel(mspi).OldCol = oldcol
    macSetPixel(mspi).NewCol = col

    That's all for today
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