Creating Undo button for image processing

Hi, i have created a simple image processing project, i have about 12 buttons that perform different effects to an image, i wanna do something like "undo" button, for example, if i choose the Negative effect, then the Blue effect, and then the Green effect, i want to make the undo button so that when i press it i can go back to the Blue effect. How can i make that happen ?

PS: i have a global variable named "LL", each button saves its effect in LL,each effect replaces the previous one and will be saved in LL.

Answer 1

[Adam]

Firstly I really wouldn't recommend using global variables.

But in the interests of a short answer to the point of the question and using your chosen method for sharing data (this same idea would work equally using a better method of data sharing between buttons):

Just create a second (global) variable called lastLL (or preferably choose a more meaningful variable name than 'LL', but again, that is a side-issue!) and before each of your buttons applies their technique to overwrite LL just set

lastLL = LL;

Then in your undo button just set

LL = lastLL;

[Ahmed El sherif]

Thanks, it worked :)

Answer 2

[David Ortegon]

Ahmed, could you please send me your code for the bottomof undo. I have a project for a course and i dont know how to apply the global variable and the explanation. thanks.