I've recently been trying out Google's Snapseed and I have to say that their UI for this is really intuitive.
When you swipe up or down, the menu above fades in and changes which item is currently selected. Swiping left and right changes the value of that item. This is great as you don't have to be precisely adjusting a slider with your finger and can ...
You have every information on google:
In this article it's 7 principles about button design.
Stick to the core UI design principles
Use color to make UI buttons look actionable
Help users prioritize tasks by removing friction on-screen
Reward users with visual feedback
Location: place buttons where users can find them in the UI
Be consistent with defining ...