FS Gateware: Designing a Multiplatform Touch Interface Part 1

With more people using mobile devices and touchscreen laptops, developers need to interface with the devices' touchscreen API. Gateware should be doing the same thing if it hopes to support mobile devices. One of the big issues with designing a touch interface is the different ways that devices store the touch information. A good rule is that an interface should provide as much functionality to the user that they should need to use.

When designing this interface one should consider what major platforms support touch and which are most popular. iOS and Android devices are likely the most common touch devices with touch as a primary method of input. Windows and macOS also support touch input, but they are secondary input methods, as most Windows and macOS devices do not have touch input. Other notable devices are Nintendo Switch, Smart Watches, and embedded devices. As such, I propose this touch interface mainly for iOS and Android, but with expansion options for those other devices.

All of these different platforms have different information sent to the developer when the screen is touched. I have created a struct that supports the main information that most developers would need.

enum class GTouchState : unsigned int {
	TOUCH_BEGIN			= 0,	// Finger just hit the screen.
	TOUCH_MOVED			= 1,	// Finger moved from last position.
	TOUCH_END			= 2,	// Finger lifted off the screen.
	TOUCH_STATIONARY	= 3,	// Finger is on screen but hasn't moved.
	TOUCH_CANCELLED		= 4,	// System stopped tracking the touch.
	TOUCH_COUNT,
};
 
struct GTouchData {
	// Current location of the touch in screen coordinates
	float x, y;					
	// Change in location in screen coordinates
	float deltaX, deltaY;		
	// First recorded location of the touch in screen coordinates
	float initialX, inititalY;	
	// Change in time between the current position and delta
	float deltaTime;			
	// Pressure of the touch
	float pressure;			
	// Number of consecutive touches in the same general area
	unsigned int tapCount;		
	// What touch is this? Always less than the number of total touches on the screen
	unsigned int index;			
	// What state is this touch in?
	GTouchState state;			
};

iOS and Android support more information, but most of the information not included here is for stylus support, with information on how the stylus is aligned with specific axes. Most Gateware users won't need this information, as such I have omitted them to give some simplicity to this interface.

Another part of the API is common support for touch gestures. Many mobile users are used to common touch controls to get around their mobile device. Swipe up to go down on a page, pinch to zoom out, and two finger spin for rotate, along with others are just some of the gestures that this API should support for a better experience for the user. As such here are the common gestures that most platforms recognize.

Single Tap

Double Tap

Rotation (Two finger)

Swipe

Pan (Two Finger)

Long Press

Pinch

Here is the end for now. Expect another part to this blog once I have figured out what interface would be best for Gateware.

References:

Touch data:

https://developer.apple.com/documentation/uikit/uitouch?language=objc

https://developer.android.com/reference/android/view/MotionEvent.PointerCoords