koreader/frontend/ui/gesturedetector.lua

require "ui/geometry"

GestureRange = {
	ges = nil,
	-- spatial range limits the gesture emitting position
	range = nil,
	-- temproal range limits the gesture emitting rate
	rate = nil,
	-- span limits of this gesture
	scale = nil,
}

function GestureRange:new(o)
	local o = o or {}
	setmetatable(o, self)
	self.__index = self
	return o
end

function GestureRange:match(gs)
	if gs.ges ~= self.ges then
		return false
	end
	if self.range then
		if not self.range:contains(gs.pos) then
			return false
		end
	end
	if self.rate then
		local last_time = self.last_time or TimeVal:new{}
		if gs.time - last_time > TimeVal:new{usec = 1000000 / self.rate} then
			self.last_time = gs.time
		else
			return false
		end
	end
	if self.scale then
		if self.scale[1] > gs.span or self.scale[2] < gs.span then
			return false
		end
	end
	return true
end

--[[
Currently supported gestures:
	* single tap
	* double tap
	* hold
	* pan
	* swipe

You change the state machine by feeding it touch events, i.e. calling
GestureDetector:feedEvent(tev).

a touch event should have following format:
tev = {
	slot = 1,
	id = 46,
	x = 0,
	y = 1,
	timev = TimeVal:new{...},
}

Don't confuse tev with raw evs from kernel, tev is build according to ev.

GestureDetector:feedEvent(tev) will return a detection result when you
feed a touch release event to it.
--]]

GestureDetector = {
	-- all the time parameters are in us
	DOUBLE_TAP_INTERVAL = 300 * 1000,
	TWO_FINGER_TAP_DURATION = 300 * 1000,
	HOLD_INTERVAL = 1000 * 1000,
	SWIPE_INTERVAL = 900 * 1000,
	-- distance parameters
	DOUBLE_TAP_DISTANCE = 50,
	TWO_FINGER_TAP_REGION = 20,
	PAN_THRESHOLD = 50,

	-- states are stored in separated slots
	states = {},
	track_ids = {},
	tev_stacks = {},
	-- latest feeded touch event in each slots
	last_tevs = {},
	first_tevs = {},
	-- detecting status on each slots
	detectings = {},
	-- for single/double tap
	last_taps = {},
}

function GestureDetector:feedEvent(tevs)
	repeat
		local tev = table.remove(tevs)
		if tev then
			local slot = tev.slot
			if not self.states[slot] then
				self:clearState(slot) -- initiate state
			end
			local ges = self.states[slot](self, tev)
			if tev.id ~= -1 then
				self.last_tevs[slot] = tev
			end
			-- return no more than one gesture
			if ges then return ges end
		end
	until tev == nil
end

function GestureDetector:deepCopyEv(tev)
	return {
		x = tev.x,
		y = tev.y,
		id = tev.id,
		slot = tev.slot,
		timev = TimeVal:new{
			sec = tev.timev.sec,
			usec = tev.timev.usec,
		}
	}
end

--[[
tap2 is the later tap
--]]
function GestureDetector:isDoubleTap(tap1, tap2)
	local tv_diff = tap2.timev - tap1.timev
	return (
		math.abs(tap1.x - tap2.x) < self.DOUBLE_TAP_DISTANCE and
		math.abs(tap1.y - tap2.y) < self.DOUBLE_TAP_DISTANCE and
		(tv_diff.sec == 0 and (tv_diff.usec) < self.DOUBLE_TAP_INTERVAL)
	)
end

function GestureDetector:isTwoFingerTap(tev0, tev1)
	local x_diff0 = math.abs(tev0.x - self.first_tevs[0].x)
	local x_diff1 = math.abs(tev1.x - self.first_tevs[1].x)
	local y_diff0 = math.abs(tev0.y - self.first_tevs[0].y)
	local y_diff1 = math.abs(tev1.y - self.first_tevs[1].y)
	local tv_diff0 = tev0.timev - self.first_tevs[0].timev
	local tv_diff1 = tev1.timev - self.first_tevs[1].timev
	return (
		x_diff0 < self.TWO_FINGER_TAP_REGION and
		x_diff1 < self.TWO_FINGER_TAP_REGION and
		y_diff0 < self.TWO_FINGER_TAP_REGION and
		y_diff1 < self.TWO_FINGER_TAP_REGION and
		tv_diff0.sec == 0 and tv_diff0.usec < self.TWO_FINGER_TAP_DURATION and
		tv_diff1.sec == 0 and tv_diff1.usec < self.TWO_FINGER_TAP_DURATION
	)
end

--[[
compare last_pan with first_tev in this slot
return pan direction and distance
--]]
function GestureDetector:getPath(tev)
	local slot = tev.slot
	local x_diff = self.last_tevs[slot].x - self.first_tevs[slot].x
	local y_diff = self.last_tevs[slot].y - self.first_tevs[slot].y
	local direction = nil
	local distance = math.sqrt(x_diff*x_diff + y_diff*y_diff)
	if x_diff == 0 and y_diff == 0 then
	elseif (math.abs(x_diff) > math.abs(y_diff)) then
		direction = x_diff < 0 and "left" or "right"
	else
		direction = y_diff < 0 and "up" or "down"
	end
	return direction, distance
end

function GestureDetector:isSwipe(tev)
	local slot = tev.slot
	local tv_diff = self.first_tevs[slot].timev - self.last_tevs[slot].timev
	if (tv_diff.sec == 0) and (tv_diff.usec < self.SWIPE_INTERVAL) then
		local x_diff = self.last_tevs[slot].x - self.first_tevs[slot].x
		local y_diff = self.last_tevs[slot].y - self.first_tevs[slot].y
		if x_diff ~= 0 or y_diff ~= 0 then
			return true
		end
	end
end

--[[
Warning! this method won't update self.state, you need to do it
in each state method!
--]]
function GestureDetector:switchState(state_new, tev, param)
	--@TODO do we need to check whether state is valid?    (houqp)
	return self[state_new](self, tev, param)
end

function GestureDetector:clearState(slot)
	self.states[slot] = self.initialState
	self.detectings[slot] = false
	self.first_tevs[slot] = nil
	self.last_tevs[slot] = nil
end

function GestureDetector:initialState(tev)
	local slot = tev.slot
	if tev.id then
		-- a event ends
		if tev.id == -1 then
			self.detectings[slot] = false
		else
			self.track_ids[slot] = tev.id
		end
	end
	if tev.x and tev.y then
		-- user starts a new touch motion
		if not self.detectings[slot] then
			self.detectings[slot] = true
			self.first_tevs[slot] = self:deepCopyEv(tev)
			-- default to tap state
			return self:switchState("tapState", tev)
		end
	end
end

--[[
this method handles both single and double tap
--]]
function GestureDetector:tapState(tev)
	DEBUG("in tap state...")
	local slot = tev.slot
	if slot == 1 then
		if tev.id == -1 and self.last_tevs[0] ~= nil then
			if self:isTwoFingerTap(self.last_tevs[0], tev) then
				local pos0 = Geom:new{
					x = self.last_tevs[0].x,
					y = self.last_tevs[0].y,
					w = 0, h = 0,
				}
				local pos1 = Geom:new{
					x = tev.x,
					y = tev.y,
					w = 0, h = 0,
				}
				local ges_ev = {
					ges = "two_finger_tap",
					span = pos0:distance(pos1),
					time = tev.timev,
				}
				DEBUG("two-finger tap detected with span", pos0:distance(pos1))
				self:clearState(0)
				self:clearState(1)
				return ges_ev
			else
				self:clearState(0)
				self:clearState(1)
			end
		end
	elseif tev.id == -1 then
		-- end of tap event
		if self.last_tevs[slot] ~= nil then
			local ges_ev = {
				-- default to single tap
				ges = "tap",
				pos = Geom:new{
					x = self.last_tevs[slot].x,
					y = self.last_tevs[slot].y,
					w = 0, h = 0,
				},
				time = tev.timev,
			}
			-- cur_tap is used for double tap detection
			local cur_tap = {
				x = tev.x,
				y = tev.y,
				timev = tev.timev,
			}

			if self.last_taps[slot] ~= nil and
			self:isDoubleTap(self.last_taps[slot], cur_tap) then
				-- it is a double tap
				self:clearState(slot)
				ges_ev.ges = "double_tap"
				self.last_taps[slot] = nil
				DEBUG("double tap detected in slot", slot)
				return ges_ev
			end

			-- set current tap to last tap
			self.last_taps[slot] = cur_tap

			DEBUG("set up tap timer")
			-- deadline should be calculated by adding current tap time and the interval
			local deadline = cur_tap.timev + TimeVal:new{
				sec = 0, usec = self.DOUBLE_TAP_INTERVAL,
			}
			Input:setTimeout(function()
				DEBUG("in tap timer", self.last_taps[slot] ~= nil)
				-- double tap will set last_tap to nil so if it is not, then
				-- user must only tapped once
				if self.last_taps[slot] ~= nil then
					self.last_taps[slot] = nil
					-- we are using closure here
					DEBUG("single tap detected in slot", slot)
					return ges_ev
				end
			end, deadline)
			-- we are already at the end of touch event
			-- so reset the state
			self:clearState(slot)
		else
			-- last tev in this slot is cleared by last two finger tap
			self:clearState(slot)
			return {
				ges = "tap",
				pos = Geom:new{
					x = tev.x,
					y = tev.y,
					w = 0, h = 0,
				},
				time = tev.timev,
			}
		end
	elseif self.states[slot] ~= self.tapState then
		-- switched from other state, probably from initialState
		-- we return nil in this case
		self.states[slot] = self.tapState
		DEBUG("set up hold timer")
		local deadline = tev.timev + TimeVal:new{
			sec = 0, usec = self.HOLD_INTERVAL
		}
		Input:setTimeout(function()
			if self.states[slot] == self.tapState then
				-- timer set in tapState, so we switch to hold
				DEBUG("hold gesture detected in slot", slot)
				return self:switchState("holdState", tev, true)
			end
		end, deadline)
	else
		-- it is not end of touch event, see if we need to switch to
		-- other states
		if (tev.x and math.abs(tev.x - self.first_tevs[slot].x) >= self.PAN_THRESHOLD) or
		(tev.y and math.abs(tev.y - self.first_tevs[slot].y) >= self.PAN_THRESHOLD) then
			-- if user's finger moved long enough in X or
			-- Y distance, we switch to pan state
			return self:switchState("panState", tev)
		end
	end
end

function GestureDetector:panState(tev)
	DEBUG("in pan state...")
	local slot = tev.slot
	if tev.id == -1 then
		-- end of pan, signal swipe gesture if necessary
		if self:isSwipe(tev) then
			local swipe_direction, swipe_distance = self:getPath(tev)
			DEBUG("swipe", swipe_direction, swipe_distance, "detected in slot", slot)
			local start_pos = Geom:new{
					x = self.first_tevs[slot].x,
					y = self.first_tevs[slot].y,
					w = 0, h = 0,
			}
			self:clearState(slot)
			return {
				ges = "swipe",
				-- use first pan tev coordination as swipe start point
				pos = start_pos,
				direction = swipe_direction,
				distance = swipe_distance,
				time = tev.timev,
			}
		end
		DEBUG("pan release detected in slot", slot)
		local release_pos = Geom:new{
			x = self.last_tevs[slot].x,
			y = self.last_tevs[slot].y,
			w = 0, h = 0,
		}
		local pan_release = {
			ges = "pan_release",
			pos = release_pos,
			time = tev.timev,
		}
		self:clearState(slot)
		return pan_release
	else
		if self.states[slot] ~= self.panState then
			self.states[slot] = self.panState
		end
		local pan_direction, pan_distance = self:getPath(tev)
		local pan_ev = {
			ges = "pan",
			relative = {
				-- default to pan 0
				x = 0,
				y = 0,
			},
			pos = nil,
			direction = pan_direction,
			distance = pan_distance,
			time = tev.timev,
		}
		pan_ev.relative.x = tev.x - self.last_tevs[slot].x
		pan_ev.relative.y = tev.y - self.last_tevs[slot].y
		pan_ev.pos = Geom:new{
			x = self.last_tevs[slot].x,
			y = self.last_tevs[slot].y,
			w = 0, h = 0,
		}
		return pan_ev
	end
end

function GestureDetector:holdState(tev, hold)
	DEBUG("in hold state...")
	local slot = tev.slot
	-- when we switch to hold state, we pass additional param "hold"
	if tev.id ~= -1 and hold and self.last_tevs[slot].x and self.last_tevs[slot].y then
		self.states[slot] = self.holdState
		return {
			ges = "hold",
			pos = Geom:new{
				x = self.last_tevs[slot].x,
				y = self.last_tevs[slot].y,
				w = 0, h = 0,
			},
			time = tev.timev,
		}
	end
	if tev.id == -1 and self.last_tevs[slot] ~= nil then
		-- end of hold, signal hold release
		DEBUG("hold_release detected in slot", slot)
		local last_x = self.last_tevs[slot].x
		local last_y = self.last_tevs[slot].y
		self:clearState(slot)
		return {
			ges = "hold_release",
			pos = Geom:new{
				x = last_x,
				y = last_y,
				w = 0, h = 0,
			},
			time = tev.timev,
		}
	end
end

--[[
  @brief change gesture's x and y coordinates according to screen view mode

  @param ges gesture that you want to adjust
  @return adjusted gesture.
--]]
function GestureDetector:adjustGesCoordinate(ges)
	if Screen.cur_rotation_mode == 1 then
		-- in landscape mode
		if ges.pos then
			ges.pos.x, ges.pos.y = (Screen.width - ges.pos.y), (ges.pos.x)
		end
		if ges.ges == "swipe" or ges.ges == "pan" then
			if ges.direction == "down" then
				ges.direction = "left"
			elseif ges.direction == "up" then
				ges.direction = "right"
			elseif ges.direction == "right" then
				ges.direction = "down"
			elseif ges.direction == "left" then
				ges.direction = "up"
			end
		end
	end

	return ges
end