Surface impact alerts

data/lang/ui-core/en.json

@@ -975,6 +975,18 @@
     "description": "Tooltip: describe what the thrust/velocity indicator shows",
     "message": "Show current velocity for each direction (thin lines) and thrust (thick background)"
   },
+  "HUD_WARNING_DESCENT_RATE": {
+     "description": "Shown on HUD as a warning flasher",
+     "message": "DESCENT RATE"
+  },
+  "HUD_WARNING_IMPACT": {
+     "description": "Alert tooltip",
+     "message": "Impact warning"
+  },
+  "HUD_WARNING_IMPACT_IMMINENT": {
+     "description": "Alert tooltip",
+     "message": "Impact imminent"
+  },
   "HULL_DOES_NOT_REQUIRE_REPAIR": {
     "description": "",
     "message": "Hull does not require repair."

data/pigui/modules/master-alarm.lua

@@ -5,10 +5,19 @@ local Engine = require 'Engine'
 local Game = require 'Game'
 
 local ui = require 'pigui'
+local pionillium = ui.fonts.pionillium
+local colors = ui.theme.colors
+local icons = ui.theme.icons
+
+local lui = require 'Lang'.GetResource("ui-core")
+
+local Vector2 = _G.Vector2
 
 local alreadyAlertedTemp = false
 local alreadyAlertedFuel = false
 local alreadyAlertedPres = false
+local alreadyAlertedDescent = false
+local alreadyAlertedImpact = false
 
 local function alarm ()
 	--check hull temperature
@@ -46,6 +55,81 @@ local function alarm ()
 			alreadyAlertedPres = false
 		end
 	end
+
+	--check descent speed
+	if frame and not frame:IsDynamic() and frame.superType ~= 'STARPORT' then --we only need to check descent speed if we are approaching a celestial body
+		local velocity = Game.player:GetVelocityRelTo(frame)
+		local position = Game.player:GetPositionRelTo(frame)
+		local altitude = Game.player:GetAltitudeRelTo(frame)
+		local approach_speed = position:dot(velocity) / position:length() --perpendicular to horizon
+		local recover_distance = Game.player:GetDistanceToZeroV(approach_speed,"forward") --braking distance basically
+
+		local reticuleCircleRadius = math.min(ui.screenWidth, ui.screenHeight) / 8 -- required for icon placement
+		local uiTextPos = Vector2(ui.screenWidth / 2, ui.screenHeight / 3 - 10) --sits just above HUD circle
+		local uiPos = ui.pointOnClock(center, reticuleCircleRadius * 1.2 , 10) --left side of the reticule, above frame info
+		local iconSize = Vector2(24, 24)
+
+		local max_accel = Game.player:GetAcceleration("forward") --max acceleration axis of the ship, which is always forward with all Pioneer ships
+		local up_accel = Game.player:GetAcceleration("up") --up acceleration
+
+		local response_time_factor = 2 --Gives reponse time to player (seconds). Presence of atmosphere makes this time longer.
+		--Higher the value, earlier the warning. Too high = annoying, too low = death, probably.
+
+		local evasion_factor = 20
+		--The lower the evasion_factor value, the higher altitude the descent rate alarm changes mode. Depends on planet radius.
+		--6500000 / 20 = 325000
+		--For example, above Earth, alarm changes mode at 325km altitude
+		--This should be about where the planet/star becomes the player's horizon instead of a distant orb in space.
+
+		local surface_gravity = frame.path:GetSystemBody().gravity --surface gravity of the body we need to avoid
+		local body_radius = frame.path:GetSystemBody().radius --radius of the body we need to avoid
+
+		--required to calculate periapsis radius
+		local player_mass = Game.player.staticMass + Game.player.fuelMassLeft
+		local eccentricity_vector = ((velocity:length()^2 - surface_gravity*player_mass/position:length())*position-position:dot(velocity)*velocity)/surface_gravity*player_mass
+		local eccentricity = eccentricity_vector:length()
+		local semi_major_axis = 1 / ((2 / position:length()) - (velocity:length()^2 / surface_gravity*player_mass))
+		local periapsis_radius = semi_major_axis * (1 - eccentricity)
+
+		--with the following formula, alert triggers if
+		--approach speed is over 25 m/s
+		--periapsis is below body surface (ignoring atmosphere and terrain)
+		--if the approach speed keeps increasing under planetary gravity at max possible rate (V1^2 = V0^2 + 2*a*h; V1: final speed, V0: initial speed, a:acceleration(gravity), h:altitude), player has less than "response_time_factor" to start boosting upwards to avoid a crash (atmo ignored)
+		--player is closer to the body than the altitude calculated via evasion_factor
+		if approach_speed < -25 and periapsis_radius < body_radius and (altitude - recover_distance) / ((approach_speed^2 + 2*surface_gravity*recover_distance)^(1/2)) < response_time_factor and body_radius/altitude > evasion_factor and Game.player:GetCurrentAICommand() ~= "CMD_DOCK" then
+			alreadyAlertedImpact = false
+			if Game.CurrentView() == "world" then
+				ui.addStyledText(uiTextPos, ui.anchor.center, ui.anchor.top, lui.HUD_WARNING_DESCENT_RATE, colors.alertRed, pionillium.large, nil, colors.lightBlackBackground)
+			end
+			if not alreadyAlertedDescent then
+				ui.playSfx("alarm_descent", 1.0, 1.0)
+				alreadyAlertedDescent = true
+			end
+
+		--with the following formula, alert triggers if
+		--braking distance is longer than distance to the body (player can not decelerate before hitting the body)
+		--player is still far enough away from the body
+		elseif approach_speed < -25 and recover_distance > altitude and periapsis_radius < body_radius and body_radius/altitude <= evasion_factor and (periapsis_radius + (1/2)*max_accel*(altitude / -approach_speed)^2) >= body_radius then
+			alreadyAlertedDescent = false
+			if Game.CurrentView() == "world" then
+				ui.addIcon(uiPos, icons.impact_warning, colors.alertYellow, iconSize, ui.anchor.center, ui.anchor.center, lui.HUD_WARNING_IMPACT)
+			end
+			if not alreadyAlertedImpact then
+				ui.playSfx("impact_chime", 1.0, 1.0)
+				alreadyAlertedImpact = true
+			end
+
+		--with the following formula, alert triggers if
+		--player ship's acceleration rate would not allow them to avoid a collision by simply accelerating sideways
+		--exact calculations require complex integrals, this alert is accurate enough but just a tiny bit on the pessimistic side for extra safety measures
+		elseif approach_speed < -25 and recover_distance > altitude and periapsis_radius < body_radius and body_radius/altitude <= evasion_factor and (periapsis_radius + (1/2)*max_accel*(altitude / -approach_speed)^2) < body_radius and Game.CurrentView() == "world" then
+			ui.addIcon(uiPos, icons.impact_warning, colors.alertRed, iconSize, ui.anchor.center, ui.anchor.center, lui.HUD_WARNING_IMPACT_IMMINENT)
+		else -- clean up warning status so we can warn the player the next time they are in danger
+			alreadyAlertedImpact = false
+			alreadyAlertedDescent = false
+		end
+	end
+
 end
 
 ui.registerModule("game", alarm)

data/pigui/themes/default.lua

@@ -305,6 +305,7 @@ theme.icons = {
 	route = 231,
 	route_destination = 232,
 	route_dist = 233,
+	impact_warning = 234,
 	-- TODO: manual / autopilot
 	-- dummy, until actually defined correctly
 	mouse_move_direction = 14