[Garkin]

I have written a small addon to test how shields works:

ShieldInfo.txt

## APIVersion: 100009
## Title: Shield Info v0.1
## Version: 0.1
## Author: Garkin
## SavedVariables: SHIELD_INFO_SV

ShieldInfo.xml
ShieldInfo.lua

ShieldInfo.xml

<GuiXml>
   <Controls>
      <TopLevelControl name="ShieldInfo_Template" clampedToScreen="true" mouseEnabled="false" movable="false" hidden="true" virtual="true">
         <Dimensions x="200" y="64" />
         <Controls>
 
            <Backdrop alpha="0.3" hidden="true">
               <Anchor point="TOPLEFT" offsetX="-8" offsetY="-8" />
               <Anchor point="BOTTOMRIGHT" offsetX="8" offsetY="8" />
               <Edge file="EsoUI/Art/Tooltips/UI-Border.dds" edgeFileWidth="128" edgeFileHeight="16" />
               <Center file="EsoUI/Art/Tooltips/UI-TooltipCenter.dds" />
               <Insets left="16" top="16" right="-16" bottom="-16" />
 
               <Controls>
                  <Texture textureFile="EsoUI/Art/Tooltips/munge_overlay.dds" addressMode="WRAP">
                     <AnchorFill />
                  </Texture>
               </Controls>
 
               <OnInitialized>
                  self:GetParent().bd = self
               </OnInitialized>
            </Backdrop>
 
            <Texture textureFile="EsoUI/Art/Repair/inventory_tabicon_repair_up.dds">
               <Anchor point="LEFT" />
               <Dimensions x="64" y="64" />
               <OnInitialized>
                  self:GetParent().icon = self
               </OnInitialized>
            </Texture>
 
            <Label font="ZoFontTooltipTitle" color="INTERFACE_COLOR_TYPE_TEXT_COLORS:INTERFACE_TEXT_COLOR_NORMAL" verticalAlignment="CENTER">
               <Anchor point="RIGHT" />
               <Dimensions x="130" y="64" />
               <OnInitialized>
                  self:GetParent().label = self
               </OnInitialized>
            </Label>
 
         </Controls>
      </TopLevelControl>
   </Controls>
</GuiXml>

ShieldInfo.lua

local ADDON_NAME = "ShieldInfo"
local EM = GetEventManager()
local WM = GetWindowManager()
local SV, UI
local current = 0
local maximum = 0
 
 
local function SetupUI(state)
   UI:SetMouseEnabled(state)
   UI:SetMovable(state)
 
   UI.bd:SetHidden(not state)
   UI:SetHidden(not (state or (current > 0)))
 
   if current > 0 then
      UI.label:SetText(("%d/%d"):format(current, maximum))
   else
      UI.label:SetText("current/max")
   end
 
   if not state then
      local valid, point, target, relPoint, x, y = UI:GetAnchor(0)
 
      if valid then
         SV.Anchor = { p = point, t = target:GetName(), r = relPoint, x = x, y = y }
      end 
   end
end
 
local function OnMouseUp(self, button, upInside)
   if upInside then
      if button == 2 then
         ClearMenu()
         AddMenuItem("Save & Hide", function() SetupUI(false) end)
         ShowMenu(self)
      end
   end
end
 
local function UnitAttributeVisual(eventCode, unitTag, unitAttributeVisual, statType, attributeType, powerType, value1, value2, value3, value4)
   if unitTag == "player" and unitAttributeVisual == ATTRIBUTE_VISUAL_POWER_SHIELDING and attributeType == ATTRIBUTE_HEALTH then
      if eventCode == EVENT_UNIT_ATTRIBUTE_VISUAL_UPDATED then
         current = current + (value2 - value1)
         maximum = maximum + (value4 - value3)
      elseif eventCode == EVENT_UNIT_ATTRIBUTE_VISUAL_ADDED then
         current = current + value1
         maximum = maximum + value2
      elseif eventCode == EVENT_UNIT_ATTRIBUTE_VISUAL_REMOVED then
         current = current - value1
         maximum = maximum - value2
      end
   end
 
   if current > 0 then
      UI.label:SetText(("%d/%d"):format(current, maximum))
      UI:SetHidden(false)
   else
      UI:SetHidden(true)
   end
end
 
local function OnLoaded(event, name)
   if name == ADDON_NAME then
      EM:UnregisterForEvent(name, event)
 
      SV = ZO_SavedVars:New("SHIELD_INFO_SV", 1, { Anchor = { p = BOTTOM, t = "GuiRoot", r = CENTER, x = 0, y = -100 }, firstTime = true })
 
      UI = WM:CreateControlFromVirtual(nil, GuiRoot, "ShieldInfo_Template")
 
      UI:SetHandler("OnMouseUp", OnMouseUp)
 
      if SV.firstTime then
         SV.firstTime = false
         d("=== Shield Info ===")
         d("Adjust ShieldInfo position and then right-click to hide window and save its position.")
         d("Type /si to unlock ShieldInfo window again.")
         SetupUI(true)
      end
 
      UI:SetAnchor(SV.Anchor.p, _G[SV.Anchor.t], SV.Anchor.r, SV.Anchor.x, SV.Anchor.y)
 
      UI:RegisterForEvent(EVENT_UNIT_ATTRIBUTE_VISUAL_ADDED, UnitAttributeVisual)
      UI:RegisterForEvent(EVENT_UNIT_ATTRIBUTE_VISUAL_REMOVED, UnitAttributeVisual)
      UI:RegisterForEvent(EVENT_UNIT_ATTRIBUTE_VISUAL_UPDATED, UnitAttributeVisual)
 
      SLASH_COMMANDS["/si"] = function() SetupUI(true) end
   end
end
 
EM:RegisterForEvent(ADDON_NAME, EVENT_ADD_ON_LOADED, OnLoaded)

Download link: https://www.dropbox.com/s/p1orffil60...ldInfo_0.1.zip