Refactor drawing functions to use offscreen buffer for improved performance and reduced flickering

inventoryManager.lua

@@ -96,33 +96,36 @@ end
 -- Drawing helpers
 -------------------------------------------------
 
+-- Drawing target (set to offscreen buffer in drawDashboard)
+local draw = nil
+
 local function monWrite(x, y, text, fg, bg)
-    mon.setCursorPos(x, y)
-    if fg then mon.setTextColor(fg) end
-    if bg then mon.setBackgroundColor(bg) end
-    mon.write(text)
+    draw.setCursorPos(x, y)
+    if fg then draw.setTextColor(fg) end
+    if bg then draw.setBackgroundColor(bg) end
+    draw.write(text)
 end
 
 local function monFill(y, color)
-    local w, _ = mon.getSize()
-    mon.setCursorPos(1, y)
-    mon.setBackgroundColor(color)
-    mon.write(string.rep(" ", w))
+    local w, _ = draw.getSize()
+    draw.setCursorPos(1, y)
+    draw.setBackgroundColor(color)
+    draw.write(string.rep(" ", w))
 end
 
 local function monCenter(y, text, fg, bg)
-    local w, _ = mon.getSize()
+    local w, _ = draw.getSize()
     local x = math.floor((w - #text) / 2) + 1
     monWrite(x, y, text, fg, bg)
 end
 
 local function monBar(x, y, width, ratio, barColor, bgColor)
     local filled = math.floor(ratio * width)
-    mon.setCursorPos(x, y)
-    mon.setBackgroundColor(barColor)
-    mon.write(string.rep(" ", filled))
-    mon.setBackgroundColor(bgColor)
-    mon.write(string.rep(" ", width - filled))
+    draw.setCursorPos(x, y)
+    draw.setBackgroundColor(barColor)
+    draw.write(string.rep(" ", filled))
+    draw.setBackgroundColor(bgColor)
+    draw.write(string.rep(" ", width - filled))
 end
 
 local function drawButton(x, y, text, fg, bg, padLeft, padRight)
@@ -146,8 +149,10 @@ local function drawDashboard()
     local w, h = mon.getSize()
     touchZones = {}
 
-    mon.setBackgroundColor(colors.black)
-    mon.clear()
+    -- Create offscreen buffer (invisible)
+    draw = window.create(mon, 1, 1, w, h, false)
+    draw.setBackgroundColor(colors.black)
+    draw.clear()
 
     -- ===== Title bar =====
     monFill(1, colors.blue)
@@ -310,6 +315,9 @@ local function drawDashboard()
     -- Bottom accent
     monFill(h, colors.blue)
     monCenter(h, " Tap item to order ", colors.lightBlue, colors.blue)
+
+    -- Flush buffer to monitor in one go
+    draw.setVisible(true)
 end
 
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