Example of u8glib draw loop

Example of an u8glib draw loop that works with WiFi by keeping the draw
loop execution time to a minimum.

lua_examples/u8glib/u8g_drawloop.lua

@@ -0,0 +1,75 @@
+------------------------------------------------------------------------------
+-- u8glib example which shows how to implement the draw loop without causing
+-- timeout issues with the WiFi stack. This is done by drawing one page at
+-- a time, allowing the ESP SDK to do it's house keeping between the page
+-- draws.
+--
+-- This example assumes you have an SSD1306 display connected to pins 4 and 5
+-- using I2C and that the profont22r is compiled into the firmware.
+-- Please edit the init_display function to match your setup.
+--  
+-- Example:
+-- dofile("u8g_displayloop.lua")
+------------------------------------------------------------------------------
+
+local updateDrawFunc
+local disp
+local font
+
+function init_display()
+  local sda = 4
+  local sdl = 5
+  local sla = 0x3c
+  i2c.setup(0,sda,sdl, i2c.SLOW)
+  disp = u8g.ssd1306_128x64_i2c(sla)
+  font = u8g.font_profont22r
+end
+
+local function setLargeFont()
+  disp:setFont(font)
+  disp:setFontRefHeightExtendedText()
+  disp:setDefaultForegroundColor()
+  disp:setFontPosTop()
+end
+
+-- Draws one page and schedules the next page, if there is one
+local function drawPages()
+  updateDrawFunc()
+  if (disp:nextPage() == true) then
+    node.task.post(drawPages)
+  end
+end  
+
+-- Start the draw loop with the draw implementation in the provided function callback
+function updateDisplay(func)
+  updateDrawFunc = func
+  disp:firstPage()
+  node.task.post(drawPages)
+end
+
+function drawHello()
+  setLargeFont()
+  disp:drawStr(30,22, "Hello")
+end
+
+function drawWorld()
+  setLargeFont()
+  disp:drawStr(30,22, "World")
+end
+
+local drawDemo = { drawHello, drawWorld }
+local drawIndex = 1
+
+function demoLoop()
+  -- Start the draw loop with one of the demo functions
+  updateDisplay(drawDemo[drawIndex])
+  drawIndex = drawIndex + 1
+  if drawDemo[drawIndex] == nil then
+    drawIndex = 1
+  end  
+end
+
+-- Initialise the display and start the demo loop
+init_display()
+demoLoop()
+tmr.alarm(4, 5000, 1, demoLoop)