add an offscreen buffer example code

Author: boochow

README.md

@@ -2,17 +2,15 @@
 
 This is a modified version of [GuyCarver's ST7735.py](https://github.com/GuyCarver/MicroPython/blob/master/lib/ST7735.py) ST7735 TFT LCD driver for MicroPython.
 
-This version is for micropython-esp32.
-
 A font file is necessary for displaying text (some font files are in [GuyCarver's repo](https://github.com/GuyCarver/MicroPython/tree/master/lib)).
 
 Text nowrap option added(default: nowrap=False).
 
-graphicstest.py is a sample code. I wrote this to make it similar to [Adafruit's graphicstest sketch for Arduino](https://github.com/adafruit/Adafruit-ST7735-Library/tree/master/examples/graphicstest). 
+`graphicstest.py` is a sample code. I wrote this to make it similar to [Adafruit's graphicstest sketch for Arduino](https://github.com/adafruit/Adafruit-ST7735-Library/tree/master/examples/graphicstest). 
 
-If graphicstest.py doesn't work correctly, try replaceing initr() at line 8 to initg() or initb() or initb2(). You can also change rgb(True) to rgb(False) to switch red and blue pixels if your LCD module shows incorrect colors.
+If `graphicstest.py` doesn't work correctly, try replaceing `initr()` at line 8 to `initg()` or `initb()` or `initb2()`. You can also change `rgb(True)` to `rgb(False)` to switch red and blue pixels if your LCD module shows incorrect colors.
 
-Pin connections:
+Pin connections for ESP32:
 
 LCD |ESP32-DevKitC
 ----|----
@@ -27,6 +25,8 @@ GND |GND
 
 [![YouTube image here](https://img.youtube.com/vi/xIy8DPBZsIk/0.jpg)](https://www.youtube.com/watch?v=xIy8DPBZsIk)
 
-tftbmp.py is another sample similar to [Adafruit's tftbmp sketch for Arduino](https://github.com/adafruit/Adafruit-ST7735-Library/blob/master/examples/spitftbitmap/spitftbitmap.ino).
+`tftbmp.py` is another sample similar to [Adafruit's tftbmp sketch for Arduino](https://github.com/adafruit/Adafruit-ST7735-Library/blob/master/examples/spitftbitmap/spitftbitmap.ino).
+
+Place bmp file named `test128x160.bmp` in the file system of MicroPython using file uploading tool such as [ampy](https://github.com/adafruit/ampy), etc.
 
-Place bmp file named 'test128x160.bmp' in the file system of MicroPython using file uploading tool such as [ampy](https://github.com/adafruit/ampy), etc.
+`offscreen-buffer.py` shows how you can use an offscreen frame buffer which is an instance of FrameBuffer class. I tested this on Raspberry Pi Pico. See https://github.com/boochow/MicroPython-ST7735/issues/9 for the pin connections.

offscreen-buffer.py

@@ -0,0 +1,29 @@
+from machine import SPI,Pin
+from ST7735 import TFT
+spi = SPI(0, baudrate=20000000, polarity=0, phase=0, sck=Pin(2), mosi=Pin(3), miso=Pin(0))
+tft=TFT(spi,4,5,1)
+tft.initr()
+tft.rgb(True)
+tft.fill(TFT.BLACK)
+
+from framebuf import FrameBuffer, RGB565
+buf = bytearray(128*160*2)
+fb = FrameBuffer(buf, 128, 160, RGB565)
+
+tft._setwindowloc((0,0),(127,159))
+
+size=20
+(xmax, ymax) = (128-size, 160-size)
+(x, y) = (size, size)
+(vx, vy) = (1, 1)
+
+while True:
+ fb.fill(0)
+ fb.ellipse(x, y, size, size, 0xffff, True)
+ x += vx
+ if x == xmax or x == size:
+ vx = -vx
+ y += vy
+ if y == ymax or y == size:
+ vy = -vy
+ tft._writedata(buf)