Lab 5: Drawing Rectangles
This driver splits what framebuf combined into one command. display.rect(x, y, w, h, color) always draws an outline — there is no fill flag. display.fill_rect(x, y, w, h, color) is the separate call for a solid block. There's still no "erase" command anywhere in this kit: drawing in black is erasing, since black is just an unlit pixel.
Sample Program Code
A border, a blocky retro face, and a mouth bar with teeth erased out of it in black:
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43 | # Lab 05: Drawing Rectangles
# This driver splits what framebuf combined. rect() always draws an
# outline and takes no fill flag; fill_rect() draws the solid block:
#
# display.rect(x, y, w, h, color) <- outline only
# display.fill_rect(x, y, w, h, color) <- solid
#
# There is still no "erase" command. Drawing in black is erasing, and on
# this display fill_rect(..., BLACK) is the fastest eraser you have --
# it is the one call that sends a long run of identical pixels.
import config
display = config.init_display()
WHITE = config.WHITE
BLACK = config.BLACK
display.fill(BLACK)
# a border. On a round screen a rectangular border gets its corners
# clipped, so this one is pulled well inside the safe radius.
display.rect(40, 40, 160, 160, WHITE)
# a retro blocky face: square eye sockets with a filled pupil inside each
display.rect(60, 80, 48, 40, WHITE)
display.fill_rect(76, 92, 16, 16, WHITE)
display.rect(132, 80, 48, 40, WHITE)
display.fill_rect(148, 92, 16, 16, WHITE)
# a wide filled mouth bar with black teeth erased out of it
display.fill_rect(66, 150, 108, 24, WHITE)
for tooth_x in range(88, 174, 20):
display.fill_rect(tooth_x, 150, 6, 24, BLACK)
# Things to try:
#
# 1. Widen the border to display.rect(10, 10, 220, 220, WHITE) and run it
# again. The corners disappear and you are left with four arcs.
#
# 2. Erase just the mouth: fill_rect(66, 150, 108, 24, BLACK). One call
# takes it back, and nothing else on screen moves. That is the trick
# lab 29 is built on.
|
Here's what that program draws:
The Fastest Eraser You Have
fill_rect(..., BLACK) sends one long run of identical pixels, which makes it the cheapest way to take something back on a display with no frame buffer to simply overwrite in RAM. That single fact — erasing is just filling with black, and filling a rectangle is the fastest thing this driver does — is what makes later labs like partial redraw (Lab 29) possible at all.
Try widening the border to span nearly the whole square (say, rect(10, 10, 220, 220, WHITE)) and run it again. The corners disappear and you're left with four disconnected arcs — the same round-screen lesson from Lab 2, now showing up in a shape you built yourself.