tests: screen: add sierpinski_carpet test

Author: bradjc

examples/tests/screen/sierpinski_carpet/Makefile

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+# Makefile for user application
+
+# Specify this directory relative to the current application.
+TOCK_USERLAND_BASE_DIR = ../../../..
+
+# Which files to compile.
+C_SRCS := $(wildcard *.c)
+
+APP_HEAP_SIZE := 5000
+
+# Include userland master makefile. Contains rules and flags for actually
+# building the application.
+include $(TOCK_USERLAND_BASE_DIR)/AppMakefile.mk

examples/tests/screen/sierpinski_carpet/README.md

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+Sierpiński Carpet
+=================
+
+This is a screen test app that draws a [Sierpiński
+carpet](https://en.wikipedia.org/wiki/Sierpi%C5%84ski_carpet) to the screen.

examples/tests/screen/sierpinski_carpet/main.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <libtock-sync/display/screen.h>
+
+uint8_t* buffer;
+
+static void write_pixel(int x, int y, uint8_t v) {
+  int vertical       = y / 8;
+  int byte_index     = x + (vertical * 64);
+  int vertical_pixel = y % 8;
+
+  uint8_t original = buffer[byte_index];
+  uint8_t new      = (original & ~(1 << vertical_pixel)) | ((v & 0x1) << vertical_pixel);
+  buffer[byte_index] = new;
+}
+
+static void draw_black_square_middle(uint16_t x, uint16_t y, uint16_t width) {
+  if (width < 3) return;
+
+  uint16_t third = width / 3;
+
+  // Write all pixels for the new square.
+  for (int i = x + third; i < x + third + third; i++) {
+    for (int j = y + third; j < y + third + third; j++) {
+      write_pixel(i, j, 0);
+    }
+  }
+
+  // Recurse for surrounding squares.
+  for (int i = 0; i < 3; i++) {
+    for (int j = 0; j < 3; j++) {
+      if (i == 1 && j == 1) continue;
+      draw_black_square_middle(x + (third * i), y + (third * j), third);
+    }
+  }
+}
+
+int main(void) {
+  returncode_t err;
+
+  uint32_t width, height;
+
+  err = libtock_screen_get_resolution(&width, &height);
+  if (err != RETURNCODE_SUCCESS) return -1;
+
+  // Make width smaller of width and height.
+  if (width > height) width = height;
+
+  // Allocate buffer.
+  uint32_t buffer_size = width * width;
+  buffer = malloc(sizeof(uint8_t) * buffer_size);
+
+  // Fill in the display buffer.
+  memset(buffer, 0xff, buffer_size);
+  draw_black_square_middle(0, 0, width);
+  libtocksync_screen_set_frame(0, 0, width, width);
+  libtocksync_screen_write(buffer, buffer_size, buffer_size / 8);
+
+  return 0;
+}