drivers/ws281x: add VT100 backend for native

To quickly iterate on animations it is handy to being able to simulate
the output on native.

This adds a VT100 terminal backend to the ws281x driver that outputs
the colors straight to the terminal.

drivers/Makefile.dep

@@ -678,17 +678,26 @@ endif
 
 ifneq (,$(filter ws281x,$(USEMODULE)))
   FEATURES_OPTIONAL += arch_avr8
+  FEATURES_OPTIONAL += arch_native
   ifeq (,$(filter ws281x_%,$(USEMODULE)))
     ifneq (,$(filter arch_avr8,$(FEATURES_USED)))
       USEMODULE += ws281x_atmega
     endif
+    ifneq (,$(filter arch_native,$(FEATURES_USED)))
+      USEMODULE += ws281x_vt100
+    endif
   endif
   ifneq (,$(filter ws281x_atmega,$(USEMODULE)))
     FEATURES_REQUIRED += arch_avr8
   endif
   USEMODULE += xtimer
 endif
 
+ifneq (,$(filter ws281x_vt100,$(USEMODULE)))
+  CFLAGS += -DWS281X_HAVE_PREPARE_TRANSMISSION
+  CFLAGS += -DWS281X_HAVE_END_TRANSMISSION
+endif
+
 ifneq (,$(filter xbee,$(USEMODULE)))
   FEATURES_REQUIRED += periph_uart
   FEATURES_REQUIRED += periph_gpio

drivers/ws281x/vt100.c

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2019 Benjamin Valentin
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     drivers_ws281x
+ *
+ * @{
+ *
+ * @file
+ * @brief       Implementation of `ws281x_write()` for VT100 terminals
+ *
+ * @author      Benjamin Valentin <benpicco@googlemail.com>
+ *
+ * @}
+ */
+#include <stdio.h>
+#include "ws281x.h"
+
+void ws281x_write_buffer(ws281x_t *dev, const void *buf, size_t size)
+{
+    (void) dev;
+    const uint8_t *src = buf;
+
+    for (unsigned i = 0; i < size; ++i) {
+        int r = src[WS281X_BYTES_PER_DEVICE * i + WS281X_OFFSET_R];
+        int g = src[WS281X_BYTES_PER_DEVICE * i + WS281X_OFFSET_G];
+        int b = src[WS281X_BYTES_PER_DEVICE * i + WS281X_OFFSET_B];
+        printf("\033[48;2;%d;%d;%dm ", r, g, b);
+    }
+}
+
+void ws281x_prepare_transmission(ws281x_t *dev)
+{
+    (void) dev;
+
+    /* clear the line and reset cursor position */
+    printf("\033[2K\r");
+}
+
+void ws281x_end_transmission(ws281x_t *dev)
+{
+    (void) dev;
+
+    /* set color back to normal */
+    printf("\033[0m");
+}