add dragon example

examples/dragon/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.16.0)
+set(EXTRA_COMPONENT_DIRS "../../components/")
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+project(dragon_example)

examples/dragon/README.md

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+A demo showing a Full-Screen Image
+==================================
+
+*The image size is chosen to fit a 1200 * 825 display!*
+
+Image by David REVOY / CC BY (https://creativecommons.org/licenses/by/3.0)
+https://commons.wikimedia.org/wiki/File:Durian_-_Sintel-wallpaper-dragon.jpg

examples/dragon/main/CMakeLists.txt

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+set(app_sources "main.c")
+
+idf_component_register(SRCS ${app_sources} REQUIRES epd_driver)

examples/dragon/main/main.c

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+/* Simple firmware for a ESP32 displaying a static image on an EPaper Screen.
+ *
+ * Write an image into a header file using a 3...2...1...0 format per pixel,
+ * for 4 bits color (16 colors - well, greys.) MSB first.  At 80 MHz, screen
+ * clears execute in 1.075 seconds and images are drawn in 1.531 seconds.
+ */
+
+#include "esp_heap_caps.h"
+#include "esp_log.h"
+#include "esp_timer.h"
+#include "esp_types.h"
+#include "freertos/FreeRTOS.h"
+#include "freertos/task.h"
+#include "sdkconfig.h"
+#include <stdio.h>
+#include <string.h>
+
+#include "epd_driver.h"
+#include "dragon.h"
+
+uint8_t *img_buf;
+
+void delay(uint32_t millis) { vTaskDelay(millis / portTICK_PERIOD_MS); }
+
+uint32_t millis() { return esp_timer_get_time() / 1000; }
+
+void loop() {
+  epd_poweron();
+  epd_clear();
+  volatile uint32_t t1 = millis();
+  epd_draw_grayscale_image(epd_full_screen(), img_buf);
+  volatile uint32_t t2 = millis();
+  printf("EPD draw took %dms.\n", t2 - t1);
+
+  epd_poweroff();
+
+  delay(5000);
+}
+
+void epd_task() {
+  epd_init();
+
+  while (1) {
+    loop();
+  };
+}
+
+void app_main() {
+  // copy the image data to SRAM for faster display time
+  img_buf = (uint8_t *)heap_caps_malloc(EPD_WIDTH * EPD_HEIGHT / 2, MALLOC_CAP_SPIRAM);
+  if (img_buf == NULL) {
+     ESP_LOGE("epd_task", "Could not allocate framebuffer in PSRAM!");
+  }
+
+  memcpy(img_buf, dragon_data, EPD_WIDTH * EPD_HEIGHT / 2);
+  heap_caps_print_heap_info(MALLOC_CAP_INTERNAL);
+  heap_caps_print_heap_info(MALLOC_CAP_SPIRAM);
+
+  xTaskCreatePinnedToCore(&epd_task, "epd task", 10000, NULL, 2, NULL, 1);
+}