u8g2 + epaper reference ESP-IDF

main.c

#include <stdint.h>
#include <stdio.h>

#include "u8g2.h"
#include "epd_gdey042t81.h"


#define SCREEN_WIDTH       400
#define SCREEN_HEIGHT      300

#define BYTES_PER_ROW      (SCREEN_WIDTH / 8)
#define FRAMEBUFFER_SIZE   (BYTES_PER_ROW * SCREEN_HEIGHT)
#define TILE_HEIGHT        ((SCREEN_HEIGHT + 7) / 8)


static u8g2_t u8g2;

/*
 * This is BOTH:
 *
 *   - u8g2's drawing framebuffer
 *   - the framebuffer passed to epd_display()
 *
 * No second framebuffer and no conversion.
 */
static uint8_t framebuffer[FRAMEBUFFER_SIZE];


/*
 * u8g2 needs display geometry.
 *
 * tile_width  = 400 / 8 = 50 bytes per row
 * tile_height = ceil(300 / 8) = 38
 *
 * pixel_width  = 400
 * pixel_height = 300
 */
static const u8x8_display_info_t display_info = {
    .chip_enable_level = 0,
    .chip_disable_level = 1,

    .post_chip_enable_wait_ns = 0,
    .pre_chip_disable_wait_ns = 0,
    .reset_pulse_width_ms = 0,
    .post_reset_wait_ms = 0,

    .sda_setup_time_ns = 0,
    .sck_pulse_width_ns = 0,
    .sck_clock_hz = 0,
    .spi_mode = 0,

    .i2c_bus_clock_100kHz = 0,

    .data_setup_time_ns = 0,
    .write_pulse_width_ns = 0,

    .tile_width = SCREEN_WIDTH / 8,
    .tile_height = TILE_HEIGHT,

    .default_x_offset = 0,
    .flipmode_x_offset = 0,

    .pixel_width = SCREEN_WIDTH,
    .pixel_height = SCREEN_HEIGHT,
};


/*
 * u8g2 doesn't send anything to a physical display.
 *
 * We only use this callback to provide the display geometry.
 */
static uint8_t display_callback(u8x8_t *u8x8, uint8_t msg, uint8_t arg_int, void *arg_ptr)
{
    (void)arg_int;
    (void)arg_ptr;

    if (msg == U8X8_MSG_DISPLAY_SETUP_MEMORY)
        u8x8->display_info = &display_info;

    return 1;
}


/*
 * Initialize u8g2 as a framebuffer-only renderer.
 */
static void graphics_init(void)
{
    u8g2_SetupDisplay(
        &u8g2,
        display_callback,
        u8x8_dummy_cb,
        u8x8_dummy_cb,
        u8x8_dummy_cb
    );

    /*
     * IMPORTANT:
     *
     * horizontal_right_lsb gives us:
     *
     *   framebuffer[y * 50 + x / 8]
     *
     * with:
     *
     *   x=0 -> bit 7
     *   x=1 -> bit 6
     *   ...
     *   x=7 -> bit 0
     *
     * This is exactly the format expected by epd_gdey042t81.c.
     */
    u8g2_SetupBuffer(
        &u8g2,
        framebuffer,
        TILE_HEIGHT,
        u8g2_ll_hvline_horizontal_right_lsb,
        U8G2_R0
    );
}


/*
 * Draw our screen.
 */
static void render_screen(void)
{
    u8g2_ClearBuffer(&u8g2);

    u8g2_SetDrawColor(&u8g2, 1);

    u8g2_SetFont(&u8g2, u8g2_font_helvB24_tf);
    u8g2_DrawStr(&u8g2, 20, 45, "Hello e-paper!");

    u8g2_SetFont(&u8g2, u8g2_font_helvB14_tf);
    u8g2_DrawStr(&u8g2, 20, 75, "u8g2 + GDEY042T81");

    u8g2_DrawFrame(
        &u8g2,
        10,
        100,
        SCREEN_WIDTH - 20,
        100
    );

    u8g2_DrawLine(
        &u8g2,
        20,
        220,
        SCREEN_WIDTH - 20,
        220
    );

    u8g2_DrawDisc(
        &u8g2,
        SCREEN_WIDTH / 2,
        260,
        25,
        U8G2_DRAW_ALL
    );
}


/*
 * Full display update.
 *
 * framebuffer is already in exactly the format expected by
 * epd_display().
 */
static void display_full(void)
{
    epd_display(framebuffer);
}


/*
 * Fast full display update.
 */
static void display_full_fast(void)
{
    epd_display_fast(framebuffer);
}


/*
 * Establish the framebuffer as the partial-refresh base image.
 */
static void display_set_basemap(void)
{
    epd_set_basemap(framebuffer);
}


void app_main(void)
{
    printf("Starting graphics renderer\n");
    printf("Screen: %d x %d\n", SCREEN_WIDTH, SCREEN_HEIGHT);
    printf("Bytes/row: %d\n", BYTES_PER_ROW);
    printf("Framebuffer: %d bytes\n", FRAMEBUFFER_SIZE);

    /*
     * Initialize the GDEY042T81.
     *
     * This also initializes the SPI interface.
     */
    epd_init_fast();

    /*
     * Initialize u8g2.
     *
     * No u8g2 display hardware is involved.
     */
    graphics_init();

    /*
     * Draw into framebuffer[].
     */
    render_screen();

    /*
     * framebuffer[] is directly passed to the e-paper driver.
     */
    display_full_fast();

    /*
     * Or:
     *
     * display_full();
     *
     * Or establish this image as the partial-refresh base:
     *
     * display_set_basemap();
     */

    /*
     * The pointer returned by u8g2 is the same buffer.
     */
    uint8_t *fb = u8g2_GetBufferPtr(&u8g2);

    printf("u8g2 framebuffer: %p\n", (void *)fb);
    printf("our framebuffer:  %p\n", (void *)framebuffer);

    while (1)
        vTaskDelay(pdMS_TO_TICKS(1000));
}