Display Component

The display component houses ESPHome’s powerful rendering and display engine. Fundamentally, there are these types of displays:

For graphical displays, which offer the greatest flexibility, there are two options:

Display Rendering Engine

ESPHome’s own powerful rendering engine can handle many common tasks such as drawing basic shapes, printing text with fonts of your choice, or even rendering images.

To achieve all this flexibility displays tie in directly into ESPHome’s lambda system. So when you want to write some text or sensor values to the screen you will be writing in C++ code using an API that is designed to

  • be simple and to be used without programming experience

  • but also be flexible enough to work with more complex tasks like displaying an analog clock.

In this section we will be discussing how to use ESPHome’s display rendering engine from ESPHome and some basic commands. Please note that this only applies to displays that can control each pixel individually.

Note

Display hardware is complex and sometimes doesn’t behave as expected. If you’re having trouble with your display, please see Troubleshooting below.

So, first a few basics: When setting up a display platform in ESPHome there will be a configuration option called lambda: which will be called every time ESPHome wants to re-render the display. In each cycle, the display is automatically cleared before the lambda is executed. You can disable this behavior by setting auto_clear_enabled: false. In the lambda, you can write code like in any lambda in ESPHome. Display lambdas are additionally passed a variable called it which represents the rendering engine object.

../../_images/display_rendering_line.png 
display:
  - platform: ...
    # ...
    lambda: |-
      // Write your display rendering code here

      // For example, draw a line from [x=0,y=0] to [x=50,y=50]
      it.line(0, 0, 50, 50);

Note

Lambdas are essentially just a lightly modified version of C++. So don’t forget to end each line with a semicolon (;). Otherwise you will be greeted by a long error message at the compilation stage.

If you compile and upload the configuration above, you should see a black (or white, depending on the display) line which starts at the top left and goes a few pixels down at a 45° angle. (If it’s in another corner, use the rotation: option to rotate the display to your liking)

This already highlights one of the things you must learn before diving into writing your own custom display code: The top left is always the origin of the pixel coordinate system. Also, all points in this coordinate system are a pair of integers like 50, 50 which represent the shift to the right and shift downwards. So, in other words, x always represents the horizontal axis (width) and y the vertical axis (height). And the convention in the rendering engine is always first specify the x coordinate and then the y coordinate.

Basic Shapes

Now that you know a bit more about ESPHome’s coordinate system, let’s draw some basic shapes like lines, rectangles, circles or even polygons:

../../_images/display_rendering_shapes.png 
display:
  - platform: ...
    # ...
    lambda: |-
      // Draw a line from [0,0] to [100,50]
      it.line(0, 0, 100, 50);
      // Draw the outline of a rectangle with the top left at [5,20], a width of 30 and a height of 42
      it.rectangle(5, 20, 30, 42);
      // Draw the same rectangle a few pixels apart, but this time filled
      it.filled_rectangle(40, 40, 30, 42);

      // Circles! Let's draw one with the center at [20,40] and a radius of 10
      it.circle(20, 40, 10);
      // ... and the same thing filled again
      it.filled_circle(20, 75, 10);

      // Triangles... Let's draw the outline of a triangle from the [x,y] coordinates of its three points
      // [25,5], [100,5], [80,25]
      it.triangle(25, 5, 100, 5, 80, 25);
      // and a filled triangle !
      it.filled_triangle(115, 5, 95, 25, 125, 70);

      // Regular Polygons? Let's draw a filled, pointy-topped hexagon inscribed in a circle
      // centered on [170,45] with a radius of 20
      it.filled_regular_polygon(170, 45, 20, EDGES_HEXAGON);
      // and the outline of flat-topped octagon around it!
      it.regular_polygon(170, 45, 40, EDGES_OCTAGON, VARIATION_FLAT_TOP);
      // Need to rotate the polygon, or retrieve the coordinates of its vertices? Check the API!

All the above methods can optionally also be called with an argument at the end which specifies in which color to draw. For monochrome displays, only COLOR_ON (the default if color is not given) and COLOR_OFF are supported.

display:
  - platform: ...
    # ...
    lambda: |-
      // Turn the whole display on
      it.fill(COLOR_ON);
      // Turn the whole display off
      it.fill(COLOR_OFF);

      // Turn a single pixel off at [50,60]
      it.draw_pixel_at(50, 60, COLOR_OFF);

For color displays (e.g. TFT displays), you can use the Color class.

../../_images/display_rendering_colors.png 
display:
  - platform: ...
    # ...
    lambda: |-
      auto black = Color(0, 0, 0);
      auto red = Color(255, 0, 0);
      auto green = Color(0, 255, 0);
      auto blue = Color(0, 0, 255);
      auto white = Color(255, 255, 255);
      it.filled_circle(20, 32, 15, black);
      it.filled_circle(40, 32, 15, red);
      it.filled_circle(60, 32, 15, green);
      it.filled_circle(80, 32, 15, blue);
      it.filled_circle(100, 32, 15, white);

Additionally, you have access to two helper methods which will fetch the width and height of the display:

display:
  - platform: ...
    # ...
    lambda: |-
      // Draw a circle in the middle of the display
      it.filled_circle(it.get_width() / 2, it.get_height() / 2, 20);

      // Turn off bottom half of the screen
      it.filled_rectangle(0, it.get_height()/2, it.get_width(), it.get_height()/2, COLOR_OFF);

You can view the full API documentation for the rendering engine in the “API Reference” in the See Also section.

Drawing Static Text

To be able to display text, you need to prepare some fonts. ESPHome’s font renderer allows you to use OpenType/TrueType/Bitmap fonts for your texts. This is very flexiblle because you can prepare various sets of fonts at different sizes with a different number of glyphs which is extremely convenient when we’re talking about flash space.

In your display code, you can render static text by referencing the font and just entering your string enclosed in double quotes:

display:
  - platform: ...
    # ...
    lambda: |-
      // Print the string "Hello World!" at [0,10]
      it.print(0, 10, id(my_font), "Hello World!");

By default, ESPHome will align the text at the top left. That means if you enter the coordinates [0,10] for your text, the top left of the text will be at [0,10]. If you want to draw some text at the right side of the display, it is however sometimes useful to choose a different text alignment. When you enter [0,10] you’re really telling ESPHome that it should position the anchor point of the text at [0,10]. When using a different alignment, like TOP_RIGHT, the text will be positioned left of the anchor pointed, so that, as the name implies, the anchor point is a the top right corner of the text.

display:
  - platform: ...
    # ...
    lambda: |-
      // Aligned on left by default
      it.print(0, 0, id(my_font), "Left aligned");

      // Aligned on right edge
      it.print(it.get_width(), 0, id(my_font), TextAlign::TOP_RIGHT, "Right aligned");

As with basic shapes, you can also specify a color for the text:

display:
  - platform: ...
    # ...
    lambda: |-
      // Syntax is always: it.print(<x>, <y>, <font>, [color=COLOR_ON], [align=TextAlign::TOP_LEFT], <text>);
      it.print(0, 0, id(my_font), COLOR_ON, "Left aligned");

In case of fonts rendered at higher bit depths, the background color has to be specified after the text in order for antialiasing to work:

display:
  - platform: ...
    # ...
    lambda: |-
      // Syntax is always: it.print(<x>, <y>, <font>, [color=COLOR_ON], [align], <text>, [color=COLOR_OFF]);
      it.print(0, 0, id(my_font_with_icons), COLOR_ON, TextAlign::CENTER, "Just\U000f05d4here. Already\U000F02D1this.", COLOR_OFF);
../../_images/display_rendering_text.png

Formatted Text

Static text by itself is not too impressive. What we really want is to display dynamic content like sensor values on the display!. That’s where printf comes in. printf is a formatting engine from the C era and ESPHome chose to use because … well, I’m too lazy to create a fully-fledged format engine where the existing stuff is way better documented :)

printf can do way more stuff than you will probably ever need, but it’s also quite simple for the basic stuff. For example, a printf call can look like this:

sensor:
  - platform: ...
    # ...
    id: my_sensor

display:
  - platform: ...
    # ...
    lambda: |-
      it.printf(0, 0, id(my_font), "The sensor value is: %.1f", id(my_sensor).state);
      // If the sensor has the value 30.02, the result will be: "The sensor value is: 30.0"

As you can see, when you call printf most of the string is printed as-is, but when this weird percent sign with some stuff after it is encountered, it is magically replaced by the argument after the format (here id(my_sensor).state).

Every time you type a percent sign % in a printf format string, it will treat the following letters as a format tag until a so-called “specifier” is encountered (in this case f). You can read more about it here, but for ESPHome there are really just a few things you need to know.

Let’s break %.1f down:

  • % - initiate the format string

  • .1 - round the decimal number to 1 digits after the decimal point.

  • f - the specifier which tells printf the data type of the argument. Here it is a f(loat).

For example, if you would like to print a sensor value with two digits of accuracy, you would write %.2f and with zero digits of accuracy (without a decimal) %.0f.

Another interesting format string is %7.2f, which would become the right-justified string "  20.51" for a value of 20.506.

  • % - initiate the format

  • 7 - means that the number will be right-justified and be padded on the left by spaces if the result would be shorter than 7 characters long.

  • .2 - round the decimal number to 2 digits after the decimal point.

  • f - specifier: f(loat).

You can even have as many formatted items as you want in a single printf call. Just make sure the put the arguments after the format string in the right order.

display:
  - platform: ...
    # ...
    lambda: |-
      // %% - literal % sign
      it.printf(0, 0, id(my_font), "Temperature: %.1f°C, Humidity: %.1f%%", id(temperature).state, id(humidity).state);

To display a text string from a text_sensor, append .c_str() to the end of your variable.

display:
  - platform: ...
    # ...
    lambda: |-
      it.printf(0, 0, id(my_font), "Text to follow: %s", id(template_text).state.c_str());

When using anti-aliased fonts you will probably need to specify the color to draw the characters, and the background color to mix in for anti-aliasing. This requires the full version of printf, e.g.:

display:
  - platform: ...
    # ...
    lambda: |-
        it.printf(10, 100, id(roboto), Color(0x123456), COLOR_OFF, display::TextAlign::BASELINE, "%f", id(heap_free).state);

The last printf tip for use in displays I will discuss here is how to display binary sensor values. You could of course just check the state with an if statement as the first few lines in the example below, but if you want to be efficient you can use an inline if too. With the %s print specifier you can tell it to use any string you pass it, like "ON" or "OFF".

binary_sensor:
  - platform: ...
    # ...
    id: my_binary_sensor

display:
  - platform: ...
    # ...
    lambda: |-
      if (id(my_binary_sensor).state) {
        it.print(0, 0, id(my_font), "state: ON");
      } else {
        it.print(0, 0, id(my_font), "state: OFF");
      }
      // Shorthand:
      it.printf(0, 0, id(my_font), "State: %s", id(my_binary_sensor).state ? "ON" : "OFF");

Note

For displaying external data on the display, for example data from your Home Assistant instance, you can use the MQTT Subscribe Text Sensor (see the example there for more information).

Displaying Time

You can display current time using a time component. Please see the example here.

Screen Clipping

Screen clipping can be useful when you just want to show a part of an image or make sure that what you draw on the screen does not go outside a specific region on the screen.

With start_clipping(left, top, right, bottom); start you the clipping process and when you are done drawing in that region you can stop the clipping process with end_clipping(); . You can nest as many start_clipping(); as you want as long you end them as many times as well.

binary_sensor:
  - platform: ...
    # ...
    id: my_binary_sensor

color:
  - name: my_red
    red: 100%

display:
  - platform: ...
    # ...
    lambda: |-
      if (id(my_binary_sensor).state) {
        it.print(0, 0, id(my_font), "state: ON");
      } else {
        it.print(0, 0, id(my_font), "state: OFF");
      }
      // Shorthand:
      it.start_clipping(40,0,140,20);
      it.printf(0, 0, id(my_font), id(my_red), "State: %s", id(my_binary_sensor).state ? "ON" : "OFF");
      it.end_clipping();

After you started clipping you can manipulate the region with extend_clipping(left, top, right, bottom); and shrink_clipping(left, top, right, bottom); within previous set clipping region.

With get_clipping(); you get a Rect object back with the latest set clipping region.

class Rect {
    int16_t x;  ///< X/Left coordinate
    int16_t y;  ///< Y/Top coordinate
    int16_t w;  ///< Width
    int16_t h;  ///< Height
    int16_t x2();  ///< Right coordinate
    int16_t y2();  ///< bottom coordinate
  };

With is_clipping(); tells you if clipping is activated.

Color

When using RGB-capable displays in ESPHome you may wish to use custom colors. A color component exists for just this purpose:

color:
  - id: my_light_red
    red: 100%
    green: 20%
    blue: 25%
    white: 0%

Alternatively, you can use <color>_int to specify the color as an int value:

color:
  - id: my_light_red
    red_int: 255
    green_int: 51
    blue_int: 64
    white_int: 0

Or, if you are more comforatble with hex values, you can use hex:

color:
  - id: my_light_red
    hex: FF3340

Configuration variables:

  • red (Optional, percentage): The percentage of the red component. Defaults to 100%.

  • red_int (Optional, integer): The brightness of the red component on a scale of 0 to 255. Defaults to 255.

  • green (Optional, percentage): The percentage of the green component. Defaults to 100%.

  • green_int (Optional, integer): The brightness of the green component on a scale of 0 to 255. Defaults to 255.

  • blue (Optional, percentage): The percentage of the blue component. Defaults to 100%.

  • blue_int (Optional, integer): The brightness of the blue component on a scale of 0 to 255. Defaults to 255.

  • white (Optional, percentage): The percentage of the white component. Defaults to 100%.

  • white_int (Optional, integer): The brightness of the white component on a scale of 0 to 255. Defaults to 255.

  • hex (Optional, string): The color in hexadecimal representation. Defaults to FFFFFF.

RGB displays use red, green, and blue, while grayscale displays may use white.

Display Pages

Certain display types also allow you to show “pages”. With pages you can create drawing lambdas that you can switch between. For example with pages you can set up 3 screens, each with different content, and switch between them on a timer.

display:
  - platform: ...
    # ...
    id: my_display
    pages:
      - id: page1
        lambda: |-
          it.print(0, 10, id(my_font), "This is page 1!");
      - id: page2
        lambda: |-
          it.print(0, 10, id(my_font), "This is page 2!");

You can then switch between these with three different actions:

show_next / show_previous: Shows the next or previous page, wraps around at the end.

on_...:
  - display.page.show_next: my_display
  - display.page.show_previous: my_display

# For example cycle through pages on a timer
interval:
  - interval: 5s
    then:
      - display.page.show_next: my_display
      - component.update: my_display

display.page.show: Show a specific page

on_...:
  - display.page.show: page1

  # Templated
  - display.page.show: !lambda |-
      if (id(my_binary_sensor).state) {
        return id(page1);
      } else {
        return id(page2);
      }

Note

To trigger a redraw right after the page show use a component.update action:

# For example cycle through pages on a timer
interval:
  - interval: 5s
    then:
      - display.page.show_next: my_display
      - component.update: my_display

display.is_displaying_page: This condition returns true while the specified page is being shown.

# In some trigger:
on_...:
  - if:
      condition:
        display.is_displaying_page: page1
      then:
        ...
  - if:
      condition:
        display.is_displaying_page:
          id: my_display
          page_id: page2
      then:
        ...

on_page_change: This automation will be triggered when the page that is shown changes.

display:
  - platform: ...
    # ...
    on_page_change:
      - from: page1
        to: page2
        then:
          lambda: |-
            ESP_LOGD("display", "Page changed from 1 to 2");

  • from (Optional, ID): A page id. If set the automation is only triggered if changing from this page. Defaults to all pages.

  • to (Optional, ID): A page id. If set the automation is only triggered if changing to this page. Defaults to all pages.

Additionally the old page will be given as the variable from and the new one as the variable to.

Troubleshooting

Using the Color Test Card

If you’re experiencing issues with your color display, the show_test_card: true option can help you to identify what might be wrong.

  • It will show bars for Red, Green and Blue, graduating to black and white.

  • Together with that it will show the letters “R”, “G” and “B” to validate the display geometry.

  • There will be a rectangle around the corners of the display with a marker at the 0,0 corner which should be at the top left of the screen.

../../_images/test_card.jpg

When all points above are shown correctly then the display is working as expected. To help the graphics display team determine the best way to help you, a picture of the result of this option is very helpful.

Should you create an issue in GitHub regarding your display, please be sure to include a link to where you purchased the display so that we can validate the configuration you’ve used.

Note

For displays in 8 bit mode you will see distinct color blocks rather than a smooth gradient.

See Also