Image (lv_img)

Overview

Images are the basic object to display from the flash (as arrays) or externally as files. Images can display symbols (LV_SYMBOL_...) too.

Using the Image decoder interface custom image formats can be supported as well.

Parts and Styles

The images has only a main part called LV_IMG_PART_MAIN which uses the typical background style propeties to draw a background rectangle and the image properties. The padding values are used to make the background virtually larger. (It won't change the image's real size but the size modification is applied only during drawing)

Usage

Image source

To provide maximum flexibility, the source of the image can be:

  • a variable in the code (a C array with the pixels).

  • a file stored externally (like on an SD card).

  • a text with Symbols.

To set the source of an image, use lv_img_set_src(img, src).

To generate a pixel array from a PNG, JPG or BMP image, use the Online image converter tool and set the converted image with its pointer: lv_img_set_src(img1, &converted_img_var); To make the variable visible in the C file, you need to declare it with LV_IMG_DECLARE(converted_img_var).

To use external files, you also need to convert the image files using the online converter tool but now you should select the binary Output format. You also need to use LVGL's file system module and register a driver with some functions for the basic file operation. Got to the File system to learn more. To set an image sourced from a file, use lv_img_set_src(img, "S:folder1/my_img.bin").

You can set a symbol similarly to Labels. In this case, the image will be rendered as text according to the font specified in the style. It enables to use of light-weighted mono-color "letters" instead of real images. You can set symbol like lv_img_set_src(img1, LV_SYMBOL_OK).

Label as an image

Images and labels are sometimes used to convey the same thing. For example, to describe what a button does. Therefore, images and labels are somewhat interchangeable. To handle these images can even display texts by using LV_SYMBOL_DUMMY as the prefix of the text. For example, lv_img_set_src(img, LV_SYMBOL_DUMMY "Some text").

Transparency

The internal (variable) and external images support 2 transparency handling methods:

  • Chrome keying - Pixels with LV_COLOR_TRANSP (lv_conf.h) color will be transparent.

  • Alpha byte - An alpha byte is added to every pixel.

Palette and Alpha index

Besides True color (RGB) color format, the following formats are also supported:

  • Indexed - Image has a palette.

  • Alpha indexed - Only alpha values are stored.

These options can be selected in the font converter. To learn more about the color formats, read the Images section.

Recolor

The images can be re-colored in run-time to any color according to the brightness of the pixels. It is very useful to show different states (selected, inactive, pressed, etc.) of an image without storing more versions of the same image. This feature can be enabled in the style by setting img.intense between LV_OPA_TRANSP (no recolor, value: 0) and LV_OPA_COVER (full recolor, value: 255). The default value is LV_OPA_TRANSP so this feature is disabled.

Auto-size

It is possible to automatically set the size of the image object to the image source's width and height if enabled by the lv_img_set_auto_size(image, true) function. If auto-size is enabled, then when a new file is set, the object size is automatically changed. Later, you can modify the size manually. The auto-size is enabled by default if the image is not a screen.

Mosaic

If the object size is greater than the image size in any directions, then the image will be repeated like a mosaic. It's a very useful feature to create a large image from only a very narrow source. For example, you can have a 300 x 1 image with a special gradient and set it as a wallpaper using the mosaic feature.

Offset

With lv_img_set_offset_x(img, x_ofs) and lv_img_set_offset_y(img, y_ofs), you can add some offset to the displayed image. It is useful if the object size is smaller than the image source size. Using the offset parameter a Texture atlas or a "running image" effect can be created by Animating the x or y offset.

Transformations

Using the lv_img_set_zoom(img, factor) the images will be zoomed. Set factor to 256 or LV_IMG_ZOOM_NONE to disable zooming. A larger value enlarges the images (e.g. 512 double size), a smaller value shrinks it (e.g. 128 half size). Fractional scale works as well. E.g. 281 for 10% enlargement.

To rotate the image use lv_img_set_angle(img, angle). Angle has 0.1 degree precision, so for 45.8° set 458.

By default, the pivot point of the rotation is the center of the image. It can be changed with lv_img_set_pivot(img, pivot_x, pivot_y). 0;0 is the top left corner.

The quality of the transformation can be adjusted with lv_img_set_antialias(img, true/false). With enabled anti-aliasing the transformations has a higher quality but they are slower.

The transformations require the whole image to be available. Therefore indexed images (LV_IMG_CF_INDEXED_...), alpha only images (LV_IMG_CF_ALPHA_...) or images from files can be transformed. In other words transformations work only on true color images stored as C array, or if a custom Image decoder returns the whole image.

Note that, the real coordinates of image object won't change during transformation. That is lv_obj_get_width/height/x/y() will returned the original, non-zoomed coordinates.

Rotate

The images can be rotated with

Events

Only the Generic events are sent by the object type.

Learn more about Events.

Keys

No Keys are processed by the object type.

Learn more about Keys.

Example

C

Image from variable and symbol

Simple Image example in LittlevGL

code

#include "../../../lv_examples.h"
#if LV_USE_IMG

/* Find the image here: https://github.com/lvgl/lv_examples/tree/master/assets */
LV_IMG_DECLARE(img_cogwheel_argb);

void lv_ex_img_1(void)
{
    lv_obj_t * img1 = lv_img_create(lv_scr_act(), NULL);
    lv_img_set_src(img1, &img_cogwheel_argb);
    lv_obj_align(img1, NULL, LV_ALIGN_CENTER, 0, -20);

    lv_obj_t * img2 = lv_img_create(lv_scr_act(), NULL);
    lv_img_set_src(img2, LV_SYMBOL_OK "Accept");
    lv_obj_align(img2, img1, LV_ALIGN_OUT_BOTTOM_MID, 0, 20);
}

#endif

Image recoloring

Image recolor example in LittlevGL

code

#include "../../../lv_examples.h"
#if LV_USE_IMG

#define SLIDER_WIDTH 20

static void create_sliders(void);
static void slider_event_cb(lv_obj_t * slider, lv_event_t event);

static lv_obj_t * red_slider, * green_slider, * blue_slider, * intense_slider;
static lv_obj_t * img1;
LV_IMG_DECLARE(img_cogwheel_argb);

void lv_ex_img_2(void)
{
    /*Create 4 sliders to adjust RGB color and re-color intensity*/
    create_sliders();

    /* Now create the actual image */
    img1 = lv_img_create(lv_scr_act(), NULL);
    lv_img_set_src(img1, &img_cogwheel_argb);
    lv_obj_align(img1, NULL, LV_ALIGN_IN_RIGHT_MID, -20, 0);
}

static void slider_event_cb(lv_obj_t * slider, lv_event_t event)
{
    if(event == LV_EVENT_VALUE_CHANGED) {
        /* Recolor the image based on the sliders' values */
        lv_color_t color  = lv_color_make(lv_slider_get_value(red_slider), lv_slider_get_value(green_slider), lv_slider_get_value(blue_slider));
        lv_opa_t intense = lv_slider_get_value(intense_slider);
        lv_obj_set_style_local_image_recolor_opa(img1, LV_IMG_PART_MAIN, LV_STATE_DEFAULT, intense);
        lv_obj_set_style_local_image_recolor(img1, LV_IMG_PART_MAIN, LV_STATE_DEFAULT, color);
    }
}

static void create_sliders(void)
{
    /* Create a set of RGB sliders */
    /* Use the red one as a base for all the settings */
    red_slider = lv_slider_create(lv_scr_act(), NULL);
    lv_slider_set_range(red_slider, 0, 255);
    lv_obj_set_size(red_slider, SLIDER_WIDTH, 200); /* Be sure it's a vertical slider */
    lv_obj_set_style_local_bg_color(red_slider, LV_SLIDER_PART_INDIC, LV_STATE_DEFAULT, LV_COLOR_RED);
    lv_obj_set_event_cb(red_slider, slider_event_cb);

    /* Copy it for the other three sliders */
    green_slider = lv_slider_create(lv_scr_act(), red_slider);
    lv_obj_set_style_local_bg_color(green_slider, LV_SLIDER_PART_INDIC, LV_STATE_DEFAULT, LV_COLOR_LIME);

    blue_slider = lv_slider_create(lv_scr_act(), red_slider);
    lv_obj_set_style_local_bg_color(blue_slider, LV_SLIDER_PART_INDIC, LV_STATE_DEFAULT, LV_COLOR_BLUE);

    intense_slider = lv_slider_create(lv_scr_act(), red_slider);
    lv_obj_set_style_local_bg_color(intense_slider, LV_SLIDER_PART_INDIC, LV_STATE_DEFAULT, LV_COLOR_GRAY);
    lv_slider_set_value(intense_slider, 255, LV_ANIM_OFF);

    lv_obj_align(red_slider, NULL, LV_ALIGN_IN_LEFT_MID, 20, 0);
    lv_obj_align(green_slider, red_slider, LV_ALIGN_OUT_RIGHT_MID, 20, 0);
    lv_obj_align(blue_slider, green_slider, LV_ALIGN_OUT_RIGHT_MID, 20, 0);
    lv_obj_align(intense_slider, blue_slider, LV_ALIGN_OUT_RIGHT_MID, 20, 0);
}

#endif

MicroPython

No examples yet.

API

Typedefs

typedef uint8_t lv_img_part_t

Enums

enum [anonymous]

Values:

enumerator LV_IMG_PART_MAIN

Functions

lv_obj_t *lv_img_create(lv_obj_t *par, const lv_obj_t *copy)

Create an image objects

Return

pointer to the created image

Parameters
  • par: pointer to an object, it will be the parent of the new button

  • copy: pointer to a image object, if not NULL then the new object will be copied from it

void lv_img_set_src(lv_obj_t *img, const void *src_img)

Set the pixel map to display by the image

Parameters
  • img: pointer to an image object

  • data: the image data

void lv_img_set_auto_size(lv_obj_t *img, bool autosize_en)

Enable the auto size feature. If enabled the object size will be same as the picture size.

Parameters
  • img: pointer to an image

  • en: true: auto size enable, false: auto size disable

void lv_img_set_offset_x(lv_obj_t *img, lv_coord_t x)

Set an offset for the source of an image. so the image will be displayed from the new origin.

Parameters
  • img: pointer to an image

  • x: the new offset along x axis.

void lv_img_set_offset_y(lv_obj_t *img, lv_coord_t y)

Set an offset for the source of an image. so the image will be displayed from the new origin.

Parameters
  • img: pointer to an image

  • y: the new offset along y axis.

void lv_img_set_pivot(lv_obj_t *img, lv_coord_t pivot_x, lv_coord_t pivot_y)

Set the rotation center of the image. The image will be rotated around this point

Parameters
  • img: pointer to an image object

  • pivot_x: rotation center x of the image

  • pivot_y: rotation center y of the image

void lv_img_set_angle(lv_obj_t *img, int16_t angle)

Set the rotation angle of the image. The image will be rotated around the set pivot set by lv_img_set_pivot()

Parameters
  • img: pointer to an image object

  • angle: rotation angle in degree with 0.1 degree resolution (0..3600: clock wise)

void lv_img_set_zoom(lv_obj_t *img, uint16_t zoom)

Set the zoom factor of the image.

Parameters
  • img: pointer to an image object

  • zoom: the zoom factor.

    • 256 or LV_ZOOM_IMG_NONE for no zoom

    • <256: scale down

    • >256 scale up

    • 128 half size

    • 512 double size

void lv_img_set_antialias(lv_obj_t *img, bool antialias)

Enable/disable anti-aliasing for the transformations (rotate, zoom) or not

Parameters
  • img: pointer to an image object

  • antialias: true: anti-aliased; false: not anti-aliased

const void *lv_img_get_src(lv_obj_t *img)

Get the source of the image

Return

the image source (symbol, file name or C array)

Parameters
  • img: pointer to an image object

const char *lv_img_get_file_name(const lv_obj_t *img)

Get the name of the file set for an image

Return

file name

Parameters
  • img: pointer to an image

bool lv_img_get_auto_size(const lv_obj_t *img)

Get the auto size enable attribute

Return

true: auto size is enabled, false: auto size is disabled

Parameters
  • img: pointer to an image

lv_coord_t lv_img_get_offset_x(lv_obj_t *img)

Get the offset.x attribute of the img object.

Return

offset.x value.

Parameters
  • img: pointer to an image

lv_coord_t lv_img_get_offset_y(lv_obj_t *img)

Get the offset.y attribute of the img object.

Return

offset.y value.

Parameters
  • img: pointer to an image

uint16_t lv_img_get_angle(lv_obj_t *img)

Get the rotation angle of the image.

Return

rotation angle in degree (0..359)

Parameters
  • img: pointer to an image object

void lv_img_get_pivot(lv_obj_t *img, lv_point_t *center)

Get the rotation center of the image.

Parameters
  • img: pointer to an image object

  • center: rotation center of the image

uint16_t lv_img_get_zoom(lv_obj_t *img)

Get the zoom factor of the image.

Return

zoom factor (256: no zoom)

Parameters
  • img: pointer to an image object

bool lv_img_get_antialias(lv_obj_t *img)

Get whether the transformations (rotate, zoom) are anti-aliased or not

Return

true: anti-aliased; false: not anti-aliased

Parameters
  • img: pointer to an image object

struct lv_img_ext_t

Public Members

const void *src
lv_point_t offset
lv_coord_t w
lv_coord_t h
uint16_t angle
lv_point_t pivot
uint16_t zoom
uint8_t src_type
uint8_t auto_size
uint8_t cf
uint8_t antialias