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font.md (14247B)
1 ```eval_rst 2 .. include:: /header.rst 3 :github_url: |github_link_base|/overview/font.md 4 ``` 5 # Fonts 6 7 In LVGL fonts are collections of bitmaps and other information required to render images of individual letters (glyph). 8 A font is stored in a `lv_font_t` variable and can be set in a style's *text_font* field. For example: 9 ```c 10 lv_style_set_text_font(&my_style, &lv_font_montserrat_28); /*Set a larger font*/ 11 ``` 12 13 Fonts have a **bpp (bits per pixel)** property. It shows how many bits are used to describe a pixel in a font. The value stored for a pixel determines the pixel's opacity. 14 This way, with higher *bpp*, the edges of the letter can be smoother. The possible *bpp* values are 1, 2, 4 and 8 (higher values mean better quality). 15 16 The *bpp* property also affects the amount of memory needed to store a font. For example, *bpp = 4* makes a font nearly four times larger compared to *bpp = 1*. 17 18 ## Unicode support 19 20 LVGL supports **UTF-8** encoded Unicode characters. 21 Your editor needs to be configured to save your code/text as UTF-8 (usually this the default) and be sure that, `LV_TXT_ENC` is set to `LV_TXT_ENC_UTF8` in *lv_conf.h*. (This is the default value) 22 23 To test it try 24 ```c 25 lv_obj_t * label1 = lv_label_create(lv_scr_act(), NULL); 26 lv_label_set_text(label1, LV_SYMBOL_OK); 27 ``` 28 29 If all works well, a ✓ character should be displayed. 30 31 ## Built-in fonts 32 33 There are several built-in fonts in different sizes, which can be enabled in `lv_conf.h` with *LV_FONT_...* defines. 34 ### Normal fonts 35 Containing all the ASCII characters, the degree symbol (U+00B0), the bullet symbol (U+2022) and the built-in symbols (see below). 36 - `LV_FONT_MONTSERRAT_12` 12 px font 37 - `LV_FONT_MONTSERRAT_14` 14 px font 38 - `LV_FONT_MONTSERRAT_16` 16 px font 39 - `LV_FONT_MONTSERRAT_18` 18 px font 40 - `LV_FONT_MONTSERRAT_20` 20 px font 41 - `LV_FONT_MONTSERRAT_22` 22 px font 42 - `LV_FONT_MONTSERRAT_24` 24 px font 43 - `LV_FONT_MONTSERRAT_26` 26 px font 44 - `LV_FONT_MONTSERRAT_28` 28 px font 45 - `LV_FONT_MONTSERRAT_30` 30 px font 46 - `LV_FONT_MONTSERRAT_32` 32 px font 47 - `LV_FONT_MONTSERRAT_34` 34 px font 48 - `LV_FONT_MONTSERRAT_36` 36 px font 49 - `LV_FONT_MONTSERRAT_38` 38 px font 50 - `LV_FONT_MONTSERRAT_40` 40 px font 51 - `LV_FONT_MONTSERRAT_42` 42 px font 52 - `LV_FONT_MONTSERRAT_44` 44 px font 53 - `LV_FONT_MONTSERRAT_46` 46 px font 54 - `LV_FONT_MONTSERRAT_48` 48 px font 55 56 ### Special fonts 57 - `LV_FONT_MONTSERRAT_12_SUBPX` Same as normal 12 px font but with [subpixel rendering](#subpixel-rendering) 58 - `LV_FONT_MONTSERRAT_28_COMPRESSED` Same as normal 28 px font but stored as a [compressed font](#compress-fonts) with 3 bpp 59 - `LV_FONT_DEJAVU_16_PERSIAN_HEBREW` 16 px font with normal range + Hebrew, Arabic, Persian letters and all their forms 60 - `LV_FONT_SIMSUN_16_CJK`16 px font with normal range plus 1000 of the most common CJK radicals 61 - `LV_FONT_UNSCII_8` 8 px pixel perfect font with only ASCII characters 62 - `LV_FONT_UNSCII_16` 16 px pixel perfect font with only ASCII characters 63 64 65 The built-in fonts are **global variables** with names like `lv_font_montserrat_16` for a 16 px height font. To use them in a style, just add a pointer to a font variable like shown above. 66 67 The built-in fonts with *bpp = 4* contain the ASCII characters and use the [Montserrat](https://fonts.google.com/specimen/Montserrat) font. 68 69 In addition to the ASCII range, the following symbols are also added to the built-in fonts from the [FontAwesome](https://fontawesome.com/) font. 70 71 ![](/misc/symbols.png "Built-in Symbols in LVGL") 72 73 The symbols can be used singly as: 74 ```c 75 lv_label_set_text(my_label, LV_SYMBOL_OK); 76 ``` 77 78 Or together with strings (compile time string concatenation): 79 ```c 80 lv_label_set_text(my_label, LV_SYMBOL_OK "Apply"); 81 ``` 82 83 Or more symbols together: 84 ```c 85 lv_label_set_text(my_label, LV_SYMBOL_OK LV_SYMBOL_WIFI LV_SYMBOL_PLAY); 86 ``` 87 88 ## Special features 89 90 ### Bidirectional support 91 Most languages use a Left-to-Right (LTR for short) writing direction, however some languages (such as Hebrew, Persian or Arabic) use Right-to-Left (RTL for short) direction. 92 93 LVGL not only supports RTL texts but supports mixed (a.k.a. bidirectional, BiDi) text rendering too. Some examples: 94 95 ![](/misc/bidi.png "Bidirectional text examples") 96 97 BiDi support is enabled by `LV_USE_BIDI` in *lv_conf.h* 98 99 All texts have a base direction (LTR or RTL) which determines some rendering rules and the default alignment of the text (Left or Right). 100 However, in LVGL, the base direction is not only applied to labels. It's a general property which can be set for every object. 101 If not set then it will be inherited from the parent. 102 This means it's enough to set the base direction of a screen and every object will inherit it. 103 104 The default base direction for screens can be set by `LV_BIDI_BASE_DIR_DEF` in *lv_conf.h* and other objects inherit the base direction from their parent. 105 106 To set an object's base direction use `lv_obj_set_base_dir(obj, base_dir)`. The possible base directions are: 107 - `LV_BIDI_DIR_LTR`: Left to Right base direction 108 - `LV_BIDI_DIR_RTL`: Right to Left base direction 109 - `LV_BIDI_DIR_AUTO`: Auto detect base direction 110 - `LV_BIDI_DIR_INHERIT`: Inherit base direction from the parent (or a default value for non-screen objects) 111 112 This list summarizes the effect of RTL base direction on objects: 113 - Create objects by default on the right 114 - `lv_tabview`: Displays tabs from right to left 115 - `lv_checkbox`: Shows the box on the right 116 - `lv_btnmatrix`: Shows buttons from right to left 117 - `lv_list`: Shows icons on the right 118 - `lv_dropdown`: Aligns options to the right 119 - The texts in `lv_table`, `lv_btnmatrix`, `lv_keyboard`, `lv_tabview`, `lv_dropdown`, `lv_roller` are "BiDi processed" to be displayed correctly 120 121 ### Arabic and Persian support 122 There are some special rules to display Arabic and Persian characters: the *form* of a character depends on its position in the text. 123 A different form of the same letter needs to be used when it is isolated, at start, middle or end positions. Besides these, some conjunction rules should also be taken into account. 124 125 LVGL supports these rules if `LV_USE_ARABIC_PERSIAN_CHARS` is enabled. 126 127 However, there are some limitations: 128 - Only displaying text is supported (e.g. on labels), text inputs (e.g. text area) don't support this feature. 129 - Static text (i.e. const) is not processed. E.g. texts set by `lv_label_set_text()` will be "Arabic processed" but `lv_lable_set_text_static()` won't. 130 - Text get functions (e.g. `lv_label_get_text()`) will return the processed text. 131 132 ### Subpixel rendering 133 134 Subpixel rendering allows for tripling the horizontal resolution by rendering anti-aliased edges on Red, Green and Blue channels instead of at pixel level granularity. This takes advantage of the position of physical color channels of each pixel, resulting in higher quality letter anti-aliasing. Learn more [here](https://en.wikipedia.org/wiki/Subpixel_rendering). 135 136 For subpixel rendering, the fonts need to be generated with special settings: 137 - In the online converter tick the `Subpixel` box 138 - In the command line tool use `--lcd` flag. Note that the generated font needs about three times more memory. 139 140 Subpixel rendering works only if the color channels of the pixels have a horizontal layout. That is the R, G, B channels are next to each other and not above each other. 141 The order of color channels also needs to match with the library settings. By default, LVGL assumes `RGB` order, however this can be swapped by setting `LV_SUBPX_BGR 1` in *lv_conf.h*. 142 143 ### Compressed fonts 144 The bitmaps of fonts can be compressed by 145 - ticking the `Compressed` check box in the online converter 146 - not passing the `--no-compress` flag to the offline converter (compression is applied by default) 147 148 Compression is more effective with larger fonts and higher bpp. However, it's about 30% slower to render compressed fonts. 149 Therefore, it's recommended to compress only the largest fonts of a user interface, because 150 - they need the most memory 151 - they can be compressed better 152 - and probably they are used less frequently then the medium-sized fonts, so the performance cost is smaller. 153 154 ## Add a new font 155 156 There are several ways to add a new font to your project: 157 1. The simplest method is to use the [Online font converter](https://lvgl.io/tools/fontconverter). Just set the parameters, click the *Convert* button, copy the font to your project and use it. **Be sure to carefully read the steps provided on that site or you will get an error while converting.** 158 2. Use the [Offline font converter](https://github.com/lvgl/lv_font_conv). (Requires Node.js to be installed) 159 3. If you want to create something like the built-in fonts (Montserrat font and symbols) but in a different size and/or ranges, you can use the `built_in_font_gen.py` script in `lvgl/scripts/built_in_font` folder. 160 (This requires Python and `lv_font_conv` to be installed) 161 162 To declare a font in a file, use `LV_FONT_DECLARE(my_font_name)`. 163 164 To make fonts globally available (like the built-in fonts), add them to `LV_FONT_CUSTOM_DECLARE` in *lv_conf.h*. 165 166 ## Add new symbols 167 The built-in symbols are created from the [FontAwesome](https://fontawesome.com/) font. 168 169 1. Search for a symbol on [https://fontawesome.com](https://fontawesome.com). For example the [USB symbol](https://fontawesome.com/icons/usb?style=brands). Copy its Unicode ID which is `0xf287` in this case. 170 2. Open the [Online font converter](https://lvgl.io/tools/fontconverter). Add [FontAwesome.woff](https://lvgl.io/assets/others/FontAwesome5-Solid+Brands+Regular.woff). . 171 3. Set the parameters such as Name, Size, BPP. You'll use this name to declare and use the font in your code. 172 4. Add the Unicode ID of the symbol to the range field. E.g.` 0xf287` for the USB symbol. More symbols can be enumerated with `,`. 173 5. Convert the font and copy the generated source code to your project. Make sure to compile the .c file of your font. 174 6. Declare the font using `extern lv_font_t my_font_name;` or simply use `LV_FONT_DECLARE(my_font_name);`. 175 176 **Using the symbol** 177 1. Convert the Unicode value to UTF8, for example on [this site](http://www.ltg.ed.ac.uk/~richard/utf-8.cgi?input=f287&mode=hex). For `0xf287` the *Hex UTF-8 bytes* are `EF 8A 87`. 178 2. Create a `define` string from the UTF8 values: `#define MY_USB_SYMBOL "\xEF\x8A\x87"` 179 3. Create a label and set the text. Eg. `lv_label_set_text(label, MY_USB_SYMBOL)` 180 181 Note - `lv_label_set_text(label, MY_USB_SYMBOL)` searches for this symbol in the font defined in `style.text.font` properties. To use the symbol you may need to change it. Eg ` style.text.font = my_font_name` 182 183 ## Load a font at run-time 184 `lv_font_load` can be used to load a font from a file. The font needs to have a special binary format. (Not TTF or WOFF). 185 Use [lv_font_conv](https://github.com/lvgl/lv_font_conv/) with the `--format bin` option to generate an LVGL compatible font file. 186 187 Note that to load a font [LVGL's filesystem](/overview/file-system) needs to be enabled and a driver must be added. 188 189 Example 190 ```c 191 lv_font_t * my_font; 192 my_font = lv_font_load(X/path/to/my_font.bin); 193 194 /*Use the font*/ 195 196 /*Free the font if not required anymore*/ 197 lv_font_free(my_font); 198 ``` 199 200 201 ## Add a new font engine 202 203 LVGL's font interface is designed to be very flexible but, even so, you can add your own font engine in place of LVGL's internal one. 204 For example, you can use [FreeType](https://www.freetype.org/) to real-time render glyphs from TTF fonts or use an external flash to store the font's bitmap and read them when the library needs them. 205 206 A ready to use FreeType can be found in [lv_freetype](https://github.com/lvgl/lv_lib_freetype) repository. 207 208 To do this, a custom `lv_font_t` variable needs to be created: 209 ```c 210 /*Describe the properties of a font*/ 211 lv_font_t my_font; 212 my_font.get_glyph_dsc = my_get_glyph_dsc_cb; /*Set a callback to get info about glyphs*/ 213 my_font.get_glyph_bitmap = my_get_glyph_bitmap_cb; /*Set a callback to get bitmap of a glyph*/ 214 my_font.line_height = height; /*The real line height where any text fits*/ 215 my_font.base_line = base_line; /*Base line measured from the top of line_height*/ 216 my_font.dsc = something_required; /*Store any implementation specific data here*/ 217 my_font.user_data = user_data; /*Optionally some extra user data*/ 218 219 ... 220 221 /* Get info about glyph of `unicode_letter` in `font` font. 222 * Store the result in `dsc_out`. 223 * The next letter (`unicode_letter_next`) might be used to calculate the width required by this glyph (kerning) 224 */ 225 bool my_get_glyph_dsc_cb(const lv_font_t * font, lv_font_glyph_dsc_t * dsc_out, uint32_t unicode_letter, uint32_t unicode_letter_next) 226 { 227 /*Your code here*/ 228 229 /* Store the result. 230 * For example ... 231 */ 232 dsc_out->adv_w = 12; /*Horizontal space required by the glyph in [px]*/ 233 dsc_out->box_h = 8; /*Height of the bitmap in [px]*/ 234 dsc_out->box_w = 6; /*Width of the bitmap in [px]*/ 235 dsc_out->ofs_x = 0; /*X offset of the bitmap in [pf]*/ 236 dsc_out->ofs_y = 3; /*Y offset of the bitmap measured from the as line*/ 237 dsc_out->bpp = 2; /*Bits per pixel: 1/2/4/8*/ 238 239 return true; /*true: glyph found; false: glyph was not found*/ 240 } 241 242 243 /* Get the bitmap of `unicode_letter` from `font`. */ 244 const uint8_t * my_get_glyph_bitmap_cb(const lv_font_t * font, uint32_t unicode_letter) 245 { 246 /* Your code here */ 247 248 /* The bitmap should be a continuous bitstream where 249 * each pixel is represented by `bpp` bits */ 250 251 return bitmap; /*Or NULL if not found*/ 252 } 253 ``` 254 255 ## Use font fallback 256 257 You can specify `fallback` in `lv_font_t` to provide fallback to the font. When the font 258 fails to find glyph to a letter, it will try to let font from `fallback` to handle. 259 260 `fallback` can be chained, so it will try to solve until there is no `fallback` set. 261 262 ```c 263 /* Roboto font doesn't have support for CJK glyphs */ 264 lv_font_t *roboto = my_font_load_function(); 265 /* Droid Sans Fallback has more glyphs but its typeface doesn't look good as Roboto */ 266 lv_font_t *droid_sans_fallback = my_font_load_function(); 267 /* So now we can display Roboto for supported characters while having wider characters set support */ 268 roboto->fallback = droid_sans_fallback; 269 ```