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[tocstart]: # (toc start)
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* [RAM Optimization](#ram-optimization)
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* [Flash Memory Optimization](#flash-memory-optimization)
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* [Font Optimization](#font-optimization)
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* [U8g2 Feature Selection](#u8g2-feature-selection)
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[tocend]: # (toc end)
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# RAM Optimization
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On AVR systems, use the Arduino `F()` macro. U8g2 supports the Arduino `print`
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function, which accepts the `F()` macro.
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A simple example for the `F()` macro is available as an example:
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[https://github.com/olikraus/u8g2/blob/master/sys/arduino/u8g2_page_buffer/PrintHelloWorld/PrintHelloWorld.ino](https://github.com/olikraus/u8g2/blob/master/sys/arduino/u8g2_page_buffer/PrintHelloWorld/PrintHelloWorld.ino)
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A more complex example is here:
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[https://github.com/olikraus/u8g2/blob/master/sys/arduino/u8g2_page_buffer/PrintProgmem/PrintProgmem.ino](https://github.com/olikraus/u8g2/blob/master/sys/arduino/u8g2_page_buffer/PrintProgmem/PrintProgmem.ino)
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# Flash Memory Optimization
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## Font Optimization
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Usually U8g2 fonts are available in different sizes (number of glyphs included in the
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font). The last letter of the font name indicates the character set (and the size)
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of the fonts.
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| Font Name | Character Set |
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|-------------|-----------|
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| u8g2_xxx_xe | Extended: Glyphs with unicode 32 to 701 are included in the font (v2.16.x will also include big ß) |
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| u8g2_xxx_xf | Full: Glyphs with unicode 32 to 255 are included in the font |
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| u8g2_xxx_xr | Restricted: Only characters from 32 to 127 are included |
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| u8g2_xxx_xu | Uppercase: Numbers and uppercase letters |
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| u8g2_xxx_xn | Numbers and some extra glyphs for date and time printing are included |
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| u8g2_xxx_x_something | Special selection of glyphs. See the font picture for details. |
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For example if only a number needs to be displayed with a font,
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then the font should contain only numbers. In such a case, it is better to
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select a `n` font to avoid the allocation of unneeded chars in the flash memory.
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Each font picture also includes the number of bytes, occupied by the font in
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flash memory (upper part of the picture, third line):
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These pictures are available on the [font group](fntgrp) pages for each font.
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If there is no proper set, you can always create your own custom font with
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exactly those characters, which are required for your
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project (see [FAQ](https://github.com/olikraus/u8g2/blob/master/doc/faq.txt))
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See also: [setFont](u8g2reference#setfont)
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## U8g2 Feature Selection
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U8g2 includes many features and includes several speed optimization procedures.
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Sometimes speed is not critical or some features are not required. In those
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cases, the user can disable such features in [`u8g2.h`](https://github.com/olikraus/u8g2/blob/master/csrc/u8g2.h):
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Search for `u8g2.h` on your local drive.
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For the Arduino Environment, `u8g2.h` should be in the subfolder
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`libraries/U8g2_Arduino/src/clib` of your Arduino custom library folder.
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The location of this custom library folder might be different on operating system and Arduino IDE.
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It might be `C:\Users\<name>\AppData\Local\Arduino15\` on Windows OS or
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`~/Arduino/Libraries` for Unix based systems.
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Some other pathes are mentioned [on the Arduino library hacking page](https://www.arduino.cc/en/hacking/libraries).
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All features names start with `U8G2_WITH_`. A feature is enabled with a `#define` of
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the feature name. It is disabled if the `#define` is put into comments.
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| Feature Name | Description |
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|-------------|-----------|
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| `U8G2_WITH_HVLINE_SPEED_OPTIMIZATION` | Enables speed optimization for pixel buffer writes. |
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| `U8G2_WITH_INTERSECTION` | Enables speed optimization by early intersection tests for high level graphics primitives. |
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| `U8G2_WITH_CLIP_WINDOW_SUPPORT` | Enables support for a custom clip window. If disabled, clipping will happen only against the display boundaries. |
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| `U8G2_WITH_FONT_ROTATION` | Enables string output to all four directions. If disabled, strings can be written only from left to right. |
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| `U8G2_WITH_UNICODE` | Enables support for Unicode Basic Multilingual Plane. |
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By default all the above features are enabled. The following table gives an idea on the
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flash memory reduction, if one or more features are disabled:
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| Flash | Reduction | Disabled Feature |
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|----------|----------------|-------------|
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| 8732 | | default, all features active |
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| 8500 | -2.65% | no `U8G2_WITH_CLIP_WINDOW_SUPPORT` |
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| 8316 | -4.76% | no `U8G2_WITH_FONT_ROTATION` |
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| 8606 | -1.44% | no `U8G2_WITH_UNICODE` |
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| 8692 | -0.45% | no `U8G2_WITH_INTERSECTION` |
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| 8328 | -4.62% | no `U8G2_WITH_INTERSECTION` no `U8G2_WITH_CLIP_WINDOW_SUPPORT` |
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| 8718 | -4.86% | no `U8G2_WITH_HVLINE_SPEED_OPTIMIZATION` |
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| 8026 | -8.08% | no `U8G2_WITH_FONT_ROTATION` no `U8G2_WITH_INTERSECTION` no `U8G2_WITH_CLIP_WINDOW_SUPPORT` |
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Numbers are derived from:
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* Arduino 1.84, U8g2 2.23, Arduino Uno
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* U8G2_SSD1306_128X64_NONAME_1_4W_HW_SPI
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