28 lines
1.7 KiB
Markdown
28 lines
1.7 KiB
Markdown
This is a branch of https://github.com/Bodmer/TFT_eSPI.git
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It is created to solve some problems I encountered while using Bodmer's lib in my mp3 player based on ESP32:
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1) I can only use smooth fonts to display unicode font with about 13K glyphs.
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2) The font can be placed in array, but then application uploading time becomes very long
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3) The font can be placed in SPIFFS, but then printing time is unacceptable
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4) The font loading takes huge amount of time and RAM
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5) Printing chars with high codes is much slower than chars from basic ASCII range.
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This version of TFT_eSPI solves those problems:
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1) The font can be loaded in separate partition in flash, so there is no need to re-upload it with every code upload.
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2) The font format (vlw) is converted to custom format (prt), which is:
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- all metrics are little-endian to match the CPU = no need to swap bytes
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- contains pre-calculated glyph offsets = no need to scan font for glyph sizes
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- contains pre-calculated max_descent = no need to scan font for max_descent
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3) Glyph metrics is loaded on-the-fly when printing, so no RAM is used
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4) Faster getUnicodeIndex function (FAST_UNICODE_INDEX) = glyph searching time is greatly decreased in large font
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Using partition for font is somewhat strange:
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- I can only use SPI_FLASH_MMAP_INST - instruction memory mapping, not data memory. And it forces to use 32-bit aligned access only.
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- Partition font seems a little slower than array font, but in final version of code usual array font can be used.
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This code is tested in my player only, so it can contain bugs and incompatibilities.
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Known problems:
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1. When program size grows and when using font partition, some characters stop printing as expected (very high codes), 0xBAD00BAD value is readed from flash instead of bitmap data.
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