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使用二进制字体需要将整个字体加载到存储器。 在某些情况下，如果字体很大，如大字号中文字体，则这样做可能不可取。
字体缓存使应用能够从外部存储器只能加载显示字符串所需的字母。 这意味着整个字体无需保存到在可寻址闪存或RAM上，而是只需保存在更大的文件系统上。
字体文件阅读器
FileDataReader.hpp#ifndef FILEDATAREADER_HPP
#define FILEDATAREADER_HPP
#include <fonts/FontCache.hpp>
#include <stdio.h>using namespace touchgfx;class FileDataReader : public FontDataReader
{
public:virtual ~FileDataReader() { }virtual void open(){fp = fopen("generated/fonts/bin/Font_verdana_20_4bpp.bin", "rb");}virtual void close(){fclose(fp);}virtual void setPosition(uint32_t position){fseek(fp, position, SEEK_SET);}virtual void readData(void* out, uint32_t numberOfBytes){fread(out, numberOfBytes, 1, fp);}
private:FILE* fp;
};#endif // FRONTENDAPPLICATION_HPP
创建FontCache、存储缓冲区和文件系统阅读器对象，然后安装CachedFont：
#include <gui/common/FrontendApplication.hpp>
#include <BitmapDatabase.hpp>
#include <texts/TextKeysAndLanguages.hpp>
#include <texts/TypedTextDatabase.hpp>
#include <gui/common/FileDataReader.hpp>
#include <fonts/CachedFont.hpp>
#include <fonts/FontCache.hpp>uint8_t fontdata[5120];
FileDataReader reader;
FontCache fontCache;
CachedFont cachedFont; //Cached Font objectLOCATION_PRAGMA_NOLOAD("TouchGFX_Cache")
uint16_t Cache[1024 * 604] LOCATION_ATTRIBUTE_NOLOAD("TouchGFX_Cache");FrontendApplication::FrontendApplication(Model& m, FrontendHeap& heap): FrontendApplicationBase(m, heap)
{
#ifdef SIMULATORconst uint32_t cacheSize = 0x300000; //3 MB, as exampleuint16_t* const cacheStartAddr = (uint16_t*)malloc(cacheSize);Bitmap::setCache(cacheStartAddr, cacheSize, 4);
#elseBitmap::setCache(Cache, sizeof(Cache));
#endif//setup the font cache with buffer and size; and file reader objectfontCache.setMemory(fontdata, sizeof(fontdata));fontCache.setReader(&reader);TypedText text = TypedText(T___SINGLEUSE_2OJQ);fontCache.initializeCachedFont(text, &cachedFont);//replace the linked in font in TouchGFX with cachedFontTypedTextDatabase::setFont(Typography::DEFAULT, &cachedFont);Unicode::UnicodeChar* str = const_cast<Unicode::UnicodeChar*>(text.getText());fontCache.cacheString(text, str);
}
运行模拟器
