TouchGFX之字体缓存

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

cpp 复制代码

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：

cpp 复制代码

#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 object
		
LOCATION_PRAGMA_NOLOAD("TouchGFX_Cache")
uint16_t Cache[1024 * 604] LOCATION_ATTRIBUTE_NOLOAD("TouchGFX_Cache");

FrontendApplication::FrontendApplication(Model& m, FrontendHeap& heap)
    : FrontendApplicationBase(m, heap)
{
#ifdef SIMULATOR
    const uint32_t cacheSize = 0x300000; //3 MB, as example
    uint16_t* const cacheStartAddr = (uint16_t*)malloc(cacheSize);
    Bitmap::setCache(cacheStartAddr, cacheSize, 4);
#else
    Bitmap::setCache(Cache, sizeof(Cache));
#endif
	
	//setup the font cache with buffer and size; and file reader object
	fontCache.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 cachedFont
	TypedTextDatabase::setFont(Typography::DEFAULT, &cachedFont);
	
	Unicode::UnicodeChar* str = const_cast<Unicode::UnicodeChar*>(text.getText());
	fontCache.cacheString(text, str);
}

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