最近有个项目使用到SDL_ttf库来渲染字体,但是遇到一点麻烦。大家在使用TTF_OpenFont()打开字体库之后,却无法更改字体大小,我们总不能关闭重新打开吧,因为那也太耗时了。于是乎决定修改源码,成功之后与大家分享。
1.SDL_ttf.h中添加函数extern DECLSPEC void SDLCALL TTF_SetFontSize(TTF_Font *font,int ptsize);
2.修改SDL_ttf.c
SDL_ttf使用的是freetype来加载字体库,然后再使用freetype获取字体编码绘制字体到SDL_Surface上。最初实验总是不成功,结果大量的实验,原来是没有清除font导致不正确;加上Flush_Cache(font),成功搞定。
void TTF_SetFontSize(TTF_Font *font,int ptsize)
{
FT_Fixed scale;
FT_Error error;
FT_Face face;
face = font->face;
/* Make sure that our font face is scalable (global metrics) */
if ( FT_IS_SCALABLE(face) ) {
/* Set the character size and use default DPI (72) */
error = FT_Set_Char_Size( font->face, 0, ptsize * 64, 0, 0 );
if( error ) {
TTF_SetFTError( "Couldn't set font size", error );
TTF_CloseFont( font );
return ;
}
/* Get the scalable font metrics for this font */
scale = face->size->metrics.y_scale;
font->ascent = FT_CEIL(FT_MulFix(face->ascender, scale));
font->descent = FT_CEIL(FT_MulFix(face->descender, scale));
font->height = font->ascent - font->descent + /* baseline */ 1;
font->lineskip = FT_CEIL(FT_MulFix(face->height, scale));
font->underline_offset = FT_FLOOR(FT_MulFix(face->underline_position, scale));
font->underline_height = FT_FLOOR(FT_MulFix(face->underline_thickness, scale));
} else {
/* Non-scalable font case. ptsize determines which family
* or series of fonts to grab from the non-scalable format.
* It is not the point size of the font.
* */
if ( ptsize >= font->face->num_fixed_sizes )
ptsize = font->face->num_fixed_sizes - 1;
font->font_size_family = ptsize;
error = FT_Set_Pixel_Sizes( face,
face->available_sizes[ptsize].height,
face->available_sizes[ptsize].width );
/* With non-scalale fonts, Freetype2 likes to fill many of the
* font metrics with the value of 0. The size of the
* non-scalable fonts must be determined differently
* or sometimes cannot be determined.
* */
font->ascent = face->available_sizes[ptsize].height;
font->descent = 0;
font->height = face->available_sizes[ptsize].height;
font->lineskip = FT_CEIL(font->ascent);
font->underline_offset = FT_FLOOR(face->underline_position);
font->underline_height = FT_FLOOR(face->underline_thickness);
}
if ( font->underline_height < 1 ) {
font->underline_height = 1;
}
font->glyph_italics *= font->height;
Flush_Cache(font); //这个非常重要
}
项目中使用SDL_ttf库渲染字体时发现无法改变字体大小。为解决此问题,通过修改SDL_ttf源码,添加TTF_SetFontSize函数,实现了在不关闭字体库的情况下动态调整字体大小,有效提高了效率。
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