Freetype和OpenGL的问题

Question

嘿,我在装载Freetype 2库的openGL中绘制文本时遇到了一个奇怪的问题.这是我所看到的截图.

例如http://img203.imageshack.us/img203/3316/freetypeweird.png

这是我的代码位,用于加载和呈现我的文本.

class Font
{
    Font(const String& filename)
    {
       if (FT_New_Face(Font::ftLibrary, "arial.ttf", 0, &mFace)) {
          cout << "UH OH!" << endl;
       }

       FT_Set_Char_Size(mFace, 16 * 64, 16 * 64, 72, 72);
    }

    Glyph* GetGlyph(const unsigned char ch)
    {
       if(FT_Load_Char(mFace, ch, FT_LOAD_RENDER))
          cout << "OUCH" << endl;

       FT_Glyph glyph;

       if(FT_Get_Glyph( mFace->glyph, &glyph ))
          cout << "OUCH" << endl;

       FT_BitmapGlyph bitmap_glyph = (FT_BitmapGlyph)glyph;

       Glyph* thisGlyph = new Glyph;
       thisGlyph->buffer = bitmap_glyph->bitmap.buffer;
       thisGlyph->width = bitmap_glyph->bitmap.width;
       thisGlyph->height = bitmap_glyph->bitmap.rows;

       return thisGlyph;
    }
};

相关的字形信息(宽度,高度,缓冲区)存储在以下结构中

struct Glyph {
   GLubyte* buffer;
   Uint width;
   Uint height;
};

最后,为了渲染它,我有一个名为RenderFont的类.

class RenderFont 
{
   RenderFont(Font* font)
   {
      mTextureIds = new GLuint[128];

      mFirstDisplayListId=glGenLists(128);
      glGenTextures( 128, mTextureIds );

      for(unsigned char i=0;i<128;i++)
      {
         MakeDisplayList(font, i);
      }
   }

   void MakeDisplayList(Font* font, unsigned char ch)
   {
      Glyph* glyph = font->GetGlyph(ch);

      glBindTexture( GL_TEXTURE_2D, mTextureIds[ch]);
      glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
      glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);

      glTexImage2D(GL_TEXTURE_2D, 
                   0, 
                   GL_RGBA, 
                   glyph->width, 
                   glyph->height, 
                   0,
                   GL_ALPHA, 
                   GL_UNSIGNED_BYTE, 
                   glyph->buffer);

      glNewList(mFirstDisplayListId+ch,GL_COMPILE);
      glBindTexture(GL_TEXTURE_2D, mTextureIds[ch]);

      glBegin(GL_QUADS);
      glTexCoord2d(0,1); glVertex2f(0,glyph->height);
      glTexCoord2d(0,0); glVertex2f(0,0);
      glTexCoord2d(1,0); glVertex2f(glyph->width,0);
      glTexCoord2d(1,1); glVertex2f(glyph->width,glyph->height);
      glEnd();

      glTranslatef(16, 0, 0);

      glEndList();
   }

   void Draw(const String& text, Uint size, const TransformComponent* transform, const Color32* color)
   {
      glEnable(GL_TEXTURE_2D);
      glEnable(GL_BLEND);
      glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

      glTranslatef(100, 250, 0.0f);

      glListBase(mFirstDisplayListId);

      glCallLists(text.length(), GL_UNSIGNED_BYTE, text.c_str());

      glDisable(GL_TEXTURE_2D);
      glDisable(GL_BLEND);

      glLoadIdentity();
   }

private:
   GLuint mFirstDisplayListId;
   GLuint* mTextureIds;
};

任何人都可以看到任何奇怪的事情会导致乱码吗？这很奇怪,因为如果我改变字体大小或DPI,那么正确显示的一些字母会变成乱码,而其他字母在出现之前会出现乱码.

Answer 1

我不熟悉FreeType,但是从图片中看,字符的宽度看起来与缓冲区的大小没有直接关系(即.glyph-> buffer不指向字形数组 - > width*glyth-> height bytes).

作为一个猜测,我会说所有的字符在内存中都有一个宽度(与它们在屏幕上使用的大小相反),可能是字形宽度的最大值,但是你用per-char加载它们宽度而不是正确的宽度.因此,只有使用全宽的字形才是正确的.