学步园

前面已经介绍了显示人物名称的基本框架，但是使用OpenGL显示这个名称出来是需要很复杂的步骤。由于OpenGL是图形引擎显示，也就是说所有字符的显示都是基于图形来显示，而图形的显示，就需要获取字体的图片，即是获取字体的字模。由于不能使用Windows的标准GDI来显示，那么就需要实现GDI所做的所有功能，比如从字体里读取每个字符的轮廓，然后生成合适大小的位图，再把这幅位图当作纹理贴到3D的平面上去，这样才可以在OpenGL显示字符串出来。在第二人生里的代码流程如下：

1、LLFontGL::addChar()    添加一个字符纹理图片

2、mImageGLp->bind()       绑定纹理图片。

3、LLImageGL::bindTextureInternal()      真正绑定纹理图片，在这个函数里调用glBindTexture函数来绑定纹理。

4、LLFontGL::render()            这个函数显示所有字符串。

仔细地分析一下这个函数，看看怎么样显示字符串的，如下：

#001 S32 LLFontGL::render(const LLWString &wstr,

#002                                   const S32 begin_offset,

#003                                   const F32 x, const F32 y,

#004                                   const LLColor4 &color,

#005                                   const HAlign halign, const VAlign valign,

#006                                   U8 style,

#007                                   const S32 max_chars, S32 max_pixels,

#008                                   F32* right_x,

#009                                   BOOL use_embedded,

#010                                   BOOL use_ellipses) const

#011 {

#012      LLGLEnable texture_2d(GL_TEXTURE_2D);

#013     

 

下面绑定纹理图片。

#089 

#090      // Bind the font texture

#091     

#092      mImageGLp->bind(0);

#093     

#094      glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); // Not guaranteed to be set correctly

#095     

 

下面开始循环地显示字符串。

#160 

#161      for (i = begin_offset; i < begin_offset + length; i++)

#162      {

#163             llwchar wch = wstr[i];

#164 

#165             // Handle embedded characters first, if they're enabled.

#166             // Embedded characters are a hack for notecards

#167             const embedded_data_t* ext_data = use_embedded ? getEmbeddedCharData(wch) : NULL;

#168             if (ext_data)

#169             {

……

 

#224                    // Bind the font texture

#225                    mImageGLp->bind();

#226             }

#227             else

#228             {

#229                    if (!hasGlyph(wch))

#230                    {

#231                           (const_cast<LLFontGL*>(this))->addChar(wch);

#232                    }

#233 

#234                    const LLFontGlyphInfo* fgi= getGlyphInfo(wch);

#235                    if (!fgi)

#236                    {

#237                           llerrs << "Missing Glyph Info" << llendl;

#238                           break;

#239                    }

#240                    if ((start_x + scaled_max_pixels) < (cur_x + fgi->mXBearing + fgi->mWidth))

#241                    {

#242                           // Not enough room for this character.

#243                           break;

#244                    }

#245 

#246                    // Draw the text at the appropriate location

#247                    //Specify vertices and texture coordinates

#248                    LLRectf uv_rect((fgi->mXBitmapOffset - PAD_AMT) * inv_width,

#249                                                (fgi->mYBitmapOffset + fgi->mHeight + PAD_AMT) * inv_height,

#250                                                (fgi->mXBitmapOffset + fgi->mWidth + PAD_AMT) * inv_width,

#251                                                (fgi->mYBitmapOffset - PAD_AMT) * inv_height);

#252                    LLRectf screen_rect(cur_render_x + (F32)fgi->mXBearing - PAD_AMT,

#253                                                       cur_render_y + (F32)fgi->mYBearing + PAD_AMT,

#254                                                       cur_render_x + (F32)fgi->mXBearing + (F32)fgi-

#255 >mWidth + PAD_AMT,

#256                                                       cur_render_y + (F32)fgi->mYBearing - (F32)fgi-

#257 >mHeight - PAD_AMT);

#258 

 

这里设置每个字符的纹理坐标以及顶点坐标。

#259                    drawGlyph(screen_rect, uv_rect, color, style, drop_shadow_strength);

#260 

#261                    chars_drawn++;

#262                    cur_x += fgi->mXAdvance;

#263                    cur_y += fgi->mYAdvance;

#264 

#265                    llwchar next_char = wstr[i+1];

#266                    if (next_char && (next_char < LAST_CHARACTER))

#267                    {

#268                           // Kern this puppy.

#269                           if (!hasGlyph(next_char))

#270                           {

#271                                  (const_cast<LLFontGL*>(this))->addChar(next_char);

#272                           }

#273                           cur_x += getXKerning(wch, next_char);

#274                    }

#275 

#276                    // Round after kerning.

#277                    // Must do this to cur_x, not just to cur_render_x, otherwise you

#278                    // will squish sub-pixel kerned characters too close together.

#279                    // For example, "CCCCC" looks bad.

#280                    cur_x = (F32)llfloor(cur_x + 0.5f);

#281                    //cur_y = (F32)llfloor(cur_y + 0.5f);

#282 

#283                    cur_render_x = cur_x;

#284                    cur_render_y = cur_y;

#285             }

#286      }

#287 

……

 

#320             glPopMatrix();

#321      }

#322 

#323      glPopMatrix();

#324 

#325      return chars_drawn;

#326 }

#327