NeHe 系列教程之十四：2D纹理字体

英文教程地址：lesson17

本课展示2D纹理生成字体。

首先是字体库的建立及相关字符输出函数：

namespace {GLuint  texture[2];                             // Storage For Our Font TextureGLuint  loop;                                   // Generic Loop VariableGLfloat cnt1;                                   // 1st Counter Used To Move Text & For ColoringGLfloat cnt2;                                   // 2nd Counter Used To Move Text & For Coloringstruct FyjBitmapChar{QVector<QVector2D> texCoords;int right; //字符宽度int height;//字符高度int ascillValue;};struct FyjBitmapFont{char *name;int quality;FyjBitmapChar *characters;};static FyjBitmapChar chars1[128];static FyjBitmapChar chars2[128];const FyjBitmapFont font1 = {"standard", 128, chars1};const FyjBitmapFont font2 = {"Itatic", 128, chars2};void buildFont(){float   cx;                      // Holds Our X Character Coordfloat   cy;                     // Holds Our Y Character CoordglBindTexture(GL_TEXTURE_2D, texture[0]);for (loop = 0; loop < 256; loop++) {cx = float(loop%16)/16.0f; //当前字符的x纹理坐标cy = float(loop/16)/16.0f; //当前字符的y纹理坐标if (loop < 128) {chars1[loop].texCoords<<QVector2D(cx, cy + 0.0625f)<<QVector2D(cx+0.0625f, cy+0.0625f)<<QVector2D(cx+0.0625f, cy)<<QVector2D(cx, cy);chars1[loop].height = 16;chars1[loop].right = 10;chars1[loop].ascillValue = loop+32;} else {chars2[loop-128].texCoords<<QVector2D(cx, cy + 0.0625f)<<QVector2D(cx+0.0625f, cy+0.0625f)<<QVector2D(cx+0.0625f, cy)<<QVector2D(cx, cy);chars2[loop-128].height = 12;chars2[loop-128].right = 10;chars2[loop-128].ascillValue = loop-128+32;}}}void renderBitmapCharacter(FyjBitmapChar c, int fontSize){Q_ASSERT_X(c.ascillValue >= 32 && c.ascillValue <= 127,"renderBitmapCharacter", "unspported char");glEnableClientState(GL_VERTEX_ARRAY);glEnableClientState(GL_TEXTURE_COORD_ARRAY);QVector<QVector2D> vertices;vertices<<QVector2D(0, 0)<<QVector2D(fontSize, 0)<<QVector2D(fontSize, fontSize)<<QVector2D(0, fontSize);glVertexPointer(2, GL_FLOAT, 0, vertices.constData());glTexCoordPointer(2, GL_FLOAT, 0, c.texCoords.constData());glDrawArrays(GL_QUADS, 0, 4);glDisableClientState(GL_VERTEX_ARRAY);glDisableClientState(GL_TEXTURE_COORD_ARRAY);}void renderBitmapString(GLint x, GLint y, QString string, int set, int fontSize){int numOfReturnChar = 0;if (string.isNull() || string.isEmpty())return;if (set > 1)set = 1;FyjBitmapFont currentFont;if (set == 0)currentFont = font1;elsecurrentFont = font2;glBindTexture(GL_TEXTURE_2D, texture[0]);glDisable(GL_DEPTH_TEST);glMatrixMode(GL_PROJECTION);glPushMatrix();glLoadIdentity();glOrtho(0,640,0,480,-1,1);glMatrixMode(GL_MODELVIEW);glPushMatrix();glLoadIdentity();glTranslated(x, y, 0);for(int i = 0; i < string.length(); i++) {char c = string.at(i).toAscii();if (c == '\n') {numOfReturnChar++;glLoadIdentity();glTranslated(x, y - numOfReturnChar * currentFont.characters[0].height, 0);continue;}renderBitmapCharacter(currentFont.characters[c-32], fontSize);glTranslated(currentFont.characters[c-32].right * fontSize/16, 0, 0);}glMatrixMode(GL_PROJECTION);glPopMatrix();glMatrixMode(GL_MODELVIEW);glPopMatrix();glEnable(GL_DEPTH_TEST);}void glPrint(GLint x, GLint y, int set, int fontSize, const char *fmt, ...){char   text[256];              // Holds Our Stringva_list     ap;                 // Pointer To List Of Argumentsif (fmt == NULL)                    // If There's No Textreturn;                     // Do Nothingva_start(ap, fmt);                  // Parses The String For Variablesvsprintf(text, fmt, ap);                // And Converts Symbols To Actual Numbersva_end(ap);                     // Results Are Stored In TextrenderBitmapString(x, y, QString(text), set, fontSize);}void drawTextureMappedQuad(){QVector<QVector2D> vertices;QVector<QVector2D> texCoords;glEnableClientState(GL_VERTEX_ARRAY);glEnableClientState(GL_TEXTURE_COORD_ARRAY);vertices<<QVector2D(-1.0f, 1.0f)<<QVector2D(1.0f, 1.0f)<<QVector2D(1.0f,-1.0f)<<QVector2D(-1.0f,-1.0f);texCoords<<QVector2D(0.0f,0.0f)<<QVector2D(1.0f,0.0f)<<QVector2D(1.0f,1.0f)<<QVector2D(0.0f,1.0f);glTexCoordPointer(2, GL_FLOAT, 0, texCoords.constData());glVertexPointer(2, GL_FLOAT, 0, vertices.constData());glDrawArrays(GL_QUADS, 0, 4);glDisableClientState(GL_VERTEX_ARRAY);glDisableClientState(GL_TEXTURE_COORD_ARRAY);}}

接着是字体纹理加载：

void MyGLWidget::loadTextures()
{texture[0] = bindTexture(QString(":/Font.bmp"),GL_TEXTURE_2D,GL_RGBA,QGLContext::LinearFilteringBindOption);// Create Nearest Filtered TextureglBindTexture(GL_TEXTURE_2D, texture[0]);texture[1] = bindTexture(QString(":/Bumps.bmp"),GL_TEXTURE_2D,GL_RGBA,QGLContext::LinearFilteringBindOption);// Create Linear Filtered TextureglBindTexture(GL_TEXTURE_2D, texture[1]);
}

初始化：

void MyGLWidget::initializeGL()
{loadTextures();glEnable(GL_TEXTURE_2D);buildFont();glBlendFunc(GL_SRC_ALPHA,GL_ONE);glShadeModel(GL_SMOOTH);   // Enables Smooth ShadingglClearColor(0.0f, 0.0f, 0.0f, 0.0f);  // Black BackgroundglClearDepth(1.0f);             // Depth Buffer SetupglEnable(GL_DEPTH_TEST);        // Enables Depth TestingglDepthFunc(GL_LEQUAL);        // The Type Of Depth Test To DoglHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST); // Really Nice Perspective Calculations
}

绘制：

void MyGLWidget::paintGL()
{glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);  // Clear The Screen And The Depth BufferglLoadIdentity();       // Reset The Current Modelview MatrixglBindTexture(GL_TEXTURE_2D, texture[1]);glTranslatef(0.0f,0.0f,-5.0f);glRotatef(45.0f,0.0f,0.0f,1.0f);glRotatef(cnt1*30.0f,1.0f,1.0f,0.0f);glDisable(GL_BLEND);glColor3f(1.0f,1.0f,1.0f);drawTextureMappedQuad();glRotatef(90.0f,1.0f,1.0f,0.0f);drawTextureMappedQuad();glEnable(GL_BLEND);glLoadIdentity();glColor3f(1.0f*float(cos(cnt1)),1.0f*float(sin(cnt2)),1.0f-0.5f*float(cos(cnt1+cnt2)));glPrint(int((280+250*cos(cnt1))),int(235+200*sin(cnt2)),0, 16, "NeHe");glColor3f(1.0f*float(sin(cnt2)),1.0f-0.5f*float(cos(cnt1+cnt2)),1.0f*float(cos(cnt1)));glPrint(int((280+230*cos(cnt2))),int(235+200*sin(cnt1)), 1, 24, "OpenGL");glColor3f(0.0f,0.0f,1.0f);glPrint(int(240+200*cos((cnt2+cnt1)/5)),2, 0, 16, "Giuseppe D'Agata");glColor3f(1.0f,1.0f,1.0f);glPrint(int(242+200*cos((cnt2+cnt1)/5)),2, 0, 16, "Giuseppe D'Agata");cnt1+=0.01f;cnt2+=0.0081f;
}

运行效果图：