opengl 开发笔记-绘制图形（图元）_polygon2f 2f什么意思-优快云博客

本文介绍了使用OpenGL绘制三角形、矩形和多边形的基本方法，并详细解释了如何调整窗口坐标系以匹配OpenGL内部坐标系统。通过定义顶点和颜色数据，实现了图形在不同坐标系下的正确显示。

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定义数据类型

typedef struct{
    GLfloat x;  // x 坐标 
    GLfloat y;  // y 坐标
} Vertex2F;

typedef struct{
    GLfloat r;  // red (0~1) 
    GLfloat g;  // green
    GLfloat b;  // blue
    GLfloat a;  // alpha
} Color4F;

定义顶端数据

static Color4F red_color = {1.0f,0.0f,0.0f,1.0f};
static Color4F green_color = {0.0f,1.0f,0.0f,1.0f};
static Color4F blue_color = {0.0f,0.0f,1.0f,1.0f};

static Vertex2F trangle_vertexes [3] =
{
    {10,10},{100,10},{100,100}
};

static Vertex2F rect_vertexes [4] =
{
    {20,200},{200,200},
    {20,300},{200,300}
};

static Vertex2F polygon_vertexes [6] =
{
    {350,50},{450,120},
    {450,220},{350,300},
    {250,220},{250,120},
};

绘制三角形

void draw_trangle(){
    glEnableClientState(GL_VERTEX_ARRAY);

    glColor4f(red_color.r,red_color.g,red_color.b,red_color.a);
    glVertexPointer(sizeof(Vertex2F)/sizeof(GLfloat),GL_FLOAT,0,trangle_vertexes);

    glDrawArrays(GL_TRIANGLE_STRIP,0,3);
}

绘制矩形

void draw_rect(){
    glEnableClientState(GL_VERTEX_ARRAY);

    glColor4f(green_color.r,green_color.g,green_color.b,green_color.a);
    glVertexPointer(sizeof(Vertex2F)/sizeof(GLfloat),GL_FLOAT,0,rect_vertexes);

    glDrawArrays(GL_TRIANGLE_STRIP,0,4);
}

绘制任意多边形

void draw_polygon(){
    glEnableClientState(GL_VERTEX_ARRAY);

    glColor4f(blue_color.r,blue_color.g,blue_color.b,blue_color.a);
    glVertexPointer(sizeof(Vertex2F)/sizeof(GLfloat),GL_FLOAT,0,polygon_vertexes);

    glDrawArrays(GL_TRIANGLE_FAN,0,6);
}

统一坐标系（默认opengl的尺寸是整个窗口是坐标是x=0.5,y=0.5,width=1.0,height=1.0),经过下面的处理可以让窗口的大小和opengl里面的大小一致

void reshape(int width,int height){
    glViewport(0, 0, width, height);

    const float& fovy = 60;
    const float& zeye = height /(tan(fovy*M_PI_2/180)*2);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(fovy, (GLfloat) width / height, 0.5f, 150000.0f);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    gluLookAt(width / 2, height / 2, zeye, width / 2, height / 2, 0, 0.0f, 1.0f,0.0f);
}

在display函数中调用

void display(){
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    draw_trangle();
    draw_rect();
    draw_polygon();

    glutSwapBuffers();
    glutPostRedisplay();
}

生成程序

g++ DrawShapes.cpp -lGLEW -lGL -lGLU -lglut -o DrawShapes

运行效果