opengl 开发笔记-绘制图形（图元）

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