OpenGL 基础图形绘制与投影变换

本文参考《Computer Graphics Using OpenGL》,第一个例子绘制了

1. 参数定义的House

2. a flurry of filled rectangles

3. Sierpinski曲线

含有鼠标和键盘响应函数onmouse和onkeyboard。

[cpp] view
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/************************************************************************/

/* CreateTime:2013-2-18

**Author:@Rachel Zhang

**Discription: Draw Parameter House, Flurry and Sierpinski

**3rd-party:OpenGL*/

/************************************************************************/

#include "GL/glut.h"

#include "stdlib.h"

#include <iostream>

using namespace std;

#define screenHeight 480

class GLintPoint{

public:

GLint x, y;

};

// Create a number between 0 and m(a number which will be given)

// the input m must be less than 32767 according to P49 in <Computer Graphics Using OpenGL>

int random(int m)

{

return rand()%m;

}

void drawDot (GLint x, GLint y)

{

glPointSize(3);

glBegin(GL_POINTS);

glVertex2i(x,y);

glEnd();

}

typedef struct

{

GLfloat r, g, b;

} GLfloatRGBColour;

GLfloatRGBColour colour[8] = { {0.0f, 0.0f, 0.0f}, {0.0f, 0.0f, 1.0f},

{0.0f, 1.0f, 0.0f}, {1.0f, 0.0f, 0.0f},

{0.0f, 1.0f, 1.0f}, {1.0f, 0.0f, 1.0f},

{1.0f, 1.0f, 0.0f}, {1.0f, 1.0f, 1.0f}};

void setPenColour(GLfloatRGBColour newColour)

{

glColor3f(newColour.r, newColour.g, newColour.b);

}

/************************************************************************/

/* Draw Functions */

/************************************************************************/

void parameterizedHouse(GLintPoint peak, GLint width, GLint height)

// the top of house is at the peak; the size of house is given

// by height and width

{

glBegin(GL_LINE_LOOP);

glVertex2i(peak.x, peak.y); // draw shell of house

glVertex2i(peak.x + width / 2, peak.y - 3 * height /8);

glVertex2i(peak.x + width / 2, peak.y - height);

glVertex2i(peak.x - width / 2, peak.y - height);

glVertex2i(peak.x - width / 2, peak.y - 3 * height /8);

glEnd();

}

void drawFlurry(int num, int Width, int Height)

// draw num random rectangles in a Width by Height rectangle

{

for (int i = 0; i < num; i++)

{

GLint x1 = random(Width); // place corner randomly

GLint y1 = random(Height);

GLint x2 = random(Width); // pick the size so it fits

GLint y2 = random(Height);

GLfloat lev = random(10)/10.0; // random value, in range 0 to 1

glColor3f(lev,lev,lev); // set the gray level

glRecti(x1, y1, x2, y2); // draw the rectangle

}

glFlush();

}

void drawSierpinski(GLintPoint corner[3])

{

int i, index, tcolour=0;

GLintPoint point;

point = corner[random(3)];

drawDot(point.x, point.y);

for (i = 0; i < 1000; i++)

{

index = random(3);

point.x = (point.x + corner[index].x)/2;

point.y = (point.y + corner[index].y)/2;

tcolour = (++tcolour)%7; // col = (col + 1) mod 7;

setPenColour(colour[tcolour]);

drawDot(point.x, point.y);

}

}

/************************************************************************/

/* Mouse Listener and keyboard Listener */

/************************************************************************/

void myMouse(int button, int state, int x, int y)

{

static GLintPoint corners[3];

static int numCorners;

if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN)

{

corners[numCorners].x = x;

corners[numCorners].y = screenHeight - y - 1;

if (++numCorners == 3)

{

drawSierpinski(corners);

numCorners = 0;

}

}

else if (button==GLUT_RIGHT_BUTTON)

glClear(GL_COLOR_BUFFER_BIT);

glFlush();

}

void onKeyBoard(unsigned char key,int mousex, int mousey)

{

switch (key)

{

case 'q':

exit(0);

case 'r':

static GLintPoint corners[3];

for (int i=0;i<3;i++)

{

corners[i].x = random(640);

corners[i].y = random(screenHeight);

}

drawSierpinski(corners);

default:

break;

}

}

// Initialization

void Init(void)

{

glClearColor(1.0,1.0,1.0,0.0); // Set white background color

glColor3f(0.0f,0.0f,0.0f); // Set the drawing color

glMatrixMode(GL_PROJECTION);

glLoadIdentity();

gluOrtho2D(0.0,640.0,0.0,480.0);

}

void myDisplay()

{

glClear(GL_COLOR_BUFFER_BIT); //clear the screen

GLintPoint Mypoint = {200,100};

parameterizedHouse(Mypoint,100,100);

drawFlurry(4,100,100);

glFlush();

}

void main(int argc,char *argv[])

{

glutInit(&argc, argv); // Initialize the toolkit

glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE); // Set display mode

glutInitWindowPosition(100, 150); // Set window pozition on screen

glutInitWindowSize(640, 480); // Set window size

glutCreateWindow("parameterizedHouse, Flurry and drawSierpinski"); // Open the screen window

glutDisplayFunc(myDisplay); // Register redraw function

glutMouseFunc(myMouse);

glutKeyboardFunc(onKeyBoard);

Init();

glutMainLoop(); // Go into a perpetual loop

}

效果图：



第二个例子绘制了这样一系列图形：



在其中有空间投影变换，主要应用了三个函数：

投影变换函数glViewport(), 矩阵平移函数glTranslated() 和正射投影函数 glOrtho()

上图实现代码参考《计算机图形学-用OpenGL实现第2版》：

[cpp] view
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#include <windows.h> //suitable when using Windows 95/98/NT

#include <gl/Gl.h>

#include <gl/Glu.h>

#include <gl/glut.h>

//<<<<<<<<<<<<<<<<<<< axis >>>>>>>>>>>>>>

void axis(double length)

{ // draw a z-axis, with cone at end

glPushMatrix();

glBegin(GL_LINES);

glVertex3d(0, 0, 0); glVertex3d(0,0,length); // along the z-axis

glEnd();

glTranslated(0, 0,length -0.2);

glutWireCone(0.04, 0.2, 12, 9);

glPopMatrix();

}

//<<<<<<<<<<<<<<<<<<<<<<<<<<<<< displayWire >>>>>>>>>>>>>>>>>>>>>>

void displayWire(void)

{

glMatrixMode(GL_PROJECTION); // set the view volume shape

glLoadIdentity();

glOrtho(-2.0*64/48.0, 2.0*64/48.0, -2.0, 2.0, 0.1, 100);//正射投影函数

glMatrixMode(GL_MODELVIEW); // position and aim the camera

glLoadIdentity();

gluLookAt(2.0, 2.0, 2.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);//define viewpoint transformation

//Draw axis

glClear(GL_COLOR_BUFFER_BIT); // clear the screen

glColor3d(0,0,0); // draw black lines

axis(0.5); // z-axis

glPushMatrix();

glRotated(90, 0,1.0, 0);

axis(0.5); // y-axis

glRotated(-90.0, 1, 0, 0);

axis(0.5); // z-axis

glPopMatrix();

//Draw Cube

glPushMatrix();

glTranslated(0.5, 0.5, 0.5); // multiply by a translation matrix, define center (0.5, 0.5, 0.5)

glutWireCube(1.0);

glPopMatrix();

//Draw Sphere

glPushMatrix();

glTranslated(1.0,1.0,0); // sphere at (1,1,0)

glutWireSphere(0.25, 10, 8);

glPopMatrix();

//Draw Cone

glPushMatrix();

glTranslated(1.0,0,1.0); // cone at (1,0,1)

glutWireCone(0.2, 0.5, 10, 8);

glPopMatrix();

//Draw Teapot

glPushMatrix();

glTranslated(1,1,1);

glutWireTeapot(0.2); // teapot at (1,1,1)

glPopMatrix();

//Draw Torus

glPushMatrix();

glTranslated(0, 1.0 ,0); // torus at (0,1,0)

glRotated(90.0, 1,0,0);

glutWireTorus(0.1, 0.3, 10,10);

glPopMatrix();

//十二面体

glPushMatrix();

glTranslated(1.0, 0 ,0); // dodecahedron at (1,0,0)

glScaled(0.15, 0.15, 0.15);

glutWireDodecahedron();

glPopMatrix();

glPushMatrix();

glTranslated(0, 1.0 ,1.0); // small cube at (0,1,1)

glutWireCube(0.25);

glPopMatrix();

glPushMatrix();

glTranslated(0, 0 ,1.0); // cylinder at (0,0,1)

GLUquadricObj * qobj;

qobj = gluNewQuadric();

gluQuadricDrawStyle(qobj,GLU_LINE);

gluCylinder(qobj, 0.2, 0.2, 0.4, 8,8);

glPopMatrix();

glFlush();

}

//<<<<<<<<<<<<<<<<<<<<<< main >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

void main(int argc, char **argv)

{

glutInit(&argc, argv);

glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB );

glutInitWindowSize(640,480);

glutInitWindowPosition(100, 100);

glutCreateWindow("Transformation testbed - wireframes");

glutDisplayFunc(displayWire);

glClearColor(1.0f, 1.0f, 1.0f,0.0f); // background is white

glViewport(0, 0, 640, 480);//投影变换函数

glutMainLoop();

}

Reference:
http://www.oocities.org/uniq_friq/c_files/openGL/1lab/dots.htm
from: http://blog.csdn.net/abcjennifer/article/details/8587466