在OpengGL中多次重复图像

Question

我在OpenGL中画了一个圆。我想要做的是重复展示一部分内容。 例如，不是只显示一个圆圈，而是连续显示四个半圆。 我认为这是可能的有两个for循环和使用glViewport（参数）里面。但是我没有这样做。

我在这里有我的代码，for循环在circle（）函数的开头。 如果有人能帮助我，我将不胜感激。

#include <Windows.h> 
#include <iostream> 
#include <stdio.h> 
#include <math.h> 
#include <stdlib.h> 
#include <GL/glut.h> 
#include <GL/gl.h> 
#include <GL/glu.h> 
#include <fstream> 


using namespace std; 

int pntX1, pntY1, r; 

void myInit() 
{ 
    glClearColor(1.0, 1.0, 1.0, 0.0); 
    glColor3f(0.0f, 0.0f, 0.0f); 
    glPointSize(4.0); 
    glMatrixMode(GL_PROJECTION); 
    glLoadIdentity(); 
    gluOrtho2D(0.0, 101.0, 0.0, 101.0); 
} 

void drawPolyLineFile(char * fileName) 
{ 
    fstream inStream; 
    inStream.open(fileName, ios::in); 
    if (inStream.fail()) 
     return; 
    glClear(GL_COLOR_BUFFER_BIT); 
    GLint numpolys, numlines, x, y; 
    inStream >> numpolys; 

    for (int j = 0; j < numpolys; j++) 
    { 
     inStream >> numlines; 
     glBegin(GL_LINE_STRIP); 
     for (int i = 0; i < numlines; i++) 
     { 
      inStream >> x >> y; 
      glVertex2i(x, y); 
     } 
     glEnd(); 
    } 
    glFlush(); 
    inStream.close(); 
} 

void writePixel(GLint x, GLint y) 
{ 
    glBegin(GL_POINTS); 
    glVertex2i(x + pntX1, y + pntY1); 
    glEnd(); 
} 

void circlePoints(int x, int y) { 
    writePixel(x, y); 
    writePixel(y, x); 
    writePixel(y, -x); 
    writePixel(x, -y); 
    writePixel(-x, -y); 
    writePixel(-y, -x); 
    writePixel(-y, x); 
    writePixel(-x, y); 
} 

void setWindow(GLdouble left, GLdouble right, GLdouble bottom, GLdouble top) { 
    glClearColor(1.0, 1.0, 1.0, 0.0); 
    glColor3f(0.0f, 0.0f, 0.0f); 
    glMatrixMode(GL_PROJECTION); 
    glLoadIdentity(); 
    gluOrtho2D(left, right, bottom, top); 
} 

void setViewPort(GLint left, GLint right, GLint bottom, GLint top) 
{ 
    glViewport(left, bottom, right - left, top - bottom); 
} 
void Circle() { 
    //int x1=100,y1=100,r=50; 
    //int x=0,y=r; 
    //int d = 3/2 - r; 

    //glViewport(50, 50, 50, 50); 
    /* 
    setWindow(0.0, 101.0, 0.0, 101.0); 
    for (int i = 0; i<1; i++) 
     for (int j = 0; j < 1; j++) 
     { 
      //glViewport(i * 50 +, j * 50, 50, 50); 
      glViewport(50, 50, 50, 50); 
      drawPolyLineFile("dino.dat"); 
     } 
    */ 

    //glViewport(0, 0, 0, 0); 

    glClear(GL_COLOR_BUFFER_BIT); 
    glColor3f(1, 0, 0); 

    int x = 0; 
    int r = 50; 
    int y = r; 
    int h = (1 - r); 
    int deltaE = 3; 
    int deltaSE = (-2)*r + 5; 

    circlePoints(x, y); 

    while (y > x) { 

     if (h<0) { 
      h += deltaE; 
      deltaE += 2; 
      deltaSE += 2; 
     } 
     else { 
      h += deltaSE; 
      deltaE += 2; 
      deltaSE += 4; 
      y--; 
     } 
     x++; 
     circlePoints(x, y); 
    } 

} 

void Display() { 
    glClear(GL_COLOR_BUFFER_BIT); 
    glColor3f(0.0, 0.0, 0.0); 
    glPointSize(1.0); 

    Circle(); 

    glFlush(); 
} 


int main(int argc, char *argv[]) 
{ 
    pntX1 = 50; pntY1 = 50; r = 50; 

    glutInit(&argc, argv); 
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); 
    glutInitWindowSize(101, 101.0); 
    glutInitWindowPosition(100, 150); 
    glutCreateWindow("My circles"); 


    //glViewport(0, 0, 100, 100); 

    /* 
    setWindow(0, 500.0, 0, 500.0); 
    for(int i=0; i<2; i++) 
     for(int j=0; j<2; j++) 
     { 
     glViewport(i*250, j*250, 250, 250); 
     //drawPolylineFile("circles.dat"); 
     } 
     */ 


    glutDisplayFunc(Display); 
    myInit(); 

    glutMainLoop(); 
    return 0; 
} 

Answer 1

改变Viewport是不是你所需要的，而不是使用矩阵：

for (i=0;i<N;i++) // N is number of objects you want to render 
{ 
glMatrixMode(GL_MODELVIEW); 
glPushMatrix(); 
glTranslate3(dx[i],dy[i],dz[i]); // dx,dy,dz is offset of object i where you want to draw it 
// render i-th object occurrence 
glPopMatrix(); 
} 

也希望你知道你可以绘制圆，GL_LINE_LOOP和GL_TRIANGLE_FAN元快得多。

不要更改glViewPort，因为它不是你认为的那样！它映射你的屏幕空间，如果你在渲染过程中改变它，那么你将无效深度和任何辅助缓冲区，所以你不能再使用任何先进的东西。

欲了解更多信息，请参阅：

• Understanding 4x4 homogenous transform matrices