Question

尝试使用glut for openGL 3.0版在两点之间画一条线。这是代码。

#include <GL/glut.h>
#include <stdio.h>
#include <math.h>
#include <iostream>

using namespace std;

void init(void) {

    glClearColor(1.0,1.0,1.0,0.0);
    glMatrixMode(GL_PROJECTION);
    gluOrtho2D(0.0,30.0,0.0,30.0);

}

void setPixel(GLint x, GLint y) {

    glClearColor(1.0,1.0,1.0,0.0);
    glMatrixMode(GL_PROJECTION);
    gluOrtho2D(0.0,30.0,0.0,30.0);

}

float roundValue(float v) {

    return floor(v + 0.5);
}

void lineDDA(int xa, int ya, int xb, int yb) {

    double dx = xb-xa, dy = yb-ya, steps;
    float xInc, yInc, x = xa, y = ya;    
    if (abs(dx) > abs(dy))
        steps = abs(dx);
    else
        steps = abs(dy);
    xInc = dx/(float)steps;
    yInc = dy/(float)steps;
    setPixel(x, y);
    int k;
    for (k = 0; k < steps; ++k) {
        /* code */
        x += xInc;
        y += yInc;
        setPixel(roundValue(x), roundValue(y));
    }
}

void update() {
    glClear(GL_COLOR_BUFFER_BIT);
    glPointSize(5.0f);
    glColor3f(1, 0, 0);  
    lineDDA(1, 1, 8, 7);
    lineDDA(1, 1, 8, 2);
    glFlush();
}

int main(int argc,char **argv){

    glutInit(&argc,argv);
    glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
    glutInitWindowPosition(200,100);
    glutInitWindowSize(640,480);
    glutCreateWindow("Tutorial-1: Q4");
    glLoadIdentity();
    init();
    glutDisplayFunc(update);
    glutMainLoop();
    return 0;
}

但这并没有在窗户上画任何东西。它只是保持白色。有人可以建议一个解决方案？

Answer 1

您的setPixel函数不使用其参数x和y。您没有启用线渲染模式或添加要绘制的顶点。

修复至少包含以下步骤：

在glBegin(GL_LINES);

glPointSize(5.0f);

在glEnd()

glFlush();

将setPixel修改为如下所示：

void setPixel(GLint x, GLint y)
{
    glVertex2f(x, y);
}

OpenGL没有绘制任何东西

1 个答案: