网格不显示（全黑）

Question

我不想回到昨天的同一个问题，但是在我能够使用该功能打开和关闭网格之前，我首先需要知道我的网格是否真的在工作，我整晚都在做新项目试图显示网格，但它没有显示，屏幕总是黑的，什么也没有。

#include "include\freeglut.h"   // OpenGL toolkit - in the local shared folder
#include <iostream>

//set up some constants
#define X_CENTRE 0.0      /* centre point of square */
#define Y_CENTRE 0.0
#define LENGTH   1.0      /* lengths of sides of square */

GLfloat red = 1.0, green = 1.0, blue = 1.0;
int w;
int h;

/* reshape callback function
executed when window is moved or resized */
void reshape(int width, int height)
{
glViewport(0, 0, width, height);
/* uses orthographic (parallel) projection
use xmin = -1, xmax = 1
ymin = -1, ymax = 1
znear = -1, zfar = 1 - not relevant here (2D) */
glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0);
}


/* display callback function
called whenever contents of window need to be re-displayed */
//this is the all important drawing method - all drawing code goes in here
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT);   /* clear window */
//glColor3f(red, green, blue);        /* white drawing objects */
glColor3f(0.8, 0.8, 0.8);

GLint i;

glEnable(GL_LINE_STIPPLE); //Activates the line-style feature

glLineStipple(1, 0xAAAA);  // Plots a dashed polyline

glBegin(GL_LINES);
for (i = 2; i <= 9; i++)
{
    glVertex3f(i * 0.1 * w, 0.0, 0.0);
    glVertex3f(i * 0.1 * w, 0.9 * h, 0.0);
}

for (i = 1; i <= 9; i++)
{
    glVertex3f(0.1 * w, i * 0.1 * h, 0.0);
    glVertex3f(w, i * 0.1 * h, 0.0);
}
glEnd();
glDisable(GL_LINE_STIPPLE);

glFlush();     /* execute drawing commands in buffer */
}

/* graphics initialisation */
void init(void)
{
glClearColor(0.0, 0.0, 0.0, 0.0);   /* window will be cleared to black */
}

//rename this to main(...) and change example 2 to run this main function
int main(int argc, char** argv)
{
/* window management code ... */
/* initialises GLUT and processes any command line arguments */
glutInit(&argc, argv);
/* use single-buffered window and RGBA colour model */
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
/* window width = 400 pixels, height = 400 pixels */
glutInitWindowSize(400, 400);
/* window upper left corner at (100, 100) */
glutInitWindowPosition(100, 100);
/* creates an OpenGL window with command argument in its title bar */
glutCreateWindow("Example 1");
init();
glutDisplayFunc(display);
glutReshapeFunc(reshape);

glutMainLoop();
return 0;
}

Answer 1

变量w和h没有初始化。通过 1:

初始化变量

int w = 1;
int h = 1;

但是，如果要在windowspace中设置顶点坐标，则必须更改正射投影。投影矩阵定义了相对于投影到视口上的观察者（查看者）的区域（体积）。在正交投影中，该区域（体积）由到观察者位置的 6 个距离（左、右、下、上、近、远）定义。

~~glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0);~~

glOrtho(0.0, (float)w, (float)h, 0.0, -1.0, 1.0);

函数reshape:

void reshape(int width, int height)
{
    glViewport(0, 0, width, height);
    /* uses orthographic (parallel) projection
    use xmin = -1, xmax = 1
    ymin = -1, ymax = 1
    znear = -1, zfar = 1 - not relevant here (2D) */    #
    
    w = width;
    h = height;
    glMatrixMode(GL_PROJECTION);
    glOrtho(0.0, (float)w, (float)h, 0.0, -1.0, 1.0);
    glMatrixMode(GL_MODELVIEW);
}

网格不显示（全黑）

grid not showing (it is all black)

c++

opengl

visual-c++

c++11

opengl-compat