为什么数字没有出现在屏幕上？

Question

我的最后一项工作是在已经制成的圆的中心添加一个带有纹理的3D立方体，但是由于某种原因，屏幕只是显示为黑色，没有任何图形或其他任何东西。我知道这可能是我在错误的地方添加的东西或类似的东西，但是我不知道是哪一部分给出了错误。这个问题有什么解释吗？

#include"glut.h"
#include<cmath>
#include<iostream>
using namespace std;

GLfloat angle = 0.0f;
int refreshmill = 1;

float xr = 0, yr = 0; //to control the object's movement from left to right

// XZ position of the camera
float x = 0.0f, z = 5.0f; //Module 4
float angleX = 0.0f; //Module 4

//Shift + ArrowKey rotation
float transX = 0.0f;
float transY = 0.0f;
float rotY = 0.0f;
//end

//Mouse Commands
GLfloat theta3 = 0;
GLfloat phi = 0;
GLfloat rho = 5;

GLfloat camX = 0;
GLfloat camY = 0;
GLfloat camZ = 0;
GLfloat upX = 0;
GLfloat upY = 0;
GLfloat upZ = 0;

GLdouble zoom = 0.0f;
//end

//For cube usage
#define checkImageWidth 64
#define checkImageHeight 64
static GLubyte checkImage[checkImageHeight][checkImageWidth][4];

static GLuint texName;

void timer(int value) { //to control the rotation of the object
    glutTimerFunc(refreshmill, timer, 0);
}

void myDisplay(void) {
    //Circle One
    float theta;
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(1, 0, 0);

    glRotatef(rotY, 0.0, 1.0, 0.0); //Rotation with Shift + ArrowKey

    glPushMatrix();
    glBegin(GL_POLYGON);
    for (int x = 0; x < 360; x++) {
        theta = x * 3.142 / 180;
        glVertex2f(150 * cos(theta) + xr, 150 * sin(theta) + yr);
    }
    glEnd();
    glPopMatrix();

    //Circle Two
    float theta2;

    glPushMatrix();
    glTranslatef(0.5f, 0.0f, 0.0f); // rotation
    glRotatef(angle, 0.0f, 0.0f, -0.5f); // rotation
    glBegin(GL_POLYGON);
    glColor3f(0, 0, 1);
    for (int x = 0; x < 360; x++) {
        theta2 = x * 3.142 / 180;
        glVertex2f(150 + 15 * cos(theta2) + xr, 15 * sin(theta2) + yr);
    }

    angle += 0.2; // rotation
    glEnd();
    glPopMatrix();

    //Draw Star
    glColor3ub(119, 193, 15);

    glPushMatrix();
    glBegin(GL_POLYGON);
    glVertex2d(15 + xr, 60 + yr);
    glVertex2d(75 + xr, 75 + yr); //right peak
    glVertex2d(15 + xr, 90 + yr);
    glVertex2d(0 + xr, 150 + yr); //Up-peak Changed
    glVertex2d(-15 + xr, 90 + yr);
    glVertex2d(-75 + xr, 75 + yr);
    glVertex2d(-15 + xr, 60 + yr);
    glVertex2d(0 + xr, 0 + yr);
    glEnd();
    glPopMatrix();

    //Draw cube
    glPushMatrix();
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glEnable(GL_TEXTURE_2D);
    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL); //DECAL & MODULATE
    glBindTexture(GL_TEXTURE_2D, texName);
    glBegin(GL_QUADS);
    // Front Face
    glColor3f(1.0, 1.0, 0.0); //yellow
    glTexCoord2f(0.0f, 0.0f); glVertex3f(-0.25f, -0.25f, 0.25f);
    glTexCoord2f(1.0f, 0.0f); glVertex3f(0.25f, -0.25f, 0.25f);
    glTexCoord2f(1.0f, 1.0f); glVertex3f(0.25f, 0.25f, 0.25f);
    glTexCoord2f(0.0f, 1.0f); glVertex3f(-0.25f, 0.25f, 0.25f);
    // Back Face
    glColor3f(0.0, 1.0, 1.0); //cyn
    glTexCoord2f(1.0f, 0.0f); glVertex3f(-0.25f, -0.25f, -0.25f);
    glTexCoord2f(1.0f, 1.0f); glVertex3f(-0.25f, 0.25f, -0.25f);
    glTexCoord2f(0.0f, 1.0f); glVertex3f(0.25f, 0.25f, -0.25f);
    glTexCoord2f(0.0f, 0.0f); glVertex3f(0.25f, -0.25f, -0.25f);
    // Top Face
    glColor3f(1.0, 0.0, 1.0); //mag side
    glTexCoord2f(0.0f, 1.0f); glVertex3f(-0.25f, 0.25f, -0.25f);
    glTexCoord2f(0.0f, 0.0f); glVertex3f(-0.25f, 0.25f, 0.25f);
    glTexCoord2f(1.0f, 0.0f); glVertex3f(0.25f, 0.25f, 0.25f);
    glTexCoord2f(1.0f, 1.0f); glVertex3f(0.25f, 0.25f, -0.25f);
    // Bottom Face
    glColor3f(1.0, 0.0, 0.0); //red
    glTexCoord2f(1.0f, 1.0f); glVertex3f(-0.25f, -0.25f, -0.25f);
    glTexCoord2f(0.0f, 1.0f); glVertex3f(0.25f, -0.25f, -0.25f);
    glTexCoord2f(0.0f, 0.0f); glVertex3f(0.25f, -0.25f, 0.25f);
    glTexCoord2f(1.0f, 0.0f); glVertex3f(-0.25f, -0.25f, 0.25f);
    // Right face
    glColor3f(0.0, 0.0, 1.0); //bue
    glTexCoord2f(1.0f, 0.0f); glVertex3f(0.25f, -0.25f, -0.25f);
    glTexCoord2f(1.0f, 1.0f); glVertex3f(0.25f, 0.25f, -0.25f);
    glTexCoord2f(0.0f, 1.0f); glVertex3f(0.25f, 0.25f, 0.25f);
    glTexCoord2f(0.0f, 0.0f); glVertex3f(0.25f, -0.25f, 0.25f);
    // Left Face
    glColor3f(0.0, 1.0, 0.0); //green
    glTexCoord2f(0.0f, 0.0f); glVertex3f(-0.25f, -0.25f, -0.25f);
    glTexCoord2f(1.0f, 0.0f); glVertex3f(-0.25f, -0.25f, 0.25f);
    glTexCoord2f(1.0f, 1.0f); glVertex3f(-0.25f, 0.25f, 0.25f);
    glTexCoord2f(0.0f, 1.0f); glVertex3f(-0.25f, 0.25f, -0.25f);

    glEnd();
    glDisable(GL_TEXTURE_2D);
    glPopMatrix();
}

void makeCheckImage(void){
    int i, j, c;

    for (i = 0; i < checkImageHeight; i++) {
        for (j = 0; j < checkImageWidth; j++) {
            c = ((((i & 0x8) == 0) ^ ((j & 0x8)) == 0)) * 255;
            checkImage[i][j][0] = (GLubyte)c;
            checkImage[i][j][1] = (GLubyte)c;
            checkImage[i][j][2] = (GLubyte)c;
            checkImage[i][j][3] = (GLubyte)255;
        }
    }
}

//Close code
void handleKeypress(unsigned char key, int x, int y) {
    switch (key) {
    case 27: //when the escape key is pressed the program will exit.
        exit(0);
    }
}

//Movement of drawing
void keyboard(int key, int x, int y) {

    float fraction = 0.1f;
    bool shift = false;
    int mod = glutGetModifiers();
    if (mod == GLUT_ACTIVE_SHIFT) {
        shift = true;
    }
    if (!shift) {
        switch (key) {

        case GLUT_KEY_RIGHT: xr++; break;
        case GLUT_KEY_LEFT:  xr--; break;
        case GLUT_KEY_UP:    angleX -= 1.0f; break; //Module 4
        case GLUT_KEY_DOWN:  angleX += 1.0f; break; //Module 4
        }
    }
    else {
        switch (key) {

        case GLUT_KEY_LEFT:// Rotación del dibujo hacia la izquierda en el eje de Y
            rotY -= 1.0f;
            break;
        case GLUT_KEY_RIGHT:// Rotación del dibujo hacia la derecha en el eje de Y
            rotY += 1.0f;
            break;
        }
    }
}

//Mouse Function
void MouseFunc(int button, int state, int x, int y) {

    GLdouble min_z = -100.0;
    GLdouble max_z = 100.0;

    if (button == 4 && zoom < max_z) {
        zoom += 3.0;
    }
    else if (button == 3 && zoom > min_z) {
        zoom -= 3.0;
    }
}

void renderScene(void) {
    // Clear Color and Depth Buffers
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    GLfloat camX = rho * cos(theta3*3.1415926f / 180)*sin(phi*3.1415926f / 180);
    GLfloat camY = rho * sin(theta3*3.1415926f / 180);
    GLfloat camZ = rho * cos(theta3*3.1415926f / 180)*cos(phi*3.1415926f / 180);

    // Reduce theta slightly to obtain another point on the same longitude line on the sphere.
    GLfloat dt = 1;
    GLfloat eyeXtemp = -rho * cos((theta3 - dt)*3.1415926f / 180)*sin(phi*3.1415926f / 180);
    GLfloat eyeYtemp = -rho * sin((theta3 - dt)*3.1415926f / 180);
    GLfloat eyeZtemp = -rho * cos((theta3 - dt)*3.1415926f / 180)*cos(phi*3.1415926f / 180);

    // Connect these two points to obtain the camera's up vector.
    GLfloat upX = eyeXtemp - camX;
    GLfloat upY = eyeYtemp - camY;
    GLfloat upZ = eyeZtemp - camZ;

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    //Mouse Commands
    GLdouble ortho = 250 + zoom; //Mouse wheel zoom
    glOrtho(-ortho, ortho, -ortho, ortho, -250, 250); //Mouse wheel zoom

    // Reset transformations
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt(camX, camY, camZ, 0, 0, 0, upX, upY, upZ);

    // Set the camera
    gluLookAt(x, 0.0f, z, x, 0.0f, z - 1.0f, 0.0f, 1.0f, 0.0f); //Module 4
    glRotatef(angleX, 1, 0, 0); //Module 4

    myDisplay();
    //DrawCube(0.0f, 0.0f, 0.85);

    glFlush();
    glutPostRedisplay();
    glutSwapBuffers();
}

void init() {
    glClearColor(0, 0, 0, 1);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(0.0f, 0.1f, 0.1f, 100.0f);
    glOrtho(-250, 250, -250, 250, -250, 250); //IMPORTANT- Define from negative to positive
    glMatrixMode(GL_MODELVIEW);

    //CUBE COMMANDS
    glClearColor(0.0, 0.0, 0.0, 0.0);
    glShadeModel(GL_FLAT);
    glEnable(GL_DEPTH_TEST);

    makeCheckImage();
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

    glGenTextures(1, &texName);
    glBindTexture(GL_TEXTURE_2D, texName);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,
        GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
        GL_NEAREST);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, checkImageWidth,
        checkImageHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE,
        checkImage);
}

int main(int argc, char** argv) {
    // init GLUT and create window
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(500, 500);
    glutInitWindowPosition(0, 0);
    glutCreateWindow("Homework: Circle");
    // register callbacks
    glutDisplayFunc(renderScene);
    glutTimerFunc(0, timer, 0);
    glutKeyboardFunc(handleKeypress);
    glutSpecialFunc(keyboard);
    glutMouseFunc(MouseFunc);
    // OpenGL init
    init();
    // enter GLUT event processing cycle
    glutMainLoop();
}

Answer 1

在绘制带有纹理的网格之前，第二次清除视口。

具有纹理的网格的顶点坐标在[0，1]范围内，但是在大小为500x500的视口上，正射投影在[-250，250]范围内。因此网格的大小为1像素。

使用glScale增加带有纹理的网格的大小：

例如

glPushMatrix();

// rotate the model (this is optional)
glRotatef(45, 0, 1, 0);
glRotatef(45, 1, 0, 0);

// scale the model
glScalef(200.0f, 200.0f, 200.0f);

//glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // <--- delete

glEnable(GL_TEXTURE_2D);
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL); //DECAL & MODULATE
glBindTexture(GL_TEXTURE_2D, texName);
glBegin(GL_QUADS);

// [...]

glEnd();
glDisable(GL_TEXTURE_2D);

请注意，Depth Test已启用（glEnable(GL_DEPTH_TEST);），因此几何的某些部分不可见，因为它被其他几何覆盖。