使用OpenGL画两个圆环？

Question

我想创建奥迪标志圈：

但是，我的代码的结果：

#define PI 3.14159265358979323846
#ifdef __APPLE_CC__
#include <GLUT/glut.h>
#else
#include <GL/glut.h>
#endif
#include <cstdlib>
#include <iostream>

float zoom = 1.0f;
void init() {
    // Set the background color to white 
    glClearColor(1.0, 1.0, 1.0, 1.0);
    // Set up the viewport
    glViewport(0, 0, 500, 500);
    // Initialize the projection matrix
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    // Initial zoom setup, centering at the origin
    float range = 5.0 * zoom;
    gluOrtho2D(-range, range, -range, range);

    // Initialize the modelview matrix
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

void drawCircle(GLfloat x, GLfloat y, GLfloat radius, GLint numberOfSides, GLfloat r, GLfloat g, GLfloat b, GLfloat alpha) {
    glColor4f(r, g, b, alpha);
    glBegin(GL_POLYGON);
    for (int i = 0; i < numberOfSides; i++) {
        GLfloat angle = 2.0f * PI * i / numberOfSides;
        glVertex2f(x + cos(angle) * radius, y + sin(angle) * radius);
    }
    glEnd();
}

void display() {
    // Clear the color buffer
    glClear(GL_COLOR_BUFFER_BIT);
    // Draw circles with specified fills
    drawCircle(3.0, 0.0, 2.0, 100, 0.3921f, 0.4313f, 0.4470f, 1.0f); // outer circle 1
    drawCircle(3.0, 0.0, 1.5, 100, 1.0f, 1.0f, 1.0f, 1.0f);         // innermost circle 1

    drawCircle(1.0, 0.0, 2.0, 100, 0.3921f, 0.4313f, 0.4470f, 1.0f); // outer circle 2
    drawCircle(1.0, 0.0, 1.5, 100, 1.0f, 1.0f, 1.0f, 1.0f);         // innermost circle 2

    drawCircle(-1.0, 0.0, 2.0, 100, 0.3921f, 0.4313f, 0.4470f, 1.0f); // outer circle 2
    drawCircle(-1.0, 0.0, 1.5, 100, 1.0f, 1.0f, 1.0f, 1.0f);         // innermost circle 2

    drawCircle(-3.0, 0.0, 2.0, 100, 0.3921f, 0.4313f, 0.4470f, 1.0f); // outer circle 2
    drawCircle(-3.0, 0.0, 1.5, 100, 1.0f, 1.0f, 1.0f, 1.0f);         // innermost circle 2

    // Draw the star
    glFlush();
}

int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(800, 800);
    glutInitWindowPosition(100, 100);
    glutCreateWindow("Mercedes Logo with Circle");
    init();
    // Register display callback function
    glutDisplayFunc(display);
    glutMainLoop();
    return 0;
}

...不是我所期望的:

第二个圆圈隐藏了第一个圆圈的一部分。

Answer 1

我与chatGPT经过长时间讨论后找到了答案，答案如下：

#include <GL/glut.h>
#include <cmath>

#define PI 3.14159265358979323846

float zoom = 1.0f;
void init() {
    // Set the background color to white 
    glClearColor(1.0, 1.0, 1.0, 1.0);

    // Set up the viewport
    glViewport(0, 0, 500, 500);

    // Initialize the projection matrix
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    // Initial zoom setup, centering at the origin
    float range = 2.0 * zoom;
    gluOrtho2D(-range, range, -range, range);

    // Initialize the modelview matrix
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}


void drawRingUsingQuads(float centerX, float centerY, float outerRadius, float innerRadius, int numSegments, float r, float g, float b, float alpha) {
    float angleStep = (2.0f * PI) / numSegments;

    glColor4f(r, g, b, alpha); // Set the color with alpha for transparency

    glBegin(GL_QUADS);
    for (int i = 0; i < numSegments; i++) {
        float angle = i * angleStep;
        float nextAngle = (i + 1) * angleStep;

        // Outer circle vertices
        float x1 = centerX + outerRadius * cos(angle);
        float y1 = centerY + outerRadius * sin(angle);

        float x2 = centerX + outerRadius * cos(nextAngle);
        float y2 = centerY + outerRadius * sin(nextAngle);

        // Inner circle vertices
        float x3 = centerX + innerRadius * cos(nextAngle);
        float y3 = centerY + innerRadius * sin(nextAngle);

        float x4 = centerX + innerRadius * cos(angle);
        float y4 = centerY + innerRadius * sin(angle);

        // Define the quad connecting outer and inner circles
        glVertex2f(x1, y1); // Outer vertex 1
        glVertex2f(x2, y2); // Outer vertex 2
        glVertex2f(x3, y3); // Inner vertex 2
        glVertex2f(x4, y4); // Inner vertex 1
    }
    glEnd();
}

void display() {
    glClear(GL_COLOR_BUFFER_BIT); // Clear the screen

    glEnable(GL_BLEND); // Enable blending
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); // Set blending function

    // Draw a ring using quads
    drawRingUsingQuads(0.0f, 0.0f, 0.5f, 0.3f, 100, 0.0f, 0.0f, 0.0f, 1.0f); // Black ring with full opacity

    drawRingUsingQuads(0.5f, 0.0f, 0.5f, 0.3f, 100, 0.0f, 0.0f, 0.0f, 1.0f); // Black ring with full opacity
    drawRingUsingQuads(1.0f, 0.0f, 0.5f, 0.3f, 100, 0.0f, 0.0f, 0.0f, 1.0f); // Black ring with full opacity
    glDisable(GL_BLEND); // Disable blending

    glFlush(); // Swap buffers to display drawing
}

int main(int argc, char** argv) {
    glutInit(&argc, argv); // Initialize GLUT
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); // Set display mode
    glutInitWindowSize(500, 500); // Set window size
    glutInitWindowPosition(100, 100); // Set window position
    glutCreateWindow("Circle with Hole Using Quads"); // Create window with title
    glutDisplayFunc(display); // Set display callback function

    glClearColor(1.0, 1.0, 1.0, 1.0); // Set the background color to white
    init();
    glutMainLoop(); // Enter main loop for event handling and drawing
    return 0;
}