OpenGL 中的两个三角形、直线和边框

Question

我很困惑如何制作两个不相邻的三角形（它们之间有间隙）以及一条线和一个边框。我已经完成了一个代码，但由于某种原因三角形和线条不会出现，当我评论三角形和线条代码时只有边框出现。三角形、线条和边框也有颜色，希望那个代码是正确的。

你认为我的代码有什么问题？

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

using namespace std;
void triangle();
void line();
void border();
void display();

int main(int argc, char** argv){
   glutInit(&argc, argv);
   glutCreateWindow("simple");
   glClearColor(1.0, 1.0, 0.0, 1.0);
   glutDisplayFunc(display);
   glutMainLoop();
}

void display(){
  glClear(GL_COLOR_BUFFER_BIT);
  triangle();
  line();
  border();
  glFlush();
}

void triangle() {
  glClear(GL_COLOR_BUFFER_BIT);
  glTranslatef(0.0f,0.0f,-4.0f);
    
  glBegin(GL_TRIANGLES);
    glColor3f(0.0f,0.0f,1.0f); glVertex2f(-1.0f,-0.25f);
    glColor3f(0.0f,0.0f,1.0f); glVertex2f(-0.5f,-0.25f);
    glColor3f(0.0f,0.0f,1.0f); glVertex2f(-0.75f,0.25f);

    glColor3f(0.0f,0.0f,1.0f); glVertex2f(0.5f,-0.25f);
    glColor3f(0.0f,0.0f,1.0f); glVertex2f(1.0f,-0.25f);
    glColor3f(0.0f,0.0f,1.0f); glVertex2f(0.75f,0.25f);
  glEnd();
  glFlush();
}

void line() {
  glClear(GL_COLOR_BUFFER_BIT);
  glLineWidth(5.0f);
  glBegin(GL_LINES);
    glColor3f(0.0, 0.0, 1.0); glVertex2f(-0.3, -0.3);
    glColor3f(0.0, 0.0, 1.0); glVertex2f(0.3, -0.3);
  glEnd();
  glFlush();
}

void border() {
  glClear(GL_COLOR_BUFFER_BIT);
  glLineWidth(7.0f);
  glBegin(GL_LINE_LOOP);
    glColor3f(0.0f, 0.0f, 0.0f);
    glVertex2f(-1, -1);
    glVertex2f(-1, 1);
    glVertex2f(1, 1);
    glVertex2f(1, -1);
  glEnd();
  glFlush();
}

Answer 1

问题是在绘制每个网格之前清除了颜色缓冲区。这会“清除”之前的绘制网格。在display中绘制场景之前调用glClear(GL_COLOR_BUFFER_BIT)一次，但不要在triangle、line和border中清除颜色缓冲区。只需从这些函数中删除 glClear(GL_COLOR_BUFFER_BIT)。

OpenGL 中的两个三角形、直线和边框

two triangles, line, and border in OpenGL

c++

opengl

glut

colors

shapes