在opengl中将金字塔更改为四面体

Question

首先，我是 openGL 的新手，所以我还不了解所有“基本”知识。我正在一本书中做这个练习，我已经能够画出一个金字塔，但我现在想画一个四面体。但我似乎无法理解它。我总是以奇怪或不完整的形状结束。如果我也没有做任何其他事情，请告诉我。这是代码。感谢任何帮助。

    float pt1 = 1.0f;
    float pt2 = 0.0f;
    glBegin(GL_TRIANGLES);
    // Front
    glColor3f(1.0f, 0.0f, 0.0f);     // Red
    glVertex3f(pt2, pt1, pt2);
    glVertex3f(-pt1, -pt1, pt1);
    glVertex3f(pt1, -pt1, pt1);

    // Right
    glColor3f(0.0f, 0.0f, 1.0f);     // Blue
    glVertex3f(pt2, pt1, pt2);
    glVertex3f(pt1, -pt1, pt1);
    glVertex3f(pt1, -pt1, -pt1);

    // Back
    glColor3f(0.0f, 1.0f, 0.0f);     // Green
    glVertex3f(pt2, pt1, pt2);
    glVertex3f(pt1, -pt1, -pt1);
    glVertex3f(-pt1, -pt1, -pt1);

    // Left
    glColor3f(1.0f, 1.0f, 0.0f);       // Yellow
    glVertex3f(pt2, pt1, pt2);
    glVertex3f(-pt1, -pt1, -pt1);
    glVertex3f(-pt1, -pt1, pt1);
    glEnd();

Answer 1

一个Tetrahedron由4个顶点组成：

const float s_8_9 = sqrt(0.8f / 0.9f); // = 0.9428f
const float s_2_9 = sqrt(0.2f / 0.9f); // = 0.4714f
const float s_2_3 = sqrt(0.2f / 0.3f); // = 0.8165f

float vertices[4][3] = {
    { 0.0f,   0.0f,   1.0f },
    { s_8_9,  0.0f,  -1.0f / 3.0f},
    {-s_2_9,  s_2_3, -1.0f / 3.0f},
    {-s_2_9, -s_2_3, -1.0f / 3.0f},
};

顶点形成 4 个三角形面：

int indices[4][3] = {{0, 2, 1},  {0, 3, 2},  {1, 3, 0}, {1, 2, 3}};

使用vertices和indices画四面体：

glBegin(GL_TRIANGLES);

// Front
glColor3f(1.0f, 0.0f, 0.0f);     // Red
for (int i = 0; i < 3; i++)
    glVertex3fv(vertices[indices[0][i]]);

// Right
glColor3f(0.0f, 0.0f, 1.0f);     // Blue
for (int i = 0; i < 3; i++)
    glVertex3fv(vertices[indices[1][i]]);

// Back
glColor3f(0.0f, 1.0f, 0.0f);     // Green
for (int i = 0; i < 3; i++)
    glVertex3fv(vertices[indices[2][i]]);

// Left
glColor3f(1.0f, 1.0f, 0.0f);     // Yellow
for (int i = 0; i < 3; i++)
    glVertex3fv(vertices[indices[3][i]]);

在opengl中将金字塔更改为四面体

Changing a pyramid to tetrahedron in opengl

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