OpenGL颜色半个立方体

Posted 2023-02-16

【中文标题】OpenGL颜色半个立方体

【英文标题】：OpenGL Color half of a cube

【发布时间】：2018-05-20 17:42:09

【问题描述】：

我正在尝试给半个立方体上色，让它看起来像是装满了水。在下面的代码中，我绘制了带有白色边缘的立方体：

void initGL() 
    glClearColor(0.0f, 0.0f, 0.0f, 1.0f); 
    glClearDepth(1.0f); 
    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LEQUAL); 
    glShadeModel(GL_SMOOTH);
    glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST); 


void display() 
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glMatrixMode(GL_MODELVIEW);
    glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
    glLoadIdentity(); 

    glTranslatef(-3.0f, 0.0f, -9.0f); 

    glBegin(GL_QUADS);
    glBegin(GL_LINES);

    glColor3f(1.0f, 1.0f, 1.0f); 
    glVertex3f(1.0f, 1.0f, -1.0f);
    glVertex3f(-1.0f, 1.0f, -1.0f);
    glVertex3f(-1.0f, 1.0f, 1.0f);
    glVertex3f(1.0f, 1.0f, 1.0f);

    glColor3f(1.0f, 1.0f, 1.0f); 
    glVertex3f(1.0f, -1.0f, 1.0f);
    glVertex3f(-1.0f, -1.0f, 1.0f);
    glVertex3f(-1.0f, -1.0f, -1.0f);
    glVertex3f(1.0f, -1.0f, -1.0f);

    glColor3f(1.0f, 1.0f, 1.0f); 
    glVertex3f(1.0f, 1.0f, 1.0f);
    glVertex3f(-1.0f, 1.0f, 1.0f);
    glVertex3f(-1.0f, -1.0f, 1.0f);
    glVertex3f(1.0f, -1.0f, 1.0f);

    glColor3f(1.0f, 1.0f, 1.0f); 
    glVertex3f(1.0f, -1.0f, -1.0f);
    glVertex3f(-1.0f, -1.0f, -1.0f);
    glVertex3f(-1.0f, 1.0f, -1.0f);
    glVertex3f(1.0f, 1.0f, -1.0f);

    glColor3f(1.0f, 1.0f, 1.0f); 
    glVertex3f(-1.0f, 1.0f, 1.0f);
    glVertex3f(-1.0f, 1.0f, -1.0f);
    glVertex3f(-1.0f, -1.0f, -1.0f);
    glVertex3f(-1.0f, -1.0f, 1.0f);

    glColor3f(1.0f, 1.0f, 1.0f); 
    glVertex3f(1.0f, 1.0f, -1.0f);
    glVertex3f(1.0f, 1.0f, 1.0f);
    glVertex3f(1.0f, -1.0f, 1.0f);
    glVertex3f(1.0f, -1.0f, -1.0f);
    glEnd(); 
    glutSwapBuffers();

但我不知道如何在不擦除白色边缘的情况下给它的一半上色。除此之外，我必须对其进行动画处理，以便水可以上下移动。

【参考方案1】：

请注意，glBegin、glEnd 之类的内容已被弃用（甚至 glVertexPointer 和 glEnableClientState）。 了解Fixed Function Pipeline 和Vertex Specification。

---

但根据您的代码，我建议定义一个顶点数据数组 (glVertexPointer) 以及客户端功能（glEnableClientState），以解决您的问题。 进一步定义索引数组并使用glDrawElements 从数组数据中渲染（索引）基元。

定义顶点坐标：

GLfloat water_height = -0.5f;
GLfloat vertices[] =

    -1.0f, -1.0f,         -1.0f,  // 0
     1.0f, -1.0f,         -1.0f,  // 1
     1.0f, -1.0f,          1.0f,  // 2
    -1.0f, -1.0f,          1.0f,  // 3

    -1.0f,  1.0f,         -1.0f,  // 5
     1.0f,  1.0f,         -1.0f,  // 6
     1.0f,  1.0f,          1.0f,  // 7
    -1.0f,  1.0f,          1.0f,  // 8

    -1.0f,  water_height, -1.0f,  // 9
     1.0f,  water_height, -1.0f,  // 10
     1.0f,  water_height,  1.0f,  // 11
    -1.0f,  water_height,  1.0f   // 12
;

定义“水”四边形的索引：

// 6 quad indices for the 6 sides of the water cube
GLuint water_indices[] = 
 
    0, 1, 2, 3,
    0, 1, 9, 8,
    1, 2, 10, 9,
    2, 3, 11, 10,
    3, 0, 8, 11,
    8, 9, 10, 11
;

定义边的索引：

// 8 edges for the part of the cube which is not filled with water 
GLuint edge_indices[] = 
 
    4, 5, 
    5, 6,
    6, 7,
    7, 4,
    4, 8,
    5, 9,
    6, 10,
    7, 11
;

画四边形和线条：

glVertexPointer( 3, GL_FLOAT, 0, vertices );
glEnableClientState( GL_VERTEX_ARRAY );

glColor4f( 0.3f, 0.5f, 1.0f, 1.0f );
glDrawElements( GL_QUADS, 6 * 4, GL_UNSIGNED_INT, water_indices );

glColor4f( 1.0f, 1.0f, 1.0f, 1.0f );
glDrawElements( GL_LINES, 8 * 2, GL_UNSIGNED_INT, edge_indices );

glDisableClientState( GL_VERTEX_ARRAY );

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