OpenGL glDrawElements没有颜色

Question

我想用OpenGL绘制一个使用我写的着色器的立方体，我可以看到形状但没有颜色。

#define EDGE_LENGTH 0.6 
enum VertexAttrib 
{ 
    ATTRIB_VERTEX = 0, ATTRIB_COLOR 
}; 
int main() 
{ 
    GLfloat cubeAttribs[] = 
    { 
     -EDGE_LENGTH/2, EDGE_LENGTH/2, -EDGE_LENGTH/2, // 0 front left top vertex 
     1.0f, 0.0f, 0.0f, // red 
     -EDGE_LENGTH/2, -EDGE_LENGTH/2, -EDGE_LENGTH/2, // 1 front left bottom vertex 
     1.0f, 1.0f, 0.0f, // yellow 
     EDGE_LENGTH/2, -EDGE_LENGTH/2, -EDGE_LENGTH/2, // 2 front right bottom vertex 
     0.0f, 1.0f, 0.0f, // green 
     EDGE_LENGTH/2, EDGE_LENGTH/2, -EDGE_LENGTH/2, // 3 front right top vertex 
     0.0f, 0.0f, 1.0f, // blue 
     EDGE_LENGTH/2, EDGE_LENGTH/2, EDGE_LENGTH/2, // 4 back right top vertex 
     1.0f, 0.0f, 1.0f, // purple 
     EDGE_LENGTH/2, -EDGE_LENGTH/2, EDGE_LENGTH/2, // 5 back right bottom vertex 
     1.0f, 0.5f, 0.2f, // orange 
     -EDGE_LENGTH/2, -EDGE_LENGTH/2, EDGE_LENGTH/2, // 6 back left bottom vertex 
     1.0f, 1.0f, 1.0f, // white 
     -EDGE_LENGTH/2, EDGE_LENGTH/2, EDGE_LENGTH/2, // 7 back left top vertex 
     0.0f, 1.0f, 1.0f // cyan 
    }; 
    GLushort cubeIndices[] = 
    { 
     0, 1, 2, 3, // front face 
     3, 2, 5, 4, // right face 
     4, 5, 6, 7, // back face 
     7, 6, 1, 0, // left face 
     0, 3, 4, 7, // top face 
     6, 5, 2, 1 // bottom face 
    }; 
/* create window and make GL contex */ 
    ... ... 
/* create shader program and use the program */ 
    ... ... 
    GLuint vertexArrayObject; 
    GLuint vertexBufferObject; 
    GLuint indexBuffer; 

/* create vertex array object and bind to it */ 
    glGenVertexArrays(1, &vertexArrayObject); 
    glBindVertexArray(vertexArrayObject); 
/* create vertex buffer object */ 
    glGenBuffers(1, &vertexBufferObject); 
    glBindBuffer(GL_ARRAY_BUFFER, vertexBufferObject); 
/* enable Attributes */ 
    glEnableVertexAttribArray(ATTRIB_VERTEX); 
    glEnableVertexAttribArray(ATTRIB_COLOR); 
/* send vertex position and color data to graphic card memory */ 
    glBufferData(GL_ARRAY_BUFFER, sizeof(cubeAttribs), cubeAttribs, GL_STREAM_DRAW); 
    glVertexAttribPointer(ATTRIB_VERTEX, 3, GL_FLOAT, GL_FALSE, 
         6 * sizeof(GLfloat), (const GLvoid *)0); 
    glVertexAttribPointer(ATTRIB_COLOR, 3, GL_FLOAT, GL_FALSE, 
         6 * sizeof(GLfloat), (const GLvoid *) (3 * sizeof(GLfloat))); 

/* create index buffer object */ 
    glGenBuffers(1, &indexBuffer); 
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer); 
/* send index data to graphic card memory */ 
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(cubeIndices), cubeIndices, GL_STREAM_DRAW); 

/* bind to the VAO */ 
    glBindVertexArray(vertexArrayObject); 
    while (!glfwWindowShouldClose(window)) 
    { 
     glClearColor(0.0f, 0.5f, 1.0f, 1.0f); CHECK_GL_ERROR 
     glClear(GL_COLOR_BUFFER_BIT); CHECK_GL_ERROR 
    /* draw the cube */ 
     glDrawElements(GL_QUADS, 4 * 6, GL_UNSIGNED_SHORT, (const GLvoid *)0); CHECK_GL_ERROR 
     glFlush(); 
     glfwSwapBuffers(window); 
     glfwPollEvents(); 
    } 
    return 0; 
} 

着色器相当简单。

顶点着色器：

#version 440 
layout(location = 0) in vec4 vertexPos; 
layout(location = 1) in vec3 vertexColor; 
smooth out vec3 vColor; 
void main() 
{ 
    gl_Position = vertexPos; 
    vColor = vertexColor; 
} 

片段着色器：

#version 440 
smooth in vec3 vColor; 
out vec3 outColor; 
void main() 
{ 
    outColor = vColor; 
} 

程序编译和运行，我看到蓝色背景和背方，但无颜色。我错过了什么 ？

以前我写过我的“第一个三角形”，它不是基于索引的渲染，它使用glDrawArrays渲染，颜色完美显现。着色器和程序结构几乎相同，我试图找出差异，但不知道。

Answer 1

您正在使用您告诉OpenGL的自定义片段输出。否则，如果使用兼容性配置文件，则希望通过特殊的内置变量gl_FragColor发出碎片颜色。但是使用核心配置文件，您需要使用glBindFragDataLocation将片段着色器输出与渲染缓冲区目标相关联。在大多数情况下，您只有一个渲染目标0。所以在你的情况下创建程序对象后，致电

glBindFragDataLocation(program, 0, "outColor");