没有重复三角形传输的相同网格的多个图像

Question

我使用OpenGL,GLEW和GLFW拍摄同一网格的多个图像.网格(三角形)在每次拍摄中都不会改变,只会改变ModelViewMatrix.

这是我的主循环的重要代码:

for (int i = 0; i < number_of_images; i++) {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    /* set GL_MODELVIEW matrix depending on i */
    glBegin(GL_TRIANGLES);
    for (Triangle &t : mesh) {
        for (Point &p : t) {
            glVertex3f(p.x, p.y, p.z);
        }
    }
    glReadPixels(/*...*/) // get picture and store it somewhere
    glfwSwapBuffers();
}

如您所见,我为每个要拍摄的镜头设置/传输三角形顶点.有没有解决方案,我只需要转移一次？我的网格非常大,所以这种转移需要相当长的时间.

Answer 1

在2016年,您不得使用glBegin/ glEnd.没门.改为使用Vertex Array Obejcts ; 并使用自定义顶点和/或几何着色器重新定位和修改顶点数据.使用这些技术,您可以将数据上传到GPU一次,然后您就可以使用各种变换绘制相同的网格.

以下是代码的外观大纲:

// 1. Initialization.
// Object handles:
GLuint vao;
GLuint verticesVbo;
// Generate and bind vertex array object.
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
// Generate a buffer object.
glGenBuffers(1, &verticesVbo);
// Enable vertex attribute number 0, which
// corresponds to vertex coordinates in older OpenGL versions.
const GLuint ATTRIBINDEX_VERTEX = 0;
glEnableVertexAttribArray(ATTRIBINDEX_VERTEX);
// Bind buffer object.
glBindBuffer(GL_ARRAY_BUFFER, verticesVbo);
// Mesh geometry. In your actual code you probably will generate
// or load these data instead of hard-coding.
// This is an example of a single triangle.
GLfloat vertices[] = {
    0.0f, 0.0f, -9.0f,
    0.0f, 0.1f, -9.0f,
    1.0f, 1.0f, -9.0f
};
// Determine vertex data format.
glVertexAttribPointer(ATTRIBINDEX_VERTEX, 3, GL_FLOAT, GL_FALSE, 0, 0);
// Pass actual data to the GPU.
glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat)*3*3, vertices, GL_STATIC_DRAW);
// Initialization complete - unbinding objects.
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindVertexArray(0);

// 2. Draw calls.
while(/* draw calls are needed */) {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glBindVertexArray(vao);
    // Set transformation matrix and/or other
    // transformation parameters here using glUniform* calls.
    glDrawArrays(GL_TRIANGLES, 0, 3);
    glBindVertexArray(0); // Unbinding just as an example in case if some other code will bind something else later.
}

顶点着色器可能如下所示:

layout(location=0) in vec3 vertex_pos;
uniform mat4 viewProjectionMatrix; // Assuming you set this before glDrawArrays.

void main(void) {
    gl_Position = viewProjectionMatrix * vec4(vertex_pos, 1.0f);
}

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