glDrawElements not drawing

Question

I create my buffers with the following code:

//generate buffers
glGenVertexArrays(1, &VAO);
//glGenBuffers(1, &EBO);
glGenBuffers(1, &VBO_vertices);
glGenBuffers(1, &VBO_colors);
glGenBuffers(1, &VBO_normals);

// Bind the Vertex Array Object first, then bind and set vertex buffer(s) and attribute pointer(s).
glBindVertexArray(VAO);

// Copy our vertices array in a buffer for OpenGL to use
glBindBuffer(GL_ARRAY_BUFFER, VBO_vertices);
glBufferData(GL_ARRAY_BUFFER, sizeof(float)*3*vertices.size(), &vertices[0], GL_STATIC_DRAW);


glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, vTable.size() * sizeof(int), &vTable[0], GL_STATIC_DRAW);

// Position attribute
glVertexAttribPointer((GLuint)0, 3, GL_FLOAT, GL_FALSE, 0, (GLvoid*)0); //size = 3 (X,Y,Z)
glEnableVertexAttribArray(0);


//Buffer for color
glBindBuffer(GL_ARRAY_BUFFER, VBO_colors);
glBufferData(GL_ARRAY_BUFFER, sizeof(float)*3*vertices.size(), &v_color[0], GL_STATIC_DRAW);

// Color attribute
glVertexAttribPointer((GLuint)1, 3, GL_FLOAT, GL_FALSE, 0, (GLvoid*)0); //size = 3 (R,G,B)
glEnableVertexAttribArray(1);


//Buffer for normals
glBindBuffer(GL_ARRAY_BUFFER, VBO_normals);
glBufferData(GL_ARRAY_BUFFER, sizeof(float)*3*vertices.size(), &v_normals[0], GL_STATIC_DRAW);

//normal attribute
glVertexAttribPointer((GLuint)2, 3, GL_FLOAT, GL_FALSE, 0, (GLvoid*)0); //size = 3 (R,G,B)
glEnableVertexAttribArray(2);


// Unbind the VAO
glBindVertexArray(0);

My data are :

vector<vec3> vertices, v_normals,v_color;
vector<int> vTable;

I have vertices, normals and colors per vertex and an index table with the index vertices of each triangle.

When I try to render this, nothing appears on the window.

glBindVertexArray(VAO); //Bind VAO
glDrawElements(GL_TRIANGLES, vTable.size(), GL_UNSIGNED_INT, &vTable[0]);
glBindVertexArray(0); //Unbind VAO

If I used this:

glDrawArrays(GL_TRIANGLES,0,vTable.size());

It draws something but an incomplete object, like in the link image.

image

Anybody knows what happens? Thanks in advance

Answer 1

您的glDrawElements调用是错误的，最后一个参数应该是GL_ELEMENT_ARRAY_BUFFER的字节偏移量，该偏移量保存索引，而不是指向系统内存的指针。

glDrawElements(GL_TRIANGLES, vTable.size(), GL_UNSIGNED_INT, 0);