使用VAO和VBO在3.2中绘制OpenGL线和正方形

Question

I've been experimenting with OpenGL 3.2+.

I can successfully render either a line to the screen, or a square made up of two triangles...

I think I'm using VAO and VBO's correctly, yet somehow I can not rending both of them... I experience strange renders.

Obviously, I've coded it wrong... but how are you supposed to use VAO and VBO's when rending multiple objects defined in different Arrays?

My code is far too long to post here, so I've linked a copy on Pastebin > Here <

Answer 1

When you have multiple objects to display, each in its own buffer array, each buffer needs its own vertex array object handle :

int curr_num_object = 0;

static const int vertex_array_object_fish = curr_num_object++;
static const int vertex_array_object_shark = curr_num_object++; 
static const int vertex_array_object_doughnut = curr_num_object++;


GLuint array_vertex_array_object[curr_num_object]; // one for each drawn object

glGenVertexArrays(curr_num_object, &array_vertex_array_object[0]);

then for each buffer array you bind then load its data onto the GPU :

    // -----------------  fish

glBindVertexArray(array_vertex_array_object[vertex_array_object_fish]); // fish VAO

GLuint vertex_buffer_fish;
glGenBuffers(1, & vertex_buffer_fish);
glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer_fish);
glBufferData(GL_ARRAY_BUFFER, audio_model->get_sizeof_fish_array(), audio_model->get_address_fish_array(), GL_DYNAMIC_DRAW);

glVertexAttribPointer(
    0,                  // attribute. No particular reason for 0, but must match the layout in the shader.
    2,                  // size
    GL_FLOAT,           // type
    GL_FALSE,           // normalized?
    0,                  // stride
    (void*)0            // array buffer offset
);
glEnableVertexAttribArray(0);

above only deals with the first such buffer array, fish. Each subsequent object you wish to display wants a similar set of OpenGL calls. Above is called once outside of your windowing event loop (glfw, glut ...). Notice in the 2nd parm to glVertexAttribPointer its a 2D array ... here is its header entry :

float molecules_location_fish[max_fish][num_dimensions_2D_grid]; //  X & Y per fish

Here is a second object I want to display (doughnut) with its similar calls to above fish :

// -----------

glBindVertexArray(array_vertex_array_object[vertex_array_object_doughnut]); // doughnut VAO
GLuint vertex_buffer_doughnut_box;
glGenBuffers(1, & vertex_buffer_doughnut_box);
glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer_doughnut_box);
glBufferData(GL_ARRAY_BUFFER, audio_model->get_sizeof_doughnut_box_array(), audio_model->get_address_doughnut_box_array(), GL_DYNAMIC_DRAW);

glVertexAttribPointer(
    0,                  // attribute. No particular reason for 0, but must match the layout in the shader.
    3,                  // size
    GL_FLOAT,           // type
    GL_FALSE,           // normalized?
    0,                  // stride
    (void*)0            // array buffer offset
);
glEnableVertexAttribArray(0);

// -----------

Now inside your windowing event loop, where perhaps you also make calls to update locations to data of your objects (lines, triangles, ...), you make these OpenGL calls for each object to display :

    // ---------

    glBindVertexArray(array_vertex_array_object[vertex_array_object_fish]);

    glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer_fish);

    glBufferData(GL_ARRAY_BUFFER, audio_model->get_sizeof_fish_array(), audio_model->get_address_fish_array(), GL_DYNAMIC_DRAW);
    glDrawArrays(GL_POINTS, 0, audio_model->get_curr_num_fish()); // 12*3 indices starting at 0 -> 12 triangles

And for completeness, here are the doughnut calls inside your event loop :

    glBindVertexArray(array_vertex_array_object[vertex_array_object_doughnut]);

    glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer_doughnut_box);
    glBufferData(GL_ARRAY_BUFFER,audio_model->get_sizeof_doughnut_box_array(),audio_model->get_address_doughnut_box_array(),GL_DYNAMIC_DRAW);

    glDrawArrays(GL_TRIANGLES, 0, audio_model->get_curr_num_doughnut_boxes());

Notice in my fish I display its 2D as points, whereas the doughnut is 3D and displayed as a set of triangles (not indexed)

Let us know how you get on - this initial speed bump learning OpenGL is ( ^() &)(& Here is a really nice set of tutorials : http://www.opengl-tutorial.org