glDrawElements 方法不使用索引和顶点绘制

Question

I'm trying to draw a quad on the screen using the glDrawElements method like this:

glDrawElements(GL_TRIANGLES, model.get_vertex_count(), GL_UNSIGNED_INT, 0)

To get the indices I've written this method:

@classmethod
    def bind_indices_buffer(cls, indices: list[int]):
        indices = numpy.array(indices, dtype=numpy.uint32)  # convert the data into an unsigned integer array
        vbo_id = glGenBuffers(1)
        cls.__vbos.append(vbo_id)
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vbo_id)
        glBufferData(GL_ELEMENT_ARRAY_BUFFER, indices, GL_STATIC_DRAW)

And for the vertices:

 @classmethod
    def store_data_in_attribute_list(cls, attribute_number: int, data: list[float]):
        data = numpy.array(data, dtype='float32')   # convert the data into a float32 array
        vbo_id = glGenBuffers(1)                    # create 1 VBO buffer
        cls.__vbos.append(vbo_id)                   # appends it to the VBO list in the class
        glBindBuffer(GL_ARRAY_BUFFER, vbo_id)       # binds the buffer to use it
        glBufferData(GL_ARRAY_BUFFER, data, GL_STATIC_DRAW)  # specifies the buffer, data and usage
        glVertexAttribPointer(attribute_number, 3, GL_FLOAT, False, 0, None)  # put the VBO into a VAO
        glBindBuffer(GL_ARRAY_BUFFER, 0)

If you want to see the rest of the code, I have pasted it into my last question, these snippets are the only changes

Answer 1

The type of the lase argument of glDrawElements is const GLvoid * . So the argument must be None or ctypes.c_void_p(0) , but not 0:

glDrawElements(GL_TRIANGLES, model.get_vertex_count(), GL_UNSIGNED_INT, 0)

glDrawElements(GL_TRIANGLES, model.get_vertex_count(), GL_UNSIGNED_INT, None)

Answer 2

I admit my OpenGL is a bit rusty, but IIRC glDrawElements expects a pointer to a list of indices in the last parameter (cf. https://registry.khronos.org/OpenGL-Refpages/gl4/html/glDrawElements.xhtml , and I wouldn't really know how to handle this in Python). If you just want to draw all vertices, try glDrawArrays( GL_TRIANGLES, 0, model.get_vertex_count() ) instead (cf. https://registry.khronos.org/OpenGL-Refpages/gl4/html/glDrawArrays.xhtml ).

EDIT: I was wrong, thanks to @Rabbid76 for clarification. glDrawArrays will just pull the given number of vertices from the enabled arrays in order (vertex[0], vertex[1], vertex[2], ...) while glDrawElements will use the index array to look them up (vertex[index[0]], vertex[index[1]], ...) etc.