使用不同的缓冲区在 OpenGL 中绘制多个对象

Question

使用 OpenGL 着色器，我想渲染两个对象。每个都由三角形的一组顶点位置和顶点索引定义。当我制作缓冲区时，我使用以下代码：

// Object 1 vertex positions
glBindBuffer(GL_ARRAY_BUFFER, object1_vertex_buffer);
glBufferData(GL_ARRAY_BUFFER, object1_vertices_size, object1_vertices, GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);

// Object 1 vertex indices
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, object1_index_buffer);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, object1_indices_size, object1_indices, GL_STATIC_DRAW);

// Object 2 vertex positions
glBindBuffer(GL_ARRAY_BUFFER, object2_vertex_buffer);
glBufferData(GL_ARRAY_BUFFER, object2_vertices_size, object2_vertices, GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);

// Object 2 vertex indices
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, object2_index_buffer);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, object2_indices_size, object2_indices, GL_STATIC_DRAW);

然后当我渲染场景时，我使用以下代码：

// Object 1
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, object1_index_buffer);
glDrawElements(GL_TRIANGLES, object1_num_indices, GL_UNSIGNED_INT, (void*)0);

// Object 2
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, object2_index_buffer);
glDrawElements(GL_TRIANGLES, object2_num_indices, GL_UNSIGNED_INT, (void*)0);

但是，这会导致仅绘制对象 2。我究竟做错了什么？

Answer 1

如果你有 openGL 3.3+，你应该使用 VAO：

glBindVertexArray(vao1);
// Object 1 vertex positions
glBindBuffer(GL_ARRAY_BUFFER, object1_vertex_buffer);
glBufferData(GL_ARRAY_BUFFER, object1_vertices_size, object1_vertices, GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);

// Object 1 vertex indices
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, object1_index_buffer);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, object1_indices_size, object1_indices, GL_STATIC_DRAW);

glBindVertexArray(vao2);
// Object 2 vertex positions
glBindBuffer(GL_ARRAY_BUFFER, object2_vertex_buffer);
glBufferData(GL_ARRAY_BUFFER, object2_vertices_size, object2_vertices, GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);

// Object 2 vertex indices
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, object2_index_buffer);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, object2_indices_size, object2_indices, GL_STATIC_DRAW);

然后你只需要在绘制时绑定正确的vao：

// Object 1
glBindVertexArray(vao1);
glDrawElements(GL_TRIANGLES, object1_num_indices, GL_UNSIGNED_INT, (void*)0);

// Object 2
glBindVertexArray(vao2);
glDrawElements(GL_TRIANGLES, object2_num_indices, GL_UNSIGNED_INT, (void*)0);

否则，您将需要glVertexAttribPointer在绘制之间重复绑定和调用：

// Object 1
glBindBuffer(GL_ARRAY_BUFFER, object1_vertex_buffer);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, object1_index_buffer);
glDrawElements(GL_TRIANGLES, object1_num_indices, GL_UNSIGNED_INT, (void*)0);

// Object 2
glBindBuffer(GL_ARRAY_BUFFER, object2_vertex_buffer);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, object2_index_buffer);
glDrawElements(GL_TRIANGLES, object2_num_indices, GL_UNSIGNED_INT, (void*)0);