在OpenGL中使用不同的缓冲区绘制多个对象 [英] Drawing multiple objects in OpenGL with different buffers

问题描述

使用OpenGL着色器，我想渲染两个对象.每一个都由一组三角形的顶点位置和顶点索引定义.制作缓冲区时，使用以下代码:

With OpenGL shaders, I want to render two objects. Each is defined by a set of vertex positions and vertex indices for the triangles. When I make my buffers, I use the following code:

// 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);

然后在渲染场景时，我使用以下代码:

And then when I render my scene, I use the following code:

// 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，这仅导致绘制对象2.我在做什么错了?

However, this results in only object 2 being drawn. What am I doing wrong?

推荐答案

如果您具有openGL 3.3+，则应使用VAO:

If you have openGL 3.3+ you should use a 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);

，然后在绘制时只需要绑定正确的vao:

and then you only need to bind the right vao when drawing:

// 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，您将需要在绘制之间重复bind和glVertexAttribPointer调用:

otherwise you will need to repeat the bind and glVertexAttribPointer calls between draws:

// 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);

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