绘制在OpenGL多个对象用不同的缓冲区

Question

在OpenGL中着色器，我想呈现两个对象。每个由三角形的一组顶点位置和顶点索引定义。当我把我的缓冲区，我使用下面的代码：

// 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); 

，然后当我使我的场景，我使用下面的代码：

// 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); 

然而，这仅导致物体2被抽。我究竟做错了什么？

Answer 1

如果你有openGL的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); 

，然后你只需要正确的VAO结合绘图时：

// 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); 

否则就需要重复绑定和调用glVertexAttribPointer之间绘制：

// 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); 

Answer 2

如果这是所有本代码，那么有几个问题：

• 一个人，使顶点致电glEnableVertexAttribArray属性。
• 在绘图代码中，您只重新绑定索引缓冲区，而不是顶点缓冲区。 glBindBuffer(GL_ARRAY_BUFFER,...和glVertexAttribPointer都改变了当前状态，所以你将覆盖第一个对象设置和第二个对象设置。如果你真的想不VAOs工作，你就必须结合每个绘图调用之前正确的缓冲和更新glVertexAttribPointer
• 没有使用任何VAO（VAOs在核心配置文件工作时是强制性的，但我会建议使用它们还兼容模式）