繪製在OpenGL多個對象用不同的緩衝區

Question

在OpenGL中着色器，我想呈現兩個對象。每個由三角形的一組頂點位置和頂點索引定義。當我把我的緩衝區，我使用下面的代碼：

// 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); 

，然後當我使我的場景，我使用下面的代碼：

// 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，這僅導致物體2被抽。我究竟做錯了什麼？

Answer 1

如果你有openGL的3.3+你應該使用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); 

，然後你只需要正確的VAO結合繪圖時：

// 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); 

否則就需要重複綁定和調用glVertexAttribPointer之間繪製：

// 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

如果這是所有本代碼，那麼有幾個問題：

• 一個人，使頂點致電glEnableVertexAttribArray屬性。
• 在繪圖代碼中，您只重新綁定索引緩衝區，而不是頂點緩衝區。 glBindBuffer(GL_ARRAY_BUFFER,...和glVertexAttribPointer都改變了當前狀態，所以你將覆蓋第一個對象設置和第二個對象設置。如果你真的想不VAOs工作，你就必須結合每個繪圖調用之前正確的緩衝和更新glVertexAttribPointer
• 沒有使用任何VAO（VAOs在覈心配置文件工作時是強制性的，但我會建議使用它們還兼容模式）