使用SSBO作为VBO输入下一个绘制调用

Question

我写一个着色器SSBO里面的一些顶点数据。然后我想使用写入SSBO的数据作为VBO。这些将用于下一次的平局。如何才能做到这一点？

这里，我现在该怎么做，但它仍然出现segfaults：

int new_vertex_count = …; 
int new_index_count = …; 
int* new_indices = …; 

GLuint ssbo[3]; 
glGenBuffers(3, ssbo); 


glBindBuffer(GL_SHADER_STORAGE_BUFFER, ssbo[1]); 
glBufferData(GL_SHADER_STORAGE_BUFFER, new_vertex_count * 3 * sizeof(float), nullptr, GL_DYNAMIC_DRAW); 
glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, ssbo[1]); 

glBindBuffer(GL_SHADER_STORAGE_BUFFER, ssbo[2]); 
glBufferData(GL_SHADER_STORAGE_BUFFER, new_vertex_count * 2 * sizeof(float), nullptr, GL_DYNAMIC_DRAW); 
glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 1, ssbo[2]); 

glBindVertexArray(vao); //bind the original VAO 
glPatchParameteri(GL_PATCH_VERTICES, 16); 
glEnable(GL_RASTERIZER_DISCARD); //disable displaying 
glDrawElements(GL_PATCHES, index_count, GL_UNSIGNED_INT, 0); //don't draw, just 
glMemoryBarrier(GL_SHADER_STORAGE_BARRIER_BIT); //sync writing 
glFinish(); 
glDisable(GL_RASTERIZER_DISCARD); //reanable displaying for next draw call 
glBindVertexArray(0); //unbind original VAO in order to use new VBOs 


glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ssbo[0]); 
glBufferData(GL_ELEMENT_ARRAY_BUFFER, index_count * sizeof(uint), indices, GL_STATIC_DRAW); 

glBindBuffer(GL_ARRAY_BUFFER, ssbo[1]); //bind SSBO as VBO, is this even possible? 
//or should I use new VBOs and copy? How would I copy then? 
glEnableVertexAttribArray(0); 
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0); 

glBindBuffer(GL_ARRAY_BUFFER, ssbo[2]); 
glEnableVertexAttribArray(1); 
glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, 0); 

glDrawElements(GL_PATCHES, new_index_count, new_indices, GL_UNSIGNED_INT, 0); //here the real drawing 

Answer 1

有没有这样的事，作为一个“SSBO”或“VBO”。只有缓冲对象。存储块和顶点数组是用于缓冲对象的用途，但一个特定的缓冲区不固有地链接到特定的用途。没有什么能够阻止你通过存储块写入缓冲区，然后在渲染操作中读取它。

只要你遵循incoherent memory access规则对于那些写的，当然。除非明确地使其可用，否则通过存储块写入不可用于读取操作。你可以使用glMemoryBarrier这个。和方式memory barrier works是枚举指定要能够看到任何写的结果的操作。

你要被解读为顶点属性阵列写入数据。所以，你使用：

glMemoryBarrier(GL_VERTEX_ATTRIB_ARRAY_BARRIER_BIT​);