c++ - 如何绘制存储在 SSBO 中的顶点?
问题描述
这是一个遵循OpenGL 并以 AoSoA (hybrid SoA) 格式加载/读取数据的问题。
我正在尝试使用着色器存储缓冲区对象 (SSBO) 来存储以AoSoA格式表示的顶点数据。我无法绘制顶点,这显然意味着我在某处做错了什么。问题是我似乎无法弄清楚什么或在哪里。上面最初问题的答案似乎表明我不应该使用顶点属性数组,所以问题就变成了,给定我将要呈现的代码,我该如何渲染这个 SSBO?
Vertex数据结构
constexpr auto VECTOR_WIDTH = 4;
constexpr auto VERTEX_COUNT = 16;
struct VertexData
{
std::array<float, VECTOR_WIDTH> px;
std::array<float, VECTOR_WIDTH> py;
};
// Later stored in a std::vector
std::vector<VertexData> vertices(VERTEX_COUNT / VECTOR_WIDTH);
顶点着色器(这真的应该是计算着色器吗?)
struct Vertex4
{
float px[4]; // position x
float py[4]; // position y
};
layout(std430, binding=0) buffer VertexData
{
Vertex4 vertices[];
};
void main()
{
int dataIx = gl_VertexID / 4;
int vertexIx = gl_VertexID % 4;
vec2 vertexPosition = vec2(vertices[dataIx].px[vertexIx], vertices[dataIx].py[vertexIx]);
}
分配vertexPosition
索引
// Do I need this? Where do I use it? glEnableVertexAttribArray(position_attrib_index)?
const GLuint position_attrib_index = 0;
glBindAttribLocation(program, position_attrib_index, "vertexPosition");
SSBO 设置
const GLuint ssbo_binding_point = 0;
GLuint ssbo{};
glGenBuffers(1, &ssbo);
glBindBuffer(GL_SHADER_STORAGE_BUFFER, ssbo);
//glBufferStorage(GL_SHADER_STORAGE_BUFFER, vertices.size() * sizeof(VertexData), vertices.data(), GL_MAP_WRITE_BIT);
glBufferData(GL_SHADER_STORAGE_BUFFER, vertices.size() * sizeof(VertexData), vertices.data(), GL_STATIC_DRAW);
const auto block_index = glGetProgramResourceIndex(program, GL_SHADER_STORAGE_BLOCK, "VertexData");
glShaderStorageBlockBinding(program, block_index, ssbo_binding_point);
glBindBufferBase(GL_SHADER_STORAGE_BUFFER, ssbo_binding_point, ssbo);
glBindBuffer(GL_SHADER_STORAGE_BUFFER, 0);
渲染循环
while (!glfwWindowShouldClose(window)) {
process_input(window);
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(program);
// ???
glfwSwapBuffers(window);
glfwPollEvents();
}
我似乎无法弄清楚这应该如何工作。抓住稻草,我还尝试创建一个 VAO 并稍后调用glDrawArrays(GL_POINTS, 0, VERTEX_COUNT)
,但它也不起作用:
GLuint vao{};
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
glEnableVertexAttribArray(position_attrib_index);
glVertexAttribPointer(position_attrib_index, 2, GL_FLOAT, GL_FALSE, 0, nullptr);
在我看来,我应该使用position_attrib_index
(应该指向vertexPosition
)来做某事,问题是为了什么?
完整的示例代码
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <array>
#include <iostream>
#include <vector>
void process_input(GLFWwindow *window)
{
if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS) {
glfwSetWindowShouldClose(window, true);
}
}
void glfw_error_callback(int error_code, const char *description)
{
std::cerr << "GLFW Error: [" << error_code << "] " << description << '\n';
}
void framebuffer_size_callback(GLFWwindow *window, int width, int height)
{
glViewport(0, 0, width, height);
}
auto create_glfw_window()
{
glfwInit();
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
return glfwCreateWindow(800, 600, "OpenGL and AoSoA layout", nullptr, nullptr);
}
void set_callbacks(GLFWwindow *window)
{
glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
glfwSetErrorCallback(glfw_error_callback);
}
void print_versions()
{
std::cout << "Using GLFW " << glfwGetVersionString() << '\n';
std::cout << "Using GLEW " << glewGetString(GLEW_VERSION) << '\n';
}
bool init_loader()
{
GLenum err = glewInit();
if (GLEW_OK != err) {
std::cerr << "GLEW error: " << glewGetErrorString(err);
}
return err == GLEW_OK;
}
void GLAPIENTRY MessageCallback(
GLenum source,
GLenum type,
GLuint id,
GLenum severity,
GLsizei length,
const GLchar* message,
const void* userParam = nullptr)
{
std::cerr << "[GL DEBUG] " << (type == GL_DEBUG_TYPE_ERROR ? "Error: " : "") << message << '\n';
}
constexpr auto VECTOR_WIDTH = 4;
constexpr auto VERTEX_COUNT = 16;
struct VertexData
{
std::array<float, VECTOR_WIDTH> px;
std::array<float, VECTOR_WIDTH> py;
};
static const char* vertex_shader_source =
"#version 430\n"
"struct Vertex4\n"
"{\n"
" float px[4]; // position x\n"
" float py[4]; // position y\n"
"};\n"
"layout(std430, binding=0) buffer VertexData\n"
"{\n"
" Vertex4 vertices[];\n"
"};\n"
"void main()\n"
"{\n"
" int dataIx = gl_VertexID / 4;\n"
" int vertexIx = gl_VertexID % 4;\n"
" vec2 vertexPosition = vec2(vertices[dataIx].px[vertexIx], vertices[dataIx].py[vertexIx]);\n"
"}\n";
static const char* fragment_shader_source =
"#version 430\n"
"out vec4 out_color;\n"
"void main()\n"
"{\n"
" out_color = vec4(1.0, 0.5, 0.5, 0.25);\n"
"}\n";
int main(int argc, char *argv[])
{
glewExperimental = GL_TRUE;
auto window = create_glfw_window();
if (window == nullptr) {
std::cout << "Failed to create GLFW window" << std::endl;
glfwTerminate();
return -1;
}
glfwMakeContextCurrent(window);
set_callbacks(window);
init_loader();
print_versions();
glEnable(GL_DEBUG_OUTPUT);
glDebugMessageCallback(MessageCallback, nullptr);
std::vector<VertexData> vertices(VERTEX_COUNT / VECTOR_WIDTH);
vertices[0] = {
{-0.75f, 0.75f, 0.75f, -0.75f},
{-0.75f, -0.75f, 0.75f, 0.75f}
};
vertices[1] = {
{-0.50f, 0.50f, 0.50f, -0.50f},
{-0.50f, -0.50f, 0.50f, 0.50f},
};
vertices[2] = {
{-0.25f, 0.25f, 0.25f, -0.25f},
{-0.25f, -0.25f, 0.25f, 0.25f},
};
vertices[3] = {
{-0.05f, 0.05f, 0.05f, -0.05f},
{-0.05f, -0.05f, 0.05f, 0.05f},
};
auto vertex_shader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertex_shader, 1, &vertex_shader_source, nullptr);
glCompileShader(vertex_shader);
auto fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragment_shader, 1, &fragment_shader_source, nullptr);
glCompileShader(fragment_shader);
auto program = glCreateProgram();
glAttachShader(program, vertex_shader);
glAttachShader(program, fragment_shader);
const GLuint position_attrib_index = 0;
glBindAttribLocation(program, position_attrib_index, "vertexPosition");
glLinkProgram(program);
//glUseProgram(program);
glDeleteShader(vertex_shader);
glDeleteShader(fragment_shader);
//
// SSBO
//
const GLuint ssbo_binding_point = 0;
GLuint ssbo{};
glGenBuffers(1, &ssbo);
glBindBuffer(GL_SHADER_STORAGE_BUFFER, ssbo);
//glBufferStorage(GL_SHADER_STORAGE_BUFFER, vertices.size() * sizeof(VertexData), vertices.data(), GL_MAP_WRITE_BIT);
glBufferData(GL_SHADER_STORAGE_BUFFER, vertices.size() * sizeof(VertexData), vertices.data(), GL_STATIC_DRAW);
const auto block_index = glGetProgramResourceIndex(program, GL_SHADER_STORAGE_BLOCK, "VertexData");
glShaderStorageBlockBinding(program, block_index, ssbo_binding_point);
glBindBufferBase(GL_SHADER_STORAGE_BUFFER, ssbo_binding_point, ssbo);
glBindBuffer(GL_SHADER_STORAGE_BUFFER, 0);
//
// VAO
//
//GLuint vao{};
//glGenVertexArrays(1, &vao);
//glBindVertexArray(vao);
//glEnableVertexAttribArray(position_attrib_index);
//glVertexAttribPointer(position_attrib_index, 2, GL_FLOAT, GL_FALSE, 0, nullptr);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glEnable(GL_BLEND);
glClearColor(0.15f, 0.15f, 0.2f, 1.0f);
glPointSize(10.0f);
while (!glfwWindowShouldClose(window)) {
process_input(window);
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(program);
//glDrawArrays(GL_POINTS, 0, VERTEX_COUNT);
glfwSwapBuffers(window);
glfwPollEvents();
}
glfwDestroyWindow(window);
glfwTerminate();
return 0;
}
解决方案
这是使用您拥有的数据发出平局的正确方法:
glBindVertexArray(vao);
glDrawArrays(GL_POINTS, 0, VERTEX_COUNT);
但是,您的问题是您的顶点着色器没有写入gl_Position
,因此没有任何内容被光栅化(无论发生什么未定义的行为)。您应该在着色器中设置顶点的位置,如下所示:
//...
out gl_PerVertex {
vec4 gl_Position;
};
void main()
{
int dataIx = gl_VertexID / 4;
int vertexIx = gl_VertexID % 4;
vec2 vertexPosition = vec2(vertices[dataIx].px[vertexIx], vertices[dataIx].py[vertexIx]);
gl_Position = vec4(vertexPosition, 0, 1);
}
您可以摆脱“Assign vertexPosition index”,并且您的 VAO 不需要任何属性。
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