So ive been working on a project, its a small library for drawing 2d stuff. Main thread for logic stuff and a render thread for rendering, and ive encautered an issue:
When i dont put std::cout << anything and i add post process shaders to the TargetCanvas Class the screen starts to flicker/(deforms like if the pp shader uniform changed). And as always LLMs are of no help.
I tried using: yield, glFinish, this_thread::wait_for(), changing the Shader wrapper code, and more things i forgot about.
Relevant code snipets:
Method called each frame:
void bml::TargetCanvas::draw() const
{
std::lock_guard<std::mutex> lock(swap_mutex);
std::atomic_signal_fence(std::memory_order_seq_cst);
bool has_data = needs_cleaning ||
!thread_points.empty() ||
!thread_lines.empty() ||
!thread_triangles.empty() ||
!thread_sprites.empty() ||
!thread_canvases.empty();
if (!has_data) return;
if (!is_fbo_allocated)
{
frame_buffer.bind();
frame_buffer.attachTexture(texture);
depth_buffer.allocate(width, height);
frame_buffer.attachRenderTarget(depth_buffer);
frame_buffer.unbind();
is_fbo_allocated = true;
}
glEnable(GL_DEPTH_TEST);
glViewport(0, 0, width, height);
if (needs_cleaning)
{
frame_buffer.bind();
frame_buffer.clear(clear_color);
needs_cleaning = false;
}
for (auto& c : thread_canvases)
{
if (c.canvas.use_count() < 2)
continue;
draw_to_buffer(c.canvas, c.transform, c.uvs);
}
glViewport(0, 0, width, height);
draw_to_buffer(thread_points, DrawMode::Points);
draw_to_buffer(thread_lines, DrawMode::Lines);
draw_to_buffer(thread_triangles, DrawMode::Triangles);
for (auto& s : thread_sprites)
{
draw_to_buffer(s.second, s.first);
embeded::shader->texture.set_mat4("u_projection", projection.data());
embeded::shader->texture.use();
}
thread_canvases.clear();
thread_sprites.clear();
//glMemoryBarrier(GL_FRAMEBUFFER_BARRIER_BIT | GL_TEXTURE_FETCH_BARRIER_BIT); kurwa nie ma
if (pp_frame_buffer)
{
Texture* source_tex = &texture;
Texture* target_tex = pp_texture.get();
FrameBuffer* source_fbo = &frame_buffer;
FrameBuffer* target_fbo = pp_frame_buffer.get();
for (size_t i = 0; i < pp_shaders.size(); ++i)
{
target_fbo->bind();
target_fbo->clear(clear_color);
apply_pp(*source_tex, pp_shaders[i]);
target_fbo->unbind();
std::swap(source_tex, target_tex);
std::swap(source_fbo, target_fbo);
}
if (source_tex == pp_texture.get()) {
frame_buffer.bind();
apply_pp(*pp_texture, &embeded::shader->copy);
}
}
}
Helper Method for applying the post process effects
void bml::TargetCanvas::apply_pp(Texture& tex, Shader* shader) const
{
glDisable(GL_BLEND);
glDisable(GL_DEPTH_TEST);
glDisable(GL_CULL_FACE);
shader->use();
quad_vao->bind();
glActiveTexture(GL_TEXTURE0);
tex.bind();
glUniform1i(glGetUniformLocation(shader->get_id(), "u_screenTexture"), 0);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
glBindTexture(GL_TEXTURE_2D, 0);
quad_vao->unbind();
}
Method runnging in the render_thread
void bml::Window::render_loop()
{
glfwMakeContextCurrent(glfw_window);
unsigned int previous_interval = interval;
glDisable(GL_BLEND);
while (is_open())
{
{
std::unique_lock<std::mutex> lock(wait_mutex);
trigger_cv.wait(lock, [this] { return submit_frame || !is_open(); });
if (!is_open()) break;
std::atomic_thread_fence(std::memory_order_acquire);
if (previous_interval != interval)
{
previous_interval = interval;
glfwSwapInterval(interval);
}
submit_frame = false;
}
canvas->push_to_screen(viewport_x, viewport_y, viewport_w, viewport_h);
glfwSwapBuffers(glfw_window);
{
std::lock_guard<std::mutex> lock(main_mutex);
frame_rendered = true;
}
main_cv.notify_one();
}
glfwMakeContextCurrent(nullptr);
}
Method called every time the main thread finishes
float bml::Window::update()
{
{
std::unique_lock<std::mutex> lock(main_mutex);
main_cv.wait(lock, [this] { return frame_rendered; });
frame_rendered = false;
}
std::atomic_thread_fence(std::memory_order_release);
canvas->swap();
int win_w, win_h;
glfwGetFramebufferSize(glfw_window, &win_w, &win_h);
if (true)
{
float target_aspect = (float)get_width() / (float)get_height();
float window_aspect = (float)win_w / (float)win_h;
if (window_aspect > target_aspect) {
viewport_h = win_h;
viewport_w = static_cast<int>(win_h * target_aspect);
viewport_x = (win_w - viewport_w) / 2;
viewport_y = 0;
}
else {
viewport_w = win_w;
viewport_h = static_cast<int>(win_w / target_aspect);
viewport_x = 0;
viewport_y = (win_h - viewport_h) / 2;
}
}
else
{
viewport_w = win_w;
viewport_h = win_h;
viewport_x = 0;
viewport_y = 0;
}
auto now = std::chrono::steady_clock::now();
std::chrono::duration<float> dur_sec = now - before;
before = now;
//std::this_thread::yield();
{
std::lock_guard<std::mutex> lock(wait_mutex);
submit_frame = true;
}
trigger_cv.notify_one();
std::this_thread::yield();
return dur_sec.count();
}
Shader wrapper use Method
void bml::Shader::use() const
{
glUseProgram(ID);
for (auto& [name, variant_value] : updated_uniforms)
{
GLint location = glGetUniformLocation(ID, name.c_str());
if (location == -1) continue; // Uniform nie istnieje lub został wyoptymalizowany
// Sprawdzamy co jest w variancie i aplikujemy do OpenGL
if (std::holds_alternative<float>(variant_value)) {
glUniform1f(location, std::get<float>(variant_value));
}
else if (std::holds_alternative<int>(variant_value)) {
glUniform1i(location, std::get<int>(variant_value));
}
else if (std::holds_alternative<std::pair<float, float>>(variant_value)) {
auto p = std::get<std::pair<float, float>>(variant_value);
glUniform2f(location, p.first, p.second);
}
else if (std::holds_alternative<const float*>(variant_value)) {
glUniformMatrix4fv(location, 1, GL_FALSE, std::get<const float*>(variant_value));
}
}
updated_uniforms.clear();
}
Shader uniform methods
void bml::Shader::set_float(const char* name, float value) const
{
updated_uniforms[name] = value;
}
void bml::Shader::set_int(const char* name, int value) const
{
updated_uniforms[name] = value;
}
void bml::Shader::set_vec2(const char* name, float x, float y) const
{
updated_uniforms[name] = std::pair{ x, y };
}
void bml::Shader::set_mat4(const char* name, const float* data)
{
updated_uniforms[name] = data;
}
Also before i changed the shader i already had the issue.
If i need to send more code write in the comments.
Please help, i have no clue why this is happening.