Add SDL3 GPU backend (Vulkan/Metal) with OpenGL fallback
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297
src/rendering/opengl_shader_backend.cpp
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297
src/rendering/opengl_shader_backend.cpp
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#include "rendering/opengl_shader_backend.hpp"
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#include <iostream>
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#include <vector>
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namespace Rendering {
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namespace {
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constexpr const char* VERTEX_SHADER_SRC = R"glsl(
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#version 330 core
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layout(location = 0) in vec2 aPos;
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out vec2 vUV;
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void main() {
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vUV = aPos * 0.5 + 0.5;
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gl_Position = vec4(aPos, 0.0, 1.0);
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}
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)glsl";
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void logInfo(const std::string& msg) { std::cout << "[INFO] " << msg << '\n'; }
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void logError(const std::string& msg) { std::cerr << "[ERROR] " << msg << '\n'; }
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auto compileShader(GLenum type, const char* src) -> GLuint {
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const GLuint s = glCreateShader(type);
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glShaderSource(s, 1, &src, nullptr);
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glCompileShader(s);
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GLint ok = 0;
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glGetShaderiv(s, GL_COMPILE_STATUS, &ok);
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if (ok == 0) {
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GLint len = 0;
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glGetShaderiv(s, GL_INFO_LOG_LENGTH, &len);
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std::string log(len > 0 ? len : 1, ' ');
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glGetShaderInfoLog(s, len, nullptr, log.data());
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logError("Shader compile error: " + log);
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glDeleteShader(s);
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return 0;
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}
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return s;
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}
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auto linkProgram(GLuint vs, GLuint fs) -> GLuint {
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const GLuint p = glCreateProgram();
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glAttachShader(p, vs);
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glAttachShader(p, fs);
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glLinkProgram(p);
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GLint ok = 0;
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glGetProgramiv(p, GL_LINK_STATUS, &ok);
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if (ok == 0) {
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GLint len = 0;
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glGetProgramiv(p, GL_INFO_LOG_LENGTH, &len);
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std::string log(len > 0 ? len : 1, ' ');
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glGetProgramInfoLog(p, len, nullptr, log.data());
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logError("Program link error: " + log);
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glDeleteProgram(p);
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return 0;
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}
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return p;
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}
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auto detectFeedbackChannel(const ShaderMetadata& metadata) -> int {
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if (metadata.iChannel0 == "self") { return 0; }
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if (metadata.iChannel1 == "self") { return 1; }
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if (metadata.iChannel2 == "self") { return 2; }
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if (metadata.iChannel3 == "self") { return 3; }
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return -1;
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}
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} // namespace
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OpenGLShaderBackend::~OpenGLShaderBackend() { cleanup(); }
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auto OpenGLShaderBackend::init(SDL_Window* window) -> bool {
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window_ = window;
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gl_context_ = SDL_GL_CreateContext(window_);
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if (gl_context_ == nullptr) {
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logError(std::string("SDL_GL_CreateContext error: ") + SDL_GetError());
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return false;
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}
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if (gladLoadGLLoader(reinterpret_cast<GLADloadproc>(SDL_GL_GetProcAddress)) == 0) {
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logError("Failed to initialize GL loader");
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SDL_GL_DestroyContext(gl_context_);
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gl_context_ = nullptr;
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return false;
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}
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constexpr float QUAD_VERTICES[] = {
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-1.0f, -1.0f,
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1.0f, -1.0f,
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-1.0f, 1.0f,
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1.0f, 1.0f,
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};
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glGenVertexArrays(1, &vao_);
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glGenBuffers(1, &vbo_);
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glBindVertexArray(vao_);
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glBindBuffer(GL_ARRAY_BUFFER, vbo_);
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glBufferData(GL_ARRAY_BUFFER, sizeof(QUAD_VERTICES), QUAD_VERTICES, GL_STATIC_DRAW);
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glEnableVertexAttribArray(0);
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glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(float), nullptr);
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glBindBuffer(GL_ARRAY_BUFFER, 0);
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glBindVertexArray(0);
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return true;
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}
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auto OpenGLShaderBackend::loadShader(const ShaderProgramSpec& spec) -> bool {
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const std::filesystem::path source_path = spec.folder / (spec.base_name + ".gl.glsl");
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std::string fragSrc;
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if (!loadFileToString(source_path, fragSrc)) {
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logError("Failed to load shader file: " + source_path.string());
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return false;
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}
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const int feedback = detectFeedbackChannel(spec.metadata);
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const GLuint vs = compileShader(GL_VERTEX_SHADER, VERTEX_SHADER_SRC);
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const GLuint fs = compileShader(GL_FRAGMENT_SHADER, fragSrc.c_str());
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if (vs == 0 || fs == 0) {
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if (vs != 0) { glDeleteShader(vs); }
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if (fs != 0) { glDeleteShader(fs); }
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logError("Shader compilation failed for: " + source_path.string());
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return false;
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}
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const GLuint program = linkProgram(vs, fs);
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glDeleteShader(vs);
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glDeleteShader(fs);
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if (program == 0) {
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logError("Program linking failed for: " + source_path.string());
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return false;
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}
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if (current_program_ != 0) {
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glDeleteProgram(current_program_);
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}
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current_program_ = program;
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destroyFeedbackFBO();
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feedback_channel_ = feedback;
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current_shader_uses_feedback_ = (feedback >= 0);
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if (current_shader_uses_feedback_) {
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logInfo("Shader uses self-feedback on iChannel" + std::to_string(feedback_channel_));
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}
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logInfo("Shader loaded successfully: " + spec.base_name);
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return true;
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}
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auto OpenGLShaderBackend::createFeedbackFBO(int width, int height) -> bool {
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destroyFeedbackFBO();
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glGenTextures(1, &feedback_texture_);
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glBindTexture(GL_TEXTURE_2D, feedback_texture_);
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glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
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glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
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glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
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glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
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std::vector<float> black(static_cast<std::size_t>(width) * static_cast<std::size_t>(height) * 4U, 0.0f);
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glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA32F, width, height, 0, GL_RGBA, GL_FLOAT, black.data());
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glBindTexture(GL_TEXTURE_2D, 0);
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glGenFramebuffers(1, &feedback_fbo_);
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glBindFramebuffer(GL_FRAMEBUFFER, feedback_fbo_);
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glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, feedback_texture_, 0);
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const GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
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glBindFramebuffer(GL_FRAMEBUFFER, 0);
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if (status != GL_FRAMEBUFFER_COMPLETE) {
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logError("Feedback FBO creation failed: " + std::to_string(status));
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destroyFeedbackFBO();
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return false;
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}
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feedback_width_ = width;
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feedback_height_ = height;
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logInfo("Created feedback FBO (" + std::to_string(width) + "x" + std::to_string(height) + ")");
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return true;
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}
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void OpenGLShaderBackend::destroyFeedbackFBO() {
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if (feedback_fbo_ != 0) {
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glDeleteFramebuffers(1, &feedback_fbo_);
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feedback_fbo_ = 0;
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}
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if (feedback_texture_ != 0) {
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glDeleteTextures(1, &feedback_texture_);
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feedback_texture_ = 0;
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}
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feedback_width_ = 0;
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feedback_height_ = 0;
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}
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void OpenGLShaderBackend::render(const ShaderUniforms& uniforms) {
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if (current_program_ == 0 || window_ == nullptr) { return; }
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int w = 0;
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int h = 0;
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SDL_GetWindowSize(window_, &w, &h);
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if (current_shader_uses_feedback_) {
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if (feedback_fbo_ == 0 || feedback_width_ != w || feedback_height_ != h) {
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createFeedbackFBO(w, h);
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}
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}
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glUseProgram(current_program_);
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const GLint locRes = glGetUniformLocation(current_program_, "iResolution");
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const GLint locTime = glGetUniformLocation(current_program_, "iTime");
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if (current_shader_uses_feedback_) {
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const std::string channel_name = "iChannel" + std::to_string(feedback_channel_);
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const GLint locChannel = glGetUniformLocation(current_program_, channel_name.c_str());
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if (locChannel >= 0) {
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glActiveTexture(GL_TEXTURE0 + feedback_channel_);
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glBindTexture(GL_TEXTURE_2D, feedback_texture_);
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glUniform1i(locChannel, feedback_channel_);
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}
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glBindFramebuffer(GL_FRAMEBUFFER, feedback_fbo_);
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glViewport(0, 0, w, h);
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glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
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glClear(GL_COLOR_BUFFER_BIT);
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if (locRes >= 0) { glUniform2f(locRes, static_cast<float>(w), static_cast<float>(h)); }
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if (locTime >= 0) { glUniform1f(locTime, uniforms.iTime); }
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glBindVertexArray(vao_);
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glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
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glBindVertexArray(0);
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glBindFramebuffer(GL_FRAMEBUFFER, 0);
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glViewport(0, 0, w, h);
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if (locRes >= 0) { glUniform2f(locRes, static_cast<float>(w), static_cast<float>(h)); }
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if (locTime >= 0) { glUniform1f(locTime, uniforms.iTime); }
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glBindVertexArray(vao_);
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glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
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glBindVertexArray(0);
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glActiveTexture(GL_TEXTURE0 + feedback_channel_);
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glBindTexture(GL_TEXTURE_2D, 0);
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} else {
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glViewport(0, 0, w, h);
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glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
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glClear(GL_COLOR_BUFFER_BIT);
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if (locRes >= 0) { glUniform2f(locRes, static_cast<float>(w), static_cast<float>(h)); }
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if (locTime >= 0) { glUniform1f(locTime, uniforms.iTime); }
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glBindVertexArray(vao_);
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glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
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glBindVertexArray(0);
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}
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SDL_GL_SwapWindow(window_);
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}
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void OpenGLShaderBackend::setVSync(bool vsync) {
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const int result = SDL_GL_SetSwapInterval(vsync ? 1 : 0);
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if (result == 0) {
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logInfo(vsync ? "VSync enabled" : "VSync disabled");
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} else {
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logError(std::string("Failed to set VSync: ") + SDL_GetError());
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}
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}
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void OpenGLShaderBackend::cleanup() {
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if (gl_context_ == nullptr) { return; }
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if (vbo_ != 0) { glDeleteBuffers(1, &vbo_); vbo_ = 0; }
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if (vao_ != 0) { glDeleteVertexArrays(1, &vao_); vao_ = 0; }
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if (current_program_ != 0) { glDeleteProgram(current_program_); current_program_ = 0; }
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destroyFeedbackFBO();
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current_shader_uses_feedback_ = false;
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feedback_channel_ = -1;
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SDL_GL_DestroyContext(gl_context_);
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gl_context_ = nullptr;
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window_ = nullptr;
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}
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auto makeOpenGLBackend() -> std::unique_ptr<IShaderBackend> {
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return std::make_unique<OpenGLShaderBackend>();
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}
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} // namespace Rendering
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