batches.cpp

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#include "glad.h"
#include "staplegl.hpp"
 
#include <GLFW/glfw3.h>
#include <array>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <ctime>
#include <execution>
#include <iostream>
#include <optional>
#include <span>
#include <utility>
 
/*
 
        IMPORTANT: in order for the program to correctly compile, go to
        include/staplegl/modules/gl_functions.hpp and replace the placeholder
        with the provided OpenGL loader ("glad.h").
 
*/
 
constexpr auto lerp(float a, float b, float f) -> float
{
    return a * (1.0F - f) + b * f;
}
 
struct vec3 {
    float x;
    float y;
    float z;
};
 
void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow* window);
 
void GLAPIENTRY
MessageCallback(GLenum source [[maybe_unused]],
    GLenum type,
    GLuint id [[maybe_unused]],
    GLenum severity,
    GLsizei length [[maybe_unused]],
    const GLchar* message,
    const void* userParam [[maybe_unused]])
{
    if (type == GL_DEBUG_TYPE_OTHER || type == GL_DEBUG_TYPE_PERFORMANCE)
        return;
    // NOLINTNEXTLINE
    fprintf(stderr, "GL CALLBACK: %s type = 0x%x, severity = 0x%x,\nmessage = %s\n", // NOLINT
        (type == GL_DEBUG_TYPE_ERROR ? "** GL ERROR **" : ""),
        type, severity, message);
}
 
// initial window size
const int32_t SCR_WIDTH = 1600;
const int32_t SCR_HEIGHT = 900;
 
auto main() -> int
{
    // glfw: initialize and configure
    // ------------------------------
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
 
    glfwWindowHint(GLFW_SAMPLES, 4); // MSAA
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_COMPAT_PROFILE);
 
#ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif
 
    // glfw window creation
    // --------------------
    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "Batched Rendering", nullptr, nullptr);
    if (window == nullptr) {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
 
    // glad: load all OpenGL function pointers
    // ---------------------------------------
    if (gladLoadGLLoader(reinterpret_cast<GLADloadproc>(glfwGetProcAddress)) == 0) { // NOLINT (reinterpret-cast)
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }
 
    // During init, enable debug output
    glEnable(GL_DEBUG_OUTPUT);
    glDebugMessageCallback(MessageCallback, nullptr);
 
    // antialiasing and other nice things
    glEnable(GL_MULTISAMPLE);
 
    staplegl::shader_program const basic { "batched_shader", "./shaders/batched_shader.glsl" };
 
    basic.bind();
 
    // set up vertex data (and buffer(s)) and configure vertex attributes
    // ------------------------------------------------------------------
    const std::array<const float, 12> vertices {
        0.001F, 0.001F, 0.0F, // top right
        0.001F, -0.001F, 0.0F, // bottom right
        -0.001F, -0.001F, 0.0F, // bottom left
        -0.001F, 0.001F, 0.0F, // top left
    };
 
    const std::array<const unsigned int, 6> indices {
        // note that we start from 0!
        0, 1, 3, // first Triangle
        1, 2, 3 // second Triangle
    };
 
    using namespace staplegl::shader_data_type;
 
    staplegl::vertex_buffer_layout const layout {
        { u_type::vec3, "aPos" }
    };
 
    staplegl::vertex_buffer_layout const instance_layout {
        { u_type::vec3, "instancePos" }
    };
 
    staplegl::vertex_buffer VBO(vertices, staplegl::driver_draw_hint::STATIC_DRAW);
    staplegl::vertex_buffer_inst VBO_inst({}); // empty for now
 
    VBO_inst.set_layout(instance_layout);
    VBO.set_layout(layout);
 
    staplegl::index_buffer EBO { indices };
    staplegl::vertex_array VAO;
 
    VAO.add_vertex_buffer(std::move(VBO));
    VAO.set_instance_buffer(std::move(VBO_inst));
    VAO.set_index_buffer(std::move(EBO));
 
    staplegl::vertex_buffer_layout const UBO_block_layout {
        { shader_array_type::float32_arr, "u_color", 4 }
    };
 
    staplegl::uniform_buffer UBO_block { UBO_block_layout, 1 };
 
    UBO_block.bind();
 
    std::array<float, 4> color {};
 
    VAO.bind();
 
    const float START = -0.95F;
    const float END = 0.95F;
 
    const float Z_START = 0.01F;
    const float Z_END = 1.00F;
 
    std::srand(static_cast<unsigned int>(std::time(nullptr)));
    constexpr int32_t NUM_INSTANCES = 65535;
 
    for (int i = 0; i < NUM_INSTANCES; i++) {
        std::array<float, 3> offset = {
            lerp(START, END,
                static_cast<float>(rand()) / static_cast<float>(RAND_MAX)),
            lerp(START, END,
                static_cast<float>(rand()) / static_cast<float>(RAND_MAX)),
            lerp(Z_START, Z_END,
                static_cast<float>(rand()) / static_cast<float>(RAND_MAX))
        };
 
        // I know the instance is set since it is in the optional, so I go for direct access
        VAO.instanced_data()->add_instance(offset);
    }
 
    while (glfwWindowShouldClose(window) == 0) {
 
        processInput(window);
 
        glClearColor(0.2F, 0.3F, 0.3F, 1.0F);
        glClear(GL_COLOR_BUFFER_BIT);
 
        auto timeNow = static_cast<float>(glfwGetTime());
 
        for (float& col : color) {
            col = std::sin(timeNow) / 2.0F + 0.5F;
        }
        color[3] = 1.0F;
 
        for (int i = 0; i < 4; ++i) {
            UBO_block.set_attribute_data(std::span { &color[i], 1 }, "u_color", i);
        }
 
// define a struct for the instance data
#pragma pack(push, 1)
        struct vec3 {
            float x;
            float y;
            float z;
        };
#pragma pack(pop)
 
        static_assert(sizeof(vec3) == 3 * sizeof(float));
 
        // apply a lambda to the instance data, reading it as a span of vec3
        VAO.instanced_data()->apply<vec3>(
            [](std::span<vec3> data) {
                // thanks to std::span, we can pass this GPU buffer to a parallel algorithm!
                std::for_each(std::execution::par_unseq, data.begin(), data.end(),
                    [](vec3& v) { // randomly shift the position of the instance left or right
                        const float speed = ((static_cast<float>(std::rand()) / static_cast<float>(RAND_MAX)) - 0.5F) / 1000.0F;
                        v.x += speed;
                    });
            });
 
        // draw the instances
        glDrawElementsInstanced(GL_TRIANGLES, VAO.index_data().count(), GL_UNSIGNED_INT, nullptr,
            VAO.instanced_data()->instance_count());
 
        glfwSwapBuffers(window);
        glfwPollEvents();
    }
 
    glfwTerminate();
    return 0;
}
 
void processInput(GLFWwindow* window)
{
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS) {
        glfwSetWindowShouldClose(window, 1);
    }
}
 
void framebuffer_size_callback(GLFWwindow* /*window*/, int width, int height)
{
    glViewport(0, 0, width, height);
}