Shader-Demo

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Original author	Amir Hassan (kallaballa) amir@.nosp@m.viel.nosp@m.-zu.o.nosp@m.rg
Compatibility	OpenCV >= 4.7

Renders a mandelbrot fractal zoom. Uses shaders, OpenCV and video editing together.

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// This file is part of OpenCV project.
// It is subject to the license terms in the LICENSE file found in the top-level directory
// of this distribution and at http://opencv.org/license.html.
// Copyright Amir Hassan (kallaballa) <amir@viel-zu.org>
 
#include <opencv2/v4d/v4d.hpp>
 
using std::cerr;
using std::endl;
 
/* Demo parameters */
#ifndef __EMSCRIPTEN__
constexpr long unsigned int WIDTH = 1280;
constexpr long unsigned int HEIGHT = 720;
#else
constexpr long unsigned int WIDTH = 960;
constexpr long unsigned int HEIGHT = 960;
#endif
constexpr bool OFFSCREEN = false;
const unsigned long DIAG = hypot(double(WIDTH), double(HEIGHT));
#ifndef __EMSCRIPTEN__
constexpr const char* OUTPUT_FILENAME = "shader-demo.mkv";
#endif
 
// vertex position, color
static const float vertices[] = {
//    x      y      z
        -1.0f, -1.0f, -0.0f, 1.0f, 1.0f, -0.0f, -1.0f, 1.0f, -0.0f, 1.0f, -1.0f, -0.0f };
 
static const unsigned int indices[] = {
//  2---,1
//  | .' |
//  0'---3
        0, 1, 2, 0, 3, 1 };
 
//easing function for the bungee zoom
static float easeInOutQuint(float x) {
    return x < 0.5f ? 16.0f * x * x * x * x * x : 1.0f - std::pow(-2.0f * x + 2.0f, 5.0f) / 2.0f;
}
 
using namespace cv::v4d;
 
class ShaderDemoPlan : public Plan {
    struct Params {
        /* Mandelbrot control parameters */
        int glowKernelSize_ = std::max(int(DIAG / 200 % 2 == 0 ? DIAG / 200 + 1 : DIAG / 200), 1);
        // Red, green, blue and alpha. All from 0.0f to 1.0f
        float baseColorVal_[4] = {0.2, 0.6, 1.0, 1.0};
        //contrast boost
        int contrastBoost_ = 50; //0.0-255
        //max fractal iterations
        int maxIterations_ = 1000;
        //center x coordinate
        float centerX_ = -0.119609;
        //center y coordinate
        float centerY_ = 0.13262;
        float zoomFactor_ = 1.0;
        float currentZoom_ = 1.0;
        float zoomIncr_ = 0.99;
        bool manualNavigation_ = false;
    } params_;
 
    struct Handles {
        /* GL uniform handles */
        GLint baseColorHdl_;
        GLint contrastBoostHdl_;
        GLint maxIterationsHdl_;
        GLint centerXHdl_;
        GLint centerYHdl_;
        GLint currentZoomHdl_;
        GLint resolutionHdl_;
 
        /* Shader program handle */
        GLuint shaderHdl_;
 
        /* Object handles */
        GLuint vao_;
        GLuint vbo_, ebo_;
    } handles_;
 
    struct Cache {
        cv::UMat down;
        cv::UMat up;
        cv::UMat blur;
        cv::UMat dst16;
    } cache_;
 
    cv::Size sz_;
#ifndef __EMSCRIPTEN__
    static void glow_effect(const cv::UMat& src, cv::UMat& dst, const int ksize, Cache& cache) {
        cv::bitwise_not(src, dst);
 
        cv::resize(dst, cache.down, cv::Size(), 0.5, 0.5);
        cv::boxFilter(cache.down, cache.blur, -1, cv::Size(ksize, ksize), cv::Point(-1, -1), true,
                cv::BORDER_REPLICATE);
        cv::resize(cache.blur, cache.up, src.size());
 
        cv::multiply(dst, cache.up, cache.dst16, 1, CV_16U);
        cv::divide(cache.dst16, cv::Scalar::all(255.0), dst, 1, CV_8U);
 
        cv::bitwise_not(dst, dst);
    }
#endif
 
    //Load objects and buffers
    static void load_buffers(Handles& handles) {
        GL_CHECK(glGenVertexArrays(1, &handles.vao_));
        GL_CHECK(glBindVertexArray(handles.vao_));
 
        GL_CHECK(glGenBuffers(1, &handles.vbo_));
        GL_CHECK(glGenBuffers(1, &handles.ebo_));
 
        GL_CHECK(glBindBuffer(GL_ARRAY_BUFFER, handles.vbo_));
        GL_CHECK(glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW));
 
        GL_CHECK(glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, handles.ebo_));
        GL_CHECK(glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW));
 
        GL_CHECK(glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*) 0));
        GL_CHECK(glEnableVertexAttribArray(0));
 
        GL_CHECK(glBindBuffer(GL_ARRAY_BUFFER, 0));
        GL_CHECK(glBindVertexArray(0));
    }
 
    //mandelbrot shader code adapted from my own project: https://github.com/kallaballa/FractalDive#after
    static GLuint load_shader() {
    #if !defined(__EMSCRIPTEN__) && !defined(OPENCV_V4D_USE_ES3)
        const string shaderVersion = "330";
    #else
        const string shaderVersion = "300 es";
    #endif
 
        const string vert =
                "    #version " + shaderVersion
                        + R"(
        in vec4 position;
        
        void main()
        {
            gl_Position = vec4(position.xyz, 1.0);
        })";
 
        const string frag =
                "    #version " + shaderVersion
                        + R"(
        precision lowp float;
 
        out vec4 outColor;
        
        uniform vec4 base_color;
        uniform int contrast_boost;
        uniform int max_iterations;
        uniform float current_zoom;
        uniform float center_y;
        uniform float center_x;
        uniform vec2 resolution;
 
        int get_iterations()
        {
            float pointr = (((gl_FragCoord.x / resolution[1]) - 0.5f) * current_zoom + center_x) * 5.0f;
            float pointi = (((gl_FragCoord.y / resolution[1]) - 0.5f) * current_zoom + center_y) * 5.0f;
            const float four = 4.0f;
 
            int iterations = 0;
            float zi = 0.0f;
            float zr = 0.0f;
            float zrsqr = 0.0f;
            float zisqr = 0.0f;
 
            while (iterations < max_iterations && zrsqr + zisqr < four) {
               //equals following line as a consequence of binomial expansion: zi = (((zr + zi)*(zr + zi)) - zrsqr) - zisqr
                zi = (zr + zr) * zi;
 
                zi += pointi;
                zr = (zrsqr - zisqr) + pointr;
        
                zrsqr = zr * zr;
                zisqr = zi * zi;
                ++iterations;
            }
            return iterations;
        }
         
        void determine_color()
        {
            int iter = get_iterations();
            if (iter < max_iterations) {   
                float iterations = float(iter) / float(max_iterations);
                float cb = float(contrast_boost);
        
                outColor = vec4(base_color[0] * iterations * cb, base_color[1] * iterations * cb, base_color[2] * iterations * cb, base_color[3]);
            } else {
                outColor = vec4(0,0,0,0);
            }
        }
 
        void main()
        {
            determine_color();
        })";
 
        return cv::v4d::initShader(vert.c_str(), frag.c_str(), "fragColor");
    }
 
    //Initialize shaders, objects, buffers and uniforms
    static void init_scene(const cv::Size& sz, Handles& handles) {
        GL_CHECK(glEnable(GL_BLEND));
        GL_CHECK(glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA));
        handles.shaderHdl_ = load_shader();
        load_buffers(handles);
 
        handles.baseColorHdl_ = glGetUniformLocation(handles.shaderHdl_, "base_color");
        handles.contrastBoostHdl_ = glGetUniformLocation(handles.shaderHdl_, "contrast_boost");
        handles.maxIterationsHdl_ = glGetUniformLocation(handles.shaderHdl_, "max_iterations");
        handles.currentZoomHdl_ = glGetUniformLocation(handles.shaderHdl_, "current_zoom");
        handles.centerXHdl_ = glGetUniformLocation(handles.shaderHdl_, "center_x");
        handles.centerYHdl_ = glGetUniformLocation(handles.shaderHdl_, "center_y");
        handles.resolutionHdl_ = glGetUniformLocation(handles.shaderHdl_, "resolution");
        GL_CHECK(glViewport(0, 0, sz.width, sz.height));
    }
 
    //Free OpenGL resources
    static void destroy_scene(Handles& handles) {
        glDeleteShader(handles.shaderHdl_);
        glDeleteBuffers(1, &handles.vbo_);
        glDeleteBuffers(1, &handles.ebo_);
        glDeleteVertexArrays(1, &handles.vao_);
    }
 
    //Render the mandelbrot fractal on top of a video
    static void render_scene(const cv::Size& sz, Params& params, Handles& handles) {
        //bungee zoom
        if (params.currentZoom_ >= 1) {
            params.zoomIncr_ = -0.01;
        } else if (params.currentZoom_ < 2.5e-06) {
            params.zoomIncr_ = +0.01;
        }
 
        GL_CHECK(glUseProgram(handles.shaderHdl_));
        GL_CHECK(glUniform4f(handles.baseColorHdl_, params.baseColorVal_[0], params.baseColorVal_[1], params.baseColorVal_[2], params.baseColorVal_[3]));
        GL_CHECK(glUniform1i(handles.contrastBoostHdl_, params.contrastBoost_));
        GL_CHECK(glUniform1i(handles.maxIterationsHdl_, params.maxIterations_));
        GL_CHECK(glUniform1f(handles.centerYHdl_, params.centerY_));
        GL_CHECK(glUniform1f(handles.centerXHdl_, params.centerX_));
        if (!params.manualNavigation_) {
            params.currentZoom_ += params.zoomIncr_;
            GL_CHECK(glUniform1f(handles.currentZoomHdl_, easeInOutQuint(params.currentZoom_)));
        } else {
            params.currentZoom_ = 1.0 / pow(params.zoomFactor_, 5.0f);
            GL_CHECK(glUniform1f(handles.currentZoomHdl_, params.currentZoom_));
        }
        float res[2] = {float(sz.width), float(sz.height)};
        GL_CHECK(glUniform2fv(handles.resolutionHdl_, 1, res));
 
        GL_CHECK(glBindVertexArray(handles.vao_));
        GL_CHECK(glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0));
    }
public:
    void gui(cv::Ptr<V4D> window) override {
        window->imgui([](cv::Ptr<V4D> win, ImGuiContext* ctx, Params& params) {
            CV_UNUSED(win);
            using namespace ImGui;
            SetCurrentContext(ctx);
            Begin("Fractal");
            Text("Navigation");
            SliderInt("Iterations", &params.maxIterations_, 3, 50000);
            if(SliderFloat("X", &params.centerX_, -1.0f, 1.0f))
                params.manualNavigation_ = true;
 
            if(SliderFloat("Y", &params.centerY_, -1.0f, 1.0f))
                params.manualNavigation_ = true;
 
            if(SliderFloat("Zoom", &params.zoomFactor_, 1.0f, 100.0f))
                params.manualNavigation_ = true;
    #ifndef __EMSCRIPTEN__
            Text("Glow");
            SliderInt("Kernel Size", &params.glowKernelSize_, 1, 127);
    #endif
            Text("Color");
            ColorPicker4("Color", params.baseColorVal_);
            SliderInt("Contrast boost", &params.contrastBoost_, 1, 255);
            End();
        }, params_);
    }
 
    void setup(cv::Ptr<V4D> window) override {
        sz_ = window->fbSize();
        window->gl([](const cv::Size &sz, Handles& handles) {
            init_scene(sz, handles);
        }, sz_, handles_);
    }
 
    void infer(cv::Ptr<V4D> window) override {
        window->capture();
 
        window->gl([](const cv::Size &sz, Params& params, Handles& handles) {
            render_scene(sz, params, handles);
        }, sz_, params_, handles_);
 
    #ifndef __EMSCRIPTEN__
        window->fb([](cv::UMat& framebuffer, const Params& params, Cache& cache) {
            glow_effect(framebuffer, framebuffer, params.glowKernelSize_, cache);
        }, params_, cache_);
    #endif
 
        window->write();
    }
 
    void teardown(cv::Ptr<V4D> window) override {
        window->gl([](Handles& handles) {
            destroy_scene(handles);
        }, handles_);
    }
};
 
int main(int argc, char** argv) {
#ifndef __EMSCRIPTEN__
    if (argc != 2) {
        cerr << "Usage: shader-demo <video-file>" << endl;
        exit(1);
    }
#else
    CV_UNUSED(args);
    CV_UNUSED(argv);
#endif
    try {
        cv::Ptr<V4D> window = V4D::make(WIDTH, HEIGHT, "Mandelbrot Shader Demo", IMGUI, OFFSCREEN);
 
#ifndef __EMSCRIPTEN__
        auto src = makeCaptureSource(window, argv[1]);
        window->setSource(src);
        auto sink = makeWriterSink(window, OUTPUT_FILENAME, src->fps(), cv::Size(WIDTH, HEIGHT));
        window->setSink(sink);
#else
        auto src = makeCaptureSource(window);
        window->setSource(src);
#endif
 
        window->run<ShaderDemoPlan>(0);
    } catch (std::exception& ex) {
        cerr << "Exception: " << ex.what() << endl;
    }
    return 0;
}