Cube-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 rainbow cube on blueish background using OpenGL and applies a glow effect using OpenCV.

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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>
//adapted from https://gitlab.com/wikibooks-opengl/modern-tutorials/-/blob/master/tut05_cube/cube.cpp
 
/* 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;
#ifndef __EMSCRIPTEN__
constexpr double FPS = 60;
constexpr const char* OUTPUT_FILENAME = "cube-demo.mkv";
#endif
const unsigned long DIAG = hypot(double(WIDTH), double(HEIGHT));
const int glow_kernel_size = std::max(int(DIAG / 138 % 2 == 0 ? DIAG / 138 + 1 : DIAG / 138), 1);
 
using std::cerr;
using std::endl;
 
/* OpenGL constants and variables */
const unsigned int triangles = 12;
const unsigned int vertices_index = 0;
const unsigned int colors_index = 1;
unsigned int shader_program;
unsigned int vao;
unsigned int uniform_transform;
 
cv::Ptr<cv::v4d::V4D> global_v4d;
//Simple transform & pass-through shaders
static GLuint load_shader() {
    //Shader versions "330" and "300 es" are very similar.
    //If you are careful you can write the same code for both versions.
#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"(
    precision lowp float;
    layout(location = 0) in vec3 pos;
    layout(location = 1) in vec3 vertex_color;
    
    uniform mat4 transform;
    
    out vec3 color;
    void main() {
      gl_Position = transform * vec4(pos, 1.0);
      color = vertex_color;
    }
)";
 
    const string frag =
            "    #version " + shaderVersion
                    + R"(
    precision lowp float;
    in vec3 color;
    
    out vec4 frag_color;
    
    void main() {
      frag_color = vec4(color, 1.0);
    }
)";
 
    //Initialize the shaders and returns the program
    return cv::v4d::initShader(vert.c_str(), frag.c_str(), "fragColor");
}
 
//Initializes objects, buffers, shaders and uniforms
static void init_scene(const cv::Size& sz) {
    GL_CHECK(glEnable (GL_DEPTH_TEST));
 
    //Cube vertices, colors and indices
    float vertices[] = {
            // Front face
            0.5, 0.5, 0.5, -0.5, 0.5, 0.5, -0.5, -0.5, 0.5, 0.5, -0.5, 0.5,
            // Back face
            0.5, 0.5, -0.5, -0.5, 0.5, -0.5, -0.5, -0.5, -0.5, 0.5, -0.5, -0.5
    };
 
    float vertex_colors[] = {
            1.0, 0.4, 0.6, 1.0, 0.9, 0.2, 0.7, 0.3, 0.8, 0.5, 0.3, 1.0,
            0.2, 0.6, 1.0, 0.6, 1.0, 0.4, 0.6, 0.8, 0.8, 0.4, 0.8, 0.8
    };
 
    unsigned short triangle_indices[] = {
            // Front
            0, 1, 2, 2, 3, 0,
 
            // Right
            0, 3, 7, 7, 4, 0,
 
            // Bottom
            2, 6, 7, 7, 3, 2,
 
            // Left
            1, 5, 6, 6, 2, 1,
 
            // Back
            4, 7, 6, 6, 5, 4,
 
            // Top
            5, 1, 0, 0, 4, 5
    };
 
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);
 
    unsigned int triangles_ebo;
    glGenBuffers(1, &triangles_ebo);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, triangles_ebo);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof triangle_indices, triangle_indices,
            GL_STATIC_DRAW);
 
    unsigned int verticies_vbo;
    glGenBuffers(1, &verticies_vbo);
    glBindBuffer(GL_ARRAY_BUFFER, verticies_vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof vertices, vertices, GL_STATIC_DRAW);
 
    glVertexAttribPointer(vertices_index, 3, GL_FLOAT, GL_FALSE, 0, NULL);
    glEnableVertexAttribArray(vertices_index);
 
    unsigned int colors_vbo;
    glGenBuffers(1, &colors_vbo);
    glBindBuffer(GL_ARRAY_BUFFER, colors_vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof vertex_colors, vertex_colors, GL_STATIC_DRAW);
 
    glVertexAttribPointer(colors_index, 3, GL_FLOAT, GL_FALSE, 0, NULL);
    glEnableVertexAttribArray(colors_index);
 
    glBindVertexArray(0);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
    glBindBuffer(GL_ARRAY_BUFFER, 0);
 
    shader_program = load_shader();
    uniform_transform = glGetUniformLocation(shader_program, "transform");
    glViewport(0,0, sz.width, sz.height);
}
 
//Renders a rotating rainbow-colored cube on a blueish background
static void render_scene() {
    //Clear the background
    glClearColor(0.2, 0.24, 0.4, 1);
    glClear(GL_COLOR_BUFFER_BIT);
 
    //Use the prepared shader program
    glUseProgram(shader_program);
 
    //Scale and rotate the cube depending on the current time.
    float angle = fmod(double(cv::getTickCount()) / double(cv::getTickFrequency()), 2 * M_PI);
    float scale = 0.25;
 
    cv::Matx44f scaleMat(
            scale, 0.0, 0.0, 0.0,
            0.0, scale, 0.0, 0.0,
            0.0, 0.0, scale, 0.0,
            0.0, 0.0, 0.0, 1.0);
 
    cv::Matx44f rotXMat(
            1.0, 0.0, 0.0, 0.0,
            0.0, cos(angle), -sin(angle), 0.0,
            0.0, sin(angle), cos(angle), 0.0,
            0.0, 0.0, 0.0, 1.0);
 
    cv::Matx44f rotYMat(
            cos(angle), 0.0, sin(angle), 0.0,
            0.0, 1.0, 0.0, 0.0,
            -sin(angle), 0.0,cos(angle), 0.0,
            0.0, 0.0, 0.0, 1.0);
 
    cv::Matx44f rotZMat(
            cos(angle), -sin(angle), 0.0, 0.0,
            sin(angle), cos(angle), 0.0, 0.0,
            0.0, 0.0, 1.0, 0.0,
            0.0, 0.0, 0.0, 1.0);
 
    //calculate the transform
    cv::Matx44f transform = scaleMat * rotXMat * rotYMat * rotZMat;
    //set the corresponding uniform
    glUniformMatrix4fv(uniform_transform, 1, GL_FALSE, transform.val);
    //Bind the prepared vertex array object
    glBindVertexArray(vao);
    //Draw
    glDrawElements(GL_TRIANGLES, triangles * 3, GL_UNSIGNED_SHORT, NULL);
}
 
#ifndef __EMSCRIPTEN__
//applies a glow effect to an image
static void glow_effect(const cv::UMat& src, cv::UMat& dst, const int ksize) {
    static cv::UMat resize;
    static cv::UMat blur;
    static cv::UMat dst16;
 
    cv::bitwise_not(src, dst);
 
    //Resize for some extra performance
    cv::resize(dst, resize, cv::Size(), 0.5, 0.5);
    //Cheap blur
    cv::boxFilter(resize, resize, -1, cv::Size(ksize, ksize), cv::Point(-1, -1), true,
            cv::BORDER_REPLICATE);
    //Back to original size
    cv::resize(resize, blur, src.size());
 
    //Multiply the src image with a blurred version of itself
    cv::multiply(dst, blur, dst16, 1, CV_16U);
    //Normalize and convert back to CV_8U
    cv::divide(dst16, cv::Scalar::all(255.0), dst, 1, CV_8U);
 
    cv::bitwise_not(dst, dst);
}
#endif
 
 
using namespace cv::v4d;
static bool iteration(cv::Ptr<V4D> window) {
    //Render using OpenGL
    window->gl(render_scene);
 
    //To slow for WASM
#ifndef __EMSCRIPTEN__
    //Aquire the frame buffer for use by OpenCV
    window->fb([&](cv::UMat& framebuffer) {
        glow_effect(framebuffer, framebuffer, glow_kernel_size);
    });
#endif
 
    window->write();
 
    return window->display();
}
 
int main() {
    cv::Ptr<V4D> window = V4D::make(WIDTH, HEIGHT, "Cube Demo", OFFSCREEN, false, 0);
    window->printSystemInfo();
#ifndef __EMSCRIPTEN__
    //Creates a writer sink (which might be hardware accelerated)
    Sink sink = makeWriterSink(OUTPUT_FILENAME, FPS, cv::Size(WIDTH, HEIGHT));
    window->setSink(sink);
#endif
    window->gl(init_scene);
    window->run(iteration);
 
    return 0;
}