[PA 2] Object Picker - Bunny 만들기

Update: 2023.04.14 Updated: 2022.04.14

Category: Computer Graphics

Tags: pa rendering

Task Lists

Load and draw mesh [9 Points]

Do not read your mesh with absolute path. If you read your mesh with absolute path, it would not run in my system. (Execution fail, Your score will be 0)
Implement picking with front and back buffer method [9 Points]
- Change color when you only pick the surface of bunny
- Draw the rendering result in the front buffer
- Draw the image of object id in the back buffer
- Read the pixel value of back buffer when you click the image and identify what object is under the cursor.

정리하면, bunny 모델을 띄우고 클릭했을 때 토끼의 색깔을 바꾸는 코드를 짜는 과제

먼저 mesh 모델을 받아와서 띄우고 -> front buffer, back buffer로 나누어서 받기
클릭할 때마다 픽셀 정보를 받아오기
bunny 색과 같은 경우 -> 다른 픽셀 값을 적용

Result Image

원래는 흰색에서 토끼 영역을 클릭하면 분홍색으로 바뀐다.

Code Implementation

tinyobj의 경우, 참고할 수 있는 리소스가 많이 없어서 어려웠다. 모델 불러오는 것부터 많이 막혔었는데 여기서 도움이 된 건 tinyobj 원본 코드 파일 주석을 참고한 거랑 헤더 파일에서 함수 원형을 뜯어보는게 제일 이해가 빠른 것 같다.

#include <iostream>
#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <tinyobjloader/tiny_obj_loader.h>
#include <glm/gtc/type_ptr.hpp>
#include <glm/gtx/string_cast.hpp>

double red = 1.0;
double green = 1.0;
double blue = 1.0;
double xpos, ypos;
float pixels[3];

// Window dimensions
const GLuint WIDTH = 1280, HEIGHT = 720;

// Function prototypes
void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode);
void mouse_button_callback(GLFWwindow* window, int button, int action, int mode){
    glfwGetCursorPos(window, &xpos, &ypos);
    
    glReadBuffer(GL_BACK);
    glReadPixels(xpos, HEIGHT-ypos, 1, 1, GL_RGB, GL_FLOAT, pixels);
    
    if (button == GLFW_MOUSE_BUTTON_LEFT && action == GLFW_PRESS){
        if (pixels[0] == 0.0f && pixels[1] == 0.0f && pixels[2] == 0.0f){
            red = 220.f/255.f, green = 81.f/255.f, blue = 120.f/255.f;
        }
        else {
            red = 1.0, green = 1.0, blue = 1.0;
        }
    }
}

// The MAIN function, from here we start the application and run the game loop
int main()
{
    std::cout << "Starting GLFW context, OpenGL 3.1" << std::endl;
    // Init GLFW
    glfwInit();
    // Set all the required options for GLFW
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 2);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 0);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_ANY_PROFILE);
    glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);

    // Create a GLFWwindow object that we can use for GLFW's functions
    GLFWwindow* window = glfwCreateWindow(WIDTH, HEIGHT, "glskeleton", NULL, NULL);
    glfwMakeContextCurrent(window);
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }

    // Set the required callback functions
    glfwSetKeyCallback(window, key_callback);
    glfwSetMouseButtonCallback(window, mouse_button_callback);

    if (!gladLoadGLLoader((GLADloadproc) glfwGetProcAddress))
    {
        std::cout << "Failed to initialize OpenGL context" << std::endl;
        return -1;
    }
    // load model
    tinyobj::attrib_t attr;
    std::vector< tinyobj::shape_t > shaps;
    std::vector< tinyobj::material_t > mats;
    std::string inputfile = "bunny.obj";
    std::string warn;
    std::string err;

    bool ret = tinyobj::LoadObj(&attr, &shaps, &mats, &warn, &err, inputfile.c_str());
      
    if (!err.empty()) { // `err` may contain warning message.
      std::cerr << err << std::endl;
    }

    if (!ret) {
      exit(1);
    }
    

    // Define the viewport dimensions
    glViewport(0, 0, WIDTH, HEIGHT);
    
    glm::mat4 matModel1 = glm::identity<glm::mat4>(); //4x4 identity matrix
    glm::mat4 matModel2 = glm::identity<glm::mat4>(); //4x4 identity matrix
    glm::mat4 matView = glm::lookAt(glm::vec3(0, 4, 4), glm::vec3(0, 0, 0), glm::vec3(0, 1, 0));
    glm::mat4 matProj = glm::perspective(glm::radians(60.0f), (float)WIDTH/HEIGHT, 0.1f, 100.0f);

    // Render loop
    while (!glfwWindowShouldClose(window))
    {
        glfwWaitEvents(); //waits for input
        
        // Check if any events have been activated (key pressed, mouse moved etc.) and call corresponding response functions
        glfwPollEvents();
        
        // Render
        // Clear the colorbuffer
        glDrawBuffer(GL_FRONT);
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
        
        // set projection matrix for this frame
        glMatrixMode(GL_PROJECTION); // set projection matrix
        // use either of following lines to set the value of projection matrix
        glLoadMatrixf(glm::value_ptr(matProj)); // you should include glm/gtc/type_ptr.hpp for glm::value_ptr
        glLoadMatrixf(&matProj[0][0]); // you can use this also.
        
        // set model view matrix for the model1
        glm::mat4 modelView1 = matView * matModel1;
        glMatrixMode(GL_MODELVIEW);
        glLoadMatrixf(glm::value_ptr(modelView1));
        
        glBegin(GL_TRIANGLES);
        glColor3d(red, green, blue);
        // draw
        for (size_t s = 0; s < shaps.size(); s++) {

            size_t idx_offset = 0;
            
            for (size_t i = 0; i < shaps[s].mesh.num_face_vertices.size(); i++) {
                
                int offset = shaps[s].mesh.num_face_vertices[i];
                
                for (size_t j = 0; j < offset; j++) {
                    // access to vertex
                    tinyobj::index_t idx = shaps[s].mesh.indices[idx_offset + j];
                    tinyobj::real_t x = attr.vertices[3*idx.vertex_index+0];
                    tinyobj::real_t y = attr.vertices[3*idx.vertex_index+1];
                    tinyobj::real_t z = attr.vertices[3*idx.vertex_index+2];
                    glVertex3f(x, y, z);
                }
                idx_offset += offset;
            }
        }
        glEnd();
        glFlush();
        
        glDrawBuffer(GL_BACK);
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
        
        // set projection matrix for this frame
        glMatrixMode(GL_PROJECTION); // set projection matrix
        // use either of following lines to set the value of projection matrix
        glLoadMatrixf(glm::value_ptr(matProj)); // you should include glm/gtc/type_ptr.hpp for glm::value_ptr
        glLoadMatrixf(&matProj[0][0]); // you can use this also.
        
        // set model view matrix for the model1
        glm::mat4 modelView2 = matView * matModel1;
        glMatrixMode(GL_MODELVIEW);
        glLoadMatrixf(glm::value_ptr(modelView2));
        
        glBegin(GL_TRIANGLES);
        glColor3d(0.0, 0.0, 0.0);
        // draw
        for (size_t s = 0; s < shaps.size(); s++) {

            size_t idx_offset = 0;
            
            for (size_t i = 0; i < shaps[s].mesh.num_face_vertices.size(); i++) {
                
                int offset = shaps[s].mesh.num_face_vertices[i];
                
                for (size_t j = 0; j < offset; j++) {
                    tinyobj::index_t idx = shaps[s].mesh.indices[idx_offset + j];
                    tinyobj::real_t x = attr.vertices[3*idx.vertex_index+0];
                    tinyobj::real_t y = attr.vertices[3*idx.vertex_index+1];
                    tinyobj::real_t z = attr.vertices[3*idx.vertex_index+2];
                    glVertex3f(x, y, z);
                }
                idx_offset += offset;
            }
        }
        glEnd();
        glFlush();
        // Swap the screen buffers
        glFinish();
    }

    // Terminates GLFW, clearing any resources allocated by GLFW.
    glfwTerminate();
    return 0;
}

// Is called whenever a key is pressed/released via GLFW
void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode)
{
    if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
        glfwSetWindowShouldClose(window, GL_TRUE);
}

맨 위로 이동하기

승빈 Binnie Shin

[PA 2] Object Picker - Bunny 만들기

Task Lists

Result Image

Code Implementation

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