「Cyrus Beckアルゴリズム」の版間の差分

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ページの作成:「'''Cyrus Beck アルゴリズム'''とは、線分をポリゴンの範囲内にクリッピングするアルゴリズムである。 Cohen Sutherlandアル…」
 
 
94行目: 94行目:
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}
</source>
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== C++での実装例 ==
<source lang="cpp">
// C++ Program to implement Cyrus Beck
 
#include <SFML/Graphics.hpp>
#include <iostream>
#include <utility>
#include <vector>
 
using namespace std;
using namespace sf;
 
// Function to draw a line in SFML
void drawline(RenderWindow* window, pair<int, int> p0, pair<int, int> p1)
{
    Vertex line[] = {
        Vertex(Vector2f(p0.first, p0.second)),
        Vertex(Vector2f(p1.first, p1.second))
    };
    window->draw(line, 2, Lines);
}
 
// Function to draw a polygon, given vertices
void drawPolygon(RenderWindow* window, pair<int, int> vertices[], int n)
{
    for (int i = 0; i < n - 1; i++)
        drawline(window, vertices[i], vertices[i + 1]);
    drawline(window, vertices[0], vertices[n - 1]);
}
 
// Function to take dot product
int dot(pair<int, int> p0, pair<int, int> p1)
{
    return p0.first * p1.first + p0.second * p1.second;
}
 
// Function to calculate the max from a vector of floats
float max(vector<float> t)
{
    float maximum = INT_MIN;
    for (int i = 0; i < t.size(); i++)
        if (t[i] > maximum)
            maximum = t[i];
    return maximum;
}
 
// Function to calculate the min from a vector of floats
float min(vector<float> t)
{
    float minimum = INT_MAX;
    for (int i = 0; i < t.size(); i++)
        if (t[i] < minimum)
            minimum = t[i];
    return minimum;
}
 
// Cyrus Beck function, returns a pair of values
// that are then displayed as a line
pair<int, int>* CyrusBeck(pair<int, int> vertices[],
                          pair<int, int> line[], int n)
{
 
    // Temporary holder value that will be returned
    pair<int, int>* newPair = new pair<int, int>[2];
 
    // Normals initialized dynamically(can do it statically also, doesn't matter)
    pair<int, int>* normal = new pair<int, int>[n];
 
    // Calculating the normals
    for (int i = 0; i < n; i++) {
        normal[i].second = vertices[(i + 1) % n].first - vertices[i].first;
        normal[i].first = vertices[i].second - vertices[(i + 1) % n].second;
       
    }
 
    // Calculating P1 - P0
    pair<int, int> P1_P0
        = make_pair(line[1].first - line[0].first,
                    line[1].second - line[0].second);
 
    // Initializing all values of P0 - PEi
    pair<int, int>* P0_PEi = new pair<int, int>[n];
 
    // Calculating the values of P0 - PEi for all edges
    for (int i = 0; i < n; i++) {
 
        // Calculating PEi - P0, so that the
        // denominator won't have to multiply by -1
        P0_PEi[i].first
            = vertices[i].first - line[0].first;
 
        // while calculating 't'
        P0_PEi[i].second = vertices[i].second - line[0].second;
       
        cout << P0_PEi[i].first << "," << P0_PEi[i].second <<endl;
    }
    cout << endl;
   
    int *numerator = new int[n], *denominator = new int[n];
 
    // Calculating the numerator and denominators
    // using the dot function
    for (int i = 0; i < n; i++) {
        numerator[i] = dot(normal[i], P0_PEi[i]);
        denominator[i] = dot(normal[i], P1_P0);
       
        cout << numerator[i] << "," << denominator[i] << endl;
    }
    cout << endl;
 
    // Initializing the 't' values dynamically
    float* t = new float[n];
 
    // Making two vectors called 't entering'
    // and 't leaving' to group the 't's
    // according to their denominators
    vector<float> tE, tL;
 
    // Calculating 't' and grouping them accordingly
    for (int i = 0; i < n; i++) {
 
        t[i] = (float)(numerator[i]) / (float)(denominator[i]);
        cout << t[i] << endl;
 
        if (denominator[i] > 0)
            tE.push_back(t[i]);
        else
            tL.push_back(t[i]);
    }
    cout << endl;
 
    // Initializing the final two values of 't'
    float temp[2];
 
    // Taking the max of all 'tE' and 0, so pushing 0
    tE.push_back(0.f);
    temp[0] = max(tE);
 
    // Taking the min of all 'tL' and 1, so pushing 1
    tL.push_back(1.f);
    temp[1] = min(tL);
 
    // Entering 't' value cannot be
    // greater than exiting 't' value,
    // hence, this is the case when the line
    // is completely outside
    if (temp[0] > temp[1]) {
        newPair[0] = make_pair(-1, -1);
        newPair[1] = make_pair(-1, -1);
        return newPair;
    }
 
    // Calculating the coordinates in terms of x and y
    newPair[0].first  = (float)line[0].first  + (float)P1_P0.first  * (float)temp[0];
    newPair[0].second = (float)line[0].second + (float)P1_P0.second * (float)temp[0];
    newPair[1].first  = (float)line[0].first  + (float)P1_P0.first  * (float)temp[1];
    newPair[1].second = (float)line[0].second + (float)P1_P0.second * (float)temp[1];
    cout << '(' << newPair[0].first << ", "
        << newPair[0].second << ") ("
        << newPair[1].first << ", "
        << newPair[1].second << ")";
 
    return newPair;
}
 
// Driver code
int main()
{
 
    // Setting up a window and loop
    // and the vertices of the polygon and line
    RenderWindow window(VideoMode(500, 500), "Cyrus Beck");
    pair<int, int> vertices[]
        = { make_pair(200, 50),
            make_pair(250, 100),
            make_pair(200, 150),
            make_pair(100, 150),
            make_pair(50, 100),
            make_pair(100, 50) };
 
    // Make sure that the vertices
    // are put in a clockwise order
    int n = sizeof(vertices) / sizeof(vertices[0]);
    pair<int, int> line[] = { make_pair(10, 10), make_pair(450, 200) };
    pair<int, int>* temp1 = CyrusBeck(vertices, line, n);
    pair<int, int> temp2[2];
    temp2[0] = line[0];
    temp2[1] = line[1];
 
    // To allow clipping and unclipping
    // of the line by just pressing a key
    bool trigger = false;
    while (window.isOpen()) {
        window.clear();
        Event event;
        if (window.pollEvent(event)) {
            if (event.type == Event::Closed)
                window.close();
            if (event.type == Event::KeyPressed)
                trigger = !trigger;
        }
        drawPolygon(&window, vertices, n);
 
        // Using the trigger value to clip
        // and unclip a line
        if (trigger) {
            line[0] = temp1[0];
            line[1] = temp1[1];
        }
        else {
            line[0] = temp2[0];
            line[1] = temp2[1];
        }
        drawline(&window, line[0], line[1]);
        window.display();
    }
    return 0;
}
</source>
[[macOS]]に[[SFML]]を入れる。
brew install sfml
[[clang]]で[[ビルド]]する。
c++ cyrusbeck.cpp -o cyrusbeck -lsfml-window -lsfml-graphics -lsfml-system
* https://www.geeksforgeeks.org/line-clipping-set-2-cyrus-beck-algorithm/


== 関連項目 ==
== 関連項目 ==
<nowiki>*</nowiki> [[クリップスペース座標]]
<nowiki>*</nowiki> [[クリップスペース座標]]
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