如何实现图像2D转换？|物体旋转

本文概述

• C
• CPP

我们必须围绕给定的枢轴点将对象旋转给定的角度, 然后打印新的坐标。

例子：

Input : {(100, 100), (150, 200), (200, 200), (200, 150)} is to be rotated about 
          (0, 0) by 90 degrees
Output : (-100, 100), (-200, 150), (-200, 200), (-150, 200)

Input : {(100, 100), (100, 200), (200, 200)} 
        is to be rotated about (50, -50) by 
         -45 degrees
Output : (191.421, 20.7107), (262.132, 91.4214), (332.843, 20.7107)

为了旋转对象, 我们需要分别旋转图形的每个顶点。

将点P(x, y)绕原点旋转角度A, 我们得到一个点P'(x', y')。 x’和y’的值可以如下计算：

我们知道,

x = rcosB, y = rsinB

x’ = rcos(A+B) = r(cosAcosB – sinAsinB) = rcosBcosA – rsinBsinA = xcosA – ysinA

y’ = rsin(A+B) = r(sinAcosB + cosAsinB) = rcosBsinA + rsinBcosA = xsinA + ycosA

旋转矩阵方程：-

C

// C program to rotate an object by
// a given angle about a given point
#include <math.h>
#include <stdio.h>
 
// Using macros to convert degree to radian
// and call sin() and cos() as these functions
// take input in radians
#define SIN(x) sin(x * 3.141592653589 / 180)
#define COS(x) cos(x * 3.141592653589 / 180)
 
// To rotate an object
void rotate( float a[][2], int n, int x_pivot, int y_pivot, int angle)
{
     int i = 0;
     while (i < n) {
         // Shifting the pivot point to the origin
         // and the given points accordingly
         int x_shifted = a[i][0] - x_pivot;
         int y_shifted = a[i][1] - y_pivot;
 
         // Calculating the rotated point co-ordinates
         // and shifting it back
         a[i][0] = x_pivot
                   + (x_shifted * COS(angle)
                      - y_shifted * SIN(angle));
         a[i][1] = y_pivot
                   + (x_shifted * SIN(angle)
                      + y_shifted * COS(angle));
         printf ( "(%f, %f) " , a[i][0], a[i][1]);
         i++;
     }
}
 
// Driver Code
int main()
{
     // 1st Example
     // The following figure is to be
     // rotated about (0, 0) by 90 degrees
     int size1 = 4; // No. of vertices
 
     // Vertex co-ordinates must be in order
     float points_list1[][2] = { { 100, 100 }, { 150, 200 }, { 200, 200 }, { 200, 150 } };
     rotate(points_list1, size1, 0, 0, 90);
 
     // 2nd Example
     // The following figure is to be
     // rotated about (50, -50) by -45 degrees
     /*int size2 = 3;//No. of vertices
     float points_list2[][2] = {{100, 100}, {100, 200}, {200, 200}};
     rotate(points_list2, size2, 50, -50, -45);*/
     return 0;
}

CPP

// C++ program to rotate an object by
// a given angle about a given point
#include <iostream>
#include <math.h>
using namespace std;
 
// Using macros to convert degree to radian
// and call sin() and cos() as these functions
// take input in radians
#define SIN(x) sin(x * 3.141592653589 / 180)
#define COS(x) cos(x * 3.141592653589 / 180)
 
// To rotate an object given as order set of points in a[]
// (x_pivot, y_pivot)
void rotate( float a[][2], int n, int x_pivot, int y_pivot, int angle)
{
     int i = 0;
     while (i < n) {
         // Shifting the pivot point to the origin
         // and the given points accordingly
         int x_shifted = a[i][0] - x_pivot;
         int y_shifted = a[i][1] - y_pivot;
 
         // Calculating the rotated point co-ordinates
         // and shifting it back
         a[i][0] = x_pivot
                   + (x_shifted * COS(angle)
                      - y_shifted * SIN(angle));
         a[i][1] = y_pivot
                   + (x_shifted * SIN(angle)
                      + y_shifted * COS(angle));
         cout << "(" << a[i][0] << ", " << a[i][1] << ") " ;
         i++;
     }
}
 
// Driver Code
int main()
{
     // 1st Example
     // The following figure is to be
     // rotated about (0, 0) by 90 degrees
     int size1 = 4; // No. of vertices
     // Vertex co-ordinates must be in order
     float points_list1[][2] = { { 100, 100 }, { 150, 200 }, { 200, 200 }, { 200, 150 } };
     rotate(points_list1, size1, 0, 0, 90);
 
     // 2nd Example
     // The following figure is to be
     // rotated about (50, -50) by -45 degrees
     /*int size2 = 3;//No. of vertices
     float points_list2[][2] = {{100, 100}, {100, 200}, {200, 200}};
     rotate(points_list2, size2, 50, -50, -45);*/
     return 0;
}

输出如下：

(-100, 100), (-200, 150), (-200, 200), (-150, 200)

参考文献：旋转矩阵