###### tags: `東京威力 TEL`
# I. 影像辨識 OpenCV
## <font color="orange"> 03. 畫圖</font>

### <font color="pink">3-1. 建立黑屏與畫直線</font>
開黑屏的寫法：

Mat black(500, 750, CV_8UC3, Scalar(0,0,0));
Mat black_2(500, 750, CV_8UC3, Scalar::all(0));

畫圖函式直接看怎麼用就可以了。
><font color = "magenza">line (圖檔, 線起點, 線終點, 線顏色, 線粗度)</font>

#include <iostream>
#include <opencv2/opencv.hpp>

using namespace std;
using namespace cv;

int main(){
    Mat black(500, 750, CV_8UC3, Scalar(0,0,0)); // 建立黑屏

    Point p1(10, 10);
    Point p2(200, 300);
    Scalar color = Scalar(255, 0, 0);
    
    line(black, p1, p2, color,3);  // 畫線

    while(1){
        imshow("black", black);
        if(waitKey(1) == 27) break; 
    }
    return 0 ;
}

:::success
CV_8UC3 的意思：
CV = OpenCV；8U = 8 bits；C3 = 3 channels。
通常未處理過的照片都是 RGB ，它的型別 (type) 就會是 CV_8UC3。
:::

### <font color="pink">3-2. 畫矩形</font>
在使用 `rectangle()` 繪製矩形前，要先建立一個 `Rect` 實例描述矩形特徵。
><font color = "magenza"> rect(座標X, 座標Y, 向右長度, 向下高度)</font>
><font color = "magenza"> rectangle(圖檔, rect特徵, 顏色, 粗細)</font>

#include <iostream>
#include <opencv2/opencv.hpp>

using namespace std;
using namespace cv;

int main(){
    Mat black(500, 500, CV_8UC3, Scalar(0,0,0));
  
    Rect rect = Rect(100, 200, 50, 80);  
  //Rect實例：在座標(100,200)，畫矩形，向右長50，向下長80。
    
    Scalar color = Scalar(0, 255, 0);
    rectangle(black, rect, color, 1);
    
    while(1){
        imshow("pic", black);
        if(waitKey(1)==27) break;
    }
    return 0 ;
}

### <font color="pink">3-3. 畫圓形</font>
><font color = "magenza"> circle(圖檔, 中心點, 半徑, 顏色, 粗細)</font>

#include <iostream>
#include <opencv2/opencv.hpp>

using namespace std;
using namespace cv;

int main(){

    Mat black(500, 500, CV_8UC3, Scalar(0,0,0));

    Point center(250, 250);
    circle(black, center, 30, Scalar(0,0,255), 2);

    while(waitKey(1)!=27){
        imshow("pic", black);
    }
    return 0;
}

### <font color="pink">3-4. 寫文字</font>
><font color = "magenza">putText(輸出圖片, 文字, 起始點, 字型, 字體大小, 顏色, 粗細, 線型, 顛倒)</font>

#include <iostream>
#include <opencv2/opencv.hpp>

using namespace std;
using namespace cv;

int main(){
    Mat black(500, 500, CV_8UC3, Scalar::all(0));
    
    putText(black, "Hello world!", Point(black.cols/3, black.rows/2), 3, 1, Scalar(0,255,0));
    imshow("text with black background", black);
    waitKey(0);
    return 0;
}

:yellow_heart: <font color = "yellow"> putText() 參數4 -- int fontFace </font>

enum HersheyFonts {
    FONT_HERSHEY_SIMPLEX        = 0, //!< normal size sans-serif font
    FONT_HERSHEY_PLAIN          = 1, //!< small size sans-serif font
    FONT_HERSHEY_DUPLEX         = 2, //!< normal size sans-serif font (more complex than FONT_HERSHEY_SIMPLEX)
    FONT_HERSHEY_COMPLEX        = 3, //!< normal size serif font
    FONT_HERSHEY_TRIPLEX        = 4, //!< normal size serif font (more complex than FONT_HERSHEY_COMPLEX)
    FONT_HERSHEY_COMPLEX_SMALL  = 5, //!< smaller version of FONT_HERSHEY_COMPLEX
    FONT_HERSHEY_SCRIPT_SIMPLEX = 6, //!< hand-writing style font
    FONT_HERSHEY_SCRIPT_COMPLEX = 7, //!< more complex variant of FONT_HERSHEY_SCRIPT_SIMPLEX
    FONT_ITALIC                 = 16 //!< flag for italic 
// fontFONT_ITALIC is not a font, but is a flag that can be combined with the other fonts to get italic text.
};