用OpenCV实现随机发生器与文本

目标

学习使用随机数发生器类(RNG)并从一个均匀分布中得到一个随机数。
利用putText函数来展现文本

代码

将使用随机数作为绘画的参数，并用大量的几何图形来组成图像。既然会随机初始化，这个过程会使用loop来自动实现。
代码在OpenCV的sample文件夹中（一般是%your_opencv_folder%\sources\samples\cpp\tutorial_code\core\Matrix）；也可以从这里获得；在本文最后也附上了。

解释

1.先从主函数开始看起。可看到首先做的事就是创建一个随机数发生器对象(RNG)。

 RNG rng(0xFFFFFFFF)

2.然后创建了一个初始为0的矩阵（全黑），确定了其高度、宽度和类型。

/// Initialize a matrix with zeros
Mat image = Mat::zeros(window_height, window_width, CV_8UC3);

/// Show it in a window during DELAY ms
imshow(window_name, image);

3.接着进行画疯狂道具

/// Draw some lines
c = Drawing _Random_Lines(image, window_name. rng);
if(c != 0) return 0;

...

/// Display text in random positoins
c = Displaying_Random_Text(image, window_name, rng);
if(c != 0) return 0;

/// Displaying the big end
c = Displaying_Big_End(image, window_name, rng);

所有这些函数都遵循相同的模式。

4.查看Drawing_Random_Lines函数。

int Drawing_Random_Lines( Mat image, char* window_name, RNG rng )
{
  int lineType = 8;
  Point pt1, pt2;

  for( int i = 0; i < NUMBER; i++ )
  {
   pt1.x = rng.uniform( x_1, x_2 );
   pt1.y = rng.uniform( y_1, y_2 );
   pt2.x = rng.uniform( x_1, x_2 );
   pt2.y = rng.uniform( y_1, y_2 );

   line( image, pt1, pt2, randomColor(rng), rng.uniform(1, 10), 8 );
   imshow( window_name, image );
   if( waitKey( DELAY ) >= 0 )
   { return -1; }
  }
  return 0;
}

共绘制了NUMBER条直线，因直线的绘制函数line所在代码块被循环了NUMBER次。
直线的端点由pt1和pt2决定，而pt1和pt2都是随机决定的（坐标值x和y都分别由函数rng.uniform(inclusive in a, exclusive b)产生）。
直线的颜色由random(rng)函数得到，其中randomColor()的实现为

static Scalar randomColor( RNG& rng )
{
  int icolor = (unsigned) rng;
  return Scalar( icolor&255, (icolor>>8)&255, (icolor>>16)&255 );
}

也是随机生成的。

5.查看Display_Random_Text函数：

int Displaying_Random_Text( Mat image, char* window_name, RNG rng )
{
  int lineType = 8;

  for ( int i = 1; i < NUMBER; i++ )
  {
    Point org;
    org.x = rng.uniform(x_1, x_2);
    org.y = rng.uniform(y_1, y_2);

    putText( image, "Testing text rendering", org, rng.uniform(0,8),
             rng.uniform(0,100)*0.05+0.1, randomColor(rng), rng.uniform(1, 10), lineType);

    imshow( window_name, image );
    if( waitKey(DELAY) >= 0 )
      { return -1; }
  }

  return 0;
}

代码与前面的类似除了下面这个表达式

putText( image, "Testing text rendering", org, rng.uniform(0,8),
         rng.uniform(0,100)*0.05+0.1, randomColor(rng), rng.uniform(1, 10), lineType);

附录：代码

/**
 * @file Drawing_2.cpp
 * @brief Simple sample code
 */

#include 
#include 
#include 
#include 

using namespace cv;

/// Global Variables
const int NUMBER = 100;
const int DELAY = 5;

const int window_width = 900;
const int window_height = 600;
int x_1 = -window_width/2;
int x_2 = window_width*3/2;
int y_1 = -window_width/2;
int y_2 = window_width*3/2;

/// Function headers
static Scalar randomColor( RNG& rng );
int Drawing_Random_Lines( Mat image, char* window_name, RNG rng );
int Drawing_Random_Rectangles( Mat image, char* window_name, RNG rng );
int Drawing_Random_Ellipses( Mat image, char* window_name, RNG rng );
int Drawing_Random_Polylines( Mat image, char* window_name, RNG rng );
int Drawing_Random_Filled_Polygons( Mat image, char* window_name, RNG rng );
int Drawing_Random_Circles( Mat image, char* window_name, RNG rng );
int Displaying_Random_Text( Mat image, char* window_name, RNG rng );
int Displaying_Big_End( Mat image, char* window_name, RNG rng );


/**
 * @function main
 */
int main( void )
{
  int c;

  /// Start creating a window
  char window_name[] = "Drawing_2 Tutorial";

  /// Also create a random object (RNG)
  RNG rng( 0xFFFFFFFF );

  /// Initialize a matrix filled with zeros
  Mat image = Mat::zeros( window_height, window_width, CV_8UC3 );
  /// Show it in a window during DELAY ms
  imshow( window_name, image );
  waitKey( DELAY );

  /// Now, let's draw some lines
  c = Drawing_Random_Lines(image, window_name, rng);
  if( c != 0 ) return 0;

  /// Go on drawing, this time nice rectangles
  c = Drawing_Random_Rectangles(image, window_name, rng);
  if( c != 0 ) return 0;

  /// Draw some ellipses
  c = Drawing_Random_Ellipses( image, window_name, rng );
  if( c != 0 ) return 0;

  /// Now some polylines
  c = Drawing_Random_Polylines( image, window_name, rng );
  if( c != 0 ) return 0;

  /// Draw filled polygons
  c = Drawing_Random_Filled_Polygons( image, window_name, rng );
  if( c != 0 ) return 0;

  /// Draw circles
  c = Drawing_Random_Circles( image, window_name, rng );
  if( c != 0 ) return 0;

  /// Display text in random positions
  c = Displaying_Random_Text( image, window_name, rng );
  if( c != 0 ) return 0;

  /// Displaying the big end!
  c = Displaying_Big_End( image, window_name, rng );
  if( c != 0 ) return 0;

  waitKey(0);
  return 0;
}

/// Function definitions

/**
 * @function randomColor
 * @brief Produces a random color given a random object
 */
static Scalar randomColor( RNG& rng )
{
  int icolor = (unsigned) rng;
  return Scalar( icolor&255, (icolor>>8)&255, (icolor>>16)&255 );
}


/**
 * @function Drawing_Random_Lines
 */
int Drawing_Random_Lines( Mat image, char* window_name, RNG rng )
{
  Point pt1, pt2;

  for( int i = 0; i < NUMBER; i++ )
  {
    pt1.x = rng.uniform( x_1, x_2 );
    pt1.y = rng.uniform( y_1, y_2 );
    pt2.x = rng.uniform( x_1, x_2 );
    pt2.y = rng.uniform( y_1, y_2 );

    line( image, pt1, pt2, randomColor(rng), rng.uniform(1, 10), 8 );
    imshow( window_name, image );
    if( waitKey( DELAY ) >= 0 )
      { return -1; }
  }

  return 0;
}

/**
 * @function Drawing_Rectangles
 */
int Drawing_Random_Rectangles( Mat image, char* window_name, RNG rng )
{
  Point pt1, pt2;
  int lineType = 8;
  int thickness = rng.uniform( -3, 10 );

  for( int i = 0; i < NUMBER; i++ )
  {
    pt1.x = rng.uniform( x_1, x_2 );
    pt1.y = rng.uniform( y_1, y_2 );
    pt2.x = rng.uniform( x_1, x_2 );
    pt2.y = rng.uniform( y_1, y_2 );

    rectangle( image, pt1, pt2, randomColor(rng), MAX( thickness, -1 ), lineType );

    imshow( window_name, image );
    if( waitKey( DELAY ) >= 0 )
      { return -1; }
  }

  return 0;
}

/**
 * @function Drawing_Random_Ellipses
 */
int Drawing_Random_Ellipses( Mat image, char* window_name, RNG rng )
{
  int lineType = 8;

  for ( int i = 0; i < NUMBER; i++ )
  {
    Point center;
    center.x = rng.uniform(x_1, x_2);
    center.y = rng.uniform(y_1, y_2);

    Size axes;
    axes.width = rng.uniform(0, 200);
    axes.height = rng.uniform(0, 200);

    double angle = rng.uniform(0, 180);

    ellipse( image, center, axes, angle, angle - 100, angle + 200,
             randomColor(rng), rng.uniform(-1,9), lineType );

    imshow( window_name, image );

    if( waitKey(DELAY) >= 0 )
      { return -1; }
  }

  return 0;
}

/**
 * @function Drawing_Random_Polylines
 */
int Drawing_Random_Polylines( Mat image, char* window_name, RNG rng )
{
  int lineType = 8;

  for( int i = 0; i< NUMBER; i++ )
  {
    Point pt[2][3];
    pt[0][0].x = rng.uniform(x_1, x_2);
    pt[0][0].y = rng.uniform(y_1, y_2);
    pt[0][1].x = rng.uniform(x_1, x_2);
    pt[0][1].y = rng.uniform(y_1, y_2);
    pt[0][2].x = rng.uniform(x_1, x_2);
    pt[0][2].y = rng.uniform(y_1, y_2);
    pt[1][0].x = rng.uniform(x_1, x_2);
    pt[1][0].y = rng.uniform(y_1, y_2);
    pt[1][1].x = rng.uniform(x_1, x_2);
    pt[1][1].y = rng.uniform(y_1, y_2);
    pt[1][2].x = rng.uniform(x_1, x_2);
    pt[1][2].y = rng.uniform(y_1, y_2);

    const Point* ppt[2] = {pt[0], pt[1]};
    int npt[] = {3, 3};

    polylines(image, ppt, npt, 2, true, randomColor(rng), rng.uniform(1,10), lineType);

    imshow( window_name, image );
    if( waitKey(DELAY) >= 0 )
      { return -1; }
  }
  return 0;
}

/**
 * @function Drawing_Random_Filled_Polygons
 */
int Drawing_Random_Filled_Polygons( Mat image, char* window_name, RNG rng )
{
  int lineType = 8;

  for ( int i = 0; i < NUMBER; i++ )
  {
    Point pt[2][3];
    pt[0][0].x = rng.uniform(x_1, x_2);
    pt[0][0].y = rng.uniform(y_1, y_2);
    pt[0][1].x = rng.uniform(x_1, x_2);
    pt[0][1].y = rng.uniform(y_1, y_2);
    pt[0][2].x = rng.uniform(x_1, x_2);
    pt[0][2].y = rng.uniform(y_1, y_2);
    pt[1][0].x = rng.uniform(x_1, x_2);
    pt[1][0].y = rng.uniform(y_1, y_2);
    pt[1][1].x = rng.uniform(x_1, x_2);
    pt[1][1].y = rng.uniform(y_1, y_2);
    pt[1][2].x = rng.uniform(x_1, x_2);
    pt[1][2].y = rng.uniform(y_1, y_2);

    const Point* ppt[2] = {pt[0], pt[1]};
    int npt[] = {3, 3};

    fillPoly( image, ppt, npt, 2, randomColor(rng), lineType );

    imshow( window_name, image );
    if( waitKey(DELAY) >= 0 )
       { return -1; }
  }
  return 0;
}

/**
 * @function Drawing_Random_Circles
 */
int Drawing_Random_Circles( Mat image, char* window_name, RNG rng )
{
  int lineType = 8;

  for (int i = 0; i < NUMBER; i++)
  {
    Point center;
    center.x = rng.uniform(x_1, x_2);
    center.y = rng.uniform(y_1, y_2);

    circle( image, center, rng.uniform(0, 300), randomColor(rng),
            rng.uniform(-1, 9), lineType );

    imshow( window_name, image );
    if( waitKey(DELAY) >= 0 )
      { return -1; }
  }

  return 0;
}

/**
 * @function Displaying_Random_Text
 */
int Displaying_Random_Text( Mat image, char* window_name, RNG rng )
{
  int lineType = 8;

  for ( int i = 1; i < NUMBER; i++ )
  {
    Point org;
    org.x = rng.uniform(x_1, x_2);
    org.y = rng.uniform(y_1, y_2);

    putText( image, "Testing text rendering", org, rng.uniform(0,8),
             rng.uniform(0,100)*0.05+0.1, randomColor(rng), rng.uniform(1, 10), lineType);

    imshow( window_name, image );
    if( waitKey(DELAY) >= 0 )
      { return -1; }
  }

  return 0;
}

/**
 * @function Displaying_Big_End
 */
int Displaying_Big_End( Mat image, char* window_name, RNG )
{
  Size textsize = getTextSize("OpenCV forever!", FONT_HERSHEY_COMPLEX, 3, 5, 0);
  Point org((window_width - textsize.width)/2, (window_height - textsize.height)/2);
  int lineType = 8;

  Mat image2;

  for( int i = 0; i < 255; i += 2 )
  {
    image2 = image - Scalar::all(i);
    putText( image2, "OpenCV forever!", org, FONT_HERSHEY_COMPLEX, 3,
             Scalar(i, i, 255), 5, lineType );

    imshow( window_name, image2 );
    if( waitKey(DELAY) >= 0 )
       { return -1; }
  }

  return 0;
}