OpenCvSharp study notes 10--random numbers and drawing text (RNG, PutText, GetTextSize)

Purpose

RNG function usage

PutText function usage

GetTextSize function usage

RNG random number generation

Generate pseudo-random numbers. Note that when the initial state is the same, the random number sequence generated each time is the same.

PutText draws text

Function description: Draw text onto an image (Chinese is not supported). Undrawn text is replaced by question marks.

//函数原型
void PutText(InputOutputArray img,
    string text,
    Point org,
    HersheyFonts fontFace,
    double fontScale,
    Scalar color,
    int thickness = 1,
    LineTypes lineType = LineTypes.Link8,
    bool bottomLeftOrigin = false)

parameter	illustrate
InputOutputArray img	image to draw text
string text	Text content to be drawn
Point org	Text insertion point. The default is the lower left corner.
HersheyFonts fontFace	text font
double fontScale	Font scale factor
Scalar color	text color
int thickness	Text line width
LineTypes lineType	text line style
bool bottomLeftOrigin	The origin of the image is the lower left corner. The default is false, which is the upper left corner. When true, the displayed text is a reflection

/// <summary>
/// 绘制文本
/// </summary>
/// <param name="image"></param>
/// <param name="winName"></param>
/// <param name="rng"></param>
/// <returns></returns>
int Display_Big_End(Mat image, string winName)
{
    var text = "OpenCvSharp";
    double fontScale = 2D;
    int thickness = 4;

    //图像中心点
    Point center = new Point(image.Width >> 1, image.Height >> 1);

    Size textSize = Cv2.GetTextSize(text, HersheyFonts.HersheyComplex, fontScale, thickness, out int baseLine);
    //文字在图像的中心
    Point org = new Point((image.Width - textSize.Width) / 2, (image.Height + textSize.Height - baseLine) / 2);

    Mat image2;
    for (int i = 0; i < 255; i += 2)
    {
        image2 = image - Scalar.All(i);

        //bottomLeftOrign=false
        Cv2.PutText(image2, text, org, HersheyFonts.HersheyComplex, fontScale, new Scalar(i, i, 255), thickness, lineType, false); 

        //文本插入点
        Cv2.Circle(image2, org, 3, Scalar.White, -1);

        //图片中心点
        Cv2.Circle(image2, center, 5, Scalar.Green, -1);

        //文本的宽高
        Cv2.Rectangle(image2, org, new Point(org.X + textSize.Width, org.Y - textSize.Height), Scalar.Red);
        
        //基线位置
        Cv2.Line(image2, new Point(org.X, org.Y + baseLine), new Point(org.X + textSize.Width, org.Y + baseLine), Scalar.White, 1);

        //bottomLeftOrign = true，以基线为镜
        var newOrg = new Point(org.X, org.Y + baseLine * 2);
        Cv2.PutText(image2, text, newOrg, HersheyFonts.HersheyComplex, fontScale, new Scalar(i, i, 255), thickness, lineType, true);
        //新的文本插入点
        Cv2.Circle(image2, newOrg, 3, Scalar.White, -1);

        Cv2.ImShow(winName, image2);
        if (Cv2.WaitKey(DELAY) >= 0) return -1;
    }
    return 0;
}

The text above will be inserted normally. The red box is the text size obtained by GetTextSize, and the white dot on the left is the insertion point. The white line is the baseline.

 GetTextSize gets the size of drawn text

Function description: Calculate the width, height and baseline y-axis offset of the drawn text.

//函数原型
Size GetTextSize(string text,
    HersheyFonts fontFace,
    double fontScale,
    int thickness,
    out int baseLine)

parameter	illustrate
string text	The text content of the size to be calculated
HersheyFonts fontFace	text font
double fontScale	Font scale factor
int thickness	text weight
out int baseLine	The y-axis offset of the bottom text relative to the insertion point.

Source code example

int Width = 600;
int NUMBER = 50;
int DELAY = 50;
LineTypes lineType = LineTypes.Link8;

public void Run(ParamBase paramBase)
{
    //注意初始值一样，每次生成的随机数序列是一样的
    //RNG rng = new RNG(0xFFFFFFFF);
    RNG rng = new RNG((ulong)DateTime.Now.Ticks);            
    var winName = "Random generator and text with OpenCV";
    try
    {
        using (Mat image = Mat.Zeros(Width, Width, MatType.CV_8UC3))
        {
            int c = 0;
            //随机画线
            c = Drawing_Random_Lines(image.Clone(), winName, rng);
            if (c != 0) return;
            //随机绘制或填充矩形
            c = Drawing_Random_Rectangels(image.Clone(), winName, rng);
            if (c != 0) return;

            //随机绘制或填充椭圆轮廓
            c = Drawing_Random_Ellipses(image.Clone(), winName, rng);
            if (c != 0) return;

            //随机显示文本
            c = Drawing_Random_Text(image.Clone(), winName, rng);
            if (c != 0) return;

            //测试PutText或GetTextSize函数
            c = Display_Big_End(image, winName);
        }
    }
    catch { }
    finally
    {
        Cv2.DestroyAllWindows();
    }

}

/// <summary>
/// 绘制文本
/// </summary>
/// <param name="image"></param>
/// <param name="winName"></param>
/// <param name="rng"></param>
/// <returns></returns>
int Display_Big_End(Mat image, string winName)
{
    var text = "OpenCvSharp";
    double fontScale = 2D;
    int thickness = 4;

    //图像中心点
    Point center = new Point(image.Width >> 1, image.Height >> 1);

    Size textSize = Cv2.GetTextSize(text, HersheyFonts.HersheyComplex, fontScale, thickness, out int baseLine);
    //文字在图像的中心
    Point org = new Point((image.Width - textSize.Width) / 2, (image.Height + textSize.Height - baseLine) / 2);

    Mat image2;
    for (int i = 0; i < 255; i += 2)
    {
        image2 = image - Scalar.All(i);

        //bottomLeftOrign=false
        Cv2.PutText(image2, text, org, HersheyFonts.HersheyComplex, fontScale, new Scalar(i, i, 255), thickness, lineType, false); 

        //文本插入点
        Cv2.Circle(image2, org, 3, Scalar.White, -1);

        //图片中心点
        Cv2.Circle(image2, center, 5, Scalar.Green, -1);

        //文本的宽高
        Cv2.Rectangle(image2, org, new Point(org.X + textSize.Width, org.Y - textSize.Height), Scalar.Red);
        
        //基线位置
        Cv2.Line(image2, new Point(org.X, org.Y + baseLine), new Point(org.X + textSize.Width, org.Y + baseLine), Scalar.White, 1);

        //bottomLeftOrign = true，以基线为镜
        var newOrg = new Point(org.X, org.Y + baseLine * 2);
        Cv2.PutText(image2, text, newOrg, HersheyFonts.HersheyComplex, fontScale, new Scalar(i, i, 255), thickness, lineType, true);
        //新的文本插入点
        Cv2.Circle(image2, newOrg, 3, Scalar.White, -1);

        Cv2.ImShow(winName, image2);
        if (Cv2.WaitKey(DELAY) >= 0) return -1;
    }
    return 0;
}

/// <summary>
/// 随机绘制文本
/// </summary>
/// <param name="image"></param>
/// <param name="winName"></param>
/// <param name="rng"></param>
/// <returns></returns>
int Drawing_Random_Text(Mat image, string winName, RNG rng)
{
    Point org = new Point();
    for (int i = 0; i < NUMBER; i++)
    {
        org.X = rng.Uniform(0, Width);
        org.Y = rng.Uniform(0, Width);
        Cv2.PutText(image, "Testing text rendering", org,
                    (HersheyFonts)rng.Uniform(0, 8),
                    rng.Uniform(0, 100) * 0.05 + 0.1,
                    randomColor(rng),
                    rng.Uniform(0, 10),
                    lineType);
        Cv2.ImShow(winName, image);
        if (Cv2.WaitKey(DELAY) >= 0) return -1;
    }
    return 0;
}

/// <summary>
/// 返回随机颜色
/// </summary>
/// <param name="rng"></param>
/// <returns></returns>
Scalar randomColor(RNG rng)
{
    //Scalar.RandomColor();
    uint iColor = (uint)rng;
    return new Scalar(iColor & 255, (iColor >> 8) & 255, (iColor >> 16) & 255);

}
/// <summary>
/// 随机画椭圆弧
/// </summary>
/// <param name="image"></param>
/// <param name="winName"></param>
/// <param name="rng"></param>
/// <returns></returns>
int Drawing_Random_Ellipses(Mat image, string winName, RNG rng)
{
    Point center = new Point();
    Size axes = new Size();
    for (int i = 0; i < NUMBER; i++)
    {
        center.X = rng.Uniform(0, Width);
        center.Y = rng.Uniform(0, Width);
        axes.Width = rng.Uniform(0, Width);
        axes.Height = rng.Uniform(0, Width);
        Cv2.Ellipse(image, center, axes, rng.Uniform(0, 361), rng.Uniform(0, 361), rng.Uniform(0, 361), randomColor(rng), RandomThickness(rng), lineType);
        Cv2.ImShow(winName, image);
        if (Cv2.WaitKey(DELAY) >= 0) return -1;
    }
    return 0;
}

/// <summary>
/// 随机画矩形
/// </summary>
/// <param name="image"></param>
/// <param name="winName"></param>
/// <param name="rng"></param>
/// <returns></returns>
int Drawing_Random_Rectangels(Mat image, string winName, RNG rng)
{
    Point pt1 = new Point();
    Point pt2 = new Point();
    for (int i = 0; i < NUMBER; i++)
    {
        pt1.X = rng.Uniform(0, Width);
        pt1.Y = rng.Uniform(0, Width);
        pt2.X = rng.Uniform(0, Width);
        pt2.Y = rng.Uniform(0, Width);
        
        Cv2.Rectangle(image, pt1, pt2, randomColor(rng), RandomThickness(rng), lineType);
        Cv2.ImShow(winName, image);
        if (Cv2.WaitKey(DELAY) >= 0) return -1;
    }
    return 0;
}

/// <summary>
/// 获取颜色线宽
/// </summary>
/// <param name="rng"></param>
/// <returns></returns>
int RandomThickness(RNG rng)
{
    int thickness = rng.Uniform(-9, 10);
    if (thickness == 0) thickness = 1;
    return thickness;
}

/// <summary>
/// 随机画线
/// </summary>
/// <param name="image"></param>
/// <param name="winName"></param>
/// <param name="rng"></param>
/// <returns></returns>
int Drawing_Random_Lines(Mat image, string winName, RNG rng)
{
    Point pt1 = new Point();
    Point pt2 = new Point();
    for (int i = 0; i < NUMBER; i++)
    {
        pt1.X = rng.Uniform(0, Width);
        pt1.Y = rng.Uniform(0, Width);
        pt2.X = rng.Uniform(0, Width);
        pt2.Y = rng.Uniform(0, Width);
        Cv2.Line(image, pt1, pt2, randomColor(rng), rng.Uniform(1, 10), lineType);
        Cv2.ImShow(winName, image);
        if (Cv2.WaitKey(DELAY) >= 0) return -1;
    }
    return 0;
}