文章目录

用处及效果

注意观察各个控件交叠的地方，是不是发现他们没有遮挡？这就是这个控件的妙处了。

准备工作

先说明一下这个控件的作用，很多时候我们需要一个图片类型的控件，但是有需要密集的放在一起，如果单纯的设置背景图或image的话交叠在一起的部分就会存在遮挡现象，所有就有了这个控件。

该控件可以根据设置的采样图片来裁剪有用的绘图区域，这样的好处就是在交叠的时候，无用区域不会遮挡。

这个用GDI+画的，另外也用到了一点三角函数，不明白的话可以先百度下

开始

添加一个类UCSampling ，继承UserControl

添加属性

/// <summary>
        /// The sampling imag
        /// </summary>
        private Bitmap samplingImag = null;
        /// <summary>
        /// Gets or sets the sampling imag.
        /// </summary>
        /// <value>The sampling imag.</value>
        [Browsable(true), Category("自定义属性"), Description("采样图片"), Localizable(true)]
        public Bitmap SamplingImag
        {
            get { return samplingImag; }
            set
            {
                samplingImag = value;
                ResetBorderPath();
                Invalidate();
            }
        }

        /// <summary>
        /// The transparent
        /// </summary>
        private Color? transparent = null;

        /// <summary>
        /// Gets or sets the transparent.
        /// </summary>
        /// <value>The transparent.</value>
        [Browsable(true), Category("自定义属性"), Description("透明色，如果为空，则使用0,0坐标处的颜色"), Localizable(true)]
        public Color? Transparent
        {
            get { return transparent; }
            set
            {
                transparent = value;
                ResetBorderPath();
                Invalidate();
            }
        }

        /// <summary>
        /// The alpha
        /// </summary>
        private int alpha = 50;

        /// <summary>
        /// Gets or sets the alpha.
        /// </summary>
        /// <value>The alpha.</value>
        [Browsable(true), Category("自定义属性"), Description("当作透明色的透明度，小于此透明度的颜色将被认定为透明，0-255"), Localizable(true)]
        public int Alpha
        {
            get { return alpha; }
            set
            {
                if (value < 0 || value > 255)
                    return;
                alpha = value;
                ResetBorderPath();
                Invalidate();
            }
        }

        /// <summary>
        /// The color threshold
        /// </summary>
        private int colorThreshold = 10;

        /// <summary>
        /// Gets or sets the color threshold.
        /// </summary>
        /// <value>The color threshold.</value>
        [Browsable(true), Category("自定义属性"), Description("透明色颜色阀值"), Localizable(true)]
        public int ColorThreshold
        {
            get { return colorThreshold; }
            set
            {
                colorThreshold = value;
                ResetBorderPath();
                Invalidate();
            }
        }

        /// <summary>
        /// The bit cache
        /// </summary>
        private Bitmap _bitCache;

在大小改变或图片改变时重新计算边界

/// <summary>
        /// The m border path
        /// </summary>
        GraphicsPath m_borderPath = new GraphicsPath();

        /// <summary>
        /// Handles the SizeChanged event of the UCSampling control.
        /// </summary>
        /// <param name="sender">The source of the event.</param>
        /// <param name="e">The <see cref="EventArgs"/> instance containing the event data.</param>
        void UCSampling_SizeChanged(object sender, EventArgs e)
        {
            ResetBorderPath();
        }

        /// <summary>
        /// Resets the border path.
        /// </summary>
        private void ResetBorderPath()
        {
            if (samplingImag == null)
            {
                m_borderPath = this.ClientRectangle.CreateRoundedRectanglePath(5);
            }
            else
            {
                var bit = new Bitmap(this.ClientRectangle.Width, this.ClientRectangle.Height);
                using (var bitg = Graphics.FromImage(bit))
                {
                    bitg.DrawImage(samplingImag, this.ClientRectangle, 0, 0, samplingImag.Width, samplingImag.Height, GraphicsUnit.Pixel);
                }
                _bitCache = bit;
                m_borderPath = new GraphicsPath();
                List<PointF> lstPoints = GetBorderPoints(bit, transparent ?? samplingImag.GetPixel(0, 0));
                m_borderPath.AddLines(lstPoints.ToArray());
                m_borderPath.CloseAllFigures();
            }
        }

        /// <summary>
        /// Gets the border points.
        /// </summary>
        /// <param name="bit">The bit.</param>
        /// <param name="transparent">The transparent.</param>
        /// <returns>List&lt;PointF&gt;.</returns>
        private List<PointF> GetBorderPoints(Bitmap bit, Color transparent)
        {
            float diameter = (float)Math.Sqrt(bit.Width * bit.Width + bit.Height * bit.Height);
            int intSplit = 0;
            intSplit = (int)(7 - (diameter - 200) / 100);
            if (intSplit < 1)
                intSplit = 1;
            List<PointF> lstPoint = new List<PointF>();
            for (int i = 0; i < 360; i += intSplit)
            {
                for (int j = (int)diameter / 2; j > 5; j--)
                {
                    Point p = GetPointByAngle(i, j, new PointF(bit.Width / 2, bit.Height / 2));
                    if (p.X < 0 || p.Y < 0 || p.X >= bit.Width || p.Y >= bit.Height)
                        continue;
                    Color _color = bit.GetPixel(p.X, p.Y);
                    if (!(((int)_color.A) <= alpha || IsLikeColor(_color, transparent)))
                    {
                        if (!lstPoint.Contains(p))
                        {
                            lstPoint.Add(p);
                        }
                        break;
                    }
                }
            }
            return lstPoint;
        }

        /// <summary>
        /// Determines whether [is like color] [the specified color1].
        /// </summary>
        /// <param name="color1">The color1.</param>
        /// <param name="color2">The color2.</param>
        /// <returns><c>true</c> if [is like color] [the specified color1]; otherwise, <c>false</c>.</returns>
        private bool IsLikeColor(Color color1, Color color2)
        {
            var cv = Math.Sqrt(Math.Pow((color1.R - color2.R), 2) + Math.Pow((color1.G - color2.G), 2) + Math.Pow((color1.B - color2.B), 2));
            if (cv <= colorThreshold)
                return true;
            else
                return false;
        }

#region 根据角度得到坐标    English:Get coordinates from angles
        /// <summary>
        /// 功能描述:根据角度得到坐标    English:Get coordinates from angles
        /// 作　　者:HZH
        /// 创建日期:2019-09-28 11:56:25
        /// 任务编号:POS
        /// </summary>
        /// <param name="angle">angle</param>
        /// <param name="radius">radius</param>
        /// <param name="origin">origin</param>
        /// <returns>返回值</returns>
        private Point GetPointByAngle(float angle, float radius, PointF origin)
        {
            float y = origin.Y + (float)Math.Sin(Math.PI * (angle / 180.00F)) * radius;
            float x = origin.X + (float)Math.Cos(Math.PI * (angle / 180.00F)) * radius;
            return new Point((int)x, (int)y);
        }
        #endregion

取边界的思路如下：

1，以控件中心为原点，按照一定的角度顺时针依次进行旋转，

2、每次旋转后，按照此角度从外向内，找到第一个不是透明的点记录下来，这就是外边界点

这个取边界算法感觉并不是太好，如果哪位小伙伴有更好的算法，希望可以探讨一下

重绘

protected override void OnPaint(PaintEventArgs e)
        {
            base.OnPaint(e);
            e.Graphics.SetGDIHigh();

            this.Region = new System.Drawing.Region(m_borderPath);
           
            if (_bitCache != null)
                e.Graphics.DrawImage(_bitCache, 0, 0);
           
        }