# Draw multiple text overlays using the OnVideoFrameBuffer event

Video Capture SDK .Net , Video Edit SDK .Net , Media Player SDK .Net

# Sample code

If video effect API to draw text overlay is not enough, you can draw overlay manually in OnVideoFrameBuffer, using Bitmap and Graphics classes. The bitmap should be 32-bit (with an alpha channel).

A version of code (simple) without an update of text or font on the fly:

        // Image
        private Bitmap logoImage = null;

        // Image RGB32 buffer
        private IntPtr logoImageBuffer = IntPtr.Zero;
        private int logoImageBufferSize = 0;

        private string text1 = "Hello World";
        private string text2 = "Hey-hey";
        private string text3 = "Ocean of pancakes";

        private void SDK_OnVideoFrameBuffer(Object sender, VideoFrameBufferEventArgs e)
        {
            // draw text to image
            if (logoImage == null)
            {
                logoImage = new Bitmap(e.Frame.Width, e.Frame.Height, PixelFormat.Format32bppArgb);

                using (var grf = Graphics.FromImage(logoImage))
                {
                    // antialiasing mode
                    grf.TextRenderingHint = TextRenderingHint.AntiAlias;

                    // drawing mode
                    grf.InterpolationMode = InterpolationMode.HighQualityBicubic;

                    // smoothing mode
                    grf.SmoothingMode = SmoothingMode.HighQuality;

                    // text 1
                    var brush1 = new SolidBrush(Color.Blue);
                    var font1 = new Font("Arial", 30, FontStyle.Regular);
                    grf.DrawString(text1, font1, brush1, 100, 100);

                    // text 2
                    var brush2 = new SolidBrush(Color.Red);
                    var font2 = new Font("Times New Roman", 35, FontStyle.Strikeout);
                    grf.DrawString(text2, font2, brush2, e.Frame.Width / 2, e.Frame.Height / 2);

                    // text 3
                    var brush3 = new SolidBrush(Color.Green);
                    var font3 = new Font("Verdana", 40, FontStyle.Italic);
                    grf.DrawString(text3, font3, brush3, 200, 200);
                }
            }

            // create image buffer if not allocated or have zero size
            if (logoImageBuffer == IntPtr.Zero || logoImageBufferSize == 0)
            {
                if (logoImageBuffer == IntPtr.Zero)
                {
                        logoImageBufferSize = ImageHelper.GetStrideRGB32(logoImage.Width) * logoImage.Height;
                        logoImageBuffer = Marshal.AllocCoTaskMem(logoImageBufferSize);
                }
                else
                {
                        logoImageBufferSize = ImageHelper.GetStrideRGB32(logoImage.Width) * logoImage.Height;

                        Marshal.FreeCoTaskMem(logoImageBuffer);
                        logoImageBuffer = Marshal.AllocCoTaskMem(logoImageBufferSize);
                }

                ImageHelper.BitmapToIntPtr(logoImage, logoImageBuffer, logoImage.Width, logoImage.Height,
                        PixelFormat.Format32bppArgb);
            }

            // Draw image
            FastImageProcessing.Draw_RGB32OnRGB24(logoImageBuffer, logoImage.Width, logoImage.Height, e.Frame.Data, e.Frame.Width, e.Frame.Height, 0, 0);

            e.UpdateData = true;
        }

A version of code with updating on the fly by a button click:

        // Image
        Bitmap logoImage = null;

        // Image RGB32 buffer
        IntPtr logoImageBuffer = IntPtr.Zero;
        int logoImageBufferSize = 0;

        // text settings
        string text1 = "Hello World";
        Font font1 = new Font("Arial", 30, FontStyle.Regular);
        SolidBrush brush1 = new SolidBrush(Color.Blue);

        string text2 = "Hey-hey";
        Font font2 = new Font("Times New Roman", 35, FontStyle.Strikeout);
        SolidBrush brush2 = new SolidBrush(Color.Red);

        string text3 = "Ocean of pancakes";
        Font font3 = new Font("Verdana", 40, FontStyle.Italic);
        SolidBrush brush3 = new SolidBrush(Color.Green);

        // update flag
        bool textUpdate = false;
        object textLock = new object();

        // Update text overlay, index is [1..3]
        void UpdateText(int index, string text, Font font, SolidBrush brush)
        {
            lock (textLock)
            {
                textUpdate = true;
            }

            switch (index)
            {
                case 1:
                    text1 = text;
                    font1 = font;
                    brush1 = brush;
                    break;
                case 2:
                    text2 = text;
                    font2 = font;
                    brush2 = brush;
                    break;
                case 3:
                    text3 = text;
                    font3 = font;
                    brush3 = brush;
                    break;
                default:
                    return;
            }
        }

        private void SDK_OnVideoFrameBuffer(Object sender, VideoFrameBufferEventArgs e)
        {
            lock (textLock)
            {
                if (textUpdate)
                {
                    logoImage.Dispose();
                    logoImage = null;
                }

                // draw text to image
                if (logoImage == null)
                {
                    logoImage = new Bitmap(e.Frame.Width, e.Frame.Height, PixelFormat.Format32bppArgb);

                    using (var grf = Graphics.FromImage(logoImage))
                    {
                        // antialiasing mode
                        grf.TextRenderingHint = TextRenderingHint.AntiAlias;

                        // drawing mode
                        grf.InterpolationMode = InterpolationMode.HighQualityBicubic;

                        // smoothing mode
                        grf.SmoothingMode = SmoothingMode.HighQuality;

                        // text 1
                        grf.DrawString(text1, font1, brush1, 100, 100);

                        // text 2
                        grf.DrawString(text2, font2, brush2, e.Frame.Width / 2, e.Frame.Height / 2);

                        // text 3
                        grf.DrawString(text3, font3, brush3, 200, 200);
                    }
                }

                // create image buffer if not allocated or have zero size
                if (logoImageBuffer == IntPtr.Zero || logoImageBufferSize == 0)
                {
                    if (logoImageBuffer == IntPtr.Zero)
                    {
                        logoImageBufferSize = ImageHelper.GetStrideRGB32(e.Frame.Width) * e.Frame.Height;
                        logoImageBuffer = Marshal.AllocCoTaskMem(logoImageBufferSize);
                    }
                    else
                    {
                        logoImageBufferSize = ImageHelper.GetStrideRGB32(e.Frame.Width) * e.Frame.Height;

                        Marshal.FreeCoTaskMem(logoImageBuffer);
                        logoImageBuffer = Marshal.AllocCoTaskMem(logoImageBufferSize);
                    }

                    ImageHelper.BitmapToIntPtr(logoImage, logoImageBuffer, logoImage.Width, logoImage.Height,
                        PixelFormat.Format32bppArgb);
                }

                if (textUpdate)
                {
                    textUpdate = false;
                    ImageHelper.BitmapToIntPtr(logoImage, logoImageBuffer, logoImage.Width, logoImage.Height,
                        PixelFormat.Format32bppArgb);
                }

                // Draw image
                FastImageProcessing.Draw_RGB32OnRGB24(logoImageBuffer, logoImage.Width, logoImage.Height, e.Frame.Data, e.Frame.Width,
                e.Frame.Height, 0, 0);

                e.UpdateData = true;
            }
        }

        private void btUpdateText1_Click(object sender, EventArgs e)
        {
            UpdateText(1, "Hello world", new Font("Arial", 48, FontStyle.Underline),
                new SolidBrush(Color.Aquamarine));
        }

# Required redists

SDK redist

Visit our GitHub page to get more code samples.