C# - Winforms Drawing on Bitmap

Question

I am having such kind of problem. I am making a small photo editor, where you can select image, change brightness contrast of the image, draw text on the image. This is the Form. . I have this methods.

private void DrawText(string text, int x, int y)
    {
        RectangleF rectf = new RectangleF(x, y, 90, 50);
        Graphics g = Graphics.FromImage(this.pictureBox1.Image);
        g.SmoothingMode = SmoothingMode.AntiAlias;
        g.InterpolationMode = InterpolationMode.HighQualityBicubic;
        g.PixelOffsetMode = PixelOffsetMode.HighQuality;
        g.DrawString(text.ToString(), new Font("Tahoma", Convert.ToInt32(this.textBoxSize.Text.ToString())), Brushes.Black, rectf);
        g.Flush();
    }

private void SetBrightness(int brightness)
    {
        if (!object.ReferenceEquals(this.pictureBox1.Image, null))
        {
            Bitmap temp = (Bitmap)this.pictureBox1.Image;
            Bitmap bmap = (Bitmap)temp.Clone();
            if (brightness < -255) brightness = -255;
            if (brightness > 255) brightness = 255;
            Color c;
            for (int i = 0; i < bmap.Width; i++)
            {
                for (int j = 0; j < bmap.Height; j++)
                {
                    c = bmap.GetPixel(i, j);
                    int cR = c.R + brightness;
                    int cG = c.G + brightness;
                    int cB = c.B + brightness;

                    if (cR < 0) cR = 1;
                    if (cR > 255) cR = 255;

                    if (cG < 0) cG = 1;
                    if (cG > 255) cG = 255;

                    if (cB < 0) cB = 1;
                    if (cB > 255) cB = 255;

                    bmap.SetPixel(i, j,
        Color.FromArgb((byte)cR, (byte)cG, (byte)cB));
                }
            }
            this.pictureBox1.Image = (Bitmap)bmap.Clone();
        }
    }

public void SetContrast(double contrast)
    {
        if (!object.ReferenceEquals(this.pictureBox1.Image, null))
        {
            Bitmap temp = (Bitmap)this.pictureBox1.Image;
            Bitmap bmap = (Bitmap)temp.Clone();
            if (contrast < -100) contrast = -100;
            if (contrast > 100) contrast = 100;
            contrast = (100.0 + contrast) / 100.0;
            contrast *= contrast;
            Color c;
            for (int i = 0; i < bmap.Width; i++)
            {
                for (int j = 0; j < bmap.Height; j++)
                {
                    c = bmap.GetPixel(i, j);
                    double pR = c.R / 255.0;
                    pR -= 0.5;
                    pR *= contrast;
                    pR += 0.5;
                    pR *= 255;
                    if (pR < 0) pR = 0;
                    if (pR > 255) pR = 255;

                    double pG = c.G / 255.0;
                    pG -= 0.5;
                    pG *= contrast;
                    pG += 0.5;
                    pG *= 255;
                    if (pG < 0) pG = 0;
                    if (pG > 255) pG = 255;

                    double pB = c.B / 255.0;
                    pB -= 0.5;
                    pB *= contrast;
                    pB += 0.5;
                    pB *= 255;
                    if (pB < 0) pB = 0;
                    if (pB > 255) pB = 255;

                    bmap.SetPixel(i, j,
        Color.FromArgb((byte)pR, (byte)pG, (byte)pB));
                }
            }
            this.pictureBox1.Image = (Bitmap)bmap.Clone();
        }
    }

And on my button CLick I am just calling this methods to do the work. What is the problem when I Draw the text for second time, it is not deleting and drawing text again, but I need the text to be drawn at different location every time and not over the old text. Can you please suggest any solution to this ? Thanks

Answer 1

There are two solutions:

1. Do not draw on the bitmap; instead draw on a transparent bitmap that is on top of it.

2. Keep the original Bitmap and copy it just before drawing on it.

Once you have changed the pixels of a bitmap you cannot undo that unless you keep the original data.