C＃-在位图上绘制Winforms

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 an invisible 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.