Drawing, images and printing with GDI+

Graphics, Pen and Brush basics, drawing to a control versus a bitmap, DPI-aware scaling, and printing through PrintDocument with a preview.

The drawing model

protected override void OnPaint(PaintEventArgs e)
{
    var g = e.Graphics;
    g.SmoothingMode = SmoothingMode.AntiAlias;
    g.PixelOffsetMode = PixelOffsetMode.HighQuality;

    using var pen = new Pen(Color.FromArgb(200, 60, 60), 2f);
    using var fill = new SolidBrush(Color.FromArgb(40, 200, 60, 60));

    var rect = new Rectangle(10, 10, 200, 120);
    g.FillRectangle(fill, rect);
    g.DrawRectangle(pen, rect);
    g.DrawLine(pen, rect.Left, rect.Bottom, rect.Right, rect.Top);
    g.DrawString("Sample", Font, Brushes.Black, rect.Location);
}

• Everything created with new - pens, brushes, fonts, bitmaps, graphics contexts on images - must be disposed. Wrap them in using.
• Static Brushes and Pens entries are shared and must not be disposed.
• DrawString renders with GDI+ text layout; TextRenderer.DrawText uses GDI and matches the rest of the UI. Prefer TextRenderer for labels, DrawString for rotated or transformed text.
• Coordinates are in device pixels; at 150 percent scaling a 200 px rectangle is physically smaller than the designer suggested.

Drawing to a bitmap

static Bitmap RenderChart(IReadOnlyList<double> values, int width, int height)
{
    var bmp = new Bitmap(width, height, PixelFormat.Format32bppPArgb);
    using var g = Graphics.FromImage(bmp);
    g.Clear(Color.White);
    g.SmoothingMode = SmoothingMode.AntiAlias;

    var max = values.Max();
    using var pen = new Pen(Color.SteelBlue, 2f);
    for (var i = 1; i < values.Count; i++)
    {
        var x1 = (i - 1) * width / (float)values.Count;
        var x2 = i * width / (float)values.Count;
        g.DrawLine(pen, x1, height - (float)(values[i - 1] / max * height),
                        x2, height - (float)(values[i] / max * height));
    }
    return bmp;
}

// on a control: a 500 x 300 bitmap shown in a 250 x 150 box
pictureBox.Image?.Dispose();
pictureBox.Image = RenderChart(values, 500, 300);
pictureBox.SizeMode = PictureBoxSizeMode.Zoom;

Render behind-the-scenes images at the pixel size they will be displayed, multiplied by the current DPI scale, then draw them with InterpolationMode.HighQualityBicubic. Scaling up a low-resolution bitmap in the paint handler is the usual cause of blurry charts.

Printing and print preview

var doc = new PrintDocument { DocumentName = "Invoice 1042" };
doc.DefaultPageSettings.Landscape = false;
doc.DefaultPageSettings.Margins = new Margins(60, 60, 60, 60);

var page = 0;
doc.PrintPage += (s, e) =>
{
    var g = e.Graphics;
    g.DrawString($"Invoice 1042 - page {page + 1}", Font, Brushes.Black, 60, 60);

    // print the same visual the screen shows, scaled to the printable area
    var area = e.MarginBounds;
    var chart = RenderChart(values, area.Width, area.Height / 2);
    g.DrawImage(chart, area.Left, area.Top + 40, area.Width, area.Height / 2);
    chart.Dispose();

    page++;
    e.HasMorePages = page * 2 < values.Count;   // decide inside the handler
};

using var preview = new PrintPreviewDialog { Document = doc, Width = 1000, Height = 700 };
preview.ShowDialog(this);

FAQ

Related

Custom controls and owner-drawn rendering High DPI, accessibility and theming

Last refreshed 2026-09-18.