打印时图片适配纸张防裁切方案咨询及DrawImageUnscaled用法疑问

First, let's clear up the DrawImageUnscaled question:

• DrawImageUnscaled renders images at their original pixel dimensions, which is exactly why your content is getting cropped. This method ignores page size, margins, and aspect ratio—so it’s not the right choice when you need to fit content to a printed page.

Step-by-Step Solution for Uncropped, Aspect-Ratio Correct Printing #

To print images without cropping while keeping their proportions intact, you need to scale each image to fit within the printable area of the page. Here’s how to implement this:

1. Get the Printable Page Bounds #

First, calculate the usable area of the page (accounting for printer margins) from the PrintPageEventArgs:

var printableWidth = e.MarginBounds.Width;
var printableHeight = e.MarginBounds.Height;

2. Calculate the Safe Scaling Factor #

Find the scaling ratio that fits the image within the printable area without stretching it. Use the smaller of the width/height ratios to preserve aspect ratio:

foreach (var chartEntry in yourChartDictionary)
{
    var chartControl = chartEntry.Key;
    // Adjust this line to match how you extract the image from your control
    using (var chartImage = chartControl.GetImage())
    {
        if (chartImage == null) continue;

        // Compute scaling ratios for width and height
        float scaleX = (float)printableWidth / chartImage.Width;
        float scaleY = (float)printableHeight / chartImage.Height;
        // Use the smaller ratio to avoid stretching
        float scaleFactor = Math.Min(scaleX, scaleY);

        // Calculate scaled dimensions
        int scaledWidth = (int)(chartImage.Width * scaleFactor);
        int scaledHeight = (int)(chartImage.Height * scaleFactor);

3. Position and Draw the Scaled Image #

Center the image within the printable area (or align to top-left if preferred) and draw it using the scaled dimensions:

// Center the image horizontally and vertically
        int posX = e.MarginBounds.Left + (printableWidth - scaledWidth) / 2;
        int posY = e.MarginBounds.Top + (printableHeight - scaledHeight) / 2;

        // Draw the properly scaled image
        e.Graphics.DrawImage(chartImage, posX, posY, scaledWidth, scaledHeight);
    }
}

Full Modified Code Snippet #

Here’s how this fits into your existing method:

private void PrintAllCharts(Dictionary<LightningChartUserControl, YourDataType> chartData, PrintPageEventArgs e)
{
    var printableWidth = e.MarginBounds.Width;
    var printableHeight = e.MarginBounds.Height;

    foreach (var entry in chartData)
    {
        var chartControl = entry.Key;
        // Replace with your actual image retrieval logic
        using (var chartImage = chartControl.GetImage())
        {
            if (chartImage == null)
                continue;

            // Calculate safe scaling factor
            float scaleX = (float)printableWidth / chartImage.Width;
            float scaleY = (float)printableHeight / chartImage.Height;
            float scale = Math.Min(scaleX, scaleY);

            int scaledWidth = (int)(chartImage.Width * scale);
            int scaledHeight = (int)(chartImage.Height * scale);

            // Center the image on the page
            int posX = e.MarginBounds.Left + (printableWidth - scaledWidth) / 2;
            int posY = e.MarginBounds.Top + (printableHeight - scaledHeight) / 2;

            // Render the scaled image
            e.Graphics.DrawImage(chartImage, posX, posY, scaledWidth, scaledHeight);
        }
    }
}

Additional Pro Tips #

• Verify Printer Settings: Ensure your print document’s DefaultPageSettings match your paper size (e.g., A4, Letter):

  printDocument1.DefaultPageSettings.PaperSize = new PaperSize(PaperName.A4, 827, 1169); // A4 in hundredths of an inch
  

• High-DPI Printing: For crisp prints with high-res images, adjust the graphics object’s DPI to match your printer’s capabilities:

  e.Graphics.DpiX = 300; // Match printer DPI if known
  e.Graphics.DpiY = 300;
  

内容的提问来源于stack exchange，提问作者Nikhil ANS