绘制大小为2X2英寸的矩形-Inches到像素转换

Question

我需要画一个矩形，应该是大小在2X2英寸左右，当打印在纸上。

我知道我可以用

 g.DrawRectangle(pen, 100,100, 100, 200);

此应用程序将只在computers.How中使用，我可以正确地将英寸转换为像素，以便在打印时得到所需的尺寸。

Answer 1

默认情况下，要按适当的大小打印图像，需要dpi和像素的正确组合。

让我们看一个例子：

// aiming at 150dpi and 4x6 inches:
float dpi = 150;
float width = 4;
float height = 6;

using (Bitmap bmp = new Bitmap((int)(dpi * width), (int)(dpi * height)))
{
    // first set the resolution
    bmp.SetResolution(dpi, dpi);
    // then create a suitable Graphics object:
    using (Graphics G = Graphics.FromImage(bmp))
    using (Pen pen = new Pen(Color.Orange))
    {
        pen.Alignment = System.Drawing.Drawing2D.PenAlignment.Center;
        G.Clear(Color.FloralWhite);
        // using pixels here:

        Size sz = new System.Drawing.Size((int)dpi * 2 - 1, (int)dpi * 2 - 1);
        G.DrawRectangle(pen, new Rectangle(new Point(0, 0), sz));
        G.DrawRectangle(pen, new Rectangle(new Point(0, 300), sz));
        G.DrawRectangle(pen, new Rectangle(new Point(0, 600), sz));
        G.DrawRectangle(pen, new Rectangle(new Point(300, 0), sz));
        G.DrawRectangle(pen, new Rectangle(new Point(300, 300), sz));
        G.DrawRectangle(pen, new Rectangle(new Point(300, 600), sz));

        // alternative code:
        // we can also set the Graphics object to measure stuff in inches;
        G.PageUnit = GraphicsUnit.Inch;
        // or fractions of it, let's use 10th:
        G.PageScale = 0.1f;
        using (Pen pen2 = new Pen(Color.MediumPurple, 1f / dpi * G.PageScale))
        {
            // draw one rectangle offset by an inch:
            G.DrawRectangle(pen2, 10f, 10f, 20f, 20f);
        }

        bmp.Save(@"D:\xxx.jpg", ImageFormat.Jpeg);
    }
}

注意，当DrawRectangle 将透支1像素时，我不得不从绘制的大小中减去1像素！

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请注意，我绘制的坐标取决于分辨率！还请注意jpeg格式是如何创建许多模糊颜色的。Png会产生更清晰的结果，特别是当你打印文本时。

还请注意我是如何在替代代码中缩小PenWidth的！