使用 System.Drawing 在 C# 中的 Bitmap 上的高效文本渲染

Question

我正在编写一个程序，它采用位图并将一些文本写入它们。 我有一个函数方法可以做到这一点，我为它提供了需要绘制的字符串、需要拟合的矩形、要使用的字体系列的名称、获得字体可能的最大尺寸然后将其绘制到提供的 bitmap 上（如果需要，以矩形为中心）

我目前使用的代码如下

public static Bitmap Write_Text(Bitmap i, string s, Rectangle r, string font, bool centered, bool bold)
        {
            //TODO check that there isnt a better way to do this
            //first off we need to make sure this rectangle we are given remains in the bounds
            //of the bitmap it will be drawn on
            //since pixels start at (0,0) we need the combined origin and dimension of the rectangle
            //to be of a lesser value than the dimenion of the rectangle (since = could give out of bounds)
            if((r.Width + r.X)<i.Width && (r.Height + r.Y) < i.Height && r.X >= 0 && r.Y >= 0)
            {
                //now we need to ensure that the graphics object that
                //draws the text is properly disposed of
                using(Graphics g = Graphics.FromImage(i))
                {
                    //The graphics object will have some settings tweaked
                    //to ensure high quality rendering 
                    g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                    //Normally Compositing Mode Would Be Set But Writing Text requires its own non enum setting
                    //and so is excluded here
                    g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
                    g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                    g.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighQuality;
                    //and one more dedicated to ensuring the text renders with nice contrast
                    //and non jagged letters
                    g.TextRenderingHint = System.Drawing.Text.TextRenderingHint.ClearTypeGridFit;

                    //now since we need to actually loop over to try and fit the text to the box 
                    //we need a control variable for a do-while loop
                    bool fits = false;
                    //and storage for the parameter for the fonts size
                    //the font can't actually be any larger than the smaller
                    //dimension of the box it goes in
                    int size = Math.Min(r.Width, r.Height);
                    do
                    {
                        //now a font family may not exist on the computer microsofts 
                        //sans seriff will be used so no need for try catches
                        Font f;
                        //If the font is to be bold set it as such
                        if (bold)
                        {
                            f = new Font(font, size, System.Drawing.FontStyle.Bold, GraphicsUnit.Pixel);
                        }
                        else
                        {
                            f = new Font(font, size, GraphicsUnit.Pixel);
                        }
                        //now we measure the string and if it fits inside the rectangle we can proceed
                        if(g.MeasureString(s,f).Width <= r.Width && g.MeasureString(s,f).Height <= r.Height)
                        {
                            fits = true;
                        }
                        else
                        {
                            //if the string doesnt fit the box decrease the size and try again
                            size--;
                        }
                        //regardless dispose of f to avoid memory leaks
                        f.Dispose();                                                                        
                    }
                    while (!fits);
                    //now we just need to make a string attributes object since the string may want to be centered
                    StringFormat Format = new StringFormat();
                    if (centered)
                    {
                        Format.Alignment = StringAlignment.Center;
                        Format.LineAlignment = StringAlignment.Center;
                    }
                    //now construct the font object that will be used for the drawing
                    //as above
                    Font ff;
                    if (bold)
                    {
                        ff = new Font(font, size, System.Drawing.FontStyle.Bold, GraphicsUnit.Pixel);
                    }
                    else
                    {
                        ff = new Font(font, size, GraphicsUnit.Pixel);
                    }
                    //now draw the text in place on the bitmap
                    g.DrawString(s, ff, Brushes.Black, r, Format);
                    //dispose of the font so its not leaking memory
                    ff.Dispose();
                    Format.Dispose();
                }
            }
            return i;
        }

问题是这段代码看起来很丑，而且速度也很慢。 所以我想我只是想知道是否有更好的方法来做到这一点，某种 function 调用或我在尝试使这一切正常工作时错过的某个地方的属性，因为我已经设法获得程序 rest对于一个相当干净的 state，它就是这个，看起来有点糟糕。

预先感谢您在此问题上提供的任何帮助。

Answer 1

因此，我在问题的评论中采纳了@Raju Joseph 的建议并分解了代码。 现在运行起来可能不会比以前快，但至少看起来更整洁，所以绘制文本的 function 现在看起来像这样

public static Bitmap Write_Text(Bitmap i, string s, Rectangle r, bool centered, string font, bool bold, bool italic)
        {
            //Since we want to avoid out of bounds errors make sure the rectangle remains within the bounds of the bitmap
            //and only execute if it does
            if(r.X>= 0 && r.Y>=0&&(r.X+r.Width < i.Width) && (r.Y + r.Height < i.Height))
            {
                //Step one is to make a graphics object that will draw the text in place
                using (Graphics g = Graphics.FromImage(i))
                {
                    //Set some of the graphics properties so that the text renders nicely
                    g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                    //Compositing Mode can't be set since string needs source over to be valid
                    g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
                    g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                    g.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighQuality;
                    //And an additional step to make sure text is proper anti-aliased and takes advantage
                    //of clear type as necessary
                    g.TextRenderingHint = System.Drawing.Text.TextRenderingHint.ClearTypeGridFit;

                    //this also requires a font object we need to make sure we dispose of properly
                    using (Font f = Functions.Generate_Font(s, font, r, bold, italic))
                    {
                        //the using function actually makes sure the font is as large as it can be for the 
                        //purpose of fitting the rectangle we just need to check if its centered
                        using (StringFormat format = new StringFormat())
                        {
                            //the format won't always be doing anything but
                            //just in case we need it
                            //and if the text is centered we need to tell the formatting
                            if (centered)
                            {
                                format.Alignment = StringAlignment.Center;
                                format.Alignment = StringAlignment.Center;
                            }
                            //and draw the text into place
                            g.DrawString(s, f, Brushes.Black, r, format);
                        }
                    }
                }
            }
            return i;
        }

通过确定需要通过 class 的不同方法处理的字体大小，如下所示

 public static Font Generate_Font(string s,string font_family, Rectangle r, bool bold, bool italic)
        {
            //First things first, the font can't be of a size larger than the rectangle in pixels so 
            //we need to find the smaller dimension as that will constrain the max size
            int Max_Size = Math.Min(r.Width, r.Height);
            //Now we loop backwards from this max size until we find a size of font that fits inside the 
            //rectangle given
            for(int size = Max_Size; size > 0; size--)
            {
                //Since a default font is used if the font family specified doesnt exist 
                //checking the family exists isnt necessary
                //However we need to cover if the font is bold or italic
                Font f;
                if (bold)
                {
                    f = new Font(font_family, size, System.Drawing.FontStyle.Bold, GraphicsUnit.Pixel);
                }
                else if (italic)
                {
                    f = new Font(font_family, size, System.Drawing.FontStyle.Italic, GraphicsUnit.Pixel);
                }
                else if (bold && italic)
                {
                    //the pipe is a bitwise or and plays with the enum flags to get both bold and italic 
                    f = new Font(font_family, size, System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic, GraphicsUnit.Pixel);
                }
                else
                {
                    //otherwise make a simple font
                    f = new Font(font_family, size, GraphicsUnit.Pixel);
                }
                //because graphics are weird we need a bitmap and graphics object to measure the string
                //we also need a sizef to store the measured results
                SizeF result;
                using(Bitmap b = new Bitmap(100,100))
                {
                    using(Graphics g = Graphics.FromImage(b))
                    {
                        result = g.MeasureString(s, f);
                    }
                }
                //if the new string fits the constraints of the rectangle we return it
                if(result.Width<= r.Width && result.Height <= r.Height)
                {
                    return f;
                }
                //if it didnt we dispose of f and try again
                f.Dispose();
            }
            //If something goes horribly wrong and no font size fits just return comic sans in 12 pt font
            //that won't upset anyone and the rectangle it will be drawn to will clip the excess anyway
            return new Font("Comic Sans", 12, GraphicsUnit.Point);
        }

可能有其他方法可以做到这一点，但这似乎足够快，而且在源代码中看起来足够整洁，所以对此竖起大拇指。

Answer 2

在性能方面，您的性能问题有两个原因。

1）加载 fonts 通常是一个耗时的过程，即使在 .NET 之外（想想当你打开字体列表时 Word 或任何其他程序绘制 Z980D14C0C85495B48B9A9134658E6121 有多慢）。 因此，如果可以的话，请尝试找到将字体对象缓存在 class 中的方法，而不是每次都重新创建它们。

2）根据文档，GDI 比 GDI+ 更快：“您可以选择 GDI 或 GDI+ 进行文本渲染；但是，GDI 通常提供更好的性能和更准确的文本测量。”，因此请尝试使用DrawText ，因为再次按照文档：“使用 TextRenderer class 中的 DrawText 方法，您可以访问 GDI 功能以在表单或控件上绘制文本。GDI 文本呈现通常提供比 GDI+ 更好的性能和更准确的文本测量。”