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

Question

I'm writing a program that takes bitmaps and writes some text onto them. I have a functional method that will do this, I provide it with the string that needs to be drawn, the rectangle it needs to be fitted to, the name of the font family to use, gets the largest size it possibly can for the font and then draws it onto the provided bitmap (centred to the rectangle if that is what is desired)

The code I am currently using is as follow

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;
        }

The problem is that this code looks ugly and its kind of slow as well. So I suppose I was just wondering if there was a better way to do this, some sort of function call or property I had missed somewhere when trying to make this all work, since I've managed to get the rest of the programs bitmap manipulation to a rather clean state, its just this, which looks kinda awful.

Thankyou in advance for any help given on this matter.

Answer 1

So I took the advise of @Raju Joseph in the comments of the question and broke the code up. It's probably not any faster to run now than before but at least it looks neater so the function that draws the text now looks like this

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;
        }

With figuring out how big the font needs to be being handled by a different method of the class which is as follow

 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);
        }

Probably some other way of doing that but this seems fast enough and it looks neat enough in source so thumbs up for that.

Answer 2

In terms of performance, there's two reasons for your performance issues.

1) Loading fonts is a time consuming process in general, even outside of .NET (Think of how slow Word or any other program is to draw the fonts when you open the font list). So try to find ways to cache the font objects in your class if you can instead of recreating them each time.

2) GDI is faster than GDI+ as per the docs : "You can choose either GDI or GDI+ for text rendering; however, GDI generally offers better performance and more accurate text measuring.", so try to use DrawText instead because, again as per the docs : "With the DrawText method in the TextRenderer class, you can access GDI functionality for drawing text on a form or control. GDI text rendering typically offers better performance and more accurate text measuring than GDI+."