Develop Reference

Draw a lot of single characters to a WinForms Control

I have a custom WinForms control which could be described as some kind of terminal control (like a control containing Putty). According to this, the control should display a lot of characters, each with a different color and background color (worst case).
Currently I'm using the (kind of obsolete) Graphics.MeasureString method to determine the size of a single character in my fixed-size font so I can calculate the position of a character at a specific row and column. Then I use Graphics.DrawString to draw the characters. To optimize the performance I create a BufferedGraphics and group characters by their properties to draw consecutive characters with the same color with just one DrawString call. (Because one DrawString call per character is really slow.)
Now the problem is that DrawString apparently calculates the width of a character slightly different from MeasureString. When I draw a complete line at once, the resulting text width is different from what I calculated using the width of a single character multiplied by the character count of the line. It's just one or two pixels (or maybe less), but you can see it clearly - especially because I'm using anti-alias so you can even see a difference of just half a pixel.
The following sample code draws a long string a on the form's graphics, followed by character 'B'. Then it draws just a 'B' on the position calculated by measuring a.
var f = new Form {
Width = 1200,
Height = 500,
Font = new Font("Consolas", 11, FontStyle.Regular)
};
f.Paint += delegate(object sender, PaintEventArgs e) {
var a = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
var size = e.Graphics.MeasureString(a, f.Font, new PointF(0, 0), StringFormat.GenericTypographic);
using (var black = new SolidBrush(Color.Black))
{
e.Graphics.DrawString(a + "B", f.Font, black, 0, 0, StringFormat.GenericTypographic);
e.Graphics.DrawString("B", f.Font, black, size.Width, 20, StringFormat.GenericTypographic);
}
};
f.Show();
And if you look closely, you will see that the second B is about one pixel more right - at least with my display settings (100% dpi scale, ClearType enabled). Although one pixel is not much, when you draw lines using unicode characters U+2500 through U+257F it looks pretty ugly if the characters aren't perfectly aligned.
Also I can't use the TextRenderer class because its MeasureString method returns integer values, but DrawString of course does not draw each character on a full pixel position (what would be required to align it with a position calculated using row/column and the measured integer character size).
So my question is: Is there any (efficient) method to draw strings which are perfectly aligned to their corresponding position calculated using the character size?
P.S.: MeasureString with a 200-character-string returns exactly 200 times the return value of MeasureString with a single-character-string.

I have had some similar issues with measuring the strings in Graphics. I have used SizeInPoints, a property from the class Font and multiplied it for the number of characters I have in the string... I dont't know if it helps.
If not it can be a "rounding" problem with the pixels... then I would try to scale up the font size (maybe 10 times), measure it and then divide it by 10 again when using the size to color the background.
I hope it helps.
Good luck! Regards!

I'm having same issue.
It seems that the behavior depends on the font size.
After changing font with following code, this issue didn't occur.
Font = new Font("Consolas", 20.0F, FontStyle.Regular, GraphicsUnit.Pixel)
However, with another font size as below this issue still occurs.
Font = new Font("Consolas", 20.3F, FontStyle.Regular, GraphicsUnit.Pixel)
My guess on background of this issue: MeasureString and DrawString uses different layout routine and they have different characteristic in rounding error of float number. Only with 'simple' font size they gives same results.
Also, this issue didn't occur with bitmap fonts.

How to draw a string without padding

I am using the GraphicsPath.AddString() function, but it draws the text with a little space around the text. Any idea how to draw the string without that padding, only the paths of the text?
My code is like this:
GraphicsPath gp = new GraphicsPath();
gp.AddString(text, font.FontFamily, (int)font.Style, font.Size,
boundsRectangle, format);
g.DrawPath(pen, gp);

What is happening is the under the hood it is probably using Graphics.MeasureString(), from the documentation :
GDI+ adds a small amount (1/6 em) to each end of every string displayed. This 1/6 em allows >for glyphs with overhanging ends (such as italic 'f'), and also gives GDI+ a small amount >of leeway to help with grid fitting expansion.
The default action of DrawString will work against you in displaying adjacent runs:
Firstly the default StringFormat adds an extra 1/6 em at each end of each output;
Secondly, when grid fitted widths are less than designed, the string is allowed to contract
by up to an em.
To avoid these problems:
Always pass MeasureString and DrawString a StringFormat based on the typographic >StringFormat (GenericTypographic).
Set the Graphics TextRenderingHint to TextRenderingHintAntiAlias. This rendering method >uses anti-aliasing and sub-pixel glyph positioning to avoid the need for grid-fitting, and >is thus inherently resolution independent.
So it looks like you should be able to fix this using the correct StringFormat.

Drawing string by GDI+ in exactly in specified point

I have problem with drawing string in c#
Here is my code:
Graphic.TextRenderingHint = System.Drawing.Text.TextRenderingHint.AntiAliasGridFit;
Pen pen = new Pen(brush, 2f);
Font font = new Font("Segoue UI", 15);
graphic.DrawString("2", font, brush, new PointF(0f, 0f));
Previously i created picturebox and i did graphic obiect from it.
The problem is that "2" is not drawing in (0;0) but in (4;5). Event if i turn off AntiAlias is still in (4;5).
I check it by drawing two lines from (0;0) to (200;0) and from (0;0) to (0;200) and according to them i calculated that error in drawing string.
Any ideas why? I need draw string in exactly point.
//Edit
i was also trying set font in this way:
Font font = new Font("Microsoft Sans Serif", 10);
and draw "2" in (0,0), the real position of "2" is (3,3). With drawing "1" error is the same (3;3).

Graphics.DrawString is automatically padding the box it uses to draw strings. The reason is that it's purpose is to draw label texts etc. for controls and therefor is "ready-made" so there is padding around the text.
Microsoft eventually realized that this approach wasn't the best for situations when one needed more accurate text drawing (ie. text editors etc.), and for that reason developed the TextRendered class which wraps GDI instead of GDI+ and give back the "old" more accurate string drawing.
Try:
TextRenderer.DrawText(e.Graphics, "2", font, new Point(0, 0), brush);
You might experience padding even with this, but here you can more reliable compensate for that. Check the link below to see what flags you can use with the method.
Note: if you need to measure text it's important to use the TextRenderer.MeasureText() for this.
For more details, go to:
http://msdn.microsoft.com/en-us/library/system.windows.forms.textrenderer.aspx
Flags:
http://msdn.microsoft.com/en-us/library/w3cdh3zw.aspx

what happens if your "string" has a descending letter, like a g or a j? each font allows for descending parts of letters, so you might need to account for that by looking at the font's metrics
http://msdn.microsoft.com/en-us/library/xwf9s90b.aspx

Drawing text centered within a rectangle

I have code, similar to the following:
string myText = "This is a test";
Font myFont = new Font("Arial", 10);
Rectangle rect = new Rectangle(10,10,100,100);
Graphics g = e.Graphics;
g.DrawString(myText, myFont, rect.X, rect.Y);
Although this works, what I would like to do is have the text vertically and horizontally centered within the dimensions of the rectangle. In addition, if its possible, I'd like to wrap the text if its too big to fit on one line. How do I do this in C#/GDI+?

I would use one of the DrawString Overloads that takes a StringFormat You would have to check the Length of your Text using MeasureString to make sure it would fit and wrap it yourself. In looking further at the StringFormatFlags it has a NoWrap Flag implying that the default is to wrap:
from last link:
Text wrapping between lines when formatting within a rectangle is disabled. This flag is implied when a point is passed instead of a rectangle, or when the specified rectangle has a zero line length.

the simple, un-researched way to do it:
to word-wrap break your strings up into smaller sub-strings. I.e.
"this is"
"a test"
you can use the String.Split() method to split your strings up into words, and then append the words together until your string has reached a certain threshold. and then make a new string.
As for centering, you can pad your individual strings with spaces. for vertical centering, you can add some newlines to the beginning of your strings.
I'll leave the arithmetic involved to you. it shouldn't be that hard.

How to get the exact text margins used by TextRenderer

System.Windows.Forms.TextRenderer.DrawText method renders formatted text with or without left and right padding depending on the value of the flags parameter:
TextFormatFlags.NoPadding - fits the text tightly into the bounding box,
TextFormatFlags.GlyphOverhangPadding - adds some left and right margins,
TextFormatFlags.LeftAndRightPadding - adds even bigger margins.
Now, my question is how can I get the exact amount of padding (left and right) added by DrawText to the text for a given device context, string, font etc?
I've dug into .NET 4 with .NET Reflector and found that TextRenderer calculates "overhang padding" which is 1/6 of the font's height and then multiplies this value to calculate left and right margins using these coefficients:
left 1.0, right 1.5 for TextFormatFlags.GlyphOverhangPadding,
left 2.0, right 2.5 for TextFormatFlags.LeftAndRightPadding.
The resulting values are rounded up and passed to the DrawTextExA or DrawTextExW native API functions. It's difficult to recreate this process because font's height is taken not from System.Drawing.Font but from System.Windows.Forms.Internal.WindowsFont and these classes return different values for the same font. And a lot of other internal BCL classes from the System.Windows.Forms.Internal namespace are involved. Decompiling all of them and reusing their code in my app is not an option, because that would be a serious .NET implementation dependency. That's why I need to know if there is some public API in WinForms or at least which Windows functions I can use to get the values of left and right margins.
Note: I've tried to TextRenderer.MeasureText with and without padding and compare the results but that gave me only the sum of left and right margins and I need them separately.
Note 2: In case you wonder why I need this: I want to draw one string with multiple fonts/colors. That involves calling DrawText once for every uniformly formatted substring with NoPadding option (so that the text doesn't spread) but I also want to add manually normal GlyphOverhangPadding at the very beginning and very end of the whole multi-format text.

The value you need for computing left and right margins is TEXTMETRIC.tmHeight, which is possible to obtain using Win32 API.
However, I found that tmHeight is just a line height of a font in pixels, so these three approaches will give you the same value (you can use whichever you like in your code):
int apiHeight = GetTextMetrics(graphics, font).tmHeight;
int gdiHeight = TextRenderer.MeasureString(...).Height;
int gdipHeight = (int)Math.Ceiling(font.GetHeight(graphics));
To obtain left and right margins, we use the same code as TextRenderer does under the hood:
private const float ItalicPaddingFactor = 0.5f;
...
float overhangPadding = (gdiHeight / 6.0f);
//NOTE: proper margins for TextFormatFlags.LeftAndRightPadding flag
//int leftMargin = (int)Math.Ceiling(overhangPadding);
//int rightMargin = (int)Math.Ceiling(overhangPadding * (2 + ItalicPaddingFactor));
//NOTE: proper margins for TextFormatFlags.GlyphOverhangPadding flag
int leftMargin = (int)Math.Ceiling(overhangPadding);
int rightMargin = (int)Math.Ceiling(overhangPadding * (1 + ItalicPaddingFactor));
Size sizeOverhangPadding = TextRenderer.MeasureText(e.Graphics, "ABC", font, Size.Empty, TextFormatFlags.GlyphOverhangPadding);
Size sizeNoPadding = TextRenderer.MeasureText(e.Graphics, "ABC", font, Size.Empty, TextFormatFlags.NoPadding);
int overallPadding = (sizeOverhangPadding.Width - sizeNoPadding.Width);
Now you can easily check that
(leftMargin + rightMargin) == overallPadding
Just to note:
I needed to solve this problem in order to implement "Search Highlight" feature in a ListView-based control that uses GDI text rendering:
Works like a charm :)

This answer is an excerpt from here - http://www.techyv.com/questions/how-get-exact-text-margins-used-textrenderer#comment-35164
If you have ever wanted a Label or TextBox in Windows Forms that performs a little more like on the web, then you've probably figured out that there's no intuitive way to make a Label or TextBox automatically adjust its height to fit the text it contains. While it may not be intuitive, it's definitely not impossible.
In this example, I'll use a TextBox (you could just as easily use a Label) that is docked to the top of a form.To use this, add aTextBox called MyTextBox to the form, and set Dock to DockStyle.Top. Wire up the Resize event of the TextBox to this event handler.
private void MyTextBox_Resize( object sender, EventArgs e )
{
// Grab a reference to the TextBox
TextBox tb = sender as TextBox;
// Figure out how much space is used for borders, etc.
int chromeHeight = tb.Height - tb.ClientSize.Height;
// Create a proposed size that is very tall, but exact in width.
Size proposedSize = new Size( tb.ClientSize.Width, int.MaxValue );
// Measure the text using the TextRenderer
Size textSize = TextRenderer.MeasureText( tb.Text, tb.Font,
proposedSize, TextFormatFlags.TextBoxControl
| TextFormatFlags.WordBreak );
// Adjust the height to include the text height, chrome height,
// and vertical margin
tb.Height = chromeHeight + textSize.Height
+ tb.Margin.Vertical;
}
If you want to resize the a Label or TextBox that is not docked (for example, one that is in a FlowLayoutPanel or other Panel, or just placed on the form), then you can handle the Form's Resize even instead, and just modify the Control's properties directly.

This might seem (very) crude, but this is the only native implementation I can think of:
DrawText draws to an IDeviceContext, which is implemented by Graphics. Now, we can take advantage of that with the following code:
Bitmap bmp = new Bitmap(....);
Graphics graphic = Graphics.FromImage(bmp);
textRenderer.DrawText(graphic,....);
graphic.Dispose();
With the new Bitmap you can go pixel by pixel and count them by some condition.
Again, this method is very crude and wasteful, but at least it's native....
This is not tested but based on the following sources:
http://msdn.microsoft.com/en-us/library/4ftkekek.aspx
http://msdn.microsoft.com/en-us/library/system.drawing.idevicecontext.aspx
http://msdn.microsoft.com/en-us/library/system.drawing.graphics.aspx
http://www.pcreview.co.uk/forums/graphics-bitmap-t1399954.html

I've done something similar a few years ago, to highlight search results (search pattern appears in bold etc.). My implementation was in DevExpress, so the code might not be relevant. If you think it's of use I can copy it, just need to find that implementation.
In System.Windows.Forms, the class to use would be Graphics. It has a MeasureCharacterRanges() method which accepts a StringFormat (start with GenericTypographic and go from there). It is much more appropriate than TextRenderer for displaying a complete string by chaining parts with different styles, fonts or brushes.
You've gone way further than me with the actual padding measuring. DevExpress's controls gave you the text bounding rectangle to start with so that was done for me.
Here's an article by Pierre Arnaud that came up for me in Google, which touches on this area. Unfortunately the GDI+ "Gory details" link there is broken.
Cheers,
Jonno

The fix is to calculate what MeasureText is going to add:
var formatFlags FormatFlags =
TextFormatFlags.NoPadding |
TextFormatFlags.SingleLine;
int largeWidth = TextRenderer.MeasureText(
" ",
font,
new Size(int.MaxValue, int.MaxValue),
formatFlags
).Width;
int smallWidth = TextRenderer.MeasureText(
" ",
font,
new Size(int.MaxValue, int.MaxValue),
formatFlags
).Width;
int extra = smallWidth - (largeWidth - smallWidth);
We calculate the width of one space and the width of two spaces. Both have the extra width added, so we can extrapolate the extra width that is being added. The added width apparently is always the same, so subtracting extra from every width returned by MeasureText gives the expected results.