ch16_Drawing Text.pdf

Programming the .NET Compact Framework in C#

By Paul Yao & David Durant

Chapter 16

Drawing Text

This chapter covers controlling the appearance of text, using classes in the System.Drawing

namespace and also by using P/Invoke to drill through to the underlying Win32 libraries for useful

text drawing features that are otherwise not available in the Compact Framework.

Author's Note: In this review chapter C#-Specific Text is highlighted in YELLOW.

Drawing Text.................................................................................................................................... 2

Compact Framework Text Drawing Support ...................................................................... 2

The DrawString Function.................................................................................................... 3

Sample: SimpleDrawString................................................................................................. 4

Font Selection.................................................................................................................................. 5

The Font Property of controls ............................................................................................. 6

Generic Fonts ..................................................................................................................... 7

Sample: GenericFonts........................................................................................................ 9

Creating Named Fonts ..................................................................................................... 11

Enumerating Fonts ........................................................................................................... 14

Sample: FontPicker .......................................................................................................... 14

Sample: FontList – Win32 Font Enumeration DLL [Comment 17.60] .............................. 16

Native Code Fonts ............................................................................................................ 20

Creating fonts in unmanaged code ..................................................................... 21

Drawing with fonts in unmanaged code .............................................................. 23

Cleanup ............................................................................................................... 23

Sample: RotateText.......................................................................................................... 24

Placing Text ................................................................................................................................... 27

Text Size and the MeasureString method ................................................................... 28

Sample: MeasureString .................................................................................................... 28

Text Alignment..................................................................................................................30

Sample: TextAlign ............................................................................................................ 31

Word Wrap........................................................................................................................ 36

Sample: WordWrap .......................................................................................................... 37

Text Color ...................................................................................................................................... 39

Foreground and Background Text Colors ........................................................................ 40

Sample: TextColor ............................................................................................................ 40

Conclusion ..................................................................................................................................... 46

The focus of this chapter is on drawing text on the screen of a smart device using the .NET

Compact Framework. As we describe in chapter 16, Compact Framework Graphics , the Compact

Framework supports a subset of the graphical output features of the Desktop Framework. (For

details on the differences, see the boxed text titled "Comparing CF and DF Text Drawing.") In

general, though, the text drawing support is quite rich. You can do all of the more commonly

required text drawing operations such as selecting different fonts by name, in different sizes and

styles, and also control the color of drawn text. Some subtle effects are not available, but this is a

small price to pay for the small memory footprint occupied by the Compact Framework.

[Comment 17.1]

Chapter 16 – Drawing Text

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Programming the .NET Compact Framework in C#

By Paul Yao & David Durant

Drawing Text

A graphical environment provides the programmer with a rich set of tools for creating a wide

range of graphical images. Such an environment makes it possible to mingle pictures with text, to

display text in a range of font sizes and styles, and to use an array of effects to convey subtle

messages to users. In such an environment, text itself is treated as a graphical object. Drawing

text in a graphical environment is paradoxically more complex than drawing text in a non-

graphical environment. In a character-oriented world such as in a console program, fixed pitch

fonts are used which place text in orderly rows and columns. In a graphical world, by contrast,

both fixed and variable pitch fonts float in a sea of pixels. The increase in complexity allows for

the free mixing of text and graphics. This freedom comes at a cost, namely the extra effort

required to tame the complexity of graphical text and to use it to enhance a program's graphical

output. [Comment 17.2]

Compact Framework Text Drawing Support

A Compact Framework program can draw text using any available font. Using TrueType

fonts, that text output can be scaled to any desired size from 8 point on up to 72 point and beyond.

That text can be drawn in any available color, although most programs are likely to use the

default system text color. [Comment 17.3]

By drilling through to the underlying Win32 libraries, a Compact Framework program can do

a few more things such as drawing rotated text, and accessing Clear Type fonts. Table 16-1

summarizes Compact Framework text drawing features, how to access these features, and this

chapter's sample programs which illustrate each feature. [Comment 17.4]

Table 16-1 Text Drawing Features and Sample Programs [Comment 17.5]

Feature

Comment

Sample Program

Call the DrawString 1 method to

draw text in a control or form.

Simple text drawing

SimpleDrawString – Shows

simplest text drawing, which involves

creation of a brush (for text color)

and use of the form's default font.

Simplest font creation

Create a font using the

FontFamily enumeration to select

between a fixed-pitch, serif, or sans-

serif font without regard to font face

name.

GenericFonts – Creates and

draws with each of the three generic

font families, in a range of styles

(regular, bold, italic, strikeout, and

underline)

Font Enumeration

Font enumeration involves getting a

list of available font face names

installed in the system. Compact

Framework does not support font

enumeration, so we rely on a Win32

DLL that does the font enumeration

work for us

FontPicker – CF program that

creates fonts of specific face name.

FontList – Win32 DLL that

enumerates available system fonts.

Rotate text

Compact Framework does not

natively support rotated fonts. For

that, you must call the Win32 font

creation functions.

RotateText – CF program that

uses P/Invoke to call Win32 font

creation program.

ClearType fonts

ClearType is a font technology that

aids in reading small text on LCD

displays. Compact Framework does

not support this, so you must instead

call Win32 font creation functions as

1 The fully-qualified name is System.Drawing.Graphics .

Chapter 16 – Drawing Text

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Programming the .NET Compact Framework in C#

By Paul Yao & David Durant

Feature

Comment

Sample Program

illustrated in the RotateText sample.

Calculate size of graphical text

Optimal positioning of text requires

calculating the size of the bounding

box of drawn text. This is

accomplished using the

MeasureString method.

MeasureString – Shows how to

use results from MeasureString

method in drawing.

Setting text alignment

By default, text is aligned to the

upper-left corner of the text box.

Compact Framework does support

alternative text alignment settings, so

different alignments require

modifying the (x,y) location where

you draw text.

TextAlign – Shows twelve ways

to align text by mixing and matching

four vertical alignments and three

horizontal alignments

Word wrap

Compact Framework supports two

versions of the DrawString method,

but only one of them supports word

wrap. The version which uses a

rectangle supports word wrap. In

addition to wrapping the text to the

indicated rectangle, the text is clipped

to that rectangle as well – that is, text

is only drawn within the specified

rectangle.

WordWrap – shows use of the

version of the DrawString method

which supports wrapping and

clipping a text string to a specified

output rectangle.

Text color

Set text foreground color by creating

a brush. Set text background color by

drawing a colored rectangle before

drawing the text.

TextColors – Shows three ways

to pick colors: (1) using named

colors, (2) using system colors, (3)

with the color picker dialog box

(requires P/Invoke)

The DrawString Function

All Compact Framework text drawing is done with the DrawString method, a member of

the Graphics class 2 , available in two overloaded implementations. We start our discussion with

the simpler of the two overloaded functions, which accepts a pair of (x,y) values for the location

where the text is to be drawn. This method does not provide automatic word-wrapping support.

So if a string is too long for the available drawing space, the "extra" characters disappear. A

second version of DrawString , which we discuss later in this chapter, does word wrapping for

you. [Comment 17.6]

The simpler version of DrawString , which takes five parameters, is defined as follows:

[Comment 17.7]

public void DrawString(

string str,

Font font,

Brush brText,

float x,

float y);

[Comment 17.8]

This first parameter, str , identifies the string to draw. While automatic word-wrap is not

supported, a carriage-return or linefeed character within the string causes the string to display in

2 The fully qualified name is System.Drawing.Graphics .

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Programming the .NET Compact Framework in C#

By Paul Yao & David Durant

multiple lines. (In C#, insert a new line using the \n or \r character; in VB, a new line is caused

by including any of the following constants in a string: vbLf , vbCr , or vbCrLf .) [Comment 17.9]

The second parameter, font , is the font used for drawing the characters. This could be the

default font (the Font property) of a control, or a font which you dynamically create. [Comment

17.10]

The third parameter, brText , identifies the brush which specifies the color of the text

foreground pixels; in the world of .NET programming, the background pixels are always left

untouched 3 when you draw text. [Comment 17.11]

The fourth and fifth parameters, x and y , indicate the text drawing location. This location is

the upper-left corner of the rectangle which bounds the text. These coordinate values are single-

precision floating point values, which is different from the integer coordinates used to draw raster

and vector graphics. [Comment 17.12]

Sample: SimpleDrawString

Our first sample program shows the simplest way to draw in a form. Figure 16-1 shows the

program's output. This program uses the form's default font to draw a character string using the

system default window text color. [Comment 17.13]

We highlight the text placement location with a pair of lines, to make it obvious that the (x,y)

location identifies the upper-left corner of an imaginary box that bounds the text string. The

Compact Framework does not have any built-in facility to request alternative text alignments,

which you might use to center a string over a column of data or center the text inside a graphical

image. The TextAlign sample, shown later in this chapter, shows some simple techniques for

manually creating eleven alternative text alignments to the default upper-left alignment.

[Comment 17.14]

Text Drawing Performance

The SimpleDrawString sample shows one way to draw text, but this is

not necessarily the fastest way to draw text. We notice a 10%

improvement in drawing speed when we create a font ahead of time,

instead of using the Font property of the control. For most purposes, the

Font property works well for drawing text. To squeeze the fastest text

drawing from the Compact Framework, however, we suggest you cache

the font and passing that font to the DrawString function. [Comment 17.15]

3 Win32 programmers may recall that the Background Color attribute in a DC allows a text

drawing operation to also affect the background pixels.

Chapter 16 – Drawing Text

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Programming the .NET Compact Framework in C#

By Paul Yao & David Durant

Fig ure 16-1 Output from SimpleDrawStr ing sample [Comment 17.16]

Listing 16-1 Fragment from SimpleDrawString.cs showing Paint event handler

private float xDraw = 10;

private float yDraw = 10;

private void

FormMain_Paint(object sender, PaintEventArgs e)

{

Brush brText = new SolidBrush(SystemColors.WindowText);

e.Graphics.DrawString("Simple Draw String", Font, brText,

xDraw, yDraw);

// Highlight origin.

int x = (int)xDraw;

int y = (int)yDraw;

Pen penBlack = new Pen(Color.Black);

e.Graphics.DrawLine(penBlack, x, y, x-8, y);

e.Graphics.DrawLine(penBlack, x, y, x, y-8);

// Cleanup

brText.Dispose();

penBlack.Dispose();

}

Font Selection

We now turn our attention to the subject of fonts. Font selection provides the primary way to

control the appearance of text. Windows CE supports two basic font technologies: bitmap fonts

Chapter 16 – Drawing Text

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