Do you really understand .shx and .ttf fonts?

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When using AutoCAD to open drawings sent by other designers, it often prompts that the corresponding font cannot be found and a dialog box for replacing fonts pops up, as shown in the following figure:

When this happens, if you don’t know the specific use of this font in the drawing, The first method is to “cancel” without replacing it, and then open the drawing to see which specific words or symbols cannot be displayed normally; The second method is to download the missing fonts from the Internet and put them in the fonts directory of the cad installation; The third method is to select a similar font in the list according to the name, But it is more effective to use this method when the general type can be seen from the font name. Due to lack of understanding of the font type, not only the font cannot be displayed normally when replacing, but sometimes a prompt similar to the following appears: "hztxt2.SHX is a large font file, not a shape file. Eref.SHX is a regular font file, not a shape file."

What is a large font file? What are regular font files? What is a shape file again? How are they different, and what does each do? In order to be able to handle text correctly, it is necessary to have an understanding of the classification of fonts.

The font files that can be used by CAD are mainly divided into two categories, one is the CAD-defined *.SHX font; one is the *.TTF font in the operating system, Such as Times New Roman, Black and so on.

Designers of these two types of fonts can add them by themselves. TTF fonts can be added by installing fonts or copying *.TTF files to the fonts directory of Windows. TTF fonts are usually used alone, and can be selected in the font drop-down box of the text style. SHX fonts can be directly copied to the fonts directory under the CAD installation directory.

There are two types of SHX fonts:

One is font, which is used to write text or symbols, such as txt.SHX, gbcbig.SHX, etc. There are two types of fonts: large font and small font, and the big font defines double-byte Asian characters are called large font files, such as Chinese (gbcbig.SHX), Korean, etc.; small fonts are generally Western characters, called regular font files, such as txt.SHX, etc.

One is the symbol shape, which is used to insert special symbols, graphics or graphics in defining line types, such as ltypeshp.SHX, aaa.SHX, gdt.SHX, etc. Symbolic shape, as the name implies, refers to a specific symbol. There are three general usages of it:

1. Routine use of SHAPE entities: load with the load command, then specify the corresponding symbol name with the shape command, and then add a SHAPE entity (common such as aaa.SHX)

2. Embed line type: Embed the symbol shape into the line type code, and then specify the line type for the entity to use (common such as ltypeshp.SHX)

3. Special symbols: such as tolerance symbols, this is for internal use, generally GDT.SHX

Although they are all SHX files, different types of fonts have different purposes, so they cannot be replaced at will. Font files of the same type cannot be replaced at will, even font files with the same name sometimes have different internal definitions. For example, there are many versions of hztxt.SHX, which is widely used in design institutes, some with steel bar symbols, and some without. Therefore, the same version of hztxt.SHX must be used to ensure that all characters can be displayed normally. Most design units now have requirements for the fonts used in drawings, so as to ensure that there are no font problems during internal design communication or cooperation. When it is necessary to communicate drawings with other units, it is recommended to attach the font files used to avoid unnecessary troubles to the other party.

In fact, the SHX fonts and large fonts (also called bigfont) in CAD are all autoCAD's own proprietary fonts. Large fonts are also SHX fonts, a special form of SHX fonts. To talk about SHX fonts, we have to talk about the development process of fonts in CAD. autoCAD also has its own font library in the fonts directory. Font files with the extension SHX are called SHX fonts. The original SHX font supports ANSI characters, and later expanded to support non-ANSI characters, that is, large fonts or bigfont, which are stored in double bytes, which is why it is called a large font. But only as a word processing patch, to be specified separately. It should be said that the large fonts at this time do not necessarily conform to the Unicode standard, so sometimes garbled characters appear. The SHX font is the early product of CAD. Starting from r14, autoCAD began to support Windows fonts, which is probably the trend of CAD development. However, since SHX fonts (including large fonts) are specially made for CAD, as far as the current situation is concerned, there are still many advantages, as shown in:

1. The storage space of dwg files is small, and the display speed is relatively fast. Especially in the case of a lot of text, the difference in the re-display speed of regen is more obvious, and there is no time difference in the update of real-time movement (pan).

2. Since Windows fonts are foreign fonts (compared to SHX fonts), they cannot be perfect in the process of generating and editing. For example, in the process of moving and copying text in TrueType fonts (Windows fonts), the length of sentences may be different from the actual length, which affects the reference positioning. For another example, the actual height of a TrueType font may be different from the specified height, and the character height cannot be specified precisely, but can only be determined by trial and error, which affects the speed of drawing and the difficulty of programming control.

3. Since the SHX font is a linear font, special attributes can be specified like a line segment to produce special effects. For example, you can specify a thickness value to produce a three-dimensional effect.

4. Compared with TrueType fonts, the aesthetic effect of SHX fonts is not ideal, but it can still meet the needs in engineering. The SHX font is equivalent to hard pen calligraphy, and there is a gap in simulating brush calligraphy.

Since SHX fonts and Windows TrueType fonts have their own strengths, they can learn from each other in the project and use them as appropriate.

END

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