css font-weight原理_html/css_WEB-ITnose
Why record it? Because today I want to set a character to be bold, and then use font-weight:200, but it has no effect. It seems ridiculous now. 400 is equivalent to normal. No matter how thick 200 is, the strange thing is that it does not become thinner. So we have to study the working principle of font-weight, the following text.
1. Introduction to useFont-weight sets the thickness of text. Text weight setting is a relatively complex font style definition. The reason why it is complex is because the thickness of the font itself changes ever-changing, and there is no unified standard. The exact definition of font weight also varies.
Property values: normal | bold | bolder | lighter | 100 | 200 | 300 | 400 | 500 | 600 | 700 | 800 | 900 | Inherited values
Default value: normal.
There are 3 ways to set the font-weight attribute value:
The first: keyword method:
There are 2 keywords, normal [default value, definition standard characters] and bold [define bold characters].
Second: Relative thickness value method:
Relative thickness is also defined by keywords, there are two, bolder [defines thicker characters] and lighter [defines thinner characters] , but its thickness is relative to the inherited value of the upper parent element. Bolder matches the next thicker font available in the font set, and conversely "lighter" does the same, matching the next thinner font. Their reference systems are all inherited values, so the thickness is relative to the inherited value.
Refer to the picture below for specific situations:
The third type: 9 number sequence from "100" to "900".
These numbers represent the font weight from the thinnest (100) to the thickest (900).
A value of 400 is equivalent to normal,
A value of 700 is equivalent to bold.
2. ExampleCode: Times New Roman effect
<html><head><meta charset="utf-8"/><title>CSS Demo</title><style>body,table,tr,td { font-family: "Times New Roman", Times;font-size: 18pt; }table { border-collapse: collapse; }</style></head><body><table border="1px" cellpadding="5px"><tr><th>关键字</th><th>效果</th></tr><tr style="font-weight: normal;"><td>normal</td><td>The quick brown fox jumps over a lazy dog.</td></tr><tr style="font-weight: bold;"><td>bold</td><td>The quick brown fox jumps over a lazy dog.</td></tr><tr style="font-weight: bolder;"><td>bolder</td><td>The quick brown fox jumps over a lazy dog.</td></tr><tr style="font-weight: lighter;"><td>lighter</td><td>The quick brown fox jumps over a lazy dog.</td></tr><tr style="font-weight: 100;"><td>100</td><td>The quick brown fox jumps over a lazy dog.</td></tr><tr style="font-weight: 200;"><td>200</td><td>The quick brown fox jumps over a lazy dog.</td></tr><tr style="font-weight: 300;"><td>300</td><td>The quick brown fox jumps over a lazy dog.</td></tr><tr style="font-weight: 400;"><td>400</td><td>The quick brown fox jumps over a lazy dog.</td></tr><tr style="font-weight: 500;"><td>500</td><td>The quick brown fox jumps over a lazy dog.</td></tr><tr style="font-weight: 600;"><td>600</td><td>The quick brown fox jumps over a lazy dog.</td></tr><tr style="font-weight: 700;"><td>700</td><td>The quick brown fox jumps over a lazy dog.</td></tr><tr style="font-weight: 800;"><td>800</td><td>The quick brown fox jumps over a lazy dog.</td></tr><tr style="font-weight: 900;"><td>900</td><td>The quick brown fox jumps over a lazy dog.</td></tr></table></body></html>3. Principle
1. Explanation of related names
OpenType: It is a scalable font (scalable font) computer font type, using PostScript format. It is a new font jointly developed by Microsoft and Adobe in the United States to replace TrueType fonts. The file extensions of this type of font are .otf, .ttf, .ttc, the type code is OTTO, and the current standard is OpenType1.6.
2. Working principle: How does the user agent determine the thickness of the font deformation?
The thickness of the font is divided into nine levels, from 100 to 900. These numerical keywords are used to define the mapping relationship with the related characteristics of the font, that is, the thickness of the font is divided into nine levels. For example, OpenType uses a nine-value numeric level. Numbers map directly to the various levels, with 100 mapping to the lightest font distortion and 900 mapping the heaviest font distortion. In fact, there is no intrinsic font weight convention in these numbers. CSS just emphasizes one point: The font thickness corresponding to each number must not be smaller than the font thickness corresponding to the number before it. That is, the font bold corresponding to each numerical value must be at least as thin as the next smallest number, and at least as thick as the previous largest number.
The above problem arises: 100, 200, 300 and 400 may all correspond to font deformations of the same thickness, while 500 and 600 may correspond to a thicker font deformation, and 700, 800 and 900 may correspond to another thicker font deformation. font deformation.
3. Correspondence between keywords and numerical values
400 is equivalent to normal, 700 is equivalent to bold, other numbers do not correspond to any font-weight attribute keywords, but can correspond to ordinary Font deformation name.
If a font variant is tagged "Normal", "Regular", "Roman" or "Book", then it is assigned 400, and any font variant tagged "Medium" corresponds to 500, however, does not correspond to 500 if the font variant marked "Medium" is the only font available.
The corresponding relationships given on MDN and W3C are as follows:
100Thin (Hairline), 200Extra Light (Ultra Light), 300Light, 400Normal, 500Medium, 600Semi Bold (Demi Bold), 700Bold, 800Extra Bold (Ultra Bold), 900Black (Heavy)
4. Methods to fill in gaps when the font family is less than 9
If a given font family has less than nine font weights, basically , the user agent needs to do more work. In this case, a predefined way is used to fill the missing gaps.
How to fill in missing values:
Please refer to font-weight.
500 missing: same as 400.
600|700|800|900 Any value is missing: the same as the thicker value at the next level. If not, it is the same as the next smaller value.
For example: if "500" and "900" are missing from a font, then the 9-level weight value of the font should be equivalent to "100, 200, 300, 400, 400, 600, 700, 800, 800".
Any value in 300|200|100 is missing: the same as the next smaller value. If not, it is the same as the next thicker value.
A picture, gray means there is no value, so the adjacent value is used.
The weight values of the font are 400, 700 and 900
The weight values of the font are 300 and 600
Generally designers will not define more than 3 levels of thickness in an article, and the thickness should jump when designing, otherwise the bold content will not be highlighted.
4. Resource linksBaidu Encyclopedia font-weight
http://baike.baidu.com/item/font-weight
w3c font-weight
http://dev.w3.org/csswg/css-fonts-3/#font-weight-prop
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