PDF Tm运算符 [英] PDF Tm operator

问题描述

我正在尝试突出显示PDF文档中的文本，但是我发现了一个Tm运算符，其操作数如下:

I'm trying to highlight text in a PDF document but I found a Tm operator with the following operands:

0 7.98 -7.98 0 90.8898 715.4183 Tm

假定Tm运算符仅在其操作数上替换文本矩阵和文本行矩阵. 根据Pdf参考，可以执行以下操作:

The Tm operator is supposed to replace the text matrix and the text line matrix solely on its operands. According to the Pdf Reference, the following operations can be done:

• 翻译[1 0 0 1 tx ty]
• 缩放[sx 0 0 sy 0 0]
• 旋转[cos(角度)sin(角度)-sin(角度)cos(角度)0 0]
• 倾斜[1 tan(alpha)tan(beta)1 0 0]

操作数的格式与上述任何转换都不匹配，从而导致以下问题.

The format of the operands doesn't match any of the above transformations, which led to the following questions.

• 前面提到的文本矩阵应该做什么?
• 几种转换的样子如何?例如缩放和旋转.

推荐答案

前面提到的文本矩阵应该做什么?

您的矩阵

0 7.98 -7.98 0 90.8898 715.4183

(这是PDF的缩写形式

(which is the PDF short form for

⌈  0        7.98    0 ⌉
| -7.98     0       0 |
⌊ 90.8898 715.4183  1 ⌋

不幸的是，确实很难画出大括号)

and unfortunately it is difficult to draw big brackets indeed)

是90°旋转，7.98的缩放和90.8898、715.4183的平移操作的组合.我将在下面分别估算这些数字:7.98 8、90.8898 91和715.4183 715:

is a combination of a 90° rotation, a scaling by 7.98, and a translation operation by 90.8898, 715.4183. I'll approximate those numbers in the following, 7.98 ≅8, 90.8898 ≅ 91, and 715.4183 ≅ 715:

⌈  0   8  0 ⌉   ⌈  0  8  0 ⌉   ⌈  1   0  0 ⌉
| -8   0  0 | = | -8  0  0 | x |  0   1  0 |
⌊ 91 715  1 ⌋   ⌊  0  0  1 ⌋   ⌊ 91 715  1 ⌋

  ⌈ 8 0 0 ⌉   ⌈  0  1  0 ⌉   ⌈  1   0  0 ⌉
= | 0 8 0 | x | -1  0  0 | x |  0   1  0 |
  ⌊ 0 0 1 ⌋   ⌊  0  0  1 ⌋   ⌊ 91 715  1 ⌋

几个转换的样子如何?例如缩放和旋转

在上面的分解中，我们有一个这样的例子，

We have such an example in the decomposition above,

⌈  0  8  0 ⌉   ⌈ 8 0 0 ⌉   ⌈  0  1  0 ⌉
| -8  0  0 | = | 0 8 0 | x | -1  0  0 |
⌊  0  0  1 ⌋   ⌊ 0 0 1 ⌋   ⌊  0  0  1 ⌋

缩放比例为8，旋转角度为90°.

a combination of a scaling by 8 and a rotation by 90°.

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