渲染选项 – 自定义 HTML 渲染

渲染选项提供了对渲染设备如何处理内容的详细控制。每个设备– PdfDevice、 XpsDevice、 DocDevice 和 ImageDevice –都有自己的选项类别： PdfRenderingOptions、 XpsRenderingOptions、 DocRenderingOptions 和 ImageRenderingOptions。通过这些选项，你可以调整页面大小、页边距和颜色，还可以应用特定于设备的设置，例如为 PDF 文件添加安全密码。无论是通过调整图像质量和分辨率来减小文件大小，还是通过优化页面布局和文本格式来增强可读性，自定义对于实现预期效果都至关重要。

本文将探讨 Aspose.HTML for Python via .NET 中的渲染选项，展示如何将 HTML 内容自定义转换为 PDF、XPS、DOCX 和图像等输出格式。这些选项包括页面大小、背景颜色和分辨率等常规设置，以及图像压缩、PDF 安全性和字体嵌入等特定于设备的设置，从而实现对最终输出的完全控制。

在这里，您可以找到演示如何使用设备特定参数的 Python 代码示例。一般选项的使用将在 “如何撰写文章"一章(编写中)中介绍。

要了解有关渲染过程的更多信息，请阅读 渲染设备 一文。

PdfRenderingOptions

除了常规选项外， PdfRenderingOptions类还支持几个特定参数，如 jpeg_quality、document_info、encryption、form_field_behaviour 和 is_tagged_pdf。

Property	Description
jpeg_quality	Specifies the quality of JPEG compression for images. The default value is 95.
document_info	This property contains information about the output PDF document.
encryption	This property gets or sets encryption details. If it is not set, then no encryption will be performed.
form_field_behaviour	This property specifies the behavior of form fields in the output PDF document.
is_tagged_pdf	If is_tagged_pdf = true, a tag structure will be added to the PDF document during rendering.

form_field_behaviour “属性用于指定 PDF 文档中表单域的行为。要了解 PDF 文件扁平化的含义以及如何使用 Aspose.HTML for Python via .NET 库进行扁平化，请参阅 HTML 到 PDF 的转换和 PDF 扁平化 章节。

下面的 Python 代码演示了如何使用 PdfRenderingOptions 类为 PDF 输出文件添加加密：

# Render HTML to PDF with password protection using Python

import os
import aspose.html as ah
import aspose.html.rendering as rn
import aspose.html.rendering.pdf as rp
import aspose.html.rendering.pdf.encryption as rpe

# Setup input and output directories
data_dir = "data/"
output_dir = "output/"
os.makedirs(output_dir, exist_ok=True)

# Prepare path to the source HTML file
document_path = os.path.join(data_dir, "document.html")

# Initialize an HTML document from the file
doc = ah.HTMLDocument(document_path)

# Create an instance of the HTML Renderer
renderer = rn.HtmlRenderer()

# Prepare path to save the converted PDF
save_path = os.path.join(output_dir, "convert-html-to-pdf-with-encryption.pdf")

# Create PDF rendering options and set password protection
options = rp.PdfRenderingOptions()
options.encryption = rpe.PdfEncryptionInfo(
    user_password="user_pwd",
    owner_password="owner_pwd",
    permissions=rpe.PdfPermissions.PRINT_DOCUMENT,
    encryption_algorithm=rpe.PdfEncryptionAlgorithm.RC4_128
)

# Create the PDF device with options and output path
device = rp.PdfDevice(options, save_path)

# Render HTML to PDF
renderer.render(device, doc)

上例展示了如何创建一个新的 PdfRenderingOptions 实例，并为 PDF 输出文件设置加密选项。为此，你需要创建一个 PdfEncryptionInfo对象，它定义了 PDF 文件的加密设置。构造函数需要四个参数：

• user_password 和 owner_password，这是打开和处理 PDF 文件所必需的；
• permissions – PDF 文件允许的权限集。在本例中，指定了 “PdfPermissions.PRINT_DOCUMENT”，使用户可以打印文档；
• encryption_algorithm – 用于保护 PDF 文件的加密算法。在本例中，使用的是 PdfEncryptionAlgorithm.RC4_128 128 位 RC4 加密算法。

ImageRenderingOptions

ImageRenderingOptions 类支持所有常规选项，并允许您配置特定选项，例如抗锯齿、文本渲染配置、图像格式选择和图像压缩。

Property	Description
compression	Sets Tagged Image File Format (TIFF) compression. By default, this property is LZW.
format	Sets the ImageFormat (JPG, PNG, BMP, TIFF, or GIF). By default, this property is PNG.
use_antialiasing	This property defines the rendering quality of the image by controlling the use of antialiasing. Antialiasing is enabled by default.
text	Gets a TextOptions object which is used for configuration of text rendering.

让我们来看看如何使用专门的 ImageRenderingOptions 对象来设置图像的 TIFF 格式和压缩率：

# Render HTML to TIFF with custom settings using Python

import os
import aspose.html as ah
import aspose.html.rendering.image as ri

# Setup input and output directories
data_dir = "data/"
output_dir = "output/"
os.makedirs(output_dir, exist_ok=True)

# Prepare paths for input HTML and output TIFF file
document_path = os.path.join(data_dir, "html_file.html")
save_path = os.path.join(output_dir, "document.tiff")

# Initialize an HTML document from the file
doc = ah.HTMLDocument(document_path)

# Create rendering options for image format (TIFF in this case)
image_options = ri.ImageRenderingOptions(ri.ImageFormat.TIFF)
image_options.compression = ri.Compression.NONE

# Create an ImageDevice and specify options and output file
device = ri.ImageDevice(image_options, save_path)

# Render HTML to TIFF
doc.render_to(device)

XpsRenderingOptions

XpsRenderingOptions继承了基本 RenderingOptions类的所有设置。在生成 XPS 文件时，你可以配置页面大小、页边距、背景颜色和其他常用选项。

# Render HTML to XPS with custom page settings using Python

import os
import aspose.html as ah
import aspose.html.rendering.xps as rx
import aspose.html.drawing as dr

# Setup input and output directories
data_dir = "data/"
output_dir = "output/"
os.makedirs(output_dir, exist_ok=True)

# Prepare a path to the source HTML file
document_path = os.path.join(data_dir, "document.html")

# Initialize the HTML document from the file
doc = ah.HTMLDocument(document_path)

# Create an instance of XPS Rendering Options
options = rx.XpsRenderingOptions()

# Set custom page size (5 x 2 inches)
options.page_setup.any_page = dr.Page(dr.Size(dr.Length.from_inches(5.0), dr.Length.from_inches(2.0)))

# Prepare a path to save the converted file
save_path = os.path.join(output_dir, "document-options.xps")

# Create an XpsDevice with the specified options and output file
device = rx.XpsDevice(options, save_path)

# Render HTML to XPS
doc.render_to(device)

DocRenderingOptions

DocRenderingOptions 类支持所有常规选项，并允许您自定义输出文件的 font_embedding_rule 和 document_format 属性。

Property	Description
font_embedding_rule	This property gets or sets the font embedding rule. Available values are Full and None. The default value is None.
document_format	This property gets or sets the file format of the output document. The default value is DOCX.

下面的示例展示了如何通过设置页面大小和字体嵌入规则，自定义输出 DOCX 文档的渲染选项：

# Render HTML to DOCX with custom settings using Python

import os
import aspose.html as ah
import aspose.html.rendering.doc as rd
import aspose.html.drawing as dr

# Setup input and output directories
data_dir = "data/"
output_dir = "output/"
os.makedirs(output_dir, exist_ok=True)

# Prepare a path to the source HTML file
document_path = os.path.join(data_dir, "nature.html")

# Initialize the HTML document from the file
doc = ah.HTMLDocument(document_path)

# Create an instance of DocRenderingOptions and set a custom page size
options = rd.DocRenderingOptions()
options.page_setup.any_page = dr.Page(dr.Size(dr.Length.from_inches(8.0), dr.Length.from_inches(10.0)))
options.font_embedding_rule = rd.FontEmbeddingRule.FULL

# Prepare a path to save the converted file
save_path = os.path.join(output_dir, "nature-options.docx")

# Create a DocDevice with the specified options and output file
device = rd.DocDevice(options, save_path)

# Render HTML to DOCX
doc.render_to(device)

Aspose.HTML 提供免费的在线 转换器，可将 HTML、XHTML、MHTML、EPUB、XML 和 Markdown 文件转换为各种流行格式。你可以轻松地将 HTML 文档转换为 PDF、XPS、DOCX、JPG、PNG、GIF、TIFF 等格式。只需选择文件，选择要转换的格式，就大功告成了。