Optimize Data URI encoding

Oct 13, 2025 by wbrum.org 104 views

Introduction

In the world of document rendering, converting between different file formats is a common task. However, when it comes to converting EMF (Enhanced Metafile Format) to SVG (Scalable Vector Graphics), things can get complicated. In this article, we will delve into the issue of SVG generated from EMF being mangled, and explore the possible causes and solutions.

The Problem

The issue at hand is that when an EMF file is converted to SVG using the Vectory library, the resulting SVG is rendered badly in HTML. Specifically, the SVG is rendered at the top of the page, and the embedded images inside the EMF are not rendered correctly. This is in contrast to the native EMF rendering in Word documents, which works fine.

Code Analysis

To understand the issue, let's take a closer look at the code that generates the SVG from EMF. The relevant code snippet is as follows:

def svg_emf_double(img)
  if emf?(img["mimetype"])
    img = emf_encode(img)
    # img.children.first.previous = emf_to_svg(img)
    img.add_first_child emf_to_svg(img)
  elsif img["mimetype"] == "image/svg+xml"
    src = svg_to_emf(img) or return
    img.add_child("<emf/>")
    img.elements.last["src"] = src
  end
end

def svg_prep(img)
  img["mimetype"] = "image/svg+xml"
  %r{^data:}.match?(img["src"]) or
    img["src"] = Vectory::Emf.from_path(img["src"]).to_uri.content
end

def emf_encode(img)
  svg_prep(img)
  img.children = "<emf src='#{img['src']}'/>"
  img["src"] = ""
  img
end

def emf_to_svg(img)
  datauri_src = img.at(ns("./emf/@src")).text
  Vectory::Emf.from_datauri(datauri_src)
    .to_svg
    .content
    .sub(/<\?[^>]+>/, "")
end

Possible Causes

Based on the code analysis, there are several possible causes for the issue:

Viewport issue: The SVG is rendered at the top of the page, which suggests that there is an issue with the viewport. The viewport is responsible for defining the size and position of the SVG in the HTML document.
Embedded image rendering: The embedded images inside the EMF are not rendered correctly, which suggests that there is an issue with the image rendering process.
Data URI encoding: The code uses Data URI encoding to encode the EMF file as a base64-encoded string. This encoding process may be causing issues with the SVG rendering.

Solutions

To solve the issue, we need to address the possible causes mentioned above. Here are some potential solutions:

Fix the viewport issue: We need to ensure that the viewport is set correctly in the SVG. This can be done by adding a viewBox attribute to the SVG element.
Improve image rendering: We need to improve the image rendering process to ensure that the embedded images are rendered correctly. This may involve using a different image rendering library or optimizing the image rendering code.
Optimize Data URI encoding: We need to optimize the Data URI encoding process to ensure that it does not cause issues with the SVG rendering. This may involve using a different encoding scheme or optimizing the encoding code.

Conclusion

In conclusion, the issue of SVG generated from EMF being mangled is a complex problem that requires a deep understanding of the code and the possible causes. By analyzing the code and identifying the possible causes, we can develop potential solutions to address the issue. By optimizing the viewport, improving image rendering, and optimizing Data URI encoding, we can ensure that the SVG is rendered correctly in HTML.

Future Work

Future work on this issue may involve:

Further code analysis: We need to continue analyzing the code to identify any other potential causes of the issue.
Testing and validation: We need to test and validate the solutions to ensure that they work correctly.
Optimization: We need to optimize the code and the solutions to ensure that they are efficient and scalable.

References

Vectory library documentation
EMF file format documentation
SVG file format documentation
SVG Generated from EMF is Mangled: A Q&A Article =====================================================

Q: What is the issue with SVG generated from EMF?

A: The issue is that when an EMF file is converted to SVG using the Vectory library, the resulting SVG is rendered badly in HTML. Specifically, the SVG is rendered at the top of the page, and the embedded images inside the EMF are not rendered correctly.

Q: What are the possible causes of the issue?

A: The possible causes of the issue are:

Viewport issue: The SVG is rendered at the top of the page, which suggests that there is an issue with the viewport. The viewport is responsible for defining the size and position of the SVG in the HTML document.
Embedded image rendering: The embedded images inside the EMF are not rendered correctly, which suggests that there is an issue with the image rendering process.
Data URI encoding: The code uses Data URI encoding to encode the EMF file as a base64-encoded string. This encoding process may be causing issues with the SVG rendering.

Q: How can I fix the viewport issue?

A: To fix the viewport issue, you need to ensure that the viewport is set correctly in the SVG. This can be done by adding a viewBox attribute to the SVG element.

Q: How can I improve image rendering?

A: To improve image rendering, you need to ensure that the embedded images are rendered correctly. This may involve using a different image rendering library or optimizing the image rendering code.

Q: How can I optimize Data URI encoding?

A: To optimize Data URI encoding, you need to ensure that the encoding process does not cause issues with the SVG rendering. This may involve using a different encoding scheme or optimizing the encoding code.

Q: What are the benefits of using Vectory library?

A: The Vectory library provides several benefits, including:

Easy conversion: The Vectory library makes it easy to convert EMF files to SVG.
High-quality rendering: The Vectory library provides high-quality rendering of SVG files.
Flexibility: The Vectory library provides flexibility in terms of customization and optimization.

Q: What are the limitations of using Vectory library?

A: The Vectory library has several limitations, including:

Complexity: The Vectory library can be complex to use, especially for beginners.
Performance: The Vectory library may not perform well with large EMF files.
Compatibility: The Vectory library may not be compatible with all EMF file formats.

Q: What are the alternatives to Vectory library?

A: There are several alternatives to the Vectory library, including:

SVG.js: SVG.js is a JavaScript library that provides a simple and easy-to-use API for working with SVG files.
D3.js: D3.js is a JavaScript library that provides a powerful and flexible API for working with SVG files.
Raphael.js: Raphael.js is a JavaScript library that provides a simple and easy-to-use API for working with SVG files.

Q: How can I troubleshoot the issue?

A: To troubleshoot the issue, you can try the following:

Check the code: Check the code for any errors or issues.
Check the EMF file: Check the EMF file for any issues or errors.
Check the SVG file: Check the SVG file for any issues or errors.
Use debugging tools: Use debugging tools such as console.log() or a debugger to identify the issue.