How to export HTML5 Canvas content as a PDF file with text layer?

HTML5 Canvas content exports to editable text PDFs

Many developers face the challenge of exporting HTML5 Canvas drawing content (including text) into editable, searchable PDF files. Simply converting Canvas to images and then to PDF will lose vector information of the text, resulting in a decrease in clarity and inability to edit or search. This article discusses how to solve this problem.

Directly using jspdf.context2d to repaint Canvas content into jsPDF, it requires completely rewriting the drawing logic, which is inefficient. This is because Canvas itself only stores pixel data and lacks metadata for text (font, size, position, etc.). Therefore, a mechanism is needed to extract or record text information on Canvas.

Currently, there is no way to convert Canvas content directly into PDFs containing editable text. jspdf.context2d only performs pixel-level copying and cannot retain vector text information. An effective solution needs to be adjusted during the Canvas drawing phase:

• Use vector graphics library: Avoid drawing text directly using fillText and other methods of Canvas API. Use SVG or other vector graphics library to draw text so that the text information will be saved in vector form, making it easy to convert to PDF vector text.

• Custom data structure: While drawing text, record the coordinates, font, size, color and other information of each text element. When generating PDFs, use this information to create text objects.

• Layered drawing: draw text separately from other graphic content and process it separately. Add text parts to PDF as vector or text.

In short, to generate a PDF containing editable text, text information must be preserved during the Canvas drawing phase, rather than attempting to compensate for it during the conversion phase. Direct conversion is not feasible and requires optimization of the drawing process.

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