repository·master·Indexed 23 days ago
https://github.com/tdewolff/canvasA library and toolkit featuring the pdftext CLI utility for inspecting, extracting, and replacing text within PDF documents. It supports various PDF text encodings (Standard, WinAnsi, MacRoman, Builtin, ToUnicode, and Type1 Differences) and provides programmatic APIs for PDF reading, writing, and stream compression/decompression. Additionally, it includes functionality to parse LaTeX strings and DVI files into canvas paths using external binaries like latex and dvisvgm.
The pdftext tool is a toolkit for extracting and replacing text within PDF files. It provides two primary modes of operation: extraction and replacement.
Extract text content from specific pages or retrieve document metadata.
Replace existing text strings at specific indices with new text, allowing for positional offsets and alignment adjustments.
When a PDF font provides a ToUnicode CMap, the system uses a pdfFontUnicode structure to map character codes to UTF-8 strings.
uint16 character codes to string destinations.The FillRule determines how overlapping subpaths are filled. You can choose between several algorithms:
NonZero (default): Fills any point enclosed by an unequal number of clockwise and counter-clockwise paths.EvenOdd: Fills any point enclosed by an uneven number of paths, regardless of direction.Positive: Fills only counter-clockwise oriented paths.Negative: Fills only clockwise oriented paths.The pdftext utility handles several types of character encodings to correctly decode text from PDF documents. These include:
ToUnicode stream provided in the PDF to map character codes to UTF-8 strings.Differences array.Flatten(tolerance float64) method. The tolerance parameter defines the maximum allowed deviation from the original curve. This returns a new path consisting only of MoveTo, LineTo, and Close commands.ReplaceArcs() method returns a new path where all ArcTo commands have been replaced by CubeTo (cubic Bézier) commands. This is useful for formats like PDF that do not natively support elliptical arcs.Use the following methods to build a path by adding segments. If the path is empty, these methods will automatically perform an initial MoveTo to (0,0) or the specified coordinates.
MoveTo(x, y float64): Starts a new independent subpath at (x, y).LineTo(x, y float64): Adds a straight line from the current position to (x, y).QuadTo(cpx, cpy, x, y float64): Adds a quadratic Bézier curve with control point (cpx, cpy) and end point (x, y).CubeTo(cpx1, cpy1, cpx2, cpy2, x, y float64): Adds a cubic Bézier curve with two control points and an end point (x, y).ArcTo(rx, ry, rot float64, large, sweep bool, x, y float64): Adds an elliptical arc. rot is rotation in degrees, large and sweep are boolean flags for arc direction and size.Close(): Closes the current subpath by drawing a line back to the last MoveTo position.The DVI2Path function parses a DVI file (the output format from TeX) and converts its contents into a *Path. To use this function, you must provide a DVIFonts implementation that can resolve font names and sizes to specific DVIFont instances.
Workflow:
DVIFonts interface to handle font lookups.DVI2Path(data, yourFontsImplementation).*Path can then be used for drawing operations in the canvas library.Use ToScanxScanner to convert a *Path into commands for a *scanx.Scanner. This is useful for scanline-based rasterization. The method requires a dy value (representing the vertical offset/height) and a Resolution. Like the vector rasterizer, it flattens curves into lines using a tolerance derived from the resolution.
func (p *Path) ToScanxScanner(ras *scanx.Scanner, dy float64, resolution Resolution)The ContainsPoint method determines if a specific coordinate (x, y) is inside the area defined by the path. This result depends on the provided FillRule.
Note: If the point lies exactly on the path's boundary, it is considered to be on the exterior.
Use these methods to inspect the geometric properties of a path:
Length(): Returns the total length of the path in millimeters. Note that lengths for cubic Béziers are approximated.IsFlat(): Returns true if the path consists exclusively of MoveTo, LineTo, and Close commands (no curves or arcs).Use NewPDFReader to create a new instance of a pdfReader. This function reads the entire content from an io.Reader and parses the PDF structure, including the trailer, encryption (if a password is provided), and the page tree (kids).
If the PDF is invalid or the version is unsupported, it returns an error. If the PDF is encrypted, you must provide the correct password to successfully parse the objects.