tresvg - Tcl SVG rendering

Tcl wrapper around resvg

resvg is an SVG rendering library. It can be used as a Rust library, as a C library, and as a CLI application to render static SVG files.
The core idea is to make a fast, small, portable SVG library with the goal to support the whole SVG spec.

Source: resvg

Compatibility :

• Tcl 8.6 or higher

Dependencies :

• tcl-cffi >= 2.0 and/or critcl (see note below)

Note

critcl and Tk are optional for rendering SVG image to photo command.

Cross-Platform :

• Windows, Linux, macOS support.

Example :

tcl-cffi demo :

package require tresvg

set svg hello.svg

# Initialize log (optional)
tresvg::initLog

# Create options
set opt [tresvg::optionsCreate]

# Parse svg file
set tree [tresvg::parseTreeFromFile $svg $opt]

# Apply transform
set transform [tresvg::transformIdentity]

# Get image size
set size [tresvg::getImageSize $tree]
set width  [expr {int([dict get $size width])}]
set height [expr {int([dict get $size height])}]

# Render
set pixmap [tresvg::render $tree $transform $width $height]

# Save to PNG
tresvg::toPNG $pixmap $width $height "/Users/nico/temp/output.png"

# Extended procedures (not a part of resvg C-API)
set xml [tresvg::getXML $tree] ; # Gets simplified XML
set version [tresvg::libVersion]

# Cleanup
tresvg::optionsDestroy $opt
tresvg::treeDestroy $tree

critcl demo :

package require Tk ; # Important to load Tk before 'tresvg' package.
package require tresvg

set svg hello.svg
set img [image create photo]

# Others args are optional (see listing commands below)
tresvg::toTkImg $svg $img

# Others examples of 'tresvg::toTkImg' command :
tresvg::toTkImg $svg $img -width 100 -height 50
tresvg::toTkImg $svg $img -scale 2 -dpi 300
tresvg::toTkImg $svg $img -mtx {1 0 0 1 0 0}
tresvg::toTkImg $svg $img -width 100 -height 50 -modeScale "fit"
tresvg::toTkImg $svg $img -initLog "true"

label .l -image $img
pack .l

Commands :

Tcl/Tk commands	args
tresvg::toPNG	pixmap width height filename
tresvg::toBase64	pixmap width height
tresvg::toTkImg	'svgFile or svgData' tkImage ?args?`

---

Commands listing :

resvg-c	tcl-cffi	critcl args	help
resvg_transform_identity	tresvg::transformIdentity	default matrix	-
resvg_init_log	tresvg::initLog	-initLog "bool_value"	Use it if you want to see any warnings.
resvg_options_create	tresvg::optionsCreate	-	Creates a new #resvg_options object.
resvg_options_destroy	tresvg::optionsDestroy	-	Destroys a #resvg_options object.
resvg_tree_destroy	tresvg::treeDestroy	-	Destroys a #resvg_tree object.
resvg_options_set_resources_dir	tresvg::optionsSetResourcesDir	-resourcesDir $path	Sets the path to the resources directory.
resvg_options_set_dpi	tresvg::optionsSetDpi	-dpi $dpi	Sets the DPI of the rendering.
resvg_options_set_stylesheet	tresvg::optionsSetStylesheet	-styleSheet $css	Sets the CSS styles used by the SVG rendering.
resvg_options_set_font_family	tresvg::optionsSetFontFamily	-fontFamily $family	Sets the font family.
resvg_options_set_font_size	tresvg::optionsSetFontSize	-fontSize $size	Sets the font size.
resvg_options_set_serif_family	tresvg::optionsSetSerifFamily	-serifFontFamily $family	Sets the serif font family.
resvg_options_set_sans_serif_family	tresvg::optionsSetSansSerifFamily	-sansSerifFontFamily $family	Sets the sans-serif font family.
resvg_options_set_cursive_family	tresvg::optionsSetCursiveFamily	-cursiveFontFamily $family	Sets the cursive font family.
resvg_options_set_fantasy_family	tresvg::optionsSetFantasyFamily	-fantasyFontFamily $family	Sets the fantasy font family.
resvg_options_set_monospace_family	tresvg::optionsSetMonospaceFamily	-monospaceFontFamily $family	Sets the monospace font family.
resvg_options_set_languages	tresvg::optionsSetLanguages	-languages $languages	Sets the languages.
resvg_options_set_shape_rendering_mode	tresvg::optionsSetShapeRenderingMode	-shapeRenderingMode $mode	Sets the shape rendering mode.
resvg_options_set_text_rendering_mode	tresvg::optionsSetTextRenderingMode	-textRenderingMode $mode	Sets the text rendering mode.
resvg_options_set_image_rendering_mode	tresvg::optionsSetImageRenderingMode	-imageRenderingMode $mode	Sets the image rendering mode.
resvg_options_load_font_data	tresvg::optionsLoadFontData	❌ not implemented yet	-
resvg_options_load_font_file	tresvg::optionsLoadFontFile	-loadFontFile $fontfile	Loads a font file.
resvg_options_load_system_fonts	tresvg::optionsLoadSystemFonts	-loadSystemFonts "bool_value"	Loads the system fonts.
resvg_parse_tree_from_file	tresvg::parseTreeFromFile	-	Parses a SVG file.
resvg_parse_tree_from_data	tresvg::parseTreeFromData	tresvg::toTkImg $svgString	Parses a SVG data.
resvg_is_image_empty	tresvg::isImageEmpty	❌ not implemented yet	Gets if an image is empty.
resvg_get_image_size	tresvg::getImageSize	❌ not implemented yet	Gets the size of an image.
resvg_get_object_bbox	tresvg::getObjectBbox	❌ not implemented yet	Gets the bounding box of an object.
resvg_get_image_bbox	tresvg::getImageBbox	❌ not implemented yet	Gets the bounding box of an image.
resvg_node_exists	tresvg::nodeExists	❌ not implemented yet	Gets if a node exists.
resvg_get_node_transform	tresvg::getNodeTransform	❌ not implemented yet	Gets the transform of a node.
resvg_get_node_bbox	tresvg::getNodeBBox	❌ not implemented yet	Gets the bounding box of a node.
resvg_get_node_stroke_bbox	tresvg::getNodeStrokeBBox	❌ not implemented yet	Gets the stroke bounding box of a node.
resvg_tree_destroy	tresvg::treeDestroy	-	Destroys a #resvg_tree object.
resvg_render	tresvg::render	tresvg::toTkImg $svg	Renders a SVG file or data to Tk image photo.
resvg_tree_to_xml (resvg extended)	tresvg::getXML	-	Gets simplified XML.
resvg_version_string (resvg extended)	tresvg::liVersion	-	Gets resvg version.
resvg_render_node	tresvg::renderNode	❌ not implemented yet	Renders a node.
struct resvg_transform	[list a b c d e f]	-mtx {a b c d e f}	Sets the transform matrix.
-	-	-width $width	Sets the width of the image.
-	-	-height $height	Sets the height of the image.
-	-	-scale $scale	Sets the scale of the image.
-	-	-modeScale "fit"	Sets the mode scale of the image.

Building :

You can either build the library yourself (if you have Rust installed or if you want to install it), or use this repository’s GitHub Actions to automatically build platform-specific binaries for you.

---

Option 1 — Build locally (Rust required)

If you already have Rust installed, you can build the C library directly from source:

cd resvg-X.XX.X/crates/c-api
cargo build --release

This command compiles the resvg C API and produces the libraries under:

target/release/

After building, copy the generated dynamic or static libraries into your tresvg package directory under one of the following platform-specific folders:

• Linux: your/path/to/lib/tresvg/linux-x86_64
• Windows: your/path/to/lib/tresvg/win32-x86_64
• macOS (Intel): your/path/to/lib/tresvg/macosx-x86_64
• macOS (ARM): your/path/to/lib/tresvg/macosx-arm

⚠️ Compilation under Windows to work with critcl: :

# Rust toolchain with GNU target
rustup target add x86_64-pc-windows-gnu
cargo build --release --target x86_64-pc-windows-gnu

This will produce dynamic libraries in /target/x86_64-pc-windows-gnu/release

---

Option 2 — Use prebuilt binaries (no Rust required)

If you prefer not to install or compile Rust yourself, you can simply use this GitHub repository.
You have two alternatives:

• On the Actions tab, then on the workflow of your choice, you can automatically download binaries for all supported platforms.
• If you decide to fork it, you can enable the workflow in your own fork to generate them automatically.

Tip

Make sure to match your platform architecture (e.g. x86_64 vs arm64).
The header file resvg.h is included in each build under the your_platform/include/ directory + resvg licenses in each folder.

License :

MIT.

Acknowledgments :

To RazrFalcon, the author of resvg, who helped me understand his library a few years ago.

Changes :

• 21-Oct-2025 : 0.1
  • Initial release.
• 26-Oct-2025 : 0.15
  • Adds a better support for critcl backend.
  • Adds others commands for tcl-cffi backend.
  • Adds gitHub Actions workflow to build resvg binaries.
  • Cosmetic changes.
• 29-Oct-2025 : 0.17
  • Uses critcl if present to replace the tresvg::encodePNG command for tcl-cffi backend,
    by using stbi_write_png_to_mem function from stb_image_write.h header file if also exists.
  • Cosmetic changes.
• 05-Nov-2025 : 0.19
  • Extends resvg C-API with 2 new commands resvg_tree_to_xml and resvg_version_string.
  • Includes <limits.h> header in crit.tcl file + fixes some problems with critcl and Tk9, thanks @andreas-kupries.
  • Adds gitHub Actions workflow to extend resvg C-API.
  • Adds a release with binaries for macOS (ARM + Intel), Windows and Linux.