tryst-vector

CPU vector rasterization (ThorVG) for tryst, Crystal's Tcl/Tk binding — antialiased curves, gradients and shadows, blitted into a Tk Photo. Tk's own canvas primitives have no native gradient fill and, on X11, no antialiasing either.

require "tryst"
require "tryst-vector"

Tryst::Vector.init

app = Tryst::App.new
canvas = app.create_widget("canvas", width: 200, height: 120)
canvas.pack(fill: "both", expand: true)

surface = Tryst::Vector::Surface.new(width: 160, height: 80)
surface.draw do |ctx|
  gradient = Tryst::Vector::Gradient.linear(0, 0, 160, 80, [
    {0.0, 60_u8, 120_u8, 240_u8, 255_u8},
    {1.0, 200_u8, 60_u8, 220_u8, 255_u8},
  ])
  ctx.rounded_rect(4, 4, 152, 72, 18).fill(gradient)
end

photo = Tryst::Photo.new(app, width: surface.pixel_width, height: surface.pixel_height)
surface.blit_to(photo)
canvas.command(:create, :image, 20, 20, image: photo.name, anchor: :nw)

app.show
app.mainloop

See examples/rounded_rect_gradient.cr for the runnable version of the above (and Examples below for how to run it).

Tryst::Vector::Surface is the seam OwnerDrawnWidget is meant to consume: #draw yields a Context with #rect/#rounded_rect/#circle/ #polygon (an arbitrary closed straight-edged shape from its own vertices — a tooltip's pointer arrow, say), each returning a Shape you call #fill/#stroke on (a flat color or a Tryst::Vector::Gradient). #blit_to(photo) writes the whole rendered buffer into a Photo you already have with no pixel conversion (ThorVG's straight-alpha output is byte-for-byte Tryst::PixelFormat::ARGB); #to_slice hands back those same bytes directly for a caller that manages its own Photo already — OwnerDrawnWidget#blit, most naturally, which needs exactly this to feed its own lazily-created Photo rather than one the caller sets up itself. scale: on Surface.new renders at a HiDPI multiple while #draw's own coordinates stay in logical pixels throughout — see Surface's own doc comment for the full story.

#arc(cx, cy, r, start_deg, sweep_deg) is Context's one stroke-only primitive (no fill concept — a partial ring drawn filled would be a pie slice; #polygon already covers that shape directly if something wants it) — 0 degrees is 12 o'clock, positive sweep_deg sweeps clockwise (screen coordinates), matching how a progress ring or spinner is actually thought about rather than math's usual 0=east/counterclockwise. #stroke takes an optional cap: (Tryst::Vector::StrokeCap — :butt (ThorVG's own default), :round, :square) — :round is what makes a swept arc read as a smooth stroke rather than a wedge with hard-cut ends; only meaningful on an open path like #arc's, harmless to pass on a closed shape.

Text isn't exposed yet (ThorVG's C API supports it; the wrapper just doesn't reach it) — revisit once something actually needs it.

Requirements

Crystal >= 1.21.0, Tcl/Tk 8.6 (whatever tryst itself needs), and ThorVG

= 1.0.

platform	package	notes
macOS (Homebrew)	thorvg	not keg-only; ships a thorvg-1.pc pkg-config file
Debian/Ubuntu (apt)	libthorvg-dev	Debian forky/sid only as of writing — not yet in trixie or any current Ubuntu release
Windows (MSYS2, UCRT64 shell)	mingw-w64-ucrt-x86_64-thorvg	pacman -S mingw-w64-ucrt-x86_64-thorvg, alongside the root README's own Crystal/Tcl/Tk packages, from the same UCRT64 shell

brew install thorvg

Examples

crystal run examples/rounded_rect_gradient.cr

Opens a small window with an antialiased rounded rect and a gradient fill — the whole seam (Surface → straight-alpha buffer → Photo → canvas image item) exercised end to end, not just in a headless spec.

Tests

shards install
crystal spec                  # host
scripts/docker-test.sh        # Debian forky, same suite

scripts/docker-test.sh builds from this repo's own root; shards install inside the image fetches tryst directly via its github: dependency. It takes the same arguments crystal spec does, so a focused run works there too.