clj-imaging

Images, SVG rasterization and plotting for Clojure — without java.desktop.

com.blockether/imaging is a thin Clojure FFM (Java 22+ java.lang.foreign) binding over a small Rust cdylib built on image, resvg/usvg and tiny-skia.

Why: AWT / Java2D / ImageIO drag the whole java.desktop module and its JNI surface into a GraalVM native image. This library replaces that with one self-contained native library, so decoding, drawing, text, SVG and charts all work in a native binary with nothing on PATH.

• Pure-Rust codecs: PNG, JPEG, WebP (incl. lossless encode), GIF, BMP, TIFF, ICO, TGA, PNM, DDS, farbfeld, QOI
• SVG → raster via resvg, with the same font stack
• Four Noto faces embedded (sans, sans-bold, sans-italic, mono) — no system fonts required
• A declarative plotting DSL (lines, areas, steps, bars, hbars, stacked bars, scatter, histogram, pie, donut, heatmap)
• No AWT, no ImageIO, no BufferedImage, no service loaders

Install

;; deps.edn
com.blockether/imaging {:mvn/version "0.1.0"}
;; plus the native library for your platform
com.blockether/imaging-native-darwin-arm64 {:mvn/version "0.1.0"}

Native artifacts are published per platform: darwin-arm64, darwin-x64, linux-x64, linux-arm64, windows-x64.

Requires JDK 22+ (FFM). Run with --enable-native-access=ALL-UNNAMED to silence the JDK 24+ warning.

Usage

(require '[com.blockether.imaging :as img])

(with-open [im (img/decode (io/file "photo.jpg"))]
  (-> im
      (img/thumbnail 800 800)
      (img/adjust {:brightness 4 :contrast 8})
      (img/save! "out.webp")))

(img/probe bytes)                  ;; => {:format "png" :width 1200 :height 800 :frames 1 ...}
(img/convert bytes {:format "webp" :max-width 1600 :max-bytes 200000})  ;; => byte[]
(img/resize im 400 300)            ;; exact size    (img/thumbnail im 256 256) fits a box

;; drawing + text, on a fresh canvas
(with-open [im (img/blank 640 240 "#101014")]
  (img/draw! im [{:op :rect :x 20 :y 20 :w 200 :h 80 :fill "#3b82f6" :radius 12}
                 {:op :line :x1 0 :y1 0 :x2 640 :y2 240 :stroke "#ffffff40" :stroke-width 2}
                 {:op :text :x 40 :y 160 :text "hello" :size 32 :fill "#fff" :weight 700}])
  (img/encode im :png))

(img/text-measure {:text "hello" :size 32 :weight 700}) ;; => {:width .. :height .. :x .. :y .. :lines 1}
(img/render-svg svg-string {:width 512})                ;; => Img

Every op is a map with :op; batch style keys (:fill :stroke :stroke-width :size :family :weight :italic) can be set per batch or per op. WebP encoding is lossless.

Plotting

(require '[com.blockether.imaging.plot :as plot])

(-> (plot/figure {:width 900 :height 500 :title "Latency" :theme :dark
                  :x {:label "run"} :y {:label "ms"}})
    (plot/lines {:name "p50" :y [12 14 11 15 13]})
    (plot/areas {:name "p99" :y [40 52 48 61 55] :fill "#ef444455"})
    (plot/save! "latency.png"))

(plot/bytes (-> (plot/figure {:title "share"})
                (plot/donut {:values [30 25 45] :labels ["a" "b" "c"]})))

Every series takes :name, :color and either :y (implicit x) or :x/:y pairs; histogram takes :values + :bins, heatmap takes a row-major :z matrix.

Memory model

Img handles are AutoCloseable and also registered with a Cleaner, guarded by one shared CAS flag — closing twice, or closing and then letting the GC collect, frees exactly once. Prefer with-open; forgetting it leaks nothing. Hot paths use Arena.ofConfined; long-lived handles use Arena.ofAuto.

Building

scripts/build-natives.sh darwin-arm64     # cargo build --release, stage into resources/prebuilds/<platform>
clojure -X:test                           # 16 tests against the real cdylib
clojure -T:build jar                      # the pure-Clojure jar
clojure -T:build native-jar :platform '"darwin-arm64"'

CI builds all five platforms; pushing a v* tag deploys imaging and every imaging-native-<platform> to Clojars.

License

MIT. Bundled Noto fonts are SIL OFL 1.1.