feat: add AVM tags for PNG write

src/js/AvmUtils.js

@@ -0,0 +1,313 @@
+// SPDX-License-Identifier: LGPL-3.0-or-later
+// Copyright 2013 - UDS/CNRS
+
+function crc32(bytes) {
+    let crc = 0xffffffff;
+
+    for (let i = 0; i < bytes.length; i++) {
+        crc ^= bytes[i];
+
+        for (let j = 0; j < 8; j++) {
+            const mask = -(crc & 1);
+            crc = (crc >>> 1) ^ (0xedb88320 & mask);
+        }
+    }
+
+    return (crc ^ 0xffffffff) >>> 0;
+}
+
+function u32be(n) {
+    return new Uint8Array([
+        (n >>> 24) & 0xff,
+        (n >>> 16) & 0xff,
+        (n >>> 8) & 0xff,
+        n & 0xff,
+    ]);
+}
+
+function concatUint8Arrays(arrays) {
+    const total = arrays.reduce((sum, array) => sum + array.length, 0);
+    const out = new Uint8Array(total);
+    let offset = 0;
+
+    for (const array of arrays) {
+        out.set(array, offset);
+        offset += array.length;
+    }
+
+    return out;
+}
+
+function escapeXml(value) {
+    return String(value)
+        .replace(/&/g, "&amp;")
+        .replace(/</g, "&lt;")
+        .replace(/>/g, "&gt;")
+        .replace(/"/g, "&quot;");
+}
+
+function renderAvmValue(value) {
+    if (Array.isArray(value)) {
+        return [
+            "<rdf:Seq>",
+            ...value.map((item) => `  <rdf:li>${escapeXml(item)}</rdf:li>`),
+            "</rdf:Seq>",
+        ].join("\n");
+    }
+
+    return escapeXml(value);
+}
+
+function serializeFitsHeaderValue(value) {
+    if (typeof value === "string") {
+        return `'${value}'`;
+    }
+
+    if (typeof value === "boolean") {
+        return value ? "T" : "F";
+    }
+
+    return `${value}`;
+}
+
+function buildFitsHeaderFromWcs(wcs) {
+    const orderedKeys = [
+        "NAXIS",
+        "NAXIS1",
+        "NAXIS2",
+        "CTYPE1",
+        "CTYPE2",
+        "CRPIX1",
+        "CRPIX2",
+        "CRVAL1",
+        "CRVAL2",
+        "CUNIT1",
+        "CUNIT2",
+        "CD1_1",
+        "CD1_2",
+        "CD2_1",
+        "CD2_2",
+        "PC1_1",
+        "PC1_2",
+        "PC2_1",
+        "PC2_2",
+        "CDELT1",
+        "CDELT2",
+        "CROTA2",
+        "LONPOLE",
+        "LATPOLE",
+        "EQUINOX",
+        "RADESYS",
+    ];
+
+    return orderedKeys
+        .filter((key) => wcs[key] !== undefined && wcs[key] !== null)
+        .map((key) => `${key.padEnd(8, " ")}= ${serializeFitsHeaderValue(wcs[key])}`)
+        .join("\n");
+}
+
+function getCoordinateFrameFromWcs(wcs) {
+    const ctype1 = `${wcs.CTYPE1 || ""}`.trim().toUpperCase();
+    const ctype2 = `${wcs.CTYPE2 || ""}`.trim().toUpperCase();
+    const radesys = `${wcs.RADESYS || ""}`.trim().toUpperCase();
+
+    if (ctype1.startsWith("GLON-") && ctype2.startsWith("GLAT-")) {
+        return "GAL";
+    }
+
+    if (ctype1.startsWith("RA---") && ctype2.startsWith("DEC--")) {
+        return radesys || "ICRS";
+    }
+
+    return null;
+}
+
+function getProjectionFromWcs(wcs) {
+    const ctype1 = `${wcs.CTYPE1 || ""}`.trim().toUpperCase();
+    const projection = ctype1.slice(-3);
+
+    return /^[A-Z0-9]{3}$/.test(projection) ? projection : null;
+}
+
+export function buildAvmFromWcs(wcs, options = {}) {
+    if (!wcs || typeof wcs !== "object") {
+        return null;
+    }
+
+    const coordinateFrame = getCoordinateFrameFromWcs(wcs);
+    const projection = getProjectionFromWcs(wcs);
+
+    if (!coordinateFrame || !projection) {
+        return null;
+    }
+
+    const avm = {
+        "MetadataVersion": "1.2",
+        "Spatial.CoordinateFrame": coordinateFrame,
+        "Spatial.ReferenceValue": [wcs.CRVAL1, wcs.CRVAL2],
+        "Spatial.ReferenceDimension": [wcs.NAXIS1, wcs.NAXIS2],
+        "Spatial.ReferencePixel": [wcs.CRPIX1, wcs.CRPIX2],
+        "Spatial.CoordsystemProjection": projection,
+        "Spatial.FITSheader": buildFitsHeaderFromWcs(wcs),
+    };
+
+    if (wcs.EQUINOX !== undefined && wcs.EQUINOX !== null) {
+        avm["Spatial.Equinox"] = wcs.EQUINOX;
+    }
+
+    if (
+        wcs.CD1_1 !== undefined &&
+        wcs.CD1_2 !== undefined &&
+        wcs.CD2_1 !== undefined &&
+        wcs.CD2_2 !== undefined
+    ) {
+        avm["Spatial.CDMatrix"] = [wcs.CD1_1, wcs.CD1_2, wcs.CD2_1, wcs.CD2_2];
+    } else if (wcs.CDELT1 !== undefined && wcs.CDELT2 !== undefined) {
+        avm["Spatial.Scale"] = [wcs.CDELT1, wcs.CDELT2];
+
+        const rotation = options.rotation ?? wcs.CROTA2;
+        if (rotation !== undefined && rotation !== null) {
+            avm["Spatial.Rotation"] = rotation;
+        }
+    }
+
+    return avm;
+}
+
+export function buildAvmXmpPacket(avm) {
+    const entries = Object.entries(avm)
+        .map(([key, value]) => `    <avm:${key}>${renderAvmValue(value)}</avm:${key}>`)
+        .join("\n");
+
+    return [
+        `<?xpacket begin="${"\uFEFF"}" id="W5M0MpCehiHzreSzNTczkc9d"?>`,
+        '<x:xmpmeta xmlns:x="adobe:ns:meta/">',
+        ' <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">',
+        '  <rdf:Description rdf:about="" xmlns:avm="http://www.communicatingastronomy.org/avm/1.0/">',
+        entries,
+        '  </rdf:Description>',
+        ' </rdf:RDF>',
+        '</x:xmpmeta>',
+        '<?xpacket end="w"?>',
+    ].join("\n");
+}
+
+function makePngChunk(type4, data) {
+    const encoder = new TextEncoder();
+    const type = encoder.encode(type4);
+
+    if (type.length !== 4) {
+        throw new Error("PNG chunk type must be 4 bytes");
+    }
+
+    const crcInput = concatUint8Arrays([type, data]);
+    const crc = crc32(crcInput);
+
+    return concatUint8Arrays([
+        u32be(data.length),
+        type,
+        data,
+        u32be(crc),
+    ]);
+}
+
+function makeXmpITXtChunk(xmpString) {
+    const encoder = new TextEncoder();
+
+    const keyword = encoder.encode("XML:com.adobe.xmp");
+    const compressionFlag = new Uint8Array([0]);
+    const compressionMethod = new Uint8Array([0]);
+    const languageTag = new Uint8Array([0]);
+    const translatedKeyword = new Uint8Array([0]);
+    const text = encoder.encode(xmpString);
+
+    const data = concatUint8Arrays([
+        keyword,
+        new Uint8Array([0]),
+        compressionFlag,
+        compressionMethod,
+        languageTag,
+        translatedKeyword,
+        text,
+    ]);
+
+    return makePngChunk("iTXt", data);
+}
+
+export function insertXmpIntoPng(pngBytes, xmpString) {
+    if (!(pngBytes instanceof Uint8Array)) {
+        throw new Error("pngBytes must be a Uint8Array");
+    }
+
+    const pngSignature = new Uint8Array([
+        0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a,
+    ]);
+
+    for (let i = 0; i < 8; i++) {
+        if (pngBytes[i] !== pngSignature[i]) {
+            throw new Error("Not a valid PNG");
+        }
+    }
+
+    const xmpChunk = makeXmpITXtChunk(xmpString);
+    let pos = 8;
+    let insertPos = -1;
+
+    while (pos + 12 <= pngBytes.length) {
+        const length =
+            (pngBytes[pos] << 24) |
+            (pngBytes[pos + 1] << 16) |
+            (pngBytes[pos + 2] << 8) |
+            pngBytes[pos + 3];
+
+        const type = String.fromCharCode(
+            pngBytes[pos + 4],
+            pngBytes[pos + 5],
+            pngBytes[pos + 6],
+            pngBytes[pos + 7],
+        );
+
+        const chunkEnd = pos + 12 + length;
+        if (chunkEnd > pngBytes.length) {
+            throw new Error("Corrupt PNG");
+        }
+
+        if (type === "IDAT" || type === "IEND") {
+            insertPos = pos;
+            break;
+        }
+
+        pos = chunkEnd;
+    }
+
+    if (insertPos === -1) {
+        throw new Error("Could not find insertion point in PNG");
+    }
+
+    return concatUint8Arrays([
+        pngBytes.subarray(0, insertPos),
+        xmpChunk,
+        pngBytes.subarray(insertPos),
+    ]);
+}
+
+export async function injectAvmIntoPngBlob(blob, avm) {
+    const pngBytes = new Uint8Array(await blob.arrayBuffer());
+    const xmp = buildAvmXmpPacket(avm);
+    const outBytes = insertXmpIntoPng(pngBytes, xmp);
+
+    return new Blob([outBytes], { type: "image/png" });
+}
+
+export function blobToDataURL(blob) {
+    return new Promise((resolve, reject) => {
+        const reader = new FileReader();
+        reader.onloadend = () => resolve(reader.result);
+        reader.onerror = () => reject(new Error("Error reading blob as data URL"));
+        reader.readAsDataURL(blob);
+    });
+}
+
+export function blobToArrayBuffer(blob) {
+    return blob.arrayBuffer();
+}

src/js/View.js

@@ -50,8 +50,55 @@ import { Color } from "./Color.js";
 import { SpectraDisplayer } from "./SpectraDisplayer.js";
 import { DefaultActionsForContextMenu } from "./DefaultActionsForContextMenu.js";
 import { Source } from "./Source.js";
+import { blobToArrayBuffer, blobToDataURL, buildAvmFromWcs, injectAvmIntoPngBlob } from "./AvmUtils.js";
 export let View = (function () {
 
+    const normalizeImageType = function (imgType) {
+        return imgType || "image/png";
+    };
+
+    const canvasToBlob = function (canvas, imgType) {
+        return new Promise((resolve, reject) => {
+            canvas.toBlob((blob) => {
+                if (blob) {
+                    resolve(blob);
+                } else {
+                    reject(new Error("Canvas toBlob failed"));
+                }
+            }, imgType);
+        });
+    };
+
+    const exportCanvasBlob = async function (view, canvas, imgType) {
+        const effectiveImgType = normalizeImageType(imgType);
+        let blob = await canvasToBlob(canvas, effectiveImgType);
+
+        if (effectiveImgType !== "image/png") {
+            return blob;
+        }
+
+        const wcs = view.aladin.getViewWCS();
+        if (!wcs || typeof wcs !== "object") {
+            return blob;
+        }
+
+        const avm = buildAvmFromWcs(wcs, {
+            rotation: view.aladin.getRotation(),
+        });
+
+        if (!avm) {
+            return blob;
+        }
+
+        try {
+            blob = await injectAvmIntoPngBlob(blob, avm);
+        } catch (error) {
+            console.warn("Could not inject AVM metadata into PNG export", error);
+        }
+
+        return blob;
+    };
+
     /** Constructor */
     function View(aladin) {
         this.aladin = aladin;
@@ -557,20 +604,16 @@ export let View = (function () {
      */
     View.prototype.getCanvasDataURL = async function (imgType, width, height, withLogo=true) {
         const c = await this.getCanvas(width, height, withLogo);
-        return c.toDataURL(imgType);
+        const blob = await exportCanvasBlob(this, c, imgType);
+        return blobToDataURL(blob);
     };
 
     /**
      * Return ArrayBuffer corresponding to the current view
      */
     View.prototype.getCanvasArrayBuffer = async function (imgType, width, height, withLogo=true) {
-        return this.getCanvasBlob(imgType, width, height, withLogo)
-            .then((blob) => {
-                const reader = new FileReader();
-                reader.onloadend = () => resolve(reader.result);
-                reader.onerror = () => reject(new Error('Error reading blob as ArrayBuffer'));
-                reader.readAsArrayBuffer(blob);
-            });
+        const blob = await this.getCanvasBlob(imgType, width, height, withLogo);
+        return blobToArrayBuffer(blob);
     }
 
     /**
@@ -578,15 +621,7 @@ export let View = (function () {
      */
     View.prototype.getCanvasBlob = async function (imgType, width, height, withLogo=true) {
         const c = await this.getCanvas(width, height, withLogo);
-        return new Promise((resolve, reject) => {
-            c.toBlob(blob => {
-                if (blob) {
-                    resolve(blob);
-                } else {
-                    reject(new Error('Canvas toBlob failed'));
-                }
-            }, imgType);
-        });
+        return exportCanvasBlob(this, c, imgType);
     }
 
     View.prototype.selectLayer = function (layer) {