feat(mermaid): enable export as PNG (closes #536)

src/public/app/components/app_context.ts

@@ -343,9 +343,8 @@ type EventMappings = {
     noteContextRemoved: {
         ntxIds: string[];
     };
-    exportSvg: {
-        ntxId: string | null | undefined;
-    };
+    exportSvg: { ntxId: string | null | undefined; };
+    exportPng: { ntxId: string | null | undefined; };
     geoMapCreateChildNote: {
         ntxId: string | null | undefined; // TODO: deduplicate ntxId
     };

src/public/app/layouts/desktop_layout.ts

@@ -91,6 +91,7 @@ import type { AppContext } from "./../components/app_context.js";
 import type { WidgetsByParent } from "../services/bundle.js";
 import SwitchSplitOrientationButton from "../widgets/floating_buttons/switch_layout_button.js";
 import ToggleReadOnlyButton from "../widgets/floating_buttons/toggle_read_only_button.js";
+import PngExportButton from "../widgets/floating_buttons/png_export_button.js";
 
 export default class DesktopLayout {
 
@@ -214,6 +215,7 @@ export default class DesktopLayout {
                                                                 .child(new GeoMapButtons())
                                                                 .child(new CopyImageReferenceButton())
                                                                 .child(new SvgExportButton())
+                                                                .child(new PngExportButton())
                                                                 .child(new BacklinksWidget())
                                                                 .child(new ContextualHelpButton())
                                                                 .child(new HideFloatingButtonsButton())

src/public/app/services/utils.ts

@@ -609,9 +609,20 @@ function createImageSrcUrl(note: { noteId: string; title: string }) {
  */
 function downloadSvg(nameWithoutExtension: string, svgContent: string) {
     const filename = `${nameWithoutExtension}.svg`;
+    const dataUrl = `data:image/svg+xml;charset=utf-8,${encodeURIComponent(svgContent)}`;
+    triggerDownload(filename, dataUrl);
+}
+
+/**
+ * Downloads the given data URL on the client device, with a custom file name.
+ *
+ * @param fileName the name to give the downloaded file.
+ * @param dataUrl the data URI to download.
+ */
+function triggerDownload(fileName: string, dataUrl: string) {
     const element = document.createElement("a");
-    element.setAttribute("href", `data:image/svg+xml;charset=utf-8,${encodeURIComponent(svgContent)}`);
-    element.setAttribute("download", filename);
+    element.setAttribute("href", dataUrl);
+    element.setAttribute("download", fileName);
 
     element.style.display = "none";
     document.body.appendChild(element);
@@ -621,6 +632,56 @@ function downloadSvg(nameWithoutExtension: string, svgContent: string) {
     document.body.removeChild(element);
 }
 
+/**
+ * Given a string representation of an SVG, renders the SVG to PNG and triggers a download of the file on the client device.
+ *
+ * Note that the SVG must specify its width and height as attributes in order for it to be rendered.
+ *
+ * @param nameWithoutExtension the name of the file. The .png suffix is automatically added to it.
+ * @param svgContent the content of the SVG file download.
+ * @returns `true` if the operation succeeded (width/height present), or `false` if the download was not triggered.
+ */
+function downloadSvgAsPng(nameWithoutExtension: string, svgContent: string) {
+    const mime = "image/svg+xml";
+
+    // First, we need to determine the width and the height from the input SVG.
+    const svgDocument = (new DOMParser()).parseFromString(svgContent, mime);
+    const width = svgDocument.documentElement?.getAttribute("width");
+    const height = svgDocument.documentElement?.getAttribute("height");
+
+    if (!width || !height) {
+        return false;
+    }
+
+    // Convert the image to a blob.
+    const svgBlob = new Blob([ svgContent ], {
+        type: mime
+    })
+
+    // Create an image element and load the SVG.
+    const imageEl = new Image();
+    imageEl.width = parseFloat(width);
+    imageEl.height = parseFloat(height);
+    imageEl.src = URL.createObjectURL(svgBlob);
+    imageEl.onload = () => {
+        // Draw the image with a canvas.
+        const canvasEl = document.createElement("canvas");
+        canvasEl.width = imageEl.width;
+        canvasEl.height = imageEl.height;
+        document.body.appendChild(canvasEl);
+
+        const ctx = canvasEl.getContext("2d");
+        ctx?.drawImage(imageEl, 0, 0);
+        URL.revokeObjectURL(imageEl.src);
+
+        const imgUri = canvasEl.toDataURL("image/png")
+        triggerDownload(`${nameWithoutExtension}.png`, imgUri);
+        document.body.removeChild(canvasEl);
+    };
+
+    return true;
+}
+
 /**
  * Compares two semantic version strings.
  * Returns:
@@ -719,6 +780,7 @@ export default {
     copyHtmlToClipboard,
     createImageSrcUrl,
     downloadSvg,
+    downloadSvgAsPng,
     compareVersions,
     isUpdateAvailable,
     isLaunchBarConfig

src/public/app/widgets/floating_buttons/png_export_button.ts

@@ -0,0 +1,24 @@
+import { t } from "../../services/i18n.js";
+import NoteContextAwareWidget from "../note_context_aware_widget.js";
+
+const TPL = `
+<button type="button"
+        class="export-svg-button"
+        title="${t("png_export_button.button_title")}">
+        <span class="bx bxs-file-png"></span>
+</button>
+`;
+
+export default class PngExportButton extends NoteContextAwareWidget {
+    isEnabled() {
+        return super.isEnabled() && ["mermaid"].includes(this.note?.type ?? "") && this.note?.isContentAvailable() && this.noteContext?.viewScope?.viewMode === "default";
+    }
+
+    doRender() {
+        super.doRender();
+
+        this.$widget = $(TPL);
+        this.$widget.on("click", () => this.triggerEvent("exportPng", { ntxId: this.ntxId }));
+        this.contentSized();
+    }
+}

src/public/app/widgets/type_widgets/abstract_svg_split_type_widget.ts

@@ -217,4 +217,12 @@ export default abstract class AbstractSvgSplitTypeWidget extends AbstractSplitTy
         utils.downloadSvg(this.note.title, this.svg);
     }
 
+    async exportPngEvent({ ntxId }: EventData<"exportPng">) {
+        if (!this.isNoteContext(ntxId) || this.note?.type !== "mermaid" || !this.svg) {
+            return;
+        }
+
+        utils.downloadSvgAsPng(this.note.title, this.svg);
+    }
+
 }

src/public/translations/en/translation.json

@@ -1708,5 +1708,8 @@
   "toggle_read_only_button": {
     "unlock-editing": "Unlock editing",
     "lock-editing": "Lock editing"
+  },
+  "png_export_button": {
+    "button_title": "Export diagram as PNG"
   }
 }