Add pan and zoom support for mermaid diagrams

layout/includes/third-party/math/mermaid.pug

@@ -1,11 +1,205 @@
 script.
   (() => {
+    const parseViewBox = viewBox => {
+      if (!viewBox) return null
+      const parts = viewBox.trim().split(/[\s,]+/).map(n => Number(n))
+      if (parts.length !== 4 || parts.some(n => Number.isNaN(n))) return null
+      return parts
+    }
+
+    const getSvgViewBox = svg => {
+      const attr = parseViewBox(svg.getAttribute('viewBox'))
+      if (attr) return attr
+
+      // Fallback: use bbox to build a viewBox
+      try {
+        const bbox = svg.getBBox()
+        if (bbox && bbox.width && bbox.height) return [bbox.x, bbox.y, bbox.width, bbox.height]
+      } catch (e) {
+        // getBBox may fail on some edge cases; ignore
+      }
+
+      const w = Number(svg.getAttribute('width')) || 0
+      const h = Number(svg.getAttribute('height')) || 0
+      if (w > 0 && h > 0) return [0, 0, w, h]
+      return [0, 0, 100, 100]
+    }
+
+    const setSvgViewBox = (svg, vb) => {
+      svg.setAttribute('viewBox', `${vb[0]} ${vb[1]} ${vb[2]} ${vb[3]}`)
+    }
+
+    const clamp = (v, min, max) => Math.max(min, Math.min(max, v))
+
+    // Zoom around a point (px, py) in the SVG viewport (in viewBox coordinates)
+    const zoomAtPoint = (vb, factor, px, py) => {
+      const w = vb[2] * factor
+      const h = vb[3] * factor
+      const nx = px - (px - vb[0]) * factor
+      const ny = py - (py - vb[1]) * factor
+      return [nx, ny, w, h]
+    }
+
+    const initMermaidGestures = wrap => {
+      const svg = wrap.querySelector('svg')
+      if (!svg) return
+
+      // Ensure viewBox exists so gestures always work
+      const initVb = getSvgViewBox(svg)
+      wrap.__mermaidInitViewBox = initVb
+      wrap.__mermaidCurViewBox = initVb.slice()
+      setSvgViewBox(svg, initVb)
+
+      // Avoid binding multiple times on themeChange/pjax
+      if (wrap.__mermaidGestureBound) return
+      wrap.__mermaidGestureBound = true
+
+      // Helper: map client (viewport) coordinate -> viewBox coordinate
+      const clientToViewBox = (clientX, clientY) => {
+        const rect = svg.getBoundingClientRect()
+        const vb = wrap.__mermaidCurViewBox || getSvgViewBox(svg)
+        const x = vb[0] + (clientX - rect.left) * (vb[2] / rect.width)
+        const y = vb[1] + (clientY - rect.top) * (vb[3] / rect.height)
+        return { x, y, rect, vb }
+      }
+
+      const state = {
+        pointers: new Map(),
+        startVb: null,
+        startDist: 0,
+        startCenter: null
+      }
+
+      const clampVb = vb => {
+        const init = wrap.__mermaidInitViewBox || vb
+        const minW = init[2] * 0.1
+        const maxW = init[2] * 10
+        const minH = init[3] * 0.1
+        const maxH = init[3] * 10
+        vb[2] = clamp(vb[2], minW, maxW)
+        vb[3] = clamp(vb[3], minH, maxH)
+        return vb
+      }
+
+      const setCurVb = vb => {
+        vb = clampVb(vb)
+        wrap.__mermaidCurViewBox = vb
+        setSvgViewBox(svg, vb)
+      }
+
+      const onPointerDown = e => {
+        // Allow only primary button for mouse
+        if (e.pointerType === 'mouse' && e.button !== 0) return
+        svg.setPointerCapture(e.pointerId)
+        state.pointers.set(e.pointerId, { x: e.clientX, y: e.clientY })
+
+        if (state.pointers.size === 1) {
+          state.startVb = (wrap.__mermaidCurViewBox || getSvgViewBox(svg)).slice()
+        } else if (state.pointers.size === 2) {
+          const pts = [...state.pointers.values()]
+          const dx = pts[0].x - pts[1].x
+          const dy = pts[0].y - pts[1].y
+          state.startDist = Math.hypot(dx, dy)
+          state.startVb = (wrap.__mermaidCurViewBox || getSvgViewBox(svg)).slice()
+          state.startCenter = { x: (pts[0].x + pts[1].x) / 2, y: (pts[0].y + pts[1].y) / 2 }
+        }
+      }
+
+      const onPointerMove = e => {
+        if (!state.pointers.has(e.pointerId)) return
+        state.pointers.set(e.pointerId, { x: e.clientX, y: e.clientY })
+
+        // Pan with 1 pointer
+        if (state.pointers.size === 1 && state.startVb) {
+          const p = [...state.pointers.values()][0]
+          const prev = { x: e.clientX - e.movementX, y: e.clientY - e.movementY }
+          // movementX/Y unreliable on touch, compute from stored last position
+          const last = wrap.__mermaidLastSinglePointer || p
+          const dxClient = p.x - last.x
+          const dyClient = p.y - last.y
+          wrap.__mermaidLastSinglePointer = p
+
+          const { rect } = clientToViewBox(p.x, p.y)
+          const vb = (wrap.__mermaidCurViewBox || getSvgViewBox(svg)).slice()
+          const dx = dxClient * (vb[2] / rect.width)
+          const dy = dyClient * (vb[3] / rect.height)
+          setCurVb([vb[0] - dx, vb[1] - dy, vb[2], vb[3]])
+          return
+        }
+
+        // Pinch zoom with 2 pointers
+        if (state.pointers.size === 2 && state.startVb && state.startDist > 0) {
+          const pts = [...state.pointers.values()]
+          const dx = pts[0].x - pts[1].x
+          const dy = pts[0].y - pts[1].y
+          const dist = Math.hypot(dx, dy)
+          if (!dist) return
+          const factor = state.startDist / dist // dist bigger => zoom in (viewBox smaller)
+
+          const cx = (pts[0].x + pts[1].x) / 2
+          const cy = (pts[0].y + pts[1].y) / 2
+          const centerClient = { x: cx, y: cy }
+
+          const pxy = clientToViewBox(centerClient.x, centerClient.y)
+          const cpx = pxy.x
+          const cpy = pxy.y
+
+          const vb = zoomAtPoint(state.startVb, factor, cpx, cpy)
+          setCurVb(vb)
+        }
+      }
+
+      const onPointerUpOrCancel = e => {
+        state.pointers.delete(e.pointerId)
+        if (state.pointers.size === 0) {
+          state.startVb = null
+          state.startDist = 0
+          state.startCenter = null
+          wrap.__mermaidLastSinglePointer = null
+        } else if (state.pointers.size === 1) {
+          // reset single pointer baseline to avoid jump
+          wrap.__mermaidLastSinglePointer = [...state.pointers.values()][0]
+        }
+      }
+
+      // Wheel zoom (mouse/trackpad)
+      const onWheel = e => {
+        // ctrlKey on mac trackpad pinch; we treat both as zoom
+        e.preventDefault()
+        const delta = e.deltaY
+        const zoomFactor = delta > 0 ? 1.1 : 0.9
+        const { x, y } = clientToViewBox(e.clientX, e.clientY)
+        const vb = (wrap.__mermaidCurViewBox || getSvgViewBox(svg)).slice()
+        setCurVb(zoomAtPoint(vb, zoomFactor, x, y))
+      }
+
+      const onDblClick = () => {
+        const init = wrap.__mermaidInitViewBox
+        if (!init) return
+        wrap.__mermaidCurViewBox = init.slice()
+        setSvgViewBox(svg, init)
+      }
+
+      svg.addEventListener('pointerdown', onPointerDown)
+      svg.addEventListener('pointermove', onPointerMove)
+      svg.addEventListener('pointerup', onPointerUpOrCancel)
+      svg.addEventListener('pointercancel', onPointerUpOrCancel)
+      svg.addEventListener('wheel', onWheel, { passive: false })
+      svg.addEventListener('dblclick', onDblClick)
+    }
+
     const runMermaid = ele => {
       window.loadMermaid = true
       const theme = document.documentElement.getAttribute('data-theme') === 'dark' ? '!{theme.mermaid.theme.dark}' : '!{theme.mermaid.theme.light}'
 
       ele.forEach((item, index) => {
         const mermaidSrc = item.firstElementChild
+
+        // Clear old render (themeChange/pjax will rerun)
+        const oldSvg = item.querySelector('svg')
+        if (oldSvg) oldSvg.remove()
+        item.__mermaidGestureBound = false
+
         const config = mermaidSrc.dataset.config ? JSON.parse(mermaidSrc.dataset.config) : {}
         if (!config.theme) {
           config.theme = theme
@@ -17,6 +211,7 @@ script.
         const renderFn = mermaid.render(mermaidID, mermaidDefinition)
         const renderMermaid = svg => {
           mermaidSrc.insertAdjacentHTML('afterend', svg)
+          initMermaidGestures(item)
         }
 
         // mermaid v9 and v10 compatibility