added first somewhat working version of scrollapp.nim

scrollapp.nim

@@ -0,0 +1,146 @@
+
+import vdom, karax, karaxdsl, jdict, jstrutils
+
+type
+  Filter = enum
+    all, active, completed
+
+const
+  WindowSize = 50 # overestimating it does not harm
+
+var
+  entries: seq[(cstring, bool)]
+  visibleA = 0
+  visibleB = WindowSize-1
+  middle = WindowSize div 2
+  selectedEntry = -1
+  filter: Filter
+
+proc onTodoEnter(ev: Event; n: VNode) =
+  entries.add((n.value, false))
+  n.value = ""
+
+proc removeHandler(ev: Event; n: VNode) =
+  let id = suffixAsInt(n.id, "remove:")
+  entries[id] = (cstring(nil), false)
+
+proc editHandler(ev: Event; n: VNode) =
+  let id = suffixAsInt(n.id, "edit:")
+  selectedEntry = id
+
+proc focusLost(ev: Event; n: VNode) = selectedEntry = -1
+
+proc editEntry(ev: Event; n: VNode) =
+  let id = suffixAsInt(n.id, "todo-edit:")
+  entries[id][0] = n.value
+  selectedEntry = -1
+
+proc toggleEntry(ev: Event; n: VNode) =
+  let id = suffixAsInt(n.id, "toggle:")
+  entries[id][1] = not entries[id][1]
+
+proc onAllDone(ev: Event; n: VNode) =
+  entries = @[]
+  selectedEntry = -1
+
+proc clearCompleted(ev: Event, n: VNode) =
+  for i in 0..<entries.len:
+    if entries[i][1]: entries[i][0] = nil
+
+proc toClass(completed: bool): cstring =
+  (if completed: cstring"completed" else: cstring(nil))
+
+proc toChecked(checked: bool): cstring =
+  (if checked: cstring"checked" else: cstring(nil))
+
+proc selected(v: Filter): cstring =
+  (if filter == v: cstring"selected" else: cstring(nil))
+
+proc createEntry(id: int; d: cstring; completed, selected: bool): VNode =
+  result = buildHtml(tr):
+    li(class=toClass(completed), key = id):
+      if not selected:
+        tdiv(class = "view"):
+          input(class = "toggle", `type` = "checkbox", checked = toChecked(completed),
+                onclick=toggleEntry, id="toggle:" & &id)
+          label(onDblClick=editHandler, id="edit:" & &id):
+            text d
+          button(class = "destroy", id="remove:" & $id, onclick=removeHandler)
+      else:
+        input(class = "edit", name = "title", id = "todo-edit:" & &id,
+          onfocusLost = focusLost,
+          onenter = editEntry, value = d, setFocus)
+
+proc createDom(): VNode =
+  result = buildHtml(tdiv(class="todomvc-wrapper")):
+    section(class = "todoapp"):
+      header(class = "header"):
+        h1:
+          text "todos"
+        input(class = "new-todo", placeholder="What needs to be done?", name = "newTodo",
+              onenter = onTodoEnter, setFocus)
+      section(class = "main"):
+        input(class = "toggle-all", `type` = "checkbox", name = "toggle")
+        label(`for` = "toggle-all", onclick = onAllDone):
+          text "Mark all as complete"
+        var entriesCount = 0
+        var completedCount = 0
+        ul(class = "todo-list"):
+          for i in visibleA..visibleB:
+            let d = entries[i]
+            if d[0] != nil:
+              let b = case filter
+                      of all: true
+                      of active: not d[1]
+                      of completed: d[1]
+              if b:
+                createEntry(i, d[0], d[1], i == selectedEntry)
+              inc completedCount, ord(d[1])
+              inc entriesCount
+      footer(class = "footer"):
+        span(class = "todo-count"):
+          strong:
+            text(&entriesCount)
+          text cstring" item" & &(if entriesCount != 1: "s left" else: " left")
+        ul(class = "filters"):
+          li:
+            anchor(class = selected(all), href = "#/"):
+              text "All"
+          li:
+            anchor(class = selected(active), href = "#/active"):
+              text "Active"
+          li:
+            anchor(class = selected(completed), href = "#/completed"):
+              text "Completed"
+        button(class = "clear-completed", onclick = clearCompleted):
+          text "Clear completed (" & &completedCount & ")"
+
+
+setOnscroll(proc(a, b: VKey; diff: int) =
+  const overshoot = 10
+  # scroll downwards:
+  if diff > 0:
+    #visibleA = a #max(a-diff, 0)
+    visibleB = min(b+diff+overshoot, entries.len-1)
+    visibleA = max(a-overshoot, 0)
+  else:
+    visibleA = max(a-diff-overshoot, 0)
+    visibleB = min(b+overshoot, entries.len-1)
+  #  visibleB = min(entries.len-1, visibleB + diff)
+  #  visibleA = max(0, visibleB - WindowSize*2)
+  #else:
+  #  visibleA = max(0, visibleA + diff)
+  #  visibleB = min(entries.len-1, visibleA + WindowSize - 1)
+  kout cstring"scrolling ", a, b, diff, visibleA, visibleB
+)
+setOnHashChange(proc(hash: cstring) =
+  if hash == cstring"#/": filter = all
+  elif hash == cstring"#/completed": filter = completed
+  elif hash == cstring"#/active": filter = active
+)
+setRenderer createDom
+
+proc onload(session: cstring) {.exportc.} =
+  for i in 0..1000:
+    entries.add((cstring"Entry " & &i, false))
+  init()