Instant preset switch, silent lock, fractional zoom

- Preset combobox now loads preset instantly on selection (no OK needed)
- Lock file silently prevents duplicate instances (no alert popup)
- Zoom supports fractional levels (0.125x, 0.25x, 0.5x) for large tilesets
- All zoom handlers use zoomStep() with predefined level table

aniphallow.lua

@@ -618,6 +618,23 @@ initPresets()
 ----------------------------------------------------------------------
 -- Helpers
 ----------------------------------------------------------------------
+-- Zoom levels: fractional for large tilesets, integer for normal
+local ZOOM_LEVELS = { 0.125, 0.25, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }
+
+local function zoomStep(currentZoom, delta)
+    -- Find closest level
+    local bestIdx = 1
+    local bestDist = math.huge
+    for i, z in ipairs(ZOOM_LEVELS) do
+        local dist = math.abs(z - currentZoom)
+        if dist < bestDist then bestDist = dist; bestIdx = i end
+    end
+    local newIdx = bestIdx + delta
+    if newIdx < 1 then newIdx = 1 end
+    if newIdx > #ZOOM_LEVELS then newIdx = #ZOOM_LEVELS end
+    return ZOOM_LEVELS[newIdx]
+end
+
 local function clamp(v, lo, hi)
     return math.max(lo, math.min(hi, v))
 end
@@ -1629,7 +1646,22 @@ openMainDialog = function()
             -- Presets section
             --------------------------------------------------------
             d:separator{ text = "Presets" }
-            d:combobox{ id = "presetSelect", option = S.currentPreset, options = getAllPresetNames() }
+            d:combobox{ id = "presetSelect", option = S.currentPreset, options = getAllPresetNames(),
+                onchange = function()
+                    local selected = d.data.presetSelect
+                    if selected and selected ~= S.currentPreset then
+                        savePreset(S.currentPreset)
+                        loadPreset(selected)
+                        S.currentPreset = selected
+                        local currentFile = app.sprite and app.sprite.filename or ""
+                        if currentFile ~= "" then filePresetMap[currentFile] = selected end
+                        saveMaster()
+                        d:close()
+                        if mainDlg then pcall(function() mainDlg:close() end) end
+                        openMainDialog()
+                    end
+                end
+            }
             d:button{ id = "presetNew", text = "New", onclick = function()
                 local nd = Dialog{ title = "New Preset" }
                 nd:entry{ id = "name", label = "Name:", text = "" }
@@ -1841,24 +1873,7 @@ openMainDialog = function()
                 local plv = d.data.previewLayoutValue
                 if plv < 1 then plv = 1 elseif plv > 20 then plv = 20 end
                 S.previewLayoutValue = plv
-                -- Check if preset changed via combobox
-                local selectedPreset = d.data.presetSelect
-                local presetChanged = false
-                if selectedPreset and selectedPreset ~= S.currentPreset then
-                    savePreset(S.currentPreset)  -- Save current first
-                    loadPreset(selectedPreset)    -- Load new
-                    S.currentPreset = selectedPreset
-                    local currentFile = app.sprite and app.sprite.filename or ""
-                    if currentFile ~= "" then filePresetMap[currentFile] = selectedPreset end
-                    presetChanged = true
-                end
                 saveAll()
-                if presetChanged then
-                    dlg:close()
-                    openMainDialog()
-                    -- Preview title will be stale but avoids repositioning window
-                    return
-                end
                 dlg:repaint()
             end
         end
@@ -2113,7 +2128,7 @@ openMainDialog = function()
         end,
         onwheel = function(ev)
             local dz = ev.deltaY < 0 and 1 or -1
-            S.sourceZoom = math.max(1, math.min(10, S.sourceZoom + dz))
+            S.sourceZoom = zoomStep(S.sourceZoom, dz)
             clampScroll()
             dlg:repaint()
         end
@@ -2288,7 +2303,7 @@ openMainDialog = function()
         end,
         onwheel = function(ev)
             local dz = ev.deltaY < 0 and 1 or -1
-            S.sourceZoom = math.max(1, math.min(10, S.sourceZoom + dz))
+            S.sourceZoom = zoomStep(S.sourceZoom, dz)
             clampScroll()
             dlg:repaint()
         end
@@ -2755,7 +2770,7 @@ openMainDialog = function()
         end,
         onwheel = function(ev)
             local dz = ev.deltaY < 0 and 1 or -1
-            local newZoom = math.max(1, math.min(10, S.gbZoomSrc + dz))
+            local newZoom = zoomStep(S.gbZoomSrc, dz)
             S.gbZoomSrc = newZoom
             S.gbZoomOpt = newZoom
             dlg:repaint()
@@ -3055,7 +3070,7 @@ openMainDialog = function()
         end,
         onwheel = function(ev)
             local dz = ev.deltaY < 0 and 1 or -1
-            local newZoom = math.max(1, math.min(10, S.gbZoomOpt + dz))
+            local newZoom = zoomStep(S.gbZoomOpt, dz)
             S.gbZoomOpt = newZoom
             S.gbZoomSrc = newZoom
             dlg:repaint()
@@ -3257,11 +3272,10 @@ local function run()
         app.alert("No sprite is open.")
         return
     end
-    -- Check if already running via lock file
+    -- Check if already running via lock file - silently ignore
     local lockF = io.open(LOCK_FILE, "r")
     if lockF then
         lockF:close()
-        app.alert("AniPhallow is already running.")
         return
     end
     -- Create lock file