rework the preview state checker

lib/imgui_helpers.lua

@@ -64,11 +64,17 @@ imgui_helpers.do_preview = function(ctx, obj, change)
     if obj.info.action ~= 'segment' or not reacoma.settings.slice_preview then
       return false
     end
-    local left = reaper.ImGui_MouseButton_Left()
-    local drag_preview = change > 0 and reacoma.settings.drag_preview
-    local end_drag_preview = not reacoma.settings.immediate_preview and not reaper.ImGui_IsMouseDown(ctx, left) and reacoma.settings.preview_pending
-    reacoma.settings.preview_pending = not end_drag_preview and (reacoma.settings.preview_pending or (change > 0 and not reacoma.settings.immediate_preview))
-    return drag_preview or end_drag_preview
+    local changing = change ~= 0
+    local dragging = reaper.ImGui_IsMouseDragging(ctx, reaper.ImGui_MouseButton_Left())
+    local mousedown = reaper.ImGui_IsMouseDown(ctx, reaper.ImGui_MouseButton_Left())
+    local mouseup = reacoma.global_state.mousedown and not mousedown
+    local immediate_preview = changing and dragging and reacoma.settings.slice_preview and reacoma.settings.immediate_preview
+    local mouseup_preview = mouseup and reacoma.settings.slice_preview
+
+    -- now store the state of the mousedown after checking
+    -- this lets you check the difference between mouse state
+    reacoma.global_state.mousedown = reaper.ImGui_IsMouseDown(ctx, reaper.ImGui_MouseButton_Left())
+    return immediate_preview or mouseup_preview
 end
 
 imgui_helpers.update_state = function(ctx, obj, update)