Update TODO_Animation.md

TODO_Animation.md

@@ -1,11 +1,8 @@
 ## Animation (continuation)
 
 ### Goal
-- Implement Animation in GacUI XMl Resource
-- Possible to provide state machine XML tags
-- Animation can be aborted at any moment, and launch a new one if necessary
-- Animation can change different part of the view model using different interpolation at the same time
-- Using `IAsync`
+- Provide XML-defined interpolation function
+- Provide new animation API
 
 ### Demo
 - Download with round progress bar
@@ -15,18 +12,41 @@
 - Downloaded text fade in
 - Progress bar fly out
 
-### Animation
+### Feature
 
-- Feature
-  - Can be canceled at any moment
-  - Can set a new start state or start from the current state
-- Exit Condition
-  - Time based
-  - Condition based
-- Playing Rate
-  - Realtime
-  - Frame animation with a fixed interval
-- Composed animation
-- With infinite looping
+#### Interpolation function
+A new xml tag will be added in <instance> to write a function:
+- `func <NAME>(start: T, end: T, target: T): IGuiGraphicsAnimationInterpolation^;`
+- `func <NAME>(start: T, end: T, target: U): IGuiGraphicsAnimationInterpolation^;`
+  - if T is a value type so it has to be change a property of type T in U
 
-### XML
+```
+interface IGuiGraphicsAnimationInterpolation
+{
+    func Interpolate(position: double):void;
+}
+```
+
+#### API
+- A group of new overloading functions are added in `GuiInstanceRootObject` which do
+  - Add animation to `root->GetControlHostInternal()->GetGraphicsHost()->GetAnimationManager()`, where `GetControlHostInternal` is a new protected abstract function.
+  - If the control host is not ready (e.g. the control has not been added to a window), then all animations will be kept and attach to the window later
+  - When the root object is deleted, all animations are stopped (set the internal flag so that the animation manager will remove them later)
+  - And has the following options:
+    - **interpolation object**
+    - **timed or infinite**
+      - for timed animation
+        - **a function** to convert passed total time to a double value
+          - default: `passed total time / total time`
+        - **a fomular** function to convert a double value from `[0..1]` to `[0..1]` to control the animation behavior
+      - for infinite animation
+        - **a function** to convert passed total time to a double value
+          - default: `passed total time`
+    - **end of animation notification**
+      - Stop an `IAsync` object
+      - Call a callback function
+
+#### Workflow
+- Author calls animation APIs themselves to start an animation
+- State machine or async coroutine is supported by "end of animation notification"
+- Add `$Await GetApplication().DoEvents();`