[#530] Add details for the sequence diagram.

docs/functional/FontRendering.md

@@ -10,7 +10,7 @@ All of the text rendered in diagrams is done through `StringRenderer` objects.
 `StringRenderer` objects are flyweight and differ only in their alignment and text decorations. This way, different diagram types can obtain a `StringRenderer` object that fits their needs for text to be aligned to a specific position, and in different font styles such as bold, italic, and underlined.
 
 `StringRenderer` interfaces with three classes to render text:
-* `UserPreferences`: The _model_ in the Model-View-Controller decomposition. User settings are stored and managed here. `StringRenderer` can retrieve the user font and size from here.
+* `UserPreferences`: The singleton _model_ in the Model-View-Controller decomposition for user settings. User setting data is stored and managed in this class. `StringRenderer` can retrieve the user font and size from here.
 * `FontMetrics`: A utility class to calculate various font metrics. `StringRenderer` will obtain the appropriate positioning of text on the GUI from FontMetrics.
 * `RenderingUtils`: `StringRenderer` delegates the actual rendering of text on the GUI to this class.
 
@@ -24,9 +24,12 @@ And the following sequence diagram illustrates a scenario where text in a `TypeN
 
 ![JetUML Class Diagram](FontRenderingSequence.png)
 
-The chain of events of a text rendered through the font management system looks like this:
 1. A call is made to StringRenderer to draw a text by some node or edge renderer.
 2. The StringRenderer object accesses the UserPreferences object to retrieve the font family and size that the text is to be rendered in.
-3. The calculation for the amount of space the text requires to be displayed on the screen is delegated to the FontMetrics utility class.
-4. Using the dimension retrieved from FontMetrics, the draw method calibrates the position within the text bounds and the text decorations.
-5. The actual rendering of the text is delegated to the RenderingUtils class which then makes a direct method call on the GraphicsContext object of the Canvas.
+3. `GraphicsContext#translate` positions itself on the `Canvas` at the indicated (x, y) coordinate (this is the top-left corner of the bounding rectangle containing the text).
+4. The actual rendering of the text is delegated to the RenderingUtils class which then makes a direct method call on the GraphicsContext object of the Canvas.
+5. `RenderingUtils#drawText` will render the text in the specified font, taking into account the offset necessary for a specific alignment (e.g. Text aligned at the center will need to be shifted to the the middle, since the `GraphicsContext` is positioned at the top-left corner of the text bounds).
+6. The bottom-half section of the sequence diagram will execute if the text needs underlining.
+7. A call to `FontMetrics#getDimension` and `FontMetrics#getBaselineOffset` is made to calculate the position and length of the underline.
+8. The line is rendered in a similar fashion as the text.
+9. The `GraphicsContext` assumes its initial position on the Canvas before the text was rendered.