[add] [doc] README; [refactor] rendering of containers

4 files changed, 182 insertions, 31 deletions

diff --git a/README.org b/README.org
index e55d9d1..0b3065b 100644
--- a/README.org
+++ b/README.org
@@ -7,7 +7,7 @@
 
 /A Sprite System in Common Lisp for Games and GUIs/
 ** Installation 
-
+   
 Ensure that sdl2 is installed on your system.
 
 *** Fetch Systems That Are Not In Quicklisp 
@@ -41,52 +41,204 @@ Then load one of the example files and call its "start" function:
 
 #+end_src
 
-** TODO Basic Use
+** Basic Use
+  
+   The best introduction is to look at and play with the examples.
+   What follows is a cursory explanation of how pieces are meant to
+   fit together.
+
 
 *** The Application 
+    
+When you want to use Wheelwork, you must make a sublcass of ~application~. The ~application~ is the main container supplied by wheelwork. It is the root of the [[*The Display Tree Protocol: Units and Containers][display tree]], holds references to [[*The Asset Protocol][loaded assets]], and handles [[*Events & Event Handling][events]] from the user.
 
-    The best introduction is to look at and play with the examples.
-    What follows is a cursory explanation of how pieces are meant to
-    fit together.
+For example, from the pong example in =examples/08-pong.lisp=, the application class looks like 
+
+#+begin_src lisp
+(defclass/std solo-pong (ww:application)
+  ((paddle ball game-over intro-text)))
+#+end_src
 
-**** Your Application
+/note: I'm using defclass-std:defclass/std to define the above, see [[https://quickdocs.org/defclass-std][here]] for more./
 
+This defines a subclass of appliation along with some state needed for the pong game.
+    
 **** The Boot Method
 
+It isn't enough to define a subclass, you must also implement a ~ww:boot~ method for your application class. The boot method is called right after the opengl context becomes available. Inside boot, you are expected to do everything necessary to start your game: load assets, create some display units, add them to the scene, and add event handlers.  Here is what the boot method looks like for the pong game.
+
+#+begin_src lisp
+
+(defmethod ww::boot ((app solo-pong))
+  "Adds the intro text and sets up the start button handler."
+  (sdl2:hide-cursor)
+  (let ((intro-text
+          (make-instance
+           'ww:text
+           :content "Press any key to start"
+           :font (ww::get-asset "Ticketing.ttf")
+           :x 160
+           :y 300
+           :scale-x 3.0
+           :scale-y 3.0)))
+    (setf (intro-text app) intro-text)
+    (ww:add-unit app intro-text))        ; add to scene
+  (ww:add-handler app #'press-to-start))
+
+#+end_src
+
+You can see that it does very little.  It first creates an instance of [[*Text][text]], with the appropriate scale and starting position. Then it just sets the app's ~intro-text~ slot to the newly created text before adding to the scene.
+
+It ends by adding a handler to the app called ~press-to-start~, where presumably, the rest of the game is set up.
+
 **** The Shutdown Method
 
-*** Display Units 
+The shutdown method is optional and is called right before the application exits. If supplied, it is a good place to do things like: make save files, close network connections, clean up foreign memory resources that are not already managed by the [[*The Asset Protocol][asset protocol]].  
+
+
+*** The Display Tree Protocol: Units and Containers
+    
+Objects that render to the screen are organized into a display tree. There are two basic kinds of objects: units and containers. Units are, roughly, "what you want to display" and containers are "when and where you want to display it".  Additionally, containers hold a list of units.
 
-**** Bitmaps
+In general, the last thing added to a container will be the last thing rendered - i.e. it will be "on top".  Containers are themselves units, so they too can be added to other containers. Nesting of containers allows you to render a one set of units before or after some other set of units.
 
-**** Text
+The application is a container, and is the only unit that does not need to be added to a scene. Nothing else will display until it becomes part of the display tree rooted at the application.
 
-**** Sprites
+Containers have "bounds", which are screen coordinates for the left, right, top, and bottom of the region inside of which units will be displayed. If a unit moves out of bounds, it will not show up on the screen, and will not receive mouse events. (It may, however, still be focused - and hence receive key events.) The bounds of the application are the visible window itself. Other containers may have custom bounds.
+
+See =examples/07-scrollarea.lisp= for an example that uses a container.
 
 **** Containers
 
+The main thing you can do with containers is add and remove units:
+
+: (add-unit app my-unit) 
+: (drop-unit my-unit) ;; it knows its container 
+
+You can also adjust their bounds, for example:
+
+: (setf (container-top my-container) 100)
+
+**** The Affine Units 
+
+Most units of any interest implement the "affine protocol".  I.e they have orientation and scale in the 2d plane of the game window. 
+
+More specifically, you can use the following accessor functions on them:
+
+   : x
+   : y
+   : width
+   : height
+   : scale-x
+   : scale-y
+   : rotation
+
+There are a few convenience functions also defined that use the above functions under-the-hood. I'm not including them here because the API is still stabilizing. 
+
+The affine units are things like:
+
++ ~bitmap~: display an image that has been loaded from a file asset (currently only png is supported)
++ ~text~: display text
++ ~frameset~: display an animated sequence of images
++ ~sprite~: display a "bundle" of framesets
+
 *** Events & Event Handling
 
-**** User Input Events vs Psuedo-Events
+Anything that "happens" in a wheelwork application happens through the course of handling some event.
+
+Wheelwork defines an ~event-handler~ class that is used to to create functions for handling events. Instances of ~event-handler~ are funcallable objects with a slot that specifies the kind of event being handled. 
+
+Event handlers are added to instances of ~interactive~, which includes most kinds of units and the application itself. Notably, the base ~container~ class is not a subclass of ~interactive~ and so cannot handle events.
 
-**** Event Handler Macros
+Wheelwork provides a macro called ~defhandler~ that can be used easily create instances of ~event-handler~ and bind them to a name. Most event handlers are created using a macro that looks like ~on-EVENTNAME~, which are discussed below. 
 
-**** Focus Events
+Here is a simple example where a handler is defined, from the pong game:
 
-**** Perframe Events
+#+begin_src lisp
+(ww:defhandler pong-mousemove
+    (ww:on-mousemotion (app)
+      (setf (ww:x  (paddle app))
+            (- x (* 0.5 (ww:width (paddle app))))
+            (dx (paddle app)) xrel))) 
+#+end_src
+
+See the example for details.
+
+There are two kinds of events: User Interaction Events and Psuedoevents.
+
+**** User Interaction Events
+
+User Interaction events are, curiously enough, generated by user interaction.  These include 
+
+: keydown
+: keyup 
+: mousewheel 
+: mousedown 
+: mouseup 
+: mousemotion 
+
+The first three will fire on whichever object has focus. The last three will fire on the first visible object that intersects with the cursor.
+
+**** Psuedoevents
+
+Psuedoevents are generated by the wheelwork itself, and include the following:
+
+Display tree events:
+
+: after-added
+: before-added 
+: before-dropped 
+
+Focus events 
+
+: focus 
+: blur 
+
+Frame events 
 
-**** Display Tree Events 
+: perframe
 
-**** Mouse Events
+See the documentation for the ~on-*~ forms for these events to get a sense of how to handle them.
 
-**** Key Events
 
-*** Extending Wheelwork
 
-**** The Display Tree Protocol
-     
-**** The Asset Protocol 
+*** The Asset Protocol 
+
+Assets are resources loaded from disk.   The application's ~asset-classifiers~ list associates file extensions (like "ttf", and "png") with classes (like ~font~ and ~png~) that load and prepare assets for use in an application.  
+
+Every asset has a "key", which is just a string path name that is relative to the application's ~asset-root~.  These keys are used by ~get-asset~ to fetch assets, possibly loading them for the first time if they have not been previously fetched. 
+
+Some classes (like ~text~ or ~bitmap~) require an instance of an asset class to fill one of their instance slots (like ~font~ or ~texture~) in order to work properly.  
+
+E.g. In ~examples/03-font-render.lisp~ you see 
+
+#+begin_src lisp
+
+(make-instance
+ 'ww::text
+ :content (format nil "Hell!~%Oh World...")
+ :font (ww::get-asset "Ticketing.ttf"
+                      :asset-args '(:oversample 2)))
+#+end_src
+
+which fetches the ~"Ticketing.ttf"~ font asset for use in rendering the text content.
+
+The asset root relative to which ~"Ticketing.ttf"~ is resolved can be set during instantiation of the application. 
+
+e.g., for the same example:
+
+#+begin_src lisp
+(make-instance
+ 'font-display
+ :fps 60
+ :refocus-on-mousedown-p nil
+ :width 800
+ :height 600
+ :title "Wheelwork Example: Font display"
+ :asset-root (merge-pathnames
+              "examples/"
+              (asdf:system-source-directory :wheelwork)))
+#+end_src
 
-**** The Affine Protocol 
 
 
diff --git a/examples/02-moving-bitmp.lisp b/examples/02-moving-bitmp.lisp
index bf05a7c..b07f1aa 100644
--- a/examples/02-moving-bitmp.lisp
+++ b/examples/02-moving-bitmp.lisp
@@ -125,8 +125,8 @@
     (ww::add-handler bm2 #'look-away)
     (ww::add-handler bm2 #'wheelie)
 
-    (ww::add-unit app bm2)
-    (ww::add-unit app bm)))
+    (ww::add-unit app bm)
+    (ww::add-unit app bm2)))
 
 
 (defun start ()
diff --git a/examples/08-pong.lisp b/examples/08-pong.lisp
index 51de28d..6fc9faa 100644
--- a/examples/08-pong.lisp
+++ b/examples/08-pong.lisp
@@ -173,19 +173,18 @@ on which boundary VAL is outside of."
 (defmethod ww::boot ((app solo-pong))
   "Adds the intro text and sets up the start button handler."
   (sdl2:hide-cursor)
-  (ww::add-unit
-   app
-   (setf (intro-text app)
+  (let ((intro-text
          (make-instance
-          'ww::text
+          'ww:text
           :content "Press any key to start"
           :font (ww::get-asset "Ticketing.ttf")
           :x 160
           :y 300
           :scale-x 3.0
           :scale-y 3.0)))
-
-  (ww::add-handler app #'press-to-start))
+    (setf (intro-text app) intro-text)
+    (ww:add-unit app intro-text))
+  (ww:add-handler app #'press-to-start))
 
 (defun start ()
   (ww::start
diff --git a/src/core/container.lisp b/src/core/container.lisp
index d332cb8..a9e6caf 100644
--- a/src/core/container.lisp
+++ b/src/core/container.lisp
@@ -75,7 +75,7 @@ necessary."
     (with-slots (left right top bottom) container 
       (gl:scissor (* left scale) (* scale bottom) (* scale (- right left)) (* scale (- top bottom)))
       (unwind-protect  
-           (dolist (u (container-units container))
+           (dolist (u (reverse (container-units container)))
              (if (visible-in-container-p u)
                (render u)))
         (gl:scissor (aref current 0) (aref current 1) (aref current 2) (aref current 3))))))