A component draws itself with (bjogui draw), a pen over Avalonia's
DrawingContext, and hears the pointer, the wheel, the keys and the focus.
It keeps a state of its own between inputs, and sends outputs that drawn
makes the app's messages. It is drawn again only when its value, its state
or its size changes, and no Avalonia class is subclassed: the picture is a
DrawingImage on a canvas.
start-headless! sets Avalonia up with no screen, drawing with Skia, so
tests/components.bjo draws components and reads their pixels. The mixer
example has knobs and a timeline.
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view-map gives a view's every message to a function first, so a part with a
message type, an update and a view of its own goes in a larger view with
the case of the larger message that carries its own.
canvas is a surface for rect, ellipse, line and path, placed by their own
numbers, and other views by at-point. on-press, on-move and on-release send
the place on the canvas. They come from whatever is drawn on it too, so
they are taken from any source, and a press takes the pointer for the drag.
examples/sketch.bjo draws with it, and docs/sketch.png is its picture.
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A tree node is a TreeViewItem: a header and items, patched by key as a
list's items are. The chosen node is chosen by its key, once the nodes are
there, and a click sends the key. SelectedItem is a direct property, which
a clear does not reset, so no choice is set as null.
The Readme now covers menus and keys, dialogs, styles and themes, and the
new controls. docs/styles.png is examples/styles.bjo.
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run-app takes #:screenshot, a path: the window saves a PNG of itself there
once it is shown and laid out, at twice its size, and closes. It defaults to
the environment variable BJOGUI_SCREENSHOT, so any program can be pictured
with no change. docs/todo.png is examples/todo.bjo, taken that way.
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gui-update is a plain function, so it cannot wait. It returns the work to do
as values. A command is an (Event %m), synced in a fiber of its own, whose
answer is the next message. A subscription is a source of messages that the
model asks for: after each update the app starts the new ones and cancels the
ones that are gone, by key. every sends a message on a timer, and
subscription takes a source of one's own.
The fibers belong to the app's scope and post their messages to the UI
thread, so gui-update and view only run there. Closing the window cancels
them. The prelude's path macros already use the name update, hence
gui-update.
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A program is a model, an update and a view. A view is a Bjolang value; an
event finds its message in the view its control was last given, and the next
view is compared with the last so only what differs is changed. Controls are
made with plain constructors and changed with SetValue, so nothing is
subclassed, and a program never names an Avalonia type.
Text, button, text input, checkbox, column and row. tests/app.bjo drives an
app through its real controls with no window.
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