Uderzo v0.8.2 Uderzo.GenRenderer behaviour View Source

Generic rendering code. This will start a process that will render a frame at a regular rate in a window of the indicated size. Rendering the frame is done by calling a callback with the current window size and height and the current mouse pointer position.

GenRenderer is using GenServer internally and is thus OTP compatible.

Usually, if you want to use Uderzo, this is the module you want to build around. See also the examples and demos in the repository.

The basic usage of GenRenderer is the same as GenServer: you use the module, supply a render_frame/5 callback and an optional init_renderer/1 callback. There are just more arguments than with GenServer ;-). Short skeleton:

defmodule MyRenderer do
  use Uderzo.GenRenderer

def start_link(...) do
  Uderzo.GenRenderer.start_link(__MODULE__, "My Demo", 800, 600, 60, [], name: __MODULE__)
end

def init_renderer([]) do
  {:ok, %{some: :state}}
end

def render_frame(window_width, window_height, mouse_x, mouse_y, state) do
  ... Paint your frame here ...
  {:ok, state}
end

One important difference with GenServer is that the init_renderer/1 callback isn't called during start time but rather as soon as Uderzo is initialized. This means that you can call functions to load fonts, etcetera, at initialization time.

Note that once called, GenRenderer just goes off and does rendering. There's no requirement to interact with it further, although you can set the user state directly, forcing a redraw if desired.

Link to this section Summary

Functions

Returns a specification to start this module under a supervisor

Get the user_state portion of %State{}. This is the data that gets passed into render

Invoked when the server is started. start_link/3 or start/3 will block until it returns

Set the user_state portion of %State{}. This is the data that gets passed into render. Calling this has the side effect of redrawing the screen

Start a GenRenderer with the indicated window height, width and title and the target FPS

Callbacks

The (optional) init callback. It either returns :ok and the initial state, or an error which will cause the GenRenderer to bail out

The rendering function. This is called fps times per second. It should try to complete quickly so that frames aren't skipped

Link to this section Functions

Returns a specification to start this module under a supervisor.

See Supervisor.

Get the user_state portion of %State{}. This is the data that gets passed into render.

Invoked when the server is started. start_link/3 or start/3 will block until it returns.

init_arg is the argument term (second argument) passed to start_link/3.

Returning {:ok, state} will cause start_link/3 to return {:ok, pid} and the process to enter its loop.

Returning {:ok, state, timeout} is similar to {:ok, state} except handle_info(:timeout, state) will be called after timeout milliseconds if no messages are received within the timeout.

Returning {:ok, state, :hibernate} is similar to {:ok, state} except the process is hibernated before entering the loop. See c:handle_call/3 for more information on hibernation.

Returning {:ok, state, {:continue, continue}} is similar to {:ok, state} except that immediately after entering the loop the c:handle_continue/2 callback will be invoked with the value continue as first argument.

Returning :ignore will cause start_link/3 to return :ignore and the process will exit normally without entering the loop or calling c:terminate/2. If used when part of a supervision tree the parent supervisor will not fail to start nor immediately try to restart the GenServer. The remainder of the supervision tree will be started and so the GenServer should not be required by other processes. It can be started later with Supervisor.restart_child/2 as the child specification is saved in the parent supervisor. The main use cases for this are:

  • The GenServer is disabled by configuration but might be enabled later.
  • An error occurred and it will be handled by a different mechanism than the Supervisor. Likely this approach involves calling Supervisor.restart_child/2 after a delay to attempt a restart.

Returning {:stop, reason} will cause start_link/3 to return {:error, reason} and the process to exit with reason reason without entering the loop or calling c:terminate/2.

Callback implementation for GenServer.init/1.

Link to this function

set_user_state(new_state) View Source

Set the user_state portion of %State{}. This is the data that gets passed into render. Calling this has the side effect of redrawing the screen.

Link to this function

start_link(module, title, window_width, window_height, target_fps, args, genserver_opts \\ []) View Source

Start a GenRenderer with the indicated window height, width and title and the target FPS.

The target_fps is a target, much rests on the speed of the rendering function for the real fps.

The final argument, genserver_opts, is just passed on to GenServer.start_link/3.

Returns GenServer.on_start.

Link to this section Callbacks

Link to this callback

init_renderer(args) View Source
init_renderer(args :: term()) :: {:ok, term()} | :error

The (optional) init callback. It either returns :ok and the initial state, or an error which will cause the GenRenderer to bail out.

Link to this callback

render_frame(window_width, window_height, mouse_x, mouse_y, state) View Source
render_frame(
  window_width :: float(),
  window_height :: float(),
  mouse_x :: float(),
  mouse_y :: float(),
  state :: term()
) :: {:ok, term()} | :error

The rendering function. This is called fps times per second. It should try to complete quickly so that frames aren't skipped.