/**
* Fired when the GUI event loop "ticks". This provides an opportunity
* to receive user input as well as send the framebuffer to be rendered.
*/
private static void GUI_OnTick(GUITickEventArgs eventArgs)
{
_game.ButtonP1Left = eventArgs.ButtonP1Left;
_game.ButtonP1Right = eventArgs.ButtonP1Right;
_game.ButtonP1Fire = eventArgs.ButtonP1Fire;
_game.ButtonP2Left = eventArgs.ButtonP2Left;
_game.ButtonP2Right = eventArgs.ButtonP2Right;
_game.ButtonP2Fire = eventArgs.ButtonP2Fire;
_game.ButtonStart1P = eventArgs.ButtonStart1P;
_game.ButtonStart2P = eventArgs.ButtonStart2P;
_game.ButtonCredit = eventArgs.ButtonCredit;
_game.ButtonTilt = eventArgs.ButtonTilt;
// If the PAUSE key was pressed (e.g. CTRL/CMD+BREAK), invoke the
// interactive debugger.
if (_game.Debug && eventArgs.ShouldBreak)
{
_game.Break();
}
if (_renderFrameNextTick)
{
eventArgs.FrameBuffer = _frameBuffer;
eventArgs.ShouldRender = true;
_renderFrameNextTick = false;
}
if (_playSoundNextTick)
{
eventArgs.ShouldPlaySounds = true;
eventArgs.SoundEffects.AddRange(_soundEffects);
_soundEffects.Clear();
_playSoundNextTick = false;
}
}
private void UpdateKeys(GUITickEventArgs tickEventArgs, SDL.SDL_Keycode keycode, bool isDown)
{
switch (keycode)
{
case SDL.SDL_Keycode.SDLK_LEFT:
tickEventArgs.ButtonP1Left = isDown;
break;
case SDL.SDL_Keycode.SDLK_RIGHT:
tickEventArgs.ButtonP1Right = isDown;
break;
case SDL.SDL_Keycode.SDLK_SPACE:
tickEventArgs.ButtonP1Fire = isDown;
break;
case SDL.SDL_Keycode.SDLK_a:
tickEventArgs.ButtonP2Left = isDown;
break;
case SDL.SDL_Keycode.SDLK_d:
tickEventArgs.ButtonP2Right = isDown;
break;
case SDL.SDL_Keycode.SDLK_p:
tickEventArgs.ButtonP2Fire = isDown;
break;
case SDL.SDL_Keycode.SDLK_1:
tickEventArgs.ButtonStart1P = isDown;
break;
case SDL.SDL_Keycode.SDLK_2:
tickEventArgs.ButtonStart2P = isDown;
break;
case SDL.SDL_Keycode.SDLK_5:
tickEventArgs.ButtonCredit = isDown;
break;
case SDL.SDL_Keycode.SDLK_t:
tickEventArgs.ButtonTilt = isDown;
break;
}
}
/**
* Used to start the GUI event loop using the SDL window to poll for events. When an event is
* received, the keyboard state is read and the OnTick event is fired. After the event completes
* a frame and/or audio can be rendered/played based on the values set in the OnTick event args.
*
* This is a BLOCKING call; the event loop will continue to be polled until (1) the user uses
* the platform specific key combination or GUI action to close the window or (2) the OnTick
* event arguments has ShouldQuit set to true.
*/
public void StartLoop()
{
// Used to keep track of the time elapsed in each loop iteration. This is used to
// notify the OnTick handlers so they can update their simulation, as well as throttle
// the update loop to targetTicskHz if needed.
var stopwatch = new Stopwatch();
// Structure used to pass data to and from the OnTick handlers. We initialize it once
// outside of the loop to avoid eating a ton of memory putting GC into a tailspin.
var tickEventArgs = new GUITickEventArgs();
// The SDL event polled for in each iteration of the loop.
SDL.SDL_Event sdlEvent;
while (true)
{
stopwatch.Restart();
tickEventArgs.KeyDown = null;
tickEventArgs.ShouldBreak = false;
while (SDL.SDL_PollEvent(out sdlEvent) != 0)
{
switch (sdlEvent.type)
{
// e.g. Command + Q, ALT+F4, or clicking X...
case SDL.SDL_EventType.SDL_QUIT:
// Break out of the SDL event loop, which will close the program.
return;
case SDL.SDL_EventType.SDL_KEYDOWN:
tickEventArgs.KeyDown = sdlEvent.key.keysym.sym;
UpdateKeys(tickEventArgs, sdlEvent.key.keysym.sym, true);
// If the break/pause or 9 key is pressed, set a flag indicating the
// emulator's should activate the interactive debugger.
if (sdlEvent.key.keysym.sym == SDL.SDL_Keycode.SDLK_PAUSE ||
sdlEvent.key.keysym.sym == SDL.SDL_Keycode.SDLK_9)
{
tickEventArgs.ShouldBreak = true;
}
break;
case SDL.SDL_EventType.SDL_KEYUP:
UpdateKeys(tickEventArgs, sdlEvent.key.keysym.sym, false);
break;
}
}
// Update the event arguments that will be sent with the event handler.
tickEventArgs.ShouldRender = false;
tickEventArgs.ShouldPlaySounds = false;
tickEventArgs.SoundEffects.Clear();
// Delegate out to the event handler so work can be done.
if (OnTick != null)
{
OnTick(tickEventArgs);
}
// We only want to re-render if the frame buffer has changed since last time because
// the SDL_RenderPresent method is relatively expensive.
if (tickEventArgs.ShouldRender && tickEventArgs.FrameBuffer != null)
{
// Render screen from the updated the frame buffer.
// NOTE: The electron beam scans from left to right, starting in the upper left corner
// of the CRT when it is in 4:3 (landscape), which is how the framebuffer is stored.
// However, since the CRT in the cabinet is rotated left (-90 degrees) to show the game
// in 3:4 (portrait) we need to perform the rotation of points below by starting in the
// bottom left corner of the window and drawing upwards, ending on the top right.
// Clear the screen.
SDL.SDL_SetRenderDrawColor(_renderer, 0, 0, 0, 0);
SDL.SDL_RenderClear(_renderer);
var bits = new System.Collections.BitArray(tickEventArgs.FrameBuffer);
var x = 0;
var y = SpaceInvaders.RESOLUTION_WIDTH - 1;
for (var i = 0; i < bits.Length; i++)
{
if (bits[i])
{
// The CRT is black/white and the framebuffer is 1-bit per pixel.
// A transparent overlay added "colors" to areas of the CRT. These
// are the approximate y locations of each area/color of the overlay:
if (y >= 182 && y <= 223)
{
SDL.SDL_SetRenderDrawColor(_renderer, 0, 255, 0, 255); // Green - player and shields
}
else if (y >= 33 && y <= 55)
{
SDL.SDL_SetRenderDrawColor(_renderer, 255, 0, 0, 255); // Red - UFO
}
else
{
SDL.SDL_SetRenderDrawColor(_renderer, 255, 255, 255, 255); // White - Everything else
}
SDL.SDL_RenderDrawPoint(_renderer, x, y);
}
y--;
if (y == -1)
{
y = SpaceInvaders.RESOLUTION_WIDTH - 1;
x++;
}
if (x == SpaceInvaders.RESOLUTION_HEIGHT)
{
break;
}
}
SDL.SDL_RenderPresent(_renderer);
}
// Handle playing sound effects.
if (soundEffects != null &&
tickEventArgs.ShouldPlaySounds &&
tickEventArgs.SoundEffects != null)
{
foreach (var sfx in tickEventArgs.SoundEffects)
{
var pointer = soundEffects[sfx];
// Result of Mix_PlayChannel, which indicates the channel the sound is playing on.
// -1 indicates an error.
var playChannelResult = -1;
switch (sfx)
{
// The UFO sound effect loops until the UFO disappears or is destroyed.
case SoundEffect.UFO_Start:
playChannelResult = SDL_mixer.Mix_PlayChannel(AUDIO_CHANNEL_UFO, pointer, AUDIO_INFINITE_LOOP);
break;
case SoundEffect.UFO_Stop:
{
SDL_mixer.Mix_Pause(AUDIO_CHANNEL_UFO);
// Mix_Pause doesn't return a channel or error code. Ensure we don't leave as -1.
playChannelResult = AUDIO_CHANNEL_UFO;
break;
}
case SoundEffect.InvaderMove1:
case SoundEffect.InvaderMove2:
case SoundEffect.InvaderMove3:
case SoundEffect.InvaderMove4:
playChannelResult = SDL_mixer.Mix_PlayChannel(AUDIO_CHANNEL_INVADER_MOVEMENT, pointer, AUDIO_NO_LOOP);
break;
default:
playChannelResult = SDL_mixer.Mix_PlayChannel(AUDIO_CHANNEL_COMMON, pointer, AUDIO_NO_LOOP);
break;
}
if (playChannelResult == -1)
{
Console.WriteLine("Error playing sound effect {0}. SDL Error: {1}", sfx, SDL.SDL_GetError());
}
}
}
// See if we need to delay to keep locked to ~ targetTicskHz.
if (stopwatch.Elapsed.TotalMilliseconds < (1000 / _targetTicksHz))
{
var delay = (1000 / _targetTicksHz) - stopwatch.Elapsed.TotalMilliseconds;
SDL.SDL_Delay((uint)delay);
}
// If the event handler indicated we should quit, then stop.
if (tickEventArgs.ShouldQuit)
{
return;
}
}
}