How can I use multiple timers to plan events in my program? - c++

Question

I am building a rockband-like program using C++ and SDL, and want to be able to time events so I can orchestrate a song in the program. Here is what I have accomplished so far:
4 circles which fall from the top of the window to the middle into 4 designated hitting spots.
The circles drop at random intervals (not using time, a random number generator determines how far from the top of the window they begin to fall)
I am able to determine when a note is hit, and a score is displayed in the top right hand corner
Simple sparks are applied around a marker to let you know a note was hit
I can open a file and read text from it
Now I want to be able to use that file to write songs for the program to read and execute. I was thinking something along the lines of "1g,2g,4y,3r etc. etc. etc." the numbers being milliseconds to wait until the next note and the letters designating which color should fall.

Answer 1

You don't really need (or want) multiple timers; just the single timer that drives your window refresh (at 30fps or whatever) is sufficient.
When you load in your song file, for each note in the song you should store the number of milliseconds that should elapse between the moment the song starts playing and the moment that particular note is played, e.g (pseudocode):
int millisCounter = 0;
int note, noteLengthMillis;
while(ReadNextNoteFromSongFile(note, noteLengthMillis))
{
songNoteRecordsVector.push_back(NoteRecord(millisCounter, note));
millisCounter += noteLengthMillis;
}
Then, when you start the game level going, at the instant the song starts playing, record the current time in milliseconds. You will use this value as your time-zero reference for as long as the song keeps playing.
Now at every video-frame (or indeed at any time), you can calculate the number of milliseconds until a given note will be played, relative to the current system-clock-time:
int NoteRecord :: GetMillisecondsUntilNoteIsPlayed(int songStartTimeMillis, int currentTimeMillis) const
{
return this->myNoteOffsetMillis - (currentTimeMillis - songStartTimeMillis);
}
Note that the value returned will be negative if the note's time-to-be-played has already passed.
Once you have that, it's just a matter of converting each note's current milliseconds-until-note-is-played result into a corresponding on-screen position, and you know where to draw the note-circle for the current frame:
int millisUntilNotePlayTime = note.GetMillisecondsUntilNoteIsPlayed(songStartTimeMillis, currentTimeMillis);
int circleY = someFixedOffsetY + (millisUntilNotePlayTime/(1000/pixelsScrolledPerSecond));
DrawCircleAt(circleX, circleY);
... and if the user presses a key, you can calculate how far off the user was from the correct time for a given note using the same function, e.g.:
int errorMillis = note.GetMillisecondsUntilNoteIsPlayed(songStartTimeMillis, currentTimeMillis);
if (errorMillis < -50)
{
printf("You're too slow!\n");
}
else if (errorMillis > 50)
{
printf("You jumped the gun!\n");
}
else
{
printf("Good job!\n");
}