How many pressed keys Flash can detect? using as3

Question

I'm developing a little game. I use the following code to detect the keys pressed by the player:

private function onKeyDown(event:KeyboardEvent):void {
        //moviment keys
        if (event.keyCode == 37 || event.keyCode == 65) {
            this.leftKeyPressed = true;
        }
        if (event.keyCode == 39 || event.keyCode == 68) {
            this.rightKeyPressed = true;
        }
        if (event.keyCode == 38 || event.keyCode == 87) {
            this.upKeyPressed = true;
        }
        if (event.keyCode == 40 || event.keyCode == 83) {
            this.downKeyPressed = true;
        }

        if (event.keyCode == this.shootKey) {
            this.shootKeyPressed = true;
        }
    }

The onKeyUp event:

private function onKeyUp(event:KeyboardEvent):void {
        if (event.keyCode == 37 || event.keyCode == 65) {
            this.leftKeyPressed = false;
        }
        if (event.keyCode == 39 || event.keyCode == 68) {
            this.rightKeyPressed = false;
        }
        if (event.keyCode == 38 || event.keyCode == 87) {
            this.upKeyPressed = false;
        }
        if (event.keyCode == 40 || event.keyCode == 83) {
            this.downKeyPressed = false;
        }
        if (event.keyCode == this.shootKey) {
            this.shootKeyPressed = false;
        }
        if (event.keyCode == changeColorKey) {
            trace('color key released');
            trace(getTimer());
            this.changeColorKeyPressed = true;
        }

    }

Basically the shootKey will be hold down by the player almost all the time. And the changeColorKey will be pressed very often but not hold down. While testing I noted that holding the shootKey and the right arrow down, the onKeyUp events for the changeColorKey don't get fired. Holding the up or down arrow key instead of the right arrow has the same effect. If I hold the left arrow key the events get fired. Why does it occour? Is there something wrong with my code?

Answer 1

The problem you are seeing is not related to your code, but to your keyboard. Depending on the keyboard technology the number and combinations of keys you can press simultaneously varies. I did a code very similar to yours a couple of years ago and I remember having the same problem you mention, while with my current keyboard that no longer happens (it seems this can support up to five simultaneous letters while the old one supported three).

Answer 2

I believe the problem has to do with the hardware keyboard also. I have tested the code myself on my keyboard, and I can't press more then 3 keys at the same time on a non-usb keyboard.

Now in your example, that should not be a problem, because you never need to press more then 3 keys. But watch out! There is another limitation that seems to be in the hardware keyboard and it has to do with the proximity of the keys you are pressing with each other.

For example, when trying your code, it seemed I could not receive a KEY_UP when I had two other keys KEYed_DOWN(meaning pressed down continually) next to the one I'm KEYing_UP(so the one I want to receive the key_up event for). So I believe that is why your code only works with the left arrow key. Your up, down and right arrow keys are probably, somehow, too close to the changeColorKey and because of this, (I'm guessing because of how the circuitry is done in a keyboard) it can't trigger it's up state.

Try moving the shootKey and/or the changeColorKey somewhere else, farther away and see if that works.