How do you add gravity with wall collision in actionscript 3? - actionscript-3

Question

I created a script that allows your character to move around with wall collision for every direction. How do I add gravity to it on the y-axis and still have it work the same way (like a platform game)?
I tried something like char.y-- when it hits the platform if it were just the floor, but all that does is slowly bring char up no matter where it is in the object, and once it reaches the top, it shakes like crazy.
A preview of the stage: http://puu.sh/63Y1g.png
//WALL COLLISION
if(walls.hitTestPoint(char.x-(char.width/2),char.y,true) && Key.isDown(Key.A)){
char.x+=5
}
if(walls.hitTestPoint(char.x+(char.width/2),char.y,true) && Key.isDown(Key.D)){
char.x-=5
}
if(walls.hitTestPoint(char.x,char.y-(char.height/2),true) && Key.isDown(Key.W)){
char.y+=5
}
if(walls.hitTestPoint(char.x,char.y+(char.height/2),true) && Key.isDown(Key.S)){
char.y-=5
}
//CHARACTER CONTROLS
char.x+=0;
if(Key.isDown(Key.A)){
char.x+=-5;
speed=-5;
}
if(Key.isDown(Key.D)){
char.x+=5;
speed=5;
}
if(Key.isDown(Key.W)){
char.y+=-5;
speed=5;
}
if(Key.isDown(Key.S)){
char.y+=5;
speed=5;
}

Answer 1

To do this really simply, something like this would suffice:
// Check if there is a floor below the char
if (!floor.hitTestPoint(char.x, char.y + (char.height/2) + 2 , true))
{
// If not, apply Gravity
char.y += 5
}
This will only apply gravity if there is no floor 2 pixels directly below the char (this will stop the jittering, feel free to try with different pixel offsets that might work better in your case), I wasn't sure how you were differentiating between the walls and floor, so replace 'floor' with how you are doing it.
===============
If you would like to add realistic accelerating gravity, you will need to add a variable to track the current vertical speed of the char, then add to that each step
eg. Each step do this instead of just adding to y
// Apply gravity
vSpeed += 5
char.y += vSpeed
But if you are going to do that you might as well start getting into vectors and more complex things, there's a lot of materials on the net for this.