Physics: Multiple Contact Points T2

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Greg_C

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Posted: 2nd Feb 2012 20:35

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I might be going about this the wrong way but here it is: The basics of what I am trying to do is make it so I can jump only when my players "feet" are on the ground. The way I thought about doing it is through the contact points that are returned through the physics. Now this works fine in most cases:

+ Code Snippet

if(agk::GetSpriteFirstContact(m_spriteID)==1 && agk::GetSpriteContactWorldY() >= (m_posY + m_spriteHeight) )
{
    bCanJump = true; 
}

The problem lies when there are multiple contacts happening at the same time. For instance if the character is running on the ground and then hits a wall the contact point that returns is not >= the bottom of my sprite because it is returning the contact point of the wall even though it is colliding with the floor.

I can get away with this with my current game but I am really just wondering what everyone else is doing to check if the player is touching the ground. Or if there are some other ideas that I could test out.

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baxslash

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Posted: 2nd Feb 2012 21:10

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I am using raycasting for this and other similar operations. You can set all of your "ground" sprites to a particular group then do a raycast from the sprite's centre down to just below where his feet are and check for a collision against that group.

It's a lot simpler than it sounds once you look at the commands. Contacts are far less predictable in my experience.

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bitJericho

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Posted: 2nd Feb 2012 21:11 Edited at: 2nd Feb 2012 21:12

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I have a sprite that I position at the player sprite's feet. I use it as a sensor.

Quote: "
I am using raycasting for this and other similar operations. You can set all of your "ground" sprites to a particular group then do a raycast from the sprite's centre down to just below where his feet are and check for a collision against that group.
"

That sounds like a better solution. I'm gonna give it a try.

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Greg_C

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Posted: 3rd Feb 2012 00:35 Edited at: 3rd Feb 2012 01:21

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That's why I ask these questions wasn't even thinking about doing a raycast. Thanks for response!

EDIT:

After looking at the raycasting functions I decided I don't really need to filter out what the character is hitting just need to know if he is hitting something:

+ Code Snippet

bool Object::CanJump()
{
	int BeginRaycastX = m_posX + (m_spriteWidth * .5);
	int BeginRaycastY = m_posY + (m_spriteHeight * .5);
	//Go 2 pixels below the sprite. 
	int EndRaycastX = BeginRaycastX + (m_spriteWidth * .5) +2;
	int EndRaycastY = BeginRaycastY + (m_spriteHeight * .5) +2;

	if(agk::PhysicsRayCast(BeginRaycastX,BeginRaycastY,EndRaycastX,EndRaycastY) == 1)
	{
		bCanJump = true;
	}
	else
	{
		bCanJump = false; 
	}
	return bCanJump;
}

Thanks for the help!

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baxslash

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Posted: 3rd Feb 2012 09:45

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Great. Glad to help!

I'm also using raycasting to decide how dark my object's shadows should be as it also returns data you can get a distance from.

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bitJericho

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Posted: 5th Feb 2012 15:18 Edited at: 5th Feb 2012 23:06

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Quote: "I'm also using raycasting to decide how dark my object's shadows should be as it also returns data you can get a distance from. "

Good thinking.

I'm using a variable on the character to let it know it's on the ground. I send two raycasts down, one on each side of his feet, and if either is on the ground then I assign a third variable:

+ Code Snippet

    char[0].right_foot_on_the_ground = SpriteRayCastGroup( 1, GetSpriteXByOffset( char[0].sprite_number )+0.2, GetSpriteYByOffset( char[0].sprite_number ), GetSpriteXByOffset( char[0].sprite_number )+0.2, GetSpriteYByOffset( char[0].sprite_number ) + GetSpriteHeight(char[0].sprite_number)/2 )
    char[0].left_foot_on_the_ground = SpriteRayCastGroup( 1, GetSpriteXByOffset( char[0].sprite_number )-0.2, GetSpriteYByOffset( char[0].sprite_number ), GetSpriteXByOffset( char[0].sprite_number )-0.2, GetSpriteYByOffset( char[0].sprite_number ) + GetSpriteHeight(char[0].sprite_number)/2 )
    char[0].on_the_ground = char[0].right_foot_on_the_ground or char[0].left_foot_on_the_ground

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AppGameKit Classic Chat / Physics: Multiple Contact Points T2