Elysian Shadows

Posted: **Mon Feb 07, 2011 12:26 am**

D-e-X wrote:I would give the class a bool collision; in the move function you should do this instead: collision = check_collision(blah...);
then in the show function do this: if(collision) apply_surface(bleh...);

When I do this I see the image popping on the screen as I want to, but it only stays for a split second. How can I keep this image on the screen?

Posted: **Mon Feb 14, 2011 10:04 pm**

Its only appearing for a split second because the collision returns back to false after you have a collision.

if( ( box.x < 0 ) || ( box.x + MOVER_WIDTH > SCREEN_WIDTH ) || ( check_collision( box, wall ) ) )
{
//Move back
box.x -= xVel;
}

//If the Mover went too far up or down or has collided with the wall
if( ( box.y < 0 ) || ( box.y + MOVER_HEIGHT > SCREEN_HEIGHT ) || ( check_collision( box, wall ) ) )
{
//Move back
box.y -= yVel;
}
}

The two bold underlined lines are always going to make your box "bounce" off whatever it is colliding with, making the collision become false again. Which is why you are only seeing the image for a split second and then it disappears. You are going about it the right way, but because you are checking for a collision each time you move the statement is no longer true once you do have a collision because the box "bounces" off the wall. Honestly, that collision code isn't that optimal for returning whether or not a collision is happening because it causes that "bounce" effect.

Doing it this way will draw your image as long as you are having a "collision". i.e you need to be moving the box into the wall.

Code: Select all

void Mover::move()
{
    //Move the Mover left or right
    box.x += xVel;

    //If the Mover went too far to the left or right or has collided with the wall
    if( ( box.x < 0 ) || ( box.x + MOVER_WIDTH > SCREEN_WIDTH ) || ( check_collision( box, wall ) ) )
    {
        //Move back
        box.x -= xVel;
        apply_surface( 200, 300, dot, screen );
    }

    //Move the Mover up or down
    box.y += yVel;

    //If the Mover went too far up or down or has collided with the wall
    if( ( box.y < 0 ) || ( box.y + MOVER_HEIGHT > SCREEN_HEIGHT ) || ( check_collision( box, wall ) ) )
    {
        //Move back
       box.y -= yVel;
       apply_surface( 200, 300, dot, screen );
    }
}

Alternatively you could store the collision in a bool flag

Code: Select all

//somewhere in your main.cpp
bool collision = false;

Code: Select all

void Mover::move()
{
    //Move the Mover left or right
    box.x += xVel;

    //If the Mover went too far to the left or right or has collided with the wall
    if( ( box.x < 0 ) || ( box.x + MOVER_WIDTH > SCREEN_WIDTH ) || ( check_collision( box, wall ) ) )
    {
        //Move back
        box.x -= xVel;
        collision = true;
    }

    //Move the Mover up or down
    box.y += yVel;

    //If the Mover went too far up or down or has collided with the wall
    if( ( box.y < 0 ) || ( box.y + MOVER_HEIGHT > SCREEN_HEIGHT ) || ( check_collision( box, wall ) ) )
    {
        //Move back
       box.y -= yVel;
       collision = true;
    }
}

Code: Select all

//somewhere in your main loop
if (collision) 
{ 
     apply_surface( 200, 300, dot, screen ); 
}

Elysian Shadows

[SOLVED] SDL LazyFoo Moving an Image Help

Re: SDL LazyFoo Moving an Image Help

Re: SDL LazyFoo Moving an Image Help