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[Jaun]

I create a simple platformer project following a tutorial on Youtube. Everything is working fine, except for one little problem that is driving me nuts. When the sprite of my character collide with a oWall object (the one I use as ground and walls), the right one is fine, but the left one is off by one pixel. A gif may exemplify what I'm trying to say better:



Here is all the code of the game (<100 lines of code):

Create Event of oHero:

Code:

myGravity= 1;
mySpeed= 4;
speedJump= 12;
speedH = 0;
speedV= 0;

Step Event of oHero (PHYSICS):

Code:

KEY_LEFT = keyboard_check(vk_left) or keyboard_check(ord('A'));
KEY_RIGHT = keyboard_check(vk_right) or keyboard_check(ord('D'));
KEY_DOWN = keyboard_check(vk_down) or keyboard_check(ord('S'));
KEY_JUMP = keyboard_check(vk_up) or keyboard_check(ord('W'));

if (place_meeting(x, y + 1, oWall))
{
    speedV = 0;
    
    if (KEY_JUMP)   speedV = -speedJump;
}

else
{
    if (speedV < 10)   speedV += myGravity;
}

if (KEY_RIGHT)  speedH = mySpeed;
if (KEY_LEFT)   speedH = -mySpeed;

if ((!KEY_LEFT and !KEY_RIGHT) or (KEY_LEFT and KEY_RIGHT))     speedH = 0;

// HORIZONTAL
if (place_meeting(x + speedH , y, oWall))
{
    while(!place_meeting(x + sign(speedH), y, oWall))
    {
        x += sign(speedH);
    }
    speedH = 0;
}
x += speedH;

// VERTICAL
if (place_meeting(x, y + speedV, oWall))
{
    while(!place_meeting(x, y + sign(speedV), oWall))
    {
        y += sign(speedV);
    }
    speedV = 0;
}
y += speedV;

Step Event of oHero (SPRITES):

Code:

if (yprevious != y)
{
    sprite_index = sHeroJumping;
    mask_index = sHeroJumpingMask;
    
    image_speed = 0;
    image_index = (y > yprevious);
}

else
{
    if (xprevious != x)
    {
        sprite_index = sHeroWalking;
        mask_index = sHeroWalkingMask;
        
        image_speed = 0.3;
    }
    
    else
    {
        if (KEY_DOWN)
        {
            sprite_index = sHeroDown;
            mask_index = sHeroDownMask;
        }
        
        else
        {
            sprite_index = sHeroIdle;
            mask_index = sHeroIdleMask;
        }
    }
}

if (speedH != 0)   image_xscale = sign(speedH);

The oHero sprite mask and all the animations mask are centered and have the same width. I'm not using anything solid neither the build-in gravity stuff of Game Maker. Every sprite have Precise Collision Checking on. I know it have something to do with image_xscale because everything works fine if I don't flip the sprite. I'm using Game Maker Studio (v1.4).

So... is image_xscale messing with the collision box? anything wrong in the code? any workaround for this problem?

[zleub]

if place_metting() is your collision function, i think in your call to (place_meeting(x, y + 1, oWall)), the sign of the + 1 should depend on your scale ?

[Jaun]

if place_metting() is your collision function, i think in your call to (place_meeting(x, y + 1, oWall)), the sign of the + 1 should depend on your scale ?

Thanks for your answer! That bit of code is for checking if there is ground just under the character, so I don't really think it has something to do with the problem.

The actual collision code is below, under the "HORIZONTAL" (and "VERTICAL") comments.

[oahda]

I don't really know GM any more, but could it be that the mask isn't perfecrly centered and then it doesn't flip when the image does?

[Juskelis]

Yeah, I think it has something to do with the collision mask not working correctly. If I remember correctly, you can draw a rect over the mask by using the "bbox_left, bbox_right, etc" variables for debugging it.

[oahda]

Isn't there a checkbox for making the mask visible? That's what I can remember, at least, but I'm not sure.

[Juskelis]

There's a way to see the mask in the image editor, but there's no prebuilt option for seeing it in game

[Conker]

Its your mask, make sure its centered correctly

[ProgramGamer]

Also as a last resort, try to flip your sprite independently from your mask by drawing manually. It worked for me once.