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#1 2018-06-07 06:52:45

Race the Hedgehog
Member
From: Sao Bernardo do Campo, Brazil
Registered: 2010-12-16
Posts: 163
Website

[Questions and Showcase] Creating a platform character from scratch

I've been planning to create several mini-games in my spare time for a while now, to bring life to my ideas and to expand my knowledge beyond art. My plan has always been to create a platform engine where I can use it as a start point and expand it from there.
I've tried to do this with Construct 2 and Game Maker Studio, but for some reason, I've always felt more comfortable working with the Open Surge Engine, perhaps because of the attachment I have, or because I'm not so available to learn new APIs as of now.
But the good thing about knowing a little bit about those other ones is that I can do my best to try to convert a script that would work in Game Maker for Open Surge. And that's exactly what I'm trying to do, using this video as a base (It might help understanding the logic behind the script):
https://youtu.be/vMOJmpOxRfQ
And for now, I'm getting great results! But I would like to ask you guys in helping me to optimize and to fix some bugs, if possible. smile

Questions and Bugs:

  • First of all, the first bug you notice, is that the collision doesn't work perfectly, it is functional, but it is not perfect. When you are about to fall on the ground, for example, you get do a little bounce before leaning completely on the ground, it's a fast process, so it's a little hard to notice. Unfortunately I have no idea what is causing this.

  • I didn't test it all that much, but I think it's possible to get stuck in some bricks corner, but you can jump to set yourself free.

  • This is not exactly a bug, but something that has been bugging me a lot. If you look at the lines of code that checks the collision, you'll see something like this:

//Collisions

       //Horizontal
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,0)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,1)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,2)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,3)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,4)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,5)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,6)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,7)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,8)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,9)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,10)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,11)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,12)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,13)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,14)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,15)<>0"

       execute "horizontal collision" if "obstacle_exists(15+ $hsp,0)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,1)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,2)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,3)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,4)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,5)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,6)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,7)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,8)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,9)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,10)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,11)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,12)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,13)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,14)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,15)<>0"

That's because it was the only way I've found to check every single corner of the sprite. The problem is, if I need a collision greater than 16x16, the code can get pretty extensive. Is there any method where I can reduce this code, or calculate it automatically? Maybe some function that counts from 0 to 16 instantaneously without stopping? I'm aware of the sensor bar method as well, but I really want to choose not to use it.

Finally, the download link:
DOWNLOAD
(To play it, go to the options in the main menu and select the stage named "1-1".)
s009.png
I will be very grateful to anyone who can help me to achieve this, I have a huge passion for this community and I hope to get back to you guys with some artworks very soon! big_smile


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#2 2018-06-07 12:48:37

svgmovement
Member
Registered: 2011-11-24
Posts: 209

Re: [Questions and Showcase] Creating a platform character from scratch

Race the Hedgehog wrote:
  • First of all, the first bug you notice, is that the collision doesn't work perfectly, it is functional, but it is not perfect. When you are about to fall on the ground, for example, you get do a little bounce before leaning completely on the ground, it's a fast process, so it's a little hard to notice. Unfortunately I have no idea what is causing this.

I looked at the code for the player and noticed this:

    state "vertical collision check"
    {
       let "$y=ypos()+sign($hsp)"
    }

Maybe $hsp should be $vsp?

Race the Hedgehog wrote:
  • This is not exactly a bug, but something that has been bugging me a lot. If you look at the lines of code that checks the collision, you'll see something like this

//Collisions

       //Horizontal
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,0)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,1)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,2)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,3)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,4)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,5)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,6)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,7)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,8)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,9)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,10)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,11)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,12)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,13)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,14)<>0"
       execute "horizontal collision" if "obstacle_exists(0+ $hsp,15)<>0"

       execute "horizontal collision" if "obstacle_exists(15+ $hsp,0)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,1)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,2)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,3)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,4)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,5)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,6)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,7)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,8)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,9)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,10)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,11)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,12)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,13)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,14)<>0"
       execute "horizontal collision" if "obstacle_exists(15+ $hsp,15)<>0"

That's because it was the only way I've found to check every single corner of the sprite. The problem is, if I need a collision greater than 16x16, the code can get pretty extensive. Is there any method where I can reduce this code, or calculate it automatically? Maybe some function that counts from 0 to 16 instantaneously without stopping? I'm aware of the sensor bar method as well, but I really want to choose not to use it.

There might be a loop function somewhere in the API.


-- svgmovement

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#3 2018-06-07 13:59:35

Alexandre
Administrator
From: Brazil
Registered: 2009-01-27
Posts: 3,279
Website

Re: [Questions and Showcase] Creating a platform character from scratch

Hey Race, it's great to see your stuff smile

svgmovement wrote:

There might be a loop function somewhere in the API.

Indeed there is. One way to do it is to use execute .. for (execute .. while will work too).
http://opensnc.sourceforge.net/wiki/ind … Fast_Loops

Example:

// let $counter be a variable between 0 and 16, inclusive.

    state "horizontal collision"
    {
        execute "horizontal collision loop" for "$counter = 0" "$counter <= 16" "$counter += 1"
        let "$hsp=0"
    }

    state "horizontal collision loop"
    {
        execute "horizontal collision check" unless "obstacle_exists($counter + sign($hsp),0)<>0"
        execute "horizontal collision check" unless "obstacle_exists($counter + sign($hsp),16)<>0"
    }

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#4 2018-06-07 21:50:30

Race the Hedgehog
Member
From: Sao Bernardo do Campo, Brazil
Registered: 2010-12-16
Posts: 163
Website

Re: [Questions and Showcase] Creating a platform character from scratch

svgmovement wrote:

There might be a loop function somewhere in the API.

Yeah, that was definitely a typo. Fixed it but didn't see any notable change.

Alexandre wrote:

Indeed there is. One way to do it is to use execute .. for (execute .. while will work too).
http://opensnc.sourceforge.net/wiki/ind … Fast_Loops

The fast loop worked! It means that it's possible now to easily customize the collision size. Just edit the value of the variables "$collision_x" and "$collision_y" in the main state.

Here is the updated file.

The problem is that the little bounce he gives when touching the ground is still happening:
bounce.gif
And he doesn't seem to reach the top very well:
topo.gif
As of the horizontal collision, sometimes it stops a pixel before it should, but pressing the key again makes fixes it:
horizontal.gif
Any guesses on what's causing it? sad


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#5 2018-06-08 02:43:43

Alexandre
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From: Brazil
Registered: 2009-01-27
Posts: 3,279
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Re: [Questions and Showcase] Creating a platform character from scratch

I remember building platformers and having trouble like these.

In my case, I had to pay attention when I was checking for collisions and how exactly did I adjust the position of the character.

If you just set the vertical speed to zero once the characters reaches the ground, it will bounce. Even though you update the $y variable in your script, you don't actually update the position of the object in your fast loop. smile

Also, since you're doing it all manually, I suggest multiplying any speed by dt() when updating positions. See more: http://opensnc.sourceforge.net/wiki/ind … e_position

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#6 2018-06-11 07:06:34

Race the Hedgehog
Member
From: Sao Bernardo do Campo, Brazil
Registered: 2010-12-16
Posts: 163
Website

Re: [Questions and Showcase] Creating a platform character from scratch

Well, I'm sort of in a dead end now.

Alexandre wrote:

In my case, I had to pay attention when I was checking for collisions and how exactly did I adjust the position of the character.

If you just set the vertical speed to zero once the characters reaches the ground, it will bounce. Even though you update the $y variable in your script, you don't actually update the position of the object in your fast loop.

What confuses me is that I'm following the same order of factors that the video tutorial uses, where the coordinates are updated shortly after checking the collision, outside the fast loop:
24eoq51.png
And it seems that updating inside the fast loop causes the player to disappear when it hits the ground, it must be my fault in the script, but I can't think of anyway of fixing it.

I'm not sure, but I think it might have something to do with these lines in the code:

    state "vertical collision loop"
    {
        execute "vertical collision fix" unless "obstacle_exists (0, $ vc_counter + sign ($ vsp)) <> 0"
        execute "vertical collision fix" unless "obstacle_exists ($ collision_x, $ vc_counter + sign ($ vsp)) <> 0"
    }

When comparing with the base code I used above, we can notice that it uses the "while" function to check the collision, with the "!" meaning "not" in the Game Maker language.
So a direct translation to the Open Surge API would be:

    state "vertical collision loop"
    {
        execute "vertical collision fix" while "not(obstacle_exists(0,$vc_counter + sign($vsp))<>0)"
        execute "vertical collision fix" while "not(obstacle_exists($collision_x,$vc_counter + sign($vsp))<>0)"
    }

But that makes the engine freeze, maybe because the condition never gets false.
I reviewed the script several times and I can not find the problem.
If it's helpful, here is the timestamp in the video I'm using where he starts programming the collision: https://youtu.be/vMOJmpOxRfQ?list=LLDx3 … VMA&t=1333


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#7 2018-06-11 13:31:16

svgmovement
Member
Registered: 2011-11-24
Posts: 209

Re: [Questions and Showcase] Creating a platform character from scratch

Try combining the two conditions in your while loops.

    state "vertical collision loop"
    {
        execute "vertical collision fix" while "(obstacle_exists(0,$vc_counter + sign($vsp))==0) and (obstacle_exists($collision_x,$vc_counter + sign($vsp))==0)"
    }

Maybe one of the loops is getting stuck?


-- svgmovement

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#8 2018-06-13 02:34:53

Race the Hedgehog
Member
From: Sao Bernardo do Campo, Brazil
Registered: 2010-12-16
Posts: 163
Website

Re: [Questions and Showcase] Creating a platform character from scratch

svgmovement wrote:

Try combining the two conditions in your while loops.
Maybe one of the loops is getting stuck?

I've tried it, but it seems to get the same result.
What gets me confused is that most of the problems comes only from the vertical collision, while the horizontal one works almost perfectly. And to make matters worse, these glitches happen at random, without having a fixed reason to why.


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#9 2018-06-13 13:12:05

svgmovement
Member
Registered: 2011-11-24
Posts: 209

Re: [Questions and Showcase] Creating a platform character from scratch

Could gravity be messing with the vertical collision?


-- svgmovement

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#10 2018-06-13 17:40:01

Alexandre
Administrator
From: Brazil
Registered: 2009-01-27
Posts: 3,279
Website

Re: [Questions and Showcase] Creating a platform character from scratch

svgmovement wrote:

Could gravity be messing with the vertical collision?

Yes, and it seems also that this code has more loops than it should. I got the following code working smoothly for plain floor collision (no slopes and no ceilings):

//Vertical Collision

    state "vertical collision check loop"
    {
       execute "vertical collision fix" while "obstacle_exists($collision_x/2,$collision_y-1+$vsp)"
    }

    state "vertical collision fix"
    {
       let "$y=ypos()-sign($vsp)"
        set_absolute_position xpos() $y
    }

bwEJfpU.png

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#11 2018-06-17 10:21:13

Race the Hedgehog
Member
From: Sao Bernardo do Campo, Brazil
Registered: 2010-12-16
Posts: 163
Website

Re: [Questions and Showcase] Creating a platform character from scratch

I did some more testing and gravity doesn't seem to influence the bugs at all, the problem really seems to be coming from the collision code itself.

Alexandre wrote:

Yes, and it seems also that this code has more loops than it should. I got the following code working smoothly for plain floor collision (no slopes and no ceilings)

I was surprised at how well it worked! Unfortunately tho, the loop removed here served to command when gravity should reset and when the player should fall after pushing itself against a ceiling. If it's needed, try testing on the level included to better understand what I mean. I implemented your code and included some additions, here is the updated script:

DOWNLOAD

I followed your tips and multiplied the values by dt(), now it seems to be moving way more fluid than before. I also fixed the movement a bit, making it less slippery.


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#12 2018-06-17 17:51:33

Alexandre
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From: Brazil
Registered: 2009-01-27
Posts: 3,279
Website

Re: [Questions and Showcase] Creating a platform character from scratch

Congratulations smile

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#13 2018-07-17 15:40:24

SynfigMaster91
Member
Registered: 2017-10-10
Posts: 144

Re: [Questions and Showcase] Creating a platform character from scratch

Is it possible making a 2D platform game like this? I mean, games like Mario, but not Sonic.

I'm planning to make a game inspired on Mickey Mania.

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#14 2018-07-17 17:39:17

Alexandre
Administrator
From: Brazil
Registered: 2009-01-27
Posts: 3,279
Website

Re: [Questions and Showcase] Creating a platform character from scratch

SynfigMaster91 wrote:

I'm planning to make a game inspired on Mickey Mania.

I believe the easiest way to do it is to use the built-in physics of the engine. Set the slope factor to zero (in the .chr file) and don't use circular bricks.

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#15 2018-07-19 14:53:47

SynfigMaster91
Member
Registered: 2017-10-10
Posts: 144

Re: [Questions and Showcase] Creating a platform character from scratch

Alexandre wrote:
SynfigMaster91 wrote:

I'm planning to make a game inspired on Mickey Mania.

I believe the easiest way to do it is to use the built-in physics of the engine. Set the slope factor to zero (in the .chr file) and don't use circular bricks.

How do I do that?

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