importing collision masks possible?

[Tanja]

i talk about making custom collision masks (black/white) for sprites with a graphic editor and importing them.
advantages: some regions of a big sprite may be conducting, so a small player can "penetrate" special regions. instead of be blocked by the whole enemy.
just a suggestion.

[Tanja]

hey wait. one could make dozens of self defined tileshapes with that. without scripting!!!

[bluemonkmn]

Two issues: tile shapes and sprite masks:

1) I considered making tile shapes visually editable in SGDK2, and I think there was even a version way back during pre-alpha that would allow arbitrary shapes, but I changed my mind about how tile shapes would work after that.  I found that tile shapes could be highly optimized by defining them with simple formulas instead of pixels.  Now when SGDK2 tests for "GetTopSolidPixel" on a tile, the answer can be provided by a simple 1-line formula.  If the tile shape was defined with arbitrary pixels, then there would be much more work to do.  I had code that would analyze and pre-calculate all the solidity values.  (Pre-calculate the result of GetTopSolidPixel for tile size 16x16 for left=0 and right=15, then for left=1 and right=14, etc.)  But the new mechanism is so much simpler I think it's much better.  The number of tile shapes is usually very limited, so I didn't feel too bad about requiring coding if you want to add new tile shapes.  In version 1 it was not even possible, so SGDK2 is at least one step better.  Also, I don't want to make it too easy to add too many tile shapes because I don't think checking for a tile shape is very highly optimized.  So if you get way too many tile shapes, things might run a little slowly (I don't know... I think it would take a lot of tile shapes and a lot of sprites checking the tiles to make a problem, but I'm still nervous).

2) Sprite masks: My hope was that allowing an the mask to be generated from alpha values would allow you to define the solidity by fiddling with the alpha levels of your image instead of needing to define the mask separately.  Of course using the alpha to define the mask does require that all your solid pixels be at least as opaque as your empty pixels.  Is that a problem?  Could you make the empty areas of your sprite just 1 bit more transparent than the other areas, and set the mask level to 254 or something?  Nobody would be able to tell the difference between alpha=254 vs alpha=255.

[Tanja]

1. i guessed that and understand it.
but: the player will be never able to walk on soft curved hills and slopes... 
(okay... when the tiles are small enough... but look at my graphics and tell me to cut them into 16 pieces each!)

2. of course the empty space around a sprite is very good covered with your method. i like that method, really. it makes defining col. masks really easy.
but i thought of ... say, a really huge dragon. ten times as big as your player. at the moment one can either be blocked by the dragon at a whole, or not.
imagine the dragon has a bright red orb at the end of his tail. but you can't reach this orb, because the whole dragon is between it and you.
now, the dragon has armor at his legs. the player can destroy the armor of the arms, then he can go "into" the dragon and destroy the armor of the legs. now the way is free.
note the three different masks i would import to achieve this.

i think this feature would make sense, when the sprites are so detailed that they have "fore- and backgrounds" where the player can walk between.

[durnurd]

As I said in another post just a few minutes ago somewhere else, you can, in fact, define curved hills if you just use sine and cosine functions when writing the solidity shape.  And remember, it's also possible for a game designer to completely rewrite the ReactToSolid function to their needs.

[Tanja]

to completely rewrite the ReactToSolid function to their needs.

do you mean the second part (with the dragon)?
now you say it.... hm. with tiles i could imagine changing the solidity after events. but for a sprite? can a sprite have a shape definition just like a tile?
eg. could i give the dragon the solid shape of an uphill tile?

[bluemonkmn]

ReactToSolid is only for making a sprite react to a tile.  Durnurd's comments were all about tile shapes.

It's possible to create the masks you showed above in three ways:
1) Make the legs slightly more transparent than the rest of the sprite when the armor has been removed (fill them with a color whose alpha is 253 instead of 255).  Then set the alpha mask level to 254.  If you make the difference small enough, then the player won't even notice that the legs are slightly transparent, but you will be able to have the mask shaped exactly how you want.
2) If the armor is a separate frame from the actual creatore, you could probably set the alpha modulation on the creature frames to 253 and leave the armor at 255 instead of setting the alpha level in the graphics editor.
3) Since it's so large, split it into multiple sprites.  The armor on the legs could be a separate sprite.  It's better to only check collisions with the armor sprites anyway because collision detection is slow if you have to check such a large sprite, and generating collision masks for large sprites takes more time an memory.

[Tanja]

ok, now i understand what you wanted to tell me about transparency in a further post  :nerd: