GameMaker mp_grid checking if path is blocked

[asollazzo]

Hi, im pretty new to the forums and GMS2 in general and am building my first game which is a hybrid tower defense / top down shooter. In the game the enemies are using a mp_grid to path through the level towards a goal and can react to walls being placed dynamically and adjust their path.

My problem comes with the path being blocked by a placed wall, i can make it detect when a wall has been placed that blocks the path and have it be deleted fine, but ideally i would when a potential placed wall will block the path that it will display as red before even placing it.

I cant figure out how to do it or even if it is possible.

Ive attached a pic of the game (all graphics are temporary) that shows a green square on the cursor indicating a potential wall placement in a position that will block the path for reference.

 

[YellowAfterlife]

mp_grid_path returns whether it was possible to find a path from x1y1 to x2y2, so you can use that

 

[asollazzo]

mp_grid_path returns whether it was possible to find a path from x1y1 to x2y2, so you can use that

Yup im using that at the moment to check when placing a wall if it has actually blocked the path and to remove it. Im just unsure of how to check it before ive actually placed it and to show the square as red to show that you cannot place a wall there.

 

[rIKmAN]

You could iterate through the points in the path and see if any of them pass through the position / cell you want to place your wall.

 

[asollazzo]

You could iterate through the points in the path and see if any of them pass through the position / cell you want to place your wall.

Sounds like a good idea but how do i determine if the point in the path meeting my cursor is one that will block the path or not and not merely being on the path ?

 

[rIKmAN]

Sounds like a good idea but how do i determine if the point in the path meeting my cursor is one that will block the path or not and not merely being on the path ?

Ah I misunderstood what you meant.

In that case you could mark the cell your cursor was over as blocked, then generate a path with this block data included (only do this once when the cursor moves to a new block), and then if a path is still able to be generated allow the block to be placed, or if the path cannot be generated then do not allow the placing of the block.

Remember to clean up after yourself and delete the extra path, free the blocked cell if the path was invalid etc.

 

[YellowAfterlife]

Yup im using that at the moment to check when placing a wall if it has actually blocked the path and to remove it. Im just unsure of how to check it before ive actually placed it and to show the square as red to show that you cannot place a wall there.

You can mp_grid_add_cell/mp_grid_add_rectangle to add the wall to grid (and get rid of it via mp_grid_clear afterwards) without placing the instance

 

[asollazzo]

Ah I misunderstood what you meant.

In that case you could mark the cell your cursor was over as blocked, then generate a path with this block data included (only do this once when the cursor moves to a new block), and then if a path is still able to be generated allow the block to be placed, or if the path cannot be generated then do not allow the placing of the block.

Remember to clean up after yourself and delete the extra path, free the blocked cell if the path was invalid etc.

Will give that a try

You can mp_grid_add_cell/mp_grid_add_rectangle to add the wall to grid (and get rid of it via mp_grid_clear afterwards) without placing the instance

Wouldnt that essentially be adding the wall/block just without the graphic and end up blocking the path aslong as my cursor is there or am i misunderstanding how it works ?

 

[rytan451]

You add the wall to the grid, check if it blocks the path, then remove the wall from the grid.

 

[asollazzo]

Thanks for the help guys, but i think this might be beyond my abilities, no matter how i try to do the block testing it ends up actually blocking the enemies path and causing problems. The only way i havent tried is having a second mp_grid just for testing blockages without effecting the enemies movement but im not sure thats ideal or viable.