Picking Cells On an Isometric Grid

Check your tiles in the reverse order you render them. Stop when you detect the mouse was over a tile or over the elevation part of a tile(if your world isn't flat). That should give you the correct tile.

If you know the mouse position in the world, you can directly compute the cell by converting a floating point position(x,y) to an integer grid cell coordinate(x,y). This how you do that, assuming:

- the grid is composed of equally sized square cells (cellSize)
- the grid is defined by two floats: Min and Max
- you want to convert the position Pos(x,y) into a grid Cell(x,y)

Cell.x = (Pos.X + Max) * 1.0/cellSize
Cell.y = (Pos.y + Max) * 1.0/cellSize

If you are using the cells to optimize collision, rendering, AI, picking, etc., to speed things up a bit you'll want to save 1.0/cellSize until your grid changes. Also, if all points in the space are greater than (0.0, 0.0) you can omit the "+ Max" from all calculations.

Quote:

Original post by EJH You want to convert a floating point position(x,y) to an integer grid cell coordinate(x,y). This how you do that, assuming: - the grid is composed of equally sized square cells (cellSize) - the grid is defined by two floats: Min and a Max - you want to convert the position Pos(x,y) into a grid Cell(x,y) Cell.x = (Pos.X + Max) * 1.0/cellSize Cell.y = (Pos.y + Max) * 1.0/cellSize To speed things up a bit you'll want to save 1.0/cellSize until your grid changes. Also, if all points in the space are greater than (0.0, 0.0) you can omit the "+ Max" from all calculations.

Are min and max the limits of my grid? i.e in a 16x16 grid min would be 0 and Max would be 16?

And would that work on an isometric grid?

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Original post by ScottH87Are min and max the limits of my grid? i.e in a 16x16 grid min would be 0 and Max would be 16?

No, Min and Max would be the corners in floating point coordinates. (should have clarified that). For example, if you had a 10*10 grid of cellSizes 1000.0 between Min(-5000.0, -5000.0) and Max(5000.0, 5000.0).

Here's some code from one of my grid implementations, if this helps at all (C#):

Quote:

Original post by ScottH87And would that work on an isometric grid?

Yes. As with normal picking, cast a ray through the mouse pointer and intersect with the plane the grid is on. Convert that intersection position to a grid cell as above.

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Original post by EJH Quote: Original post by ScottH87Are min and max the limits of my grid? i.e in a 16x16 grid min would be 0 and Max would be 16? No, Min and Max would be the corners in floating point coordinates. (should have clarified that). For example, if you had a 10*10 grid of cellSizes 1000.0 between Min(-5000.0, -5000.0) and Max(5000.0, 5000.0). Here's some code from one of my grid implementations, if this helps at all (C#): *** Source Snippet Removed ***

I'm still not sure i understand. You say that this will only work for square cells. Do you mean isometrically square (diamond) or an actual square? Because an isometric square wouldnt fit in an actual square.

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Original post by ScottH87I'm still not sure i understand. You say that this will only work for square cells. Do you mean isometrically square (diamond) or an actual square? Because an isometric square wouldnt fit in an actual square.

Yeah this is for a perfectly square grid. If your grid cells aren't square it won't work. =(

Ah this wont work for me then. Thanks anyway though. Could anybody else help with this?

What is the final orientation of your entire map? Is it in the shape of a diamond (like Age of Empires), or a square (like Starcraft)? If it's a square I have some code at home that may help (i'm at work now).

Here is a brief overview of what I did (from what I remember, it's been a while since I worked on it).
Below is a set of tiles I pulled off the gamedev article and modified slightly as a reference. You need to think of your 'Mask Tiles' as the pink square grid. I'm also assuming that you are numbering your cells in the same way they are in the gamedev article you linked.

For my example I'll use:
TileWidth = 32;
TileHeight = 16;
MapX = 70;
MapY = 26;

Once you have the map coords, divide these by the width and height of your tiles and cast as integers (to truncate the decimal).
MaskX = MapX / TileWidth; // MaskX = 2
MaskY = MapY / TileHeight; // MaskY = 1
Now you need to get the x and y position that relate to the position inside the mouse map cell. Do this with the Modulo operator.
MouseMapX = MapX % TileWidth; // 6
MouseMapY = MapY % TileHeight; // 10

Now, we know that the map location we clicked on is inside the cell 2,1 (in the pink grid). Now, look at your mouse map at position 6,10. I believe this stays in the current 2,1 cell (doing this all off the top of my head).
Now we have to take the 2,1 cell and figure out which col,row that relates to on your map.
I think I did it as follows:
The columns are the same, so the map column is also 2.
To get rows, multiply the MaskY by 2.
So your final map cell location is 2, 2.

I'm pretty sure that is correct. I'll check it again when I get home. Let me know if it's confusing or if you see any mistakes.

Iso Cell Selecting

What type of grid co-ordinates are you using, I'm having trouble as the way I did the isometric view was rotating the tiles. The tiles are 128x128 and about 180x90 in isometric:


glRotatef(60, 1, 0, 0);
glRotatef(45, 0, 0, 1):


The Camera co-ords are the coordinates of the current player multiplied by 128.

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