Translating mouse coordinates to a world position

[behindcurtain3]

Hey, I've got another question. I want to get the tile that is clicked on by the mouse but I'm having trouble translating the mouse coordinates into world coordinates. Each time I do it seems to be off a little, possibly related to the zoom?

[MichaelAquilina]

There isnt any method currently within the engine that does this (but will definitely be a feature i plan on adding). Could you show me the code your using to translate your coordinates to see if i catch anything that is off? The current zoom code can sometimes cause problems due to loss of information when converting float values to integers, so there are a number of workarounds used to fix this.

[behindcurtain3]

I don't have the exact line on me right now but its something like this

worldX = mouseState.X - (viewPort.pxDispX * viewPort.ActualZoom);
worldY = mouseState.Y - (viewPort.pxDispY * viewPort.ActualZoom);

Edit: I have tried with and without the zoom but to no avail.

[MichaelAquilina]

That seems to be relatively correct. However, you would probably need to multiply the mouse coordinate with the mouseState too:

worldX = (mouseState.X - viewPort.pxDispX) * viewPort.ActualZoom;
worldY = (mouseState.Y - viewPort.pxDispY) * viewPort.ActualZoom;

If this doesnt work either, then there is probably a bug in some part of the code that is causing this inaccuracy.

[behindcurtain3]

Hmm that doesn't work either. Here is the closest I've come (doesn't work on all zoom levels):

float worldX = mouseState.X + viewPort.pxTopLeftX + viewPort.pxDispX;
float worldY = mouseState.Y + viewPort.pxTopLeftY + viewPort.pxDispY;

int tileX = (int)(worldX / viewPort.pxTileWidth);
int tileY = (int)(worldY / viewPort.pxTileHeight);

This gets really close to the correct tile / world position but isn't exact (half the time it does get the correct tile). I tried to multiply by the ActualZoom and it makes it further off. What exactly does the Displacement represent?

[behindcurtain3]

Actually scratch the above post, this works better but its off by just enough to mess the tile detection up in some cases:

float worldX = (mouseState.X + viewPort.pxTopLeftX + viewPort.pxDispX) / viewPort.ActualZoom;
float worldY = (mouseState.Y + viewPort.pxTopLeftY + viewPort.pxDispY) / viewPort.ActualZoom;

int tileX = (int)(worldX / engine.Map.TileWidth);
int tileY = (int)(worldY / engine.Map.TileHeight);

[MichaelAquilina]

Your code is actually correct in using pxTopLeftX/Y rather than pxDispX/Y because i forgot what its use was for (the current zoom code is a bit messy admittedly). Here is an overview of what each value in ViewPortInfo represents:

• pxTileWidth / pxTileHeight - the actual width and height of tiles being drawn to the screen after the original zoom value has been applied.
• ActualZoom : The comments on this are actually pretty accurate: 'because there is a loss of data during the conversion from Map.pxTileWidth * Zoom -> (int), we need to determine what was the actual level of zoom that was applied to the tiles and use that instead. Using this calculation instead of the zoom value ensures that entities that will be drawn will be placed correctly on the screen.'
• pxWidth / pxHeight: the actual width and height of the portion of the world being shown on the screen. Calculated as follows: \ viewPortInfo.pxHeight = destRectangle.Height / viewPortInfo.ActualZoom;
• pxTopLeftX / pxTopLeftY: The top left X and Y coordinate in world map coordinates.
• TileCountX / TileCountY: The x-width and y-height of the tiles to be rendered to to the screen.
• pxDispX / pxDispY: The amount of decimal disposition that occurs because the top left coordinates of the screen are partially showing a tile. This value is used to allow smooth scrolling so this needs to be included in your calculations when converting.
• pxViewPortBounds: Rectangle object representing the viewport bounds of the world map.

From revising the above, the code you require probably needs to look something like this:

worldX = (mouseState.X *ActualZoom) + pxTopLeftX + pxDispX;

I do not have the ability to test that theory right now because i dont have the application accessible at the moment but you could try see if that gets you any closer.

Hope that helped.

[MichaelAquilina]

float worldX = (mouseState.X + viewPort.pxTopLeftX ) / viewPort.ActualZoom + viewPort.pxDispX;
float worldY = (mouseState.Y + viewPort.pxTopLeftY ) / viewPort.ActualZoom + viewPort.pxDispY;

int tileX = (int)(worldX / engine.Map.TileWidth);
int tileY = (int)(worldY / engine.Map.TileHeight);

Try that. I think pxDispX and pxDispY are already affected by ActualZoom as far as i remember.

[MichaelAquilina]

Hi, please take a look at my latest commits, they should solve your problem :)

There is now a method in ViewPortInfo called GetWorldCoordinates() which accepts a Point location on the viewport which will be translated accordingly.

Using these resultant coordinates you can just do:

int tileX = (int) (worldCoord.X / engine.Map.TileWidth);
int tileY = (int) (worldCoord.Y / engine.Map.TileHeight);

I also added detailed docstrings for each property in ViewPortInfo so that they can be more easily understood.

Hope this helps!

[behindcurtain3]

Cheers, it works perfectly!

[behindcurtain3]

Hey, wanted this implemented so bad because I added AStar pathfinding. Check the commits here: 7e41a77 and 2565445

[MichaelAquilina]

Cool stuff, i was planning on starting an implementation sometime soon but i was sidetracked by other things (the todo list seems endless!). Is there a branch on your fork where i can pull your changes form to see what youve done and test it?