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Update 2:

Let me further explain my problem since I think that i didn't make it clear enough: The Y-coordinates on the bottom of my screen should be 0. Instead it is the height of my screen. That means the "higher" i touch/click the screen the less my y-coordinate gets. Above that the origin is not inside my screen, atleast not the 0 y-coordinate.

Original post:

I'm currently developing a tower defence game for fun by using LibGDX. There are places on my map where the player is or is not allowed to put towers on. So I created different ArrayLists holding rectangles representing a tile on my map. (towerPositions)

for(int i = 0; i < map.getLayers().getCount(); i++) {
            curLay = (TiledMapTileLayer) map.getLayers().get(i);

            //For all Cells of current Layer
            for(int k = 0; k < curLay.getWidth(); k++) {
                for(int j = 0; j < curLay.getHeight(); j++) {
                    curCell = curLay.getCell(k, j);

                 //If there is a actual cell
                if(curCell != null) {
                    tileWidth = curLay.getTileWidth();
                    tileHeight = curLay.getTileHeight();
                    xTileKoord = tileWidth*k;
                    yTileKoord = tileHeight*j;

                    switch(curLay.getName()) {

                     //If layer named "TowersAllowed" picked
                    case "TowersAllowed":
                        towerPositions.add(new Rectangle(xTileKoord, yTileKoord,  tileWidth, tileHeight));

// ... AND SO ON

If the player clicks on a "allowed" field later on he has the opportunity to build a tower of his coice via a menu. Now here is the problem: The towers render, but they render at wrong position. (They appear really random on the map, no certain pattern for me)

for(Rectangle curRect : towerPositions) {
            if(curRect.contains(xCoord, yCoord)) {

                //Using a certain tower in this example (left the menu out
                if(gameControl.createTower("towerXY")) {

                    //RenderObject is just a class holding the Texture and x/y coordinates
                    renderList.add(new RenderObject(new Texture(Gdx.files.internal("TowerXY.png")), curRect.x, curRect.y));
                }
            }
        }

Later on i render it:

game.batch.begin();
    for(int i = 0; i < renderList.size() ; i++) {
        game.batch.draw(renderList.get(i).myTexture, renderList.get(i).x, renderList.get(i).y);
    }
game.batch.end();

regards

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This is a well-known feature of libGDX: the Y-axis has 0 at the bottom of the screen, not the top. (This is to be more consistent with 3D coordinate systems, which do likewise.)

There are a couple of ways to "fix" this.

  1. Use a camera. You can transform the view.
  2. In your render method, calculate the Y position as screen.height - y - sprite.height. This is easier, and often, faster.

NB: I spent about two days trying the camera method last week, and it seems to draw inverted. I recommend the second option. You can get the screen height from Gdx.graphics.getHeight(), and the sprite height from the Texture instance.

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  • \$\begingroup\$ The Y-coordinate is at the bottom the height of the screen for me, not 0. \$\endgroup\$ – ACluelessGuy Jul 20 '14 at 14:57
  • \$\begingroup\$ My problem is that that the y-coordinates behave like they were upside down (if i go up the y coords decrease). Above that the y-coordinate of 0 is not in the screen. The top still has a y-coordinate of 116 .. \$\endgroup\$ – ACluelessGuy Jul 20 '14 at 15:03
  • \$\begingroup\$ Try my solution and see for yourself. If you want a second opinion, hit up Google and look for libgdx y-axis. \$\endgroup\$ – ashes999 Jul 20 '14 at 17:25
  • 1
    \$\begingroup\$ First, thanks for your help :) But that was NOT my problem. Nevermind I figured out the problem, I wrote: xKoord = camera.unproject(touchPos).x; yKoord = camera.unproject(touchPos).y - The first operation already unprojects the whole cam, the 2nd unprojects it twice ... I hate those problems ._. How can i mark this as solved? \$\endgroup\$ – ACluelessGuy Jul 20 '14 at 17:28
  • \$\begingroup\$ @ACluelessGuy click the button below to add an answer, document your own answer to the solution, and then click the grey checkbox next to your answer. \$\endgroup\$ – ashes999 Jul 21 '14 at 9:31

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