Tile coordinate in isometric tilemap

cocos2d-x C++
#1

Hello,

I am currently trying to convert world coordinates to isometric tilemap coordinates.
After reading many topics I found, that none was a solution to my problem, so I created my own transformation.
From my understanding, the coordinate system from isometric tilemaps is like following:

  • x-axis goes from top corner to right corner
  • y-axis goes from top corner to left corner.

The tilemap is located as a child at initial position in the TileMapLayer. This TileMapLayer gets moved around to “scroll” the tilemap and has following helper method:

Code 
Vec2 TileMapLayer::getTilePositionFrom(const Vec2 &worldPos) {
    auto nodePos = _tileMap->convertToNodeSpace(worldPos);
    auto boxSize = _tileMap->getBoundingBox().size;
    auto width = boxSize.width;
    auto height = boxSize.height;

    // move to origin (translation)
    nodePos.x -= width / 2;
    nodePos.y -= height;

    // align x-axis (rotation)
    auto angle = atan(height / width);
    auto length = nodePos.length();
    nodePos.x += cos(angle) * length;
    nodePos.y += sin(angle) * length;

    // invert y-axis
    nodePos.y *= -1;

    // align y-axis (shearing/skewing)
    auto oppositeAngle = M_PI - 2 * angle;        // not everything is in radians
    auto sideLength = sqrt(width*width/4 + height*height/4);
    auto shear = tan(oppositeAngle) * sideLength;
    nodePos.x += shear * nodePos.y;

    nodePos.x = (int) nodePos.x;
    nodePos.y = (int) nodePos.y;

    // clamps to height / width of tilemap
    return clampToTileMapBounds(result);
}

After multiple draw-ups I can’t figure out my error.
At first I tried with the Mat4 transformation matrix, but it didn’t give the expected result.

Maybe the conversion to node space is wrong of some sort?
I tried many other conversions already.

Thank you for your help!

Best regards,
Julius