Your glVertex3f-calls look weird. You are drawing quads which get bigger and bigger and this results in z-fighting like on your screenshot.
For example: with (-tileSize*i) you are going left but with (tileSize*i)+tileSize you are going right and therefore stretching the whole quad with each iteration.

Reconsider how you have to place your vertices in order to achieve your goal - try to remove the minus-operators.
Later on you can try to draw triangle-strips which are faster than quads, and even use indices and vertexbuffers.

Best regards
- Martin

Your glVertex3f-calls look weird. You are drawing quads which get bigger and bigger and this results in z-fighting like on your screenshot.
For example: with (-tileSize*i) you are going left but with (tileSize*i)+tileSize you are going right and therefore stretching the whole quad with each iteration.

Reconsider how you have to place your vertices in order to achieve your goal - try to remove the minus-operators.
Later onyou can try to draw triangle-strips which are faster than quads, and even use indices and vertexbuffers.

Best regards
- Martin

Your glVertex3f-calls look weird. You are drawing quads which get bigger and bigger and this results in z-fighting like on your screenshot. 

For example: with (-tileSize*i) you are going left but with (tileSize*i)+tileSize you are going right and therefore stretching the whole quad with each iteration.

 

Reconsider how you have to place your vertices in order to achieve your goal - try to remove the minus-operators.

 

Later you can try to draw triangle-strips which are faster than quads, and even use indices and vertexbuffers.

 

Best regards

- Martin