java - Filling a square with tiles -

i have 2d tile game trying create brush sizes for. currently, code looks this:

if (ismouseclicked0) {     int grid_x = math.round(mousex / blocksize);     int grid_y = math.round(mousey / blocksize);     (int x = 0; x < brushsize; x++) {         (int y = 0; y < brushsize; y++) {             world.setat(grid_x, grid_y, b[inventoryselect]);             grid_x += x;             grid_y += y;         }     } } 

the setat() method looks this:

public void setat(int x, int y, blocktype b) {     if (x <= display.getwidth() / blocksize && y <= display.getheight() / blocksize) {         blocks[x][y] = new baseblock(b, x * blocksize, y * blocksize);     }     render(); } 

this produces output:

the tile above first tile on top left clicked mouse, can see next tile isn't rendering. i've been @ hours, i'm missing simple. help?

edit: brush size 2, should creating 4 tiles. blocksize 32, it's how big blocks are.

the problem :

grid_x += x; grid_y += y; 

you moving diagonally. might work better :

    (int x = 0; x < brushsize; x++) {         (int y = 0; y < brushsize; y++) {             world.setat(grid_x + x, grid_y + y, b[inventoryselect]);         }     }