// blocks the ball could might be touching
    struct {int x,y;} blocks[] =
    {
        {ball_gx+0,ball_gy+0}, {ball_gx+1,ball_gy+0},
        {ball_gx+0,ball_gy+1}, {ball_gx+1,ball_gy+1},
    };

    // handle collisions
    for(int i=0; i<LENGTH(blocks); i++)
    {
        // shorten names for readability (blk_x is x position, gx is grid x index)
        int gx=blocks[i].x, gy=blocks[i].y;
        int blk_x=gx*BLOCK_WIDTH, blk_y=gy*BLOCK_HEIGHT, blk_w=BLOCK_WIDTH, blk_h=BLOCK_HEIGHT;

        // check if there's a collision in the grid
        if(gx<0 || gx>=GRID_WIDTH || gy<0 || gy>=GRID_HEIGHT) continue;
        if(!state->grid[gx+gy*GRID_WIDTH]) continue;

        int x_overlap = ball->x+ball->w >= blk_x  &&  ball->x < blk_x+BLOCK_WIDTH;
        int y_overlap = ball->y+ball->h >= blk_y  &&  ball->y < blk_y+BLOCK_HEIGHT;
        int collision = x_overlap&&y_overlap;

        if(!collision) continue;

        // decrement the block strength
        state->grid[gx+gy*GRID_WIDTH]--;

        // get center point of block and distance from ball to decide which side ball is touching
        float blk_cx=blk_x+blk_w/2.0f, blk_cy=blk_y+blk_h/2.0f;
        float dx = cx-blk_cx, dy = cy-blk_cy;

        int side='\0';
        side = fabsf(dx)>fabsf(dy)? (dx<0? 'l':'r') : (dy<0? 'u':'d');

        switch(side)
        {
            case 'l': ball->x = blk_x - ball->w;    if(ball->xv > 0.0f) ball->xv = -ball->xv; break;
            case 'r': ball->x = blk_x + blk_w;      if(ball->xv < 0.0f) ball->xv = -ball->xv; break;
            case 'u': ball->y = blk_y - ball->h;    if(ball->yv > 0.0f) ball->yv = -ball->yv; break;
            case 'd': ball->y = blk_y + blk_h;      if(ball->yv < 0.0f) ball->yv = -ball->yv; break;
        }
        break;
    }