Fix font size and offset calculations

// font-loader's API is too limitied to express "any sans-serif font, ideally monospace"

const FONT_NAME: &'static str = "arial";

const FONT_RESOLUTION: f64 = 100.0;

const DIGIT_ASPECT_RATIO: f64 = 0.71; // observed width/height

const MAX_DIGITS_SCALE: usize = 2; // don't increase digit size further when distance < 10

const FONT_RESOLUTION: f64 = 100.0; // glyph height in pixels

const BORDER_RADIUS: f64 = 0.03; // relative to tile_size

const TILE_MIN_PADDING: f64 = 0.1;

const SHOW_DIGITS: f64 = 3.0;

const TILE_MIN_PADDING: f64 = 0.08;

const INITIAL_TILE_SIZE: f64 = 50.0;

const BOARD_WIDTH: i32 = 20;

                piston_window::rectangle(tile.color(), [x,y,1.0,1.0], transform, gfx);

                if let Open(Some(path)) = *tile {

                    // number rendering

                    let as_str: &str = &path.distance.to_string()[..];//[..] converts String to str

                    let digits = as_str.len() as f64;//digits aren't unicode

                    let digit_height = 0.8;

                    let digit_width = 0.6;

                    let width = digit_width*SHOW_DIGITS;

                    let scale_fill = f64::max(digit_height, width) - TILE_MIN_PADDING - BORDER_RADIUS;

                    let bottom_padding = (1.0-digit_height/scale_fill) / 2.0;

                    let left_padding = (1.0-width/scale_fill) / 2.0  +  (digit_width/(scale_fill-TILE_MIN_PADDING)) * (SHOW_DIGITS-digits);

                    let scale_factor = 1.0 / (scale_fill*FONT_RESOLUTION);

                    let as_str: &str = &path.distance.to_string()[..];

                    let digits = as_str.len(); // digits aren't unicode

                    let show_digits = usize::max(digits, MAX_DIGITS_SCALE);

                    const AVAILABLE_DIGIT_HEIGHT: f64 = 1.0-2.0*(TILE_MIN_PADDING+BORDER_RADIUS);

                    const AVAILABLE_BOX_WIDTH: f64 = AVAILABLE_DIGIT_HEIGHT;

                    let available_digit_width = AVAILABLE_BOX_WIDTH / show_digits as f64;

                    let digit_height = f64::min(AVAILABLE_DIGIT_HEIGHT, 

                                                available_digit_width / DIGIT_ASPECT_RATIO);

                    let scale_factor = digit_height / FONT_RESOLUTION;

                    let digit_width = digit_height * DIGIT_ASPECT_RATIO;

                    let box_width = digit_width*digits as f64;

                    let bottom_padding = (1.0-digit_height) / 2.0;

                    let left_box_padding = (1.0-box_width) / 2.0;

                    let left_padding = left_box_padding;

                    // debugging rectangles

                    // piston_window::rectangle(color::hex("226688"), [x+(1.0-AVAILABLE_BOX_WIDTH)/2.0,y+(1.0-AVAILABLE_DIGIT_HEIGHT)/2.0,AVAILABLE_BOX_WIDTH,AVAILABLE_DIGIT_HEIGHT], transform, gfx);

                    // piston_window::rectangle(color::hex("2266aa"), [x+(1.0-AVAILABLE_BOX_WIDTH)/2.0,y+(1.0-AVAILABLE_DIGIT_HEIGHT)/2.0,available_digit_width,AVAILABLE_DIGIT_HEIGHT], transform, gfx);

                    // piston_window::rectangle(color::hex("668888"), [x+left_box_padding,y+bottom_padding,box_width,digit_height], transform, gfx);

                    // piston_window::rectangle(color::hex("6688aa"), [x+left_box_padding,y+bottom_padding,digit_width,digit_height], transform, gfx);

                    let char_pos = transform

                        .trans(x + left_padding,  1.0 + y - bottom_padding)

                        .scale(scale_factor, scale_factor);