ToyGraphics uses the usual type of coordinate system in Computer graphics. Y-axis goes from up to down. X-axis goes from left to right. Top left corner has coordinates 0,0
Here is an article: Coordinate System of a Screen

The unit of measure is a pixel. Display resolution at Wikipedia.

You specify a point by pair of integer numbers, Int type in Kotlin. If you calculate a coordinate using floating-point arithmetics (Double type in Kotlin) then you have to use roundToInt() to round a Double number to Int. Example:

val distance = 10000.0
val screenRatio = 10.0
val x = distance/screenRatio.roundToInt()

Look at the example below and you see how it works.

package demos
import com.anysolo.toyGraphics.*

fun main() {
    val wnd = Window(800, 600)
    val gc = Graphics(wnd)

    gc.color =
    gc.drawRect(0, 0, 50, 50, fill = true)

    gc.color =
    gc.drawLine(25, 0, 25, wnd.height-1)

    gc.color =
    gc.drawLine(0, 25, wnd.width-1, 25)