How to find the coordinates of the buttons on a canvas, and click on them after using Java and Selenium?

I have an online calculator that i want to automate some operations for, like subtraction, division, etc. but the thing is that there are no elements since it is a canvas app calculator (link below). I'm wondering how can i click the buttons so im able to automate some operations?

The online calculator im trying to automate:

https://www.online-calculator.com/full-screen-calculator/

The canvas HTML code

<canvas id="canvas" width="335" height="434" style="position: absolute; display: block; background-color: rgb(255, 255, 255); width: 167.939px; height: 217px;"></canvas>

My Selenium-Java code

driver.get("https://www.online-calculator.com/full-screen-calculator/");
driver.manage().window().maximize();        
WebElement li = driver.findElements(By.tagName("iframe")).get(0);
driver.switchTo().frame(li);        
WebElement canv = driver.findElements(By.tagName("canvas")).get(0);
System.out.println(canv.getSize());
System.out.println(canv.getLocation());

try {
 Actions builder = new Actions(driver);
 builder.moveToElement(canv, x, y);
 builder.click();
 builder.perform();
    } catch (Exception e) 
    {
      // do nothing
    }

So as you see in above code, I still have to find the x and y of the operations i want to run. For ex, how can i find the coordinates of the buttons 10, 4 and the subtraction operation '-', if I want to calculate '10 - 4' and then validate that it is equal to 6. Any help would be highly appreciated. Thanks :)

Note: The canvas width, height and location will change if the window size changes ((Im thinking later of locking the window size so my tests are not flaky on different screens)).