Find something strange with Func: drawFillConvexPoly()

[BiancaZYCao]

Background & Problem Description

I am doing Affine Transform in a Triangle Mesh. After that, I create a mask Mat so that I can copy the updated triangular region to the output image further.

The mask.drawFillConvexPoly() helps me determine the triangle area:

const cv = require("opencv4nodejs") 
let mask = new cv.Mat(100, 99, cv.CV_32FC4)
const points = []
points.push(new cv.Point2(10, 10))
points.push(new cv.Point2(80, 80))
points.push(new cv.Point2(50, 10))
mask.drawFillConvexPoly(points, new cv.Vec(1.0, 1.0, 1.0), 16, 0)

If everything is correct (e.g. let mask = new cv.Mat(100, 100, cv.CV_32FC4) is just okay) , the mask should be exactly a white triangle with a black background. However, in this case, cv.imshow("mask", mask) return this:

I wanna know the reason and how to avoid this if this is not a bug.

Possibilities

• DataType of mask Mat? : (I tried cv.CV_8UC3 still got this problem)
• DataType of point2? : It seems we do not have point2f & point2i in opencv4nodejs
• cv.imshow(...) not accurate?
• Number of channels?
• points should be inside the Mat: I already avoid this as u can see in my sample code. ...

What I tried

I tried to print out some data value of pixels in the mask:

let maskAsArr = mask.splitChannels()[0].getDataAsArray()
console.log(maskAsArr[30].slice(0, 50))

It turns out some values are negative / extremely large such as 8388608, -2.3543017412042005e+21, 4.134773263365008e-38, instead of 0 or 1. After casting them into 0, most abnormal points disappear:

let maskAsArr = mask.splitChannels()[0].getDataAsArray()
    .map(function (col) {
      col = col.map(function (val) {
        if (val != 0 && val != 1) {
          val = 0
        }
        return val
      })
      return col
    })

Environment Info

OpenCV version : 4.4.0 OS: MacOSX