How to Crop a cuda.GpuMat in GoCV (opencv 4)? - opencv

Question

I am using GoCV (Open CV 4 bindings for go) and I want to crop an image represented as a cuda.GpuMat given an image.Rectangle.
With a regular gocv.Mat this operation is simple enough:
func Crop(src *gocv.Mat, rect image.Rectangle) *gocv.Mat {
res := src.Region(rect)
return &res
}
However, I do not see a similar Region method on the cuda.GpuMat in GoCv (some bindings are not implemented yet), nor do I see a region method in the C++ source/docs: https://docs.opencv.org/master/d0/d60/classcv_1_1cuda_1_1GpuMat.html.
I have managed to effectively crop using cuda.Remap as follows:
func Crop(src *cuda.GpuMat, rect image.Rectangle) *cuda.GpuMat {
rectWidth := rect.Dx()
rectHeight := rect.Dy()
dst := cuda.NewGpuMat()
map1 := gocv.NewMatWithSize(rectHeight, rectWidth, gocv.MatTypeCV32F)
defer map1.Close()
map2 := gocv.NewMatWithSize(rectHeight, rectWidth, gocv.MatTypeCV32F)
defer map2.Close()
offsetX := rect.Min.X
offsetY := rect.Min.Y
for x := 0; x < map1.Cols(); x++ {
for y := 0; y < map2.Rows(); y++ {
map1.SetFloatAt(x, y, float32(y+offsetY))
map2.SetFloatAt(x, y, float32(x+offsetX))
}
}
gmap1, gmap2 := cuda.NewGpuMat(), cuda.NewGpuMat()
defer gmap1.Close()
defer gmap2.Close()
gmap1.Upload(map1)
gmap2.Upload(map2)
cuda.Remap(*src, &dst, &gmap1, &gmap2, cuda.InterpolationDefault, cuda.BorderConstant, color.RGBA{0, 0, 0, 0})
return &dst
}
But after running some benchmarks this implementation is 1-2 orders of magnitude slower than gocv.Mat#Region.
Given that there is no Region method on cuda.GpuMat in GoCV or OpenCV4, what would be the most optimal equivalent operation?
I'm not too concerned if the GoCV bindings do not exist. I'm more interested in the OpenCV4 equivalent to Region for a GpuMat.
UPDATE
I have found another method of cropping a cuda.GpuMat, but it is also about an order of magnitude slower than gocv.Mat#Region.
func Crop2(src *cuda.GpuMat, rect image.Rectangle) *cuda.GpuMat {
rectWidth := rect.Dx()
rectHeight := rect.Dy()
dst := cuda.NewGpuMat()
sz := image.Point{
X: rectWidth,
Y: rectHeight,
}
cuda.Rotate(*src, &dst, sz, 0, -float64(rect.Min.X), -float64(rect.Min.Y), cuda.InterpolationDefault)
return &dst
}