bordor_color only works when providing filename

I want black border between my cells. This works fine when calling pheatmap() with the filename argument. However, when using the png() function directly or when viewing the image interactively in rstudio, the borders are not being drawn.

Example:

library(pheatmap)
sample_matrix <- matrix(nrow=200, ncol=200, data=1:40000)

png('matrix1.png', height=3100, width=3100)
pheatmap(sample_matrix, border_color='black')
dev.off()

pheatmap(sample_matrix, border_color='black', filename='matrix2.png', height = 10, width=10)

matrix1.png: matrix1

matrix2.png: matrix2

raivokolde / pheatmap

bordor_color only works when providing filename #55