How to use layer_fun to add a box in the aim areas

[yanglq-bioinfo]

hello
my code as follows：

Heatmap(expr,
col = colorRamp2(c(-5,0,5), c("navy","#F2F2F2","firebrick3")),
cluster_rows = F,
cluster_columns = F,
na_col = "white",
column_split = factor(anno$module),
row_split = gene_group$module,
column_title_rot = 90,
column_gap = unit(0.5, "mm"),
row_gap = unit(0.5, "mm"),
# column_title=NULL,
# row_title=NULL,
border = F,
use_raster = T,
heatmap_legend_param = list(title = "expr", at = seq(-4, 4, 2),color_bar = "continuous"),
top_annotation = ha,
layer_fun = function(j, i, x, y, width, height, fill){
v = pindex(expr, i, j)
if(min(i)==min(j)){
grid.rect(gp = gpar(lwd = 1, fill = "transparent" ,col="black",lty=2))
}
},
show_column_names = F,
show_row_names = F)

and I get this fig

However My ideal result would be like this

How Do I modify this code?