Why is rendering so slow?[BUG]

[Bhavya031]

Describe the bug
Why does rendering a scene take this long? Am I this stupid to figure it out? Because all the other code works like a charm, but when it comes to rendering, why does this take so long? Also, why doesn’t raycasting use the GPU? There’s an option for parallel processing, but it is only for the CPU because it doesn’t use the GPU. This render has been rendering for 5 hours and is still going. I switched to a VM with an A100 and 16 vCPUs, 40GB GPU RAM, and 60GB memory, but it’s the same story. How can I speed this up?

Session Info
Include the output of the sessionInfo() function here. Issues will be closed without providing this as a minimum.

R version 4.1.2 (2021-11-01)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 22.04.5 LTS

Matrix products: default
BLAS:   /usr/lib/x86_64-linux-gnu/blas/libblas.so.3.10.0
LAPACK: /usr/lib/x86_64-linux-gnu/lapack/liblapack.so.3.10.0

locale:
 [1] LC_CTYPE=C.UTF-8       LC_NUMERIC=C           LC_TIME=C.UTF-8       
 [4] LC_COLLATE=C.UTF-8     LC_MONETARY=C.UTF-8    LC_MESSAGES=C.UTF-8   
 [7] LC_PAPER=C.UTF-8       LC_NAME=C              LC_ADDRESS=C          
[10] LC_TELEPHONE=C         LC_MEASUREMENT=C.UTF-8 LC_IDENTIFICATION=C   

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
 [1] magick_2.8.5     rayshader_0.37.3 lubridate_1.9.3  forcats_1.0.0   
 [5] stringr_1.5.1    dplyr_1.1.4      purrr_1.0.2      readr_2.1.5     
 [9] tidyr_1.3.1      tibble_3.2.1     ggplot2_3.5.1    tidyverse_2.0.0 
[13] geodata_0.6-2    sf_1.0-18        elevatr_0.99.0   terra_1.7-83    

loaded via a namespace (and not attached):
 [1] rgl_1.3.1          Rcpp_1.0.13        lattice_0.20-45    png_0.1-8         
 [5] prettyunits_1.2.0  class_7.3-20       digest_0.6.37      foreach_1.5.2     
 [9] utf8_1.2.4         R6_2.5.1           rayvertex_0.11.4   e1071_1.7-16      
[13] httr_1.4.7         pillar_1.9.0       rlang_1.1.4        progress_1.2.3    
[17] curl_5.2.3         raster_3.6-30      htmlwidgets_1.6.4  munsell_0.5.1     
[21] proxy_0.4-27       compiler_4.1.2     xfun_0.48          pkgconfig_2.0.3   
[25] base64enc_0.1-3    htmltools_0.5.8.1  tidyselect_1.2.1   rayrender_0.34.3  
[29] progressr_0.14.0   codetools_0.2-18   fansi_1.0.6        crayon_1.5.3      
[33] tzdb_0.4.0         withr_3.0.1        wk_0.9.4           grid_4.1.2        
[37] jsonlite_1.8.9     gtable_0.3.5       lifecycle_1.0.4    DBI_1.2.3         
[41] pacman_0.5.1       magrittr_2.0.3     units_0.8-5        scales_1.3.0      
[45] KernSmooth_2.23-20 cli_3.6.3          stringi_1.8.4      sp_2.1-4          
[49] doParallel_1.0.17  generics_0.1.3     vctrs_0.6.5        s2_1.1.7          
[53] iterators_1.0.14   tools_4.1.2        rayimage_0.11.0    glue_1.8.0        
[57] hms_1.1.3          parallel_4.1.2     fastmap_1.2.0      slippymath_0.3.1  
[61] timechange_0.3.0   colorspace_2.1-1   classInt_0.4-10    knitr_1.48

Reproducible Example

# 1. LIBRARIES
#-------------

install.packages("pacman")
pacman::p_load(
    terra,
    elevatr,
    sf,
    geodata,
    tidyverse,
    rayshader
)

# 2. COUNTRY BORDERS
#-------------------

path <- getwd()

country_sf <- geodata::gadm(
    country = "CHE",
    level = 0,
    path = path
) |>
    sf::st_as_sf()

# 3. DOWNLOAD RIVERS
#-------------------

url <- "https://data.hydrosheds.org/file/HydroRIVERS/HydroRIVERS_v10_as_shp.zip"
destfile <- basename(url)

download.file(
    url = url,
    destfile = destfile,
    mode = "wb"
)

unzip(destfile)

# 4. LOAD RIVERS
#---------------

filename <- list.files(
    path = "HydroRIVERS_v10_as_shp",
    pattern = ".shp",
    full.names = TRUE
)

country_bbox <- sf::st_bbox(country_sf)

# xmin      ymin      xmax      ymax
#  5.956063 45.817059 10.495112 47.808483

bbox_wkt <- "POLYGON((
    5.956063 45.817059,
    5.956063 47.808483,
    10.495112 47.808483,
    10.495112 45.817059,
    5.956063 45.817059))"

country_rivers <- sf::st_read(
    filename,
    wkt_filter = bbox_wkt
) |>
    sf::st_intersection(
        country_sf
    )

plot(sf::st_geometry(country_rivers))

# 5. RIVER WIDTH
#---------------

sort(
    unique(
        country_rivers$ORD_FLOW
    )
)

crs_country <- "+proj=somerc +lat_0=46.9524055555556 +lon_0=7.43958333333333 +k_0=1 +x_0=600000 +y_0=200000 +ellps=bessel +towgs84=674.374,15.056,405.346,0,0,0,0 +units=m +no_defs +type=crs"

country_river_width <- country_rivers |>
    dplyr::mutate(
        width = as.numeric(
            ORD_FLOW
        ),
        width = dplyr::case_when(
            width == 3 ~ 16, 
            width == 4 ~ 14,
            width == 5 ~ 12,
            width == 6 ~ 10,
            width == 7 ~ 6,
            TRUE ~ 0
        )
    ) |>
    sf::st_as_sf() |>
    sf::st_transform(crs = crs_country)

# 6. DEM
#-------

dem <- elevatr::get_elev_raster(
    locations = country_sf,
    z = 9, clip = "locations"
)

dem_country <- dem |>
    terra::rast() |>
    terra::project(crs_country)

dem_matrix <- rayshader::raster_to_matrix(
    dem_country
)

# 7. RENDER SCENE
#----------------

dem_matrix |>
    rayshader::height_shade(
        texture = colorRampPalette(
            c(
                "#fcc69f",
                "#c67847"
            )
        )(128)
    ) |>
    rayshader::add_overlay(
        rayshader::generate_line_overlay(
            geometry = country_river_width,
            extent = dem_country,
            heightmap = dem_matrix,
            color = "#387B9C",
            linewidth = country_river_width$width,
            data_column_width = "width"
        ), alphalayer = 1
    ) |>
    rayshader::plot_3d(
        dem_matrix,
        zscale = 20,
        solid = FALSE,
        shadow = TRUE,
        shadow_darkness = 1,
        background = "white",
        windowsize = c(600, 600),
        zoom = .5,
        phi = 89,
        theta = 0
    )


rayshader::render_camera(
    zoom = .75
)

# 8. RENDER OBJECT
#-----------------

u <- "https://dl.polyhaven.org/file/ph-assets/HDRIs/hdr/4k/photo_studio_loft_hall_4k.hdr"
hdri_file <- basename(u)

download.file(
    url = u,
    destfile = hdri_file,
    mode = "wb"
)

file_name <- "switzerland-3d-elevation-rivers.png"

rayshader::render_highquality(
    filename = file_name,
    preview = TRUE,
    light = FALSE,
    environment_light = hdri_file,
    intensity_env = 1,
    interactive = FALSE,
    width = 3000,
    height = 3000,
    parallel=TRUE
)