Demo - Translating C code to R code

library(cairocore)

C Code for ‘Cairo Hello world’ example from FAQ

This example was taken from the CairoGraphics FAQ

#include <cairo.h>

int main (int argc, char *argv[]) {
  cairo_surface_t *surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32, 240, 80);
  cairo_t *cr = cairo_create (surface);
  
  cairo_select_font_face (cr, "serif", CAIRO_FONT_SLANT_NORMAL, CAIRO_FONT_WEIGHT_BOLD);
  cairo_set_font_size (cr, 32.0);
  cairo_set_source_rgb (cr, 0.0, 0.0, 1.0);
  cairo_move_to (cr, 10.0, 50.0);
  cairo_show_text (cr, "Hello, world");
  
  cairo_destroy (cr);
  cairo_surface_write_to_png (surface, "hello.png");
  cairo_surface_destroy (surface);
  return 0;
}

Equivalent R Code for ‘Cairo Hello world’

  • Remove type specification for assignment to variables, as this is not valid syntax in R

  • Remove trailing semi-colons. Not essential to remove, but it looks nicer

  • prefix enums (like CAIRO_FONT_SLANT_NORMAL) with the name of the enum they are contained in. (there is a helper function called enum_find() to help do this)

  • cairo_destroy() and other memory management functions do nothing in R. They can still be in your code, they just don’t do anything except print a warning message.

  • We can save the image to a PNG file, or we can view the surface directly by fetching the surface as a raster and plotting it

library(cairocore)

# enum_find('CAIRO_FORMAT_ARGB32')
surface = cairo_image_surface_create (cairo_format_t$CAIRO_FORMAT_ARGB32, 240, 80)
cr = cairo_create (surface)

cairo_select_font_face (cr, "serif", cairo_font_slant_t$CAIRO_FONT_SLANT_NORMAL, cairo_font_weight_t$CAIRO_FONT_WEIGHT_BOLD)
cairo_set_font_size (cr, 32.0)
cairo_set_source_rgb (cr, 0.0, 0.0, 1.0)
cairo_move_to (cr, 10.0, 50.0)
cairo_show_text (cr, "Hello, world")

# cairo_surface_write_to_png (surface, "hello.png")
raster_out <- cairo_image_surface_get_raster(surface)
plot(raster_out)