Moving 'gp' out of LogicalVector args

src/grid-renderer.h

@@ -58,7 +58,7 @@ class GridRenderer {
       m_grobs.push_back(
         raster_grob(
           image, NumericVector(1, x), NumericVector(1, y),
-          NumericVector(1, width), NumericVector(1, height), LogicalVector(1, interpolate, gp)
+          NumericVector(1, width), NumericVector(1, height), LogicalVector(1, interpolate), gp
         )
       );
     }

src/grid.cpp

@@ -61,6 +61,31 @@ List raster_grob(RObject image, NumericVector x_pt, NumericVector y_pt, NumericV
     stop("Function raster_grob() is not vectorized.\n");
   }
 
+  if (gp.isNULL()) { 
+    gp = gpar_empty(); 
+  }
+
+  /*
+   During the test in line 93 of test-grid-renderer.R:
+      "grid_renderer_raster(r, logo, 10, 10, width, height)"
+   that call will end up here; and when there is no "gp" param, then gp ends up
+   here as an empty list rather than NULL. But when this function returns an
+   empty R list in the "gp" element (line 114 below), then grid::grid.draw will
+   fail because it is expecting that gp element to be a gpar object instead.
+   So we need to set gp to gpar_empty().
+   [I made this code to test for an empty list using chatgpt]
+   */
+  if(TYPEOF(gp) == VECSXP) {
+    // Convert the variable to a list
+    List list_gp(gp);
+    // Check if the list is empty
+    if(list_gp.size() == 0) {
+      // uncomment this to see that grid_renderer_raster will send an empty list
+      // Rcout << "gp is an empty list\n";
+      gp = gpar_empty();
+    }
+  }
+
   // need to produce a unique name for each grob, otherwise grid gets grumpy
   static int tg_count = 0;
   if (name.isNULL()) {

tests/testthat/test-grid-constructors.R

@@ -100,7 +100,7 @@ test_that("raster_grob", {
     )
   )
 
-  # interpolate is set as requested, gp default is NULL
+  # interpolate is set as requested, gp is set to gpar() if not provided
   expect_identical(
     raster_grob(image, 10, 20, 50, 40, interpolate = FALSE, name = "abc"),
     rasterGrob(
@@ -109,7 +109,7 @@ test_that("raster_grob", {
       width = unit(50, "pt"), height = unit(40, "pt"),
       hjust = 0, vjust = 0,
       interpolate = FALSE,
-      gp = NULL,
+      gp = gpar(),
       name = "abc"
     )
   )