oiiotool: allow expr IMG[x] syntax to allow user vars as well as img labels

Signed-off-by: Larry Gritz <lg@larrygritz.com>

Author: lgritz

src/doc/oiiotool.rst

@@ -123,12 +123,17 @@ contents of an expression may be any of:
   If there is no metadata whose name matches, the expression will not have any
   substitution made and an error will be issued.
 
-  The *imagename* may be one of: `TOP` (the top or current image), `IMG[i]`
-  describing the i-th image on the stack (thus `TOP` is a synonym for
-  `IMG[0]`, the next image on the stack is `IMG[1]`, etc.), or `IMG[name]`
-  to denote an image named by filename or by label name. Remember that the
-  positions on the stack (including `TOP`) refer to *at that moment*, with
-  successive commands changing the contents of the top image.
+  The *imagename* may be one of:
+
+  * `TOP` : the top or current image;
+  * `IMG[index]` : if `index` evaluates to an integer `i`, the i-th image on
+    the stack (thus `TOP` is a synonym for `IMG[0]`, the next image on the
+    stack is `IMG[1]`, etc.);
+  * `IMG[name]` : an image named by filename or by label name.
+
+  Remember that the positions on the stack (including `TOP`) refer to *at that
+  moment*, with successive commands changing the contents of the top image. If
+  the
 
   The *metadata* may be any of:
 

src/oiiotool/expressions.cpp

@@ -155,28 +155,61 @@ Oiiotool::express_parse_atom(const string_view expr, string_view& s,
         if (Strutil::parse_prefix(s, "TOP")) {
             img = curimg;
         } else if (Strutil::parse_prefix(s, "IMG[")) {
-            int index = -1;
-            if (Strutil::parse_int(s, index) && Strutil::parse_char(s, ']')
-                && index >= 0 && index <= (int)image_stack.size()) {
-                if (index == 0)
-                    img = curimg;
-                else
-                    img = image_stack[image_stack.size() - index];
-            } else {
-                string_view name = Strutil::parse_until(s, "]");
-                auto found       = image_labels.find(name);
-                if (found != image_labels.end())
-                    img = found->second;
-                else
-                    img = ImageRecRef(new ImageRec(name, imagecache));
-                Strutil::parse_char(s, ']');
+            std::string until_bracket = Strutil::parse_until(s, "]");
+            if (until_bracket.empty() || !Strutil::parse_char(s, ']')) {
+                express_error(expr, until_bracket,
+                              "malformed IMG[] specification");
+                result = orig;
+                return false;
+            }
+            auto labelfound = image_labels.find(until_bracket);
+            if (labelfound != image_labels.end()) {
+                // Found an image label
+                img = labelfound->second;
+            } else if (Strutil::string_is_int(until_bracket)) {
+                // It's an integer... don't process more quite yet
+            } else if (Filesystem::exists(until_bracket)) {
+                // It's the name of an image file
+                img = ImageRecRef(new ImageRec(until_bracket, imagecache));
+            }
+            if (!img) {
+                // Not a label, int, or file. Evaluate it as an expression.
+                // Evaluate it as an expression and hope it's an integer or
+                // the name of an image?
+                until_bracket = express_impl(until_bracket);
+                if (Strutil::string_is_int(until_bracket)) {
+                    // Between brackets (including an expanded variable) is an
+                    // integer -- it's an index into the image stack (error if out
+                    // of range).
+                    int index = Strutil::stoi(until_bracket);
+                    if (index >= 0 && index <= (int)image_stack.size()) {
+                        img = (index == 0)
+                                  ? curimg
+                                  : image_stack[image_stack.size() - index];
+                    } else {
+                        express_error(expr, until_bracket,
+                                      "out-of-range IMG[] index");
+                        result = orig;
+                        return false;
+                    }
+                } else if (Filesystem::exists(until_bracket)) {
+                    // It's the name of an image file
+                    img = ImageRecRef(new ImageRec(until_bracket, imagecache));
+                }
+            }
+            if (!img || img->has_error()) {
+                express_error(expr, until_bracket, "not a valid image");
+                result = orig;
+                return false;
             }
         }
-        if (!img.get()) {
+        if (!img || img->has_error()) {
             express_error(expr, s, "not a valid image");
             result = orig;
             return false;
         }
+        OIIO_ASSERT(img);
+        img->read();
         bool using_bracket = false;
         if (Strutil::parse_char(s, '[')) {
             using_bracket = true;

testsuite/oiiotool-control/ref/out.txt

@@ -260,6 +260,7 @@ Constant: No
 Monochrome: No
 
 Stack holds [0] = ../common/tahoe-small.tif, [1] = ../common/tahoe-tiny.tif
+Stack holds [1] = ../common/tahoe-tiny.tif
 filename=../common/tahoe-tiny.tif file_extension=.tif file_noextension=../common/tahoe-tiny
 MINCOLOR=0,0,0 MAXCOLOR=0.745098,1,1 AVGCOLOR=0.101942,0.216695,0.425293
 Testing NIMAGES: