[parser] Change defaults to no longer be determined by very first #version statement.

Instead, subsequent `#version` statements may switch defaults back and forth until the first `default` statement.

Author: c-lipka

changes.txt

@@ -43,12 +43,15 @@ Changed Behaviour
   - Any new behaviour formerly activated by `#version 3.71` now requires
     `#version 3.8` (or higher); specifying `#version 3.71` will trigger a
     corresponding warning.
-  - Some defaults have been changed (requires `#version 3.8` as the _very first_
-    statement of the scene, or a corresponding command line / INI setting):
+  - Some defaults have been changed (requires `#version 3.8` or a corresponding
+    command line / INI setting):
       - The pigment now defaults to plain white.
       - `ambient` now defaults to 0.0 instead of 0.1.
       - The camera `right` vector length now defaults to the output image aspect
         ratio (presuming square pixels) instead of 1.33.
+    Switching back and forth between defaults via `#version` is possible until
+    the first `default` statement is encountered; after that, `#version` will
+    cause a warning instead of changing defaults.
   - Minor changes have been made to the benchmark scene. New benchmark version
     is 2.03.
   - Token counting in conditional blocks (e.g. in `#if ... #end`) has changed.

source/parser/parser.cpp

@@ -197,6 +197,9 @@ void Parser::Run()
         Default_Texture->Tnormal = nullptr;
         Default_Texture->Finish  = Create_Finish();
 
+        defaultsVersion = DefaultsVersion::kLegacy;
+        defaultsModified = false;
+
         // Initialize various defaults depending on language version as per command line / INI settings.
         InitDefaults(sceneData->EffectiveLanguageVersion());
 
@@ -356,7 +359,7 @@ void Parser::Run()
     // TODO FIXME - review whole if-statement and line after it below [trf]
     // we set this before resetting languageVersion since there's nothing to
     // be gained from disabling the defaulting of the noise generator to
-    // something other than compatibilty mode.
+    // something other than compatibility mode.
     if (sceneData->explicitNoiseGenerator == false)
         sceneData->noiseGenerator = (sceneData->EffectiveLanguageVersion() < 350 ?
                                      kNoiseGen_Original : kNoiseGen_RangeCorrected);
@@ -540,24 +543,53 @@ void Parser::InitDefaults(int version)
     MathColour pigmentColour;
     double ambientLevel;
     double rightLength;
+    DefaultsVersion newDefaults;
+
     if (version >= 380)
+        newDefaults = DefaultsVersion::k380;
+    else
+        newDefaults = DefaultsVersion::kLegacy;
+
+    if (newDefaults == defaultsVersion)
+        // nothing to change
+        return;
+
+    if (defaultsModified)
     {
-        pigmentType = PLAIN_PATTERN;
-        pigmentColour = MathColour(1.0);
-        ambientLevel = 0.0;
-        rightLength = sceneData->aspectRatio;
+        // Don't override defaults if they've already been modified by the user.
+        Warning("Scene language version changed after a 'default' statement. "
+                "The changes in defaults normally associated with the language "
+                "version change are not applied.");
+        return;
     }
-    else
+
+    switch (newDefaults)
     {
-        pigmentType = NO_PATTERN;
-        pigmentColour = MathColour(0.0);
-        ambientLevel = 0.1;
-        rightLength = 1.33;
+        case DefaultsVersion::k380:
+            pigmentType = PLAIN_PATTERN;
+            pigmentColour = MathColour(1.0);
+            ambientLevel = 0.0;
+            rightLength = sceneData->aspectRatio;
+            break;
+
+        case DefaultsVersion::kLegacy:
+            pigmentType = NO_PATTERN;
+            pigmentColour = MathColour(0.0);
+            ambientLevel = 0.1;
+            rightLength = 1.33;
+            break;
+
+        default:
+            POV_PARSER_ASSERT(false);
+            break;
     }
+
     Default_Texture->Pigment->Type = pigmentType;
     Default_Texture->Pigment->colour = TransColour(pigmentColour, 0.0, 0.0);
     Default_Texture->Finish->Ambient = MathColour(ambientLevel);
     Default_Camera.Right = Vector3d(rightLength, 0.0, 0.0);
+
+    defaultsVersion = newDefaults;
 }
 
 
@@ -6869,6 +6901,8 @@ void Parser::Parse_Default ()
     Not_In_Default = false;
     Parse_Begin();
 
+    defaultsModified = true;
+
     EXPECT
         CASE (TEXTURE_TOKEN)
             Local_Texture = Default_Texture;

source/parser/parser.h

@@ -634,6 +634,14 @@ class Parser : public SceneTask
         // parstxtr.h/parstxtr.cpp
         TEXTURE *Default_Texture;
 
+        enum class DefaultsVersion : char
+        {
+            kLegacy,    ///< Pre-v3.8 defaults.
+            k380,       ///< v3.8.0 defaults.
+        };
+        DefaultsVersion defaultsVersion;    ///< Language version active before the first `default` statement.
+        bool defaultsModified   : 1;        ///< Whether a `default` statement has been encountered.
+
         // express.h/express.cpp
         short Have_Vector;
         unsigned int Number_Of_Random_Generators;

source/parser/parser_tokenizer.cpp

@@ -2539,12 +2539,8 @@ void Parser::Parse_Directive(int After_Hash)
                                           "'#version version;'.");
                             }
 
-                            if (!sceneData->languageVersionLate && !sceneData->languageVersionSet)
-                            {
-                                // Got `#version` as the first statement of the file.
-                                // Initialize various defaults depending on language version specified.
-                                InitDefaults(sceneData->languageVersion);
-                            }
+                            // Initialize various defaults depending on language version specified.
+                            InitDefaults(sceneData->languageVersion);
 
                             // NB: This must be set _after_ parsing the value, in order for the `#version version`
                             // idiom to work properly, but _before_ any of the following code querying