Use a comment for including rpo in vanilla resource packs instead of #include

docs/Shaders.md

@@ -1,6 +1,11 @@
 # Usage in fabulous/canvas/frex shaders
 ## Getting started
-All you need to do to access respackotps values is paste the following in a file where you want them: `#include respackopts:config_supplier` 
+All you need to do to access respackotps values is paste the following in a file where you want them according to your renderer:
+| Renderer | Include snippet |
+| --- | --- |
+| Canvas | `#include respackopts:config_supplier` |
+| Vanilla/Fabulous | `//include respackopts:config_supplier` (this is done to avoid problems when loading shaders without respackopts) |
+
 However, usually you will want to still have a pack that works if respackotps is not present. In that case, canvas will still load the file,
 however, values that respackotps registers will not be available leading to compile errors. 
 To avoid this, I recommend creating a source file in your own shader which will load default values if respackotps isn't present. You can do that as follows:

src/main/java/io/gitlab/jfronny/respackopts/Respackopts.java

@@ -120,10 +120,12 @@ public class Respackopts implements ClientModInitializer {
             if (CONFIG.debugLogs)
                 LOGGER.info("Generating FREX shader code");
             StringBuilder sb = new StringBuilder();
-            sb.append("#define respackopts_loaded");
+            sb.append("#ifndef respackopts_loaded");
+            sb.append("\n#define respackopts_loaded");
             for (Map.Entry<String, ConfigBranch> e : CONFIG_BRANCH.entrySet()) {
                 e.getValue().buildShader(sb, sanitizeString(e.getKey()));
             }
+            sb.append("\n#endif");
             shaderImportSource = sb.toString();
         });
         DirFilterEventImpl.init();

src/main/java/io/gitlab/jfronny/respackopts/mixin/GLImportProcessorMixin.java

@@ -10,6 +10,6 @@ import org.spongepowered.asm.mixin.injection.ModifyArg;
 public class GLImportProcessorMixin {
     @ModifyArg(method = "readSource(Ljava/lang/String;)Ljava/util/List;", at = @At(value = "INVOKE", target = "Lnet/minecraft/client/gl/GLImportProcessor;parseImports(Ljava/lang/String;Lnet/minecraft/client/gl/GLImportProcessor$Context;Ljava/lang/String;)Ljava/util/List;"), index = 0)
     private String modify(String value) {
-        return value.replace("#include " + Respackopts.RPO_SHADER_ID, Respackopts.getShaderImportSource());
+        return value.replace("\n//include " + Respackopts.RPO_SHADER_ID, "\n" + Respackopts.getShaderImportSource());
     }
 }