rendering: add alpha cutout integration coverage

engine/src/Resources/Shader/ShaderLoader.cpp

@@ -1013,19 +1013,70 @@ std::vector<ShaderKeywordSet> BuildShaderKeywordVariantSets(
 Containers::String BuildKeywordVariantSource(
     const Containers::String& baseSource,
     const ShaderKeywordSet& requiredKeywords) {
-    Containers::String variantSource;
+    if (requiredKeywords.enabledKeywords.Empty()) {
+        return baseSource;
+    }
+
+    std::string defineBlock;
     for (const Containers::String& keyword : requiredKeywords.enabledKeywords) {
-        variantSource += "#define ";
-        variantSource += keyword;
-        variantSource += " 1\n";
+        defineBlock += "#define ";
+        defineBlock += ToStdString(keyword);
+        defineBlock += " 1\n";
     }
 
-    if (!variantSource.Empty() && !baseSource.Empty()) {
-        variantSource += '\n';
+    if (baseSource.Empty()) {
+        return Containers::String(defineBlock.c_str());
     }
 
-    variantSource += baseSource;
-    return variantSource;
+    const std::string sourceText = ToStdString(baseSource);
+
+    size_t lineStart = 0;
+    while (lineStart < sourceText.size()) {
+        const size_t lineEnd = sourceText.find_first_of("\r\n", lineStart);
+        const size_t lineLength =
+            lineEnd == std::string::npos ? sourceText.size() - lineStart : lineEnd - lineStart;
+        const std::string line = sourceText.substr(lineStart, lineLength);
+        const std::string trimmedLine = TrimCopy(line);
+
+        if (trimmedLine.empty() ||
+            trimmedLine.rfind("//", 0) == 0u ||
+            trimmedLine.rfind("/*", 0) == 0u ||
+            trimmedLine.rfind("*", 0) == 0u) {
+            if (lineEnd == std::string::npos) {
+                break;
+            }
+
+            lineStart = lineEnd + 1u;
+            if (sourceText[lineEnd] == '\r' &&
+                lineStart < sourceText.size() &&
+                sourceText[lineStart] == '\n') {
+                ++lineStart;
+            }
+            continue;
+        }
+
+        if (trimmedLine.rfind("#version", 0) != 0u) {
+            break;
+        }
+
+        size_t insertionPos = lineEnd == std::string::npos ? sourceText.size() : lineEnd + 1u;
+        if (lineEnd != std::string::npos &&
+            sourceText[lineEnd] == '\r' &&
+            insertionPos < sourceText.size() &&
+            sourceText[insertionPos] == '\n') {
+            ++insertionPos;
+        }
+
+        std::string variantSource = sourceText.substr(0, insertionPos);
+        variantSource += defineBlock;
+        variantSource += sourceText.substr(insertionPos);
+        return Containers::String(variantSource.c_str());
+    }
+
+    std::string variantSource = defineBlock;
+    variantSource += '\n';
+    variantSource += sourceText;
+    return Containers::String(variantSource.c_str());
 }
 
 bool TryParseShaderKeywordDeclarationPragma(