1 files changed, 37 insertions, 0 deletions
diff --git a/src/mbgl/style/expression/util.cpp b/src/mbgl/style/expression/util.cpp
new file mode 100644
index 0000000000..ee680dab08
--- /dev/null
+++ b/src/mbgl/style/expression/util.cpp
@@ -0,0 +1,37 @@
+#include <mbgl/style/expression/util.hpp>
+#include <mbgl/style/expression/value.hpp>
+
+namespace mbgl {
+namespace style {
+namespace expression {
+
+std::string stringifyColor(double r, double g, double b, double a) {
+    return stringify(r) + ", " +
+        stringify(g) + ", " +
+        stringify(b) + ", " +
+        stringify(a);
+}
+
+Result<Color> rgba(double r, double g, double b, double a) {
+    if (
+        r < 0 || r > 255 ||
+        g < 0 || g > 255 ||
+        b < 0 || b > 255
+    ) {
+        return EvaluationError {
+            "Invalid rgba value [" + stringifyColor(r, g, b, a)  +
+            "]: 'r', 'g', and 'b' must be between 0 and 255."
+        };
+    }
+    if (a < 0 || a > 1) {
+        return EvaluationError {
+            "Invalid rgba value [" + stringifyColor(r, g, b, a)  +
+            "]: 'a' must be between 0 and 1."
+        };
+    }
+    return Color(r / 255 * a, g / 255 * a, b / 255 * a, a);
+}
+
+} // namespace expression
+} // namespace style
+} // namespace mbgl