Add background RenderParams entry

src/fart/RenderParams.cpp

@@ -15,6 +15,10 @@ void RenderParams::merge(const RenderParams & other)
     {
         threads = other.threads;
     }
+    if (!background)
+    {
+        background = other.background;
+    }
 }
 
 void RenderParams::apply_defaults()
@@ -33,4 +37,8 @@ void RenderParams::apply_defaults()
         size_t n = std::thread::hardware_concurrency();
         threads = n > 0u ? n : 1u;
     }
+    if (!background)
+    {
+        background = Color{0.0, 0.0, 0.0, 1.0};
+    }
 }

src/fart/RenderParams.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <fart/Color.h>
 #include <stddef.h>
 
 struct RenderParams
@@ -7,6 +8,7 @@ struct RenderParams
     opt<size_t> width;
     opt<size_t> height;
     opt<size_t> threads;
+    opt<Color> background;
 
     /* Set each field that is not already set to the value from other. */
     void merge(const RenderParams & other);