Fixed bug 3902 - Add a specific KMSDRM hint for low latency video

--HG--
extra : amend_source : 533faafd8a7c6832c94728550b1ca10bab2a8018

include/SDL_hints.h

@@ -797,6 +797,16 @@ extern "C" {
  */
 #define SDL_HINT_RPI_VIDEO_LAYER           "SDL_RPI_VIDEO_LAYER"
 
+/**
+ * \brief Tell SDL the KMS/DRM video driver that we want double buffer only.
+ *
+ * By default KMS/DRM will use a triple buffer solution that wastes no CPU
+ * time on waiting for vsync after issuing a flip, but introduces a frame of
+ * latency. Waiting for vsync immediately after issuing a flip on the other
+ * hand is recommended for cases where low latency is an important factor.
+ */
+#define SDL_HINT_KMSDRM_DOUBLE_BUFFER      "SDL_KMSDRM_DOUBLE_BUFFER"
+
 /**
  *  \brief  A variable controlling what driver to use for OpenGL ES contexts.
  *