Group mouse move events from C API function

Groups together consecutive mouse move events like done in core.step()
lua function but on the C side.

It does not introduce any meaningful speedup but it theory is more efficient and
simplifies the Lua code.

The simplification of the Lua code alone is enough to justify this change?

data/core/init.lua

@@ -949,26 +949,18 @@ end
 function core.step()
   -- handle events
   local did_keymap = false
-  local mouse_moved = false
-  local mouse = { x = 0, y = 0, dx = 0, dy = 0 }
-
 
   for type, a,b,c,d in system.poll_event do
-    if type == "mousemoved" then
-      mouse_moved = true
-      mouse.x, mouse.y = a, b
-      mouse.dx, mouse.dy = mouse.dx + c, mouse.dy + d
-    elseif type == "textinput" and did_keymap then
+    if type == "textinput" and did_keymap then
       did_keymap = false
+    elseif type == "mousemoved" then
+      core.try(core.on_event, type, a, b, c, d)
     else
       local _, res = core.try(core.on_event, type, a, b, c, d)
       did_keymap = res or did_keymap
     end
     core.redraw = true
   end
-  if mouse_moved then
-    core.try(core.on_event, "mousemoved", mouse.x, mouse.y, mouse.dx, mouse.dy)
-  end
 
   local width, height = renderer.get_size()
 

src/api/system.c

@@ -201,6 +201,14 @@ top:
       return 4;
 
     case SDL_MOUSEMOTION:
+      SDL_PumpEvents();
+      SDL_Event event_plus;
+      while (SDL_PeepEvents(&event_plus, 1, SDL_GETEVENT, SDL_MOUSEMOTION, SDL_MOUSEMOTION) > 0) {
+        e.motion.x = event_plus.motion.x;
+        e.motion.y = event_plus.motion.y;
+        e.motion.xrel += event_plus.motion.xrel;
+        e.motion.yrel += event_plus.motion.yrel;
+      }
       lua_pushstring(L, "mousemoved");
       lua_pushnumber(L, e.motion.x);
       lua_pushnumber(L, e.motion.y);