diff --git a/include/justui/jpainted.h b/include/justui/jpainted.h
index 5b545fe..c7724fd 100644
--- a/include/justui/jpainted.h
+++ b/include/justui/jpainted.h
@@ -7,7 +7,6 @@
 
 #include <justui/defs.h>
 #include <justui/jwidget.h>
-#include <justui/jwidget-api.h>
 
 /* jpainted: Simple widget designed to integrate low-effort rendering
 
diff --git a/include/justui/jwidget-api.h b/include/justui/jwidget-api.h
index 149e427..968842f 100644
--- a/include/justui/jwidget-api.h
+++ b/include/justui/jwidget-api.h
@@ -6,6 +6,7 @@
 #define _J_JWIDGET_API
 
 #include <justui/defs.h>
+#include <justui/p/preproc.h>
 #include <justui/jevent.h>
 #include <gint/keyboard.h>
 
@@ -186,4 +187,38 @@ void jwidget_emit(void *w, jevent e);
    notify it of the specified event. */
 bool jwidget_event(void *w, jevent e);
 
+/* Helper macro for defining a new widget. Parameters are:
+   - Widget NAME
+   - Variadic list of overridden widget poly METHODs, can be empty
+   - Implicity, non-static poly functions `<NAME>_poly_<METHOD>`
+   And it defines:
+   - The `NAME_type_id` identifier for use with `jwidget_init()`
+   - A constructor that registers the widget and sets `NAME_type_id`.
+
+   For example:
+   ```
+   J_DEFINE_WIDGET(jpainted, csize, render)
+   ```
+
+   gets the functions `jpainted_poly_csize` and `jpainted_poly_render` from
+   context, registers the type at startup and provides `jpainted_type_id` for
+   the widget creation function. */
+
+#define J_DEFINE_WIDGET(NAME, ...) \
+    static int NAME##_type_id = -1; \
+    J_REPEAT(J_DEFINE_WIDGET_POLY_PROTO, (NAME), __VA_ARGS__) \
+    static jwidget_poly type_##NAME = { \
+        .name = #NAME, \
+        J_REPEAT(J_DEFINE_WIDGET_POLY, (NAME), __VA_ARGS__) \
+    }; \
+    __attribute__((constructor)) \
+    static void j_register_##NAME(void) { \
+        NAME##_type_id = j_register_widget(&type_##NAME); \
+    }
+
+#define J_DEFINE_WIDGET_POLY(NAME, METHOD) \
+    .METHOD = NAME##_poly_##METHOD,
+#define J_DEFINE_WIDGET_POLY_PROTO(NAME, METHOD) \
+    extern jwidget_poly_##METHOD##_t NAME##_poly_##METHOD;
+
 #endif /* _J_JWIDGET_API */
diff --git a/include/justui/p/preproc.h b/include/justui/p/preproc.h
new file mode 100644
index 0000000..a2cd84f
--- /dev/null
+++ b/include/justui/p/preproc.h
@@ -0,0 +1,64 @@
+//---
+// JustUI.util.preproc: Preprocessor utilities
+//---
+
+#ifndef _J_UTIL_PREPROC
+#define _J_UTIL_PREPROC
+
+/* J_REPEAT: Dispatch a partially-evaluated macro call on each arg in a list
+   The call `J_REPEAT(X, C, V1, ..., VN)` where `C = (C1, ..., CM)` (with the
+   parentheses) is equivalent to the series of calls
+
+   ```
+   X(C1, ..., CM, V1)
+   X(C1, ..., CM, V2)
+   ...
+   X(C1, ..., CM, VN)
+   ```
+
+   and is used to iterate on lists. There is a size limit of N≤8. */
+#define J_REPEAT1(X, C, V1, ...) \
+    J_CALL(X, C, V1) __VA_OPT__(J_REPEAT2(X, C, __VA_ARGS__))
+#define J_REPEAT2(X, C, V2, ...) \
+    J_CALL(X, C, V2) __VA_OPT__(J_REPEAT3(X, C, __VA_ARGS__))
+#define J_REPEAT3(X, C, V3, ...) \
+    J_CALL(X, C, V3) __VA_OPT__(J_REPEAT4(X, C, __VA_ARGS__))
+#define J_REPEAT4(X, C, V4, ...) \
+    J_CALL(X, C, V4) __VA_OPT__(J_REPEAT5(X, C, __VA_ARGS__))
+#define J_REPEAT5(X, C, V5, ...) \
+    J_CALL(X, C, V5) __VA_OPT__(J_REPEAT6(X, C, __VA_ARGS__))
+#define J_REPEAT6(X, C, V6, ...) \
+    J_CALL(X, C, V6) __VA_OPT__(J_REPEAT7(X, C, __VA_ARGS__))
+#define J_REPEAT7(X, C, V7, ...) \
+    J_CALL(X, C, V7) __VA_OPT__(J_REPEAT8(X, C, __VA_ARGS__))
+#define J_REPEAT8(X, C, V8, ...) \
+    ({ __VA_OPT__(_Static_assert(0, \
+        "J_REPEAT: too many macro arguments (maximum 8)");) \
+    J_CALL(X, C, V8); })
+#define J_REPEAT(X, C, ...) __VA_OPT__(J_REPEAT1(X, C, __VA_ARGS__))
+
+/* J_CALL: Perform a call to a partially evaluated macro
+   The call `J_CALL(X, C, A1, ..., AN)` where `C = (C1, ..., CM)` (with the
+   parentheses) reduces to `X(C1, ..., CM, A1, ..., AN)`, i.e. it calls the
+   already-partially-applied `X(C)` with further arguments. Both M=0 (`C=()`)
+   and N=0 (no variadic arguments) are allowed.
+
+   The main difficulty is "unfolding" `C` into the arguments of `X`. This
+   problem is dealt with by absorbing the parentheses into an ID-function macro
+   call:
+
+   ```
+       J_ID C
+   ~>  J_ID (C1, ..., CM)
+   ~>  , C1, ..., CM
+  ```
+
+   From there, the only subtletly is gobbling the commas. We gobble the comma
+   before `J_ID C` if M=0 and the comma before the other arguments if N=0. This
+   requires a few expansion stages. */
+#define J_ID(...) __VA_OPT__(,) __VA_ARGS__
+#define J_CALL3(X, ...) X(__VA_ARGS__)
+#define J_CALL2(...) J_CALL3(__VA_ARGS__)
+#define J_CALL(X, C, ...) J_CALL2(X J_ID C, ##__VA_ARGS__)
+
+#endif /* _J_UTIL_PREPROC */
diff --git a/src/jpainted.c b/src/jpainted.c
index 21fe071..905a660 100644
--- a/src/jpainted.c
+++ b/src/jpainted.c
@@ -1,8 +1,8 @@
 #include <justui/jpainted.h>
-#include <gint/std/stdlib.h>
+#include <justui/jwidget-api.h>
+#include <stdlib.h>
 
-/* Type identifier for jpainted */
-static int jpainted_type_id = -1;
+J_DEFINE_WIDGET(jpainted, csize, render)
 
 jpainted *jpainted_create(void *function, j_arg_t arg, int natural_w,
 	int natural_h, void *parent)
@@ -20,36 +20,15 @@ jpainted *jpainted_create(void *function, j_arg_t arg, int natural_w,
 	return p;
 }
 
-//---
-// Polymorphic widget operations
-//---
-
-static void jpainted_poly_csize(void *p0)
+void jpainted_poly_csize(void *p0)
 {
 	jpainted *p = p0;
 	p->widget.w = p->natural_w;
 	p->widget.h = p->natural_h;
 }
 
-static void jpainted_poly_render(void *p0, int x, int y)
+void jpainted_poly_render(void *p0, int x, int y)
 {
 	jpainted *p = p0;
 	p->paint(x, y, p->arg);
 }
-
-/* jpainted type definition */
-static jwidget_poly type_jpainted = {
-	.name    = "jpainted",
-	.csize   = jpainted_poly_csize,
-	.layout  = NULL,
-	.render  = jpainted_poly_render,
-	.event   = NULL,
-	.destroy = NULL,
-};
-
-/* Type registration */
-__attribute__((constructor))
-static void j_register_jpainted(void)
-{
-	jpainted_type_id = j_register_widget(&type_jpainted);
-}