diff --git a/Makefile b/Makefile
index 47538ca..f0a6c0d 100644
--- a/Makefile
+++ b/Makefile
@@ -44,6 +44,7 @@ libtwin.a_files-y = \
 	src/pattern.c \
 	src/spline.c \
 	src/work.c \
+	src/draw-common.c \
 	src/hull.c \
 	src/icon.c \
 	src/pixmap.c \
@@ -61,7 +62,7 @@ libtwin.a_files-$(CONFIG_LOGGING) += src/log.c
 libtwin.a_files-$(CONFIG_CURSOR) += src/cursor.c
 
 # Renderer
-libtwin.a_files-$(CONFIG_RENDERER_BUILTIN) += src/draw.c
+libtwin.a_files-$(CONFIG_RENDERER_BUILTIN) += src/draw-builtin.c
 libtwin.a_files-$(CONFIG_RENDERER_PIXMAN) += src/draw-pixman.c
 libtwin.a_cflags-$(CONFIG_RENDERER_PIXMAN) += $(shell pkg-config --cflags pixman-1)
 ifeq ($(CONFIG_RENDERER_PIXMAN), y)
diff --git a/include/twin.h b/include/twin.h
index 4098914..28a1d17 100644
--- a/include/twin.h
+++ b/include/twin.h
@@ -624,7 +624,7 @@ twin_pixmap_t *twin_make_cursor(int *hx, int *hy);
 void twin_dispatch(twin_context_t *ctx);
 
 /*
- * draw.c
+ * draw-*.c
  */
 
 void twin_composite(twin_pixmap_t *dst,
@@ -648,6 +648,10 @@ void twin_fill(twin_pixmap_t *dst,
                twin_coord_t right,
                twin_coord_t bottom);
 
+/*
+ * draw-common.c
+ */
+
 void twin_premultiply_alpha(twin_pixmap_t *px);
 
 /*
diff --git a/src/draw.c b/src/draw-builtin.c
similarity index 95%
rename from src/draw.c
rename to src/draw-builtin.c
index 09dd13c..4b23227 100644
--- a/src/draw.c
+++ b/src/draw-builtin.c
@@ -681,49 +681,6 @@ void twin_composite(twin_pixmap_t *dst,
                                msk_y, operator, width, height);
 }
 
-static twin_argb32_t _twin_apply_alpha(twin_argb32_t v)
-{
-    uint16_t t1, t2, t3;
-    twin_a8_t alpha = twin_get_8(v,
-#if __BYTE_ORDER == __BIG_ENDIAN
-                                 0
-#else
-                                 24
-#endif
-    );
-
-    /* clear RGB data if alpha is zero */
-    if (!alpha)
-        return 0;
-
-#if __BYTE_ORDER == __BIG_ENDIAN
-    /* twin needs ARGB format */
-    return alpha << 24 | twin_int_mult(twin_get_8(v, 24), alpha, t1) << 16 |
-           twin_int_mult(twin_get_8(v, 16), alpha, t2) << 8 |
-           twin_int_mult(twin_get_8(v, 8), alpha, t3) << 0;
-#else
-    return alpha << 24 | twin_int_mult(twin_get_8(v, 0), alpha, t1) << 16 |
-           twin_int_mult(twin_get_8(v, 8), alpha, t2) << 8 |
-           twin_int_mult(twin_get_8(v, 16), alpha, t3) << 0;
-#endif
-}
-
-void twin_premultiply_alpha(twin_pixmap_t *px)
-{
-    int x, y;
-    twin_pointer_t p;
-
-    if (px->format != TWIN_ARGB32)
-        return;
-
-    for (y = 0; y < px->height; y++) {
-        p.b = px->p.b + y * px->stride;
-
-        for (x = 0; x < px->width; x++)
-            p.argb32[x] = _twin_apply_alpha(p.argb32[x]);
-    }
-}
-
 /*
  * array primary    index is OVER SOURCE
  * array secondary  index is ARGB32 RGB16 A8
diff --git a/src/draw-common.c b/src/draw-common.c
new file mode 100644
index 0000000..005bd1f
--- /dev/null
+++ b/src/draw-common.c
@@ -0,0 +1,48 @@
+/*
+ * Twin - A Tiny Window System
+ * Copyright (c) 2004 Keith Packard <keithp@keithp.com>
+ * Copyright (c) 2024 National Cheng Kung University, Taiwan
+ * All rights reserved.
+ */
+
+#include "twin_private.h"
+
+static twin_argb32_t _twin_apply_alpha(twin_argb32_t v)
+{
+    uint16_t t1, t2, t3;
+    twin_a8_t alpha = twin_get_8(v,
+#if __BYTE_ORDER == __BIG_ENDIAN
+                                 0
+#else
+                                 24
+#endif
+    );
+
+    /* clear RGB data if alpha is zero */
+    if (!alpha)
+        return 0;
+
+#if __BYTE_ORDER == __BIG_ENDIAN
+    /* twin needs ARGB format */
+    return alpha << 24 | twin_int_mult(twin_get_8(v, 24), alpha, t1) << 16 |
+           twin_int_mult(twin_get_8(v, 16), alpha, t2) << 8 |
+           twin_int_mult(twin_get_8(v, 8), alpha, t3) << 0;
+#else
+    return alpha << 24 | twin_int_mult(twin_get_8(v, 0), alpha, t1) << 16 |
+           twin_int_mult(twin_get_8(v, 8), alpha, t2) << 8 |
+           twin_int_mult(twin_get_8(v, 16), alpha, t3) << 0;
+#endif
+}
+
+void twin_premultiply_alpha(twin_pixmap_t *px)
+{
+    if (px->format != TWIN_ARGB32)
+        return;
+
+    for (twin_coord_t y = 0; y < px->height; y++) {
+        twin_pointer_t p = {.b = px->p.b + y * px->stride};
+
+        for (twin_coord_t x = 0; x < px->width; x++)
+            p.argb32[x] = _twin_apply_alpha(p.argb32[x]);
+    }
+}
diff --git a/src/draw-pixman.c b/src/draw-pixman.c
index 970a727..9a96e15 100644
--- a/src/draw-pixman.c
+++ b/src/draw-pixman.c
@@ -166,47 +166,3 @@ void twin_fill(twin_pixmap_t *_dst,
 
     pixman_image_unref(dst);
 }
-
-/* Same function in draw.c */
-static twin_argb32_t _twin_apply_alpha(twin_argb32_t v)
-{
-    uint16_t t1, t2, t3;
-    twin_a8_t alpha = twin_get_8(v,
-#if __BYTE_ORDER == __BIG_ENDIAN
-                                 0
-#else
-                                 24
-#endif
-    );
-
-    /* clear RGB data if alpha is zero */
-    if (!alpha)
-        return 0;
-
-#if __BYTE_ORDER == __BIG_ENDIAN
-    /* twin needs ARGB format */
-    return alpha << 24 | twin_int_mult(twin_get_8(v, 24), alpha, t1) << 16 |
-           twin_int_mult(twin_get_8(v, 16), alpha, t2) << 8 |
-           twin_int_mult(twin_get_8(v, 8), alpha, t3) << 0;
-#else
-    return alpha << 24 | twin_int_mult(twin_get_8(v, 0), alpha, t1) << 16 |
-           twin_int_mult(twin_get_8(v, 8), alpha, t2) << 8 |
-           twin_int_mult(twin_get_8(v, 16), alpha, t3) << 0;
-#endif
-}
-
-void twin_premultiply_alpha(twin_pixmap_t *px)
-{
-    int x, y;
-    twin_pointer_t p;
-
-    if (px->format != TWIN_ARGB32)
-        return;
-
-    for (y = 0; y < px->height; y++) {
-        p.b = px->p.b + y * px->stride;
-
-        for (x = 0; x < px->width; x++)
-            p.argb32[x] = _twin_apply_alpha(p.argb32[x]);
-    }
-}