modules/drizzle: add a mapped overlay style

this introduces a style= setting with values:
style=mask	simple alpha mask overlay
style=map	displacement mapped overlay

I might add a lighting option for the style=map mode with a
moving light source or something like that, but it's already
pretty slow as-is.

This is mostly just for more testing of the snapshotting, but
there's some interesting compositions enabled like:
module=compose,layers=submit:moire:drizzle

or just moire:drizzle, when style=map happens.

1 files changed, 17 insertions, 0 deletions

diff --git a/src/til_fb.h b/src/til_fb.h
index da86605..80ffeb4 100644
--- a/src/til_fb.h
+++ b/src/til_fb.h
@@ -80,6 +80,23 @@ static inline uint32_t til_fb_fragment_get_pixel_unchecked(til_fb_fragment_t *fr
 }
 
 
+/* gets a pixel from the fragment, coordinates are clipped to the fragment's frame bounds */
+static inline uint32_t til_fb_fragment_get_pixel_clipped(til_fb_fragment_t *fragment, int x, int y)
+{
+	if (x < 0)
+		x = 0;
+	else if (x >= fragment->frame_width)
+		x = fragment->frame_width - 1;
+
+	if (y < 0)
+		y = 0;
+	else if (y >= fragment->frame_height)
+		y = fragment->frame_height - 1;
+
+	return til_fb_fragment_get_pixel_unchecked(fragment, x, y);
+}
+
+
 /* puts a pixel into the fragment, no bounds checking is performed. */
 static inline void til_fb_fragment_put_pixel_unchecked(til_fb_fragment_t *fragment, uint32_t flags, int x, int y, uint32_t pixel)
 {