From a5d30a2794ddba047e4dad0eda129d704322aead Mon Sep 17 00:00:00 2001
From: rodri <rgl@antares-labs.eu>
Date: Mon, 8 Jun 2020 20:19:38 +0000
Subject: new toy: imagelerp

---
 imagelerp.c | 99 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 mkfile      |  1 +
 2 files changed, 100 insertions(+)
 create mode 100644 imagelerp.c

diff --git a/imagelerp.c b/imagelerp.c
new file mode 100644
index 0000000..c23bdad
--- /dev/null
+++ b/imagelerp.c
@@ -0,0 +1,99 @@
+#include <u.h>
+#include <libc.h>
+#include <draw.h>
+#include <memdraw.h>
+
+double
+flerp(double a, double b, double t)
+{
+	return a + (b - a)*t;
+}
+
+double
+fclamp(double n, double min, double max)
+{
+	return n < min? min: n > max? max: n;
+}
+
+Memimage*
+lerpimages(Memimage *i0, Memimage *i1, double blendf)
+{
+	Memimage *ri;
+	Point p;
+	uchar *s0, *s1, *d;
+	int bpp;
+
+	assert(i0->chan == i1->chan);
+	assert(Dx(i0->r) == Dx(i1->r) && Dy(i0->r) == Dy(i1->r));
+
+	ri = allocmemimage(i0->r, i0->chan);
+	if(ri == nil)
+		sysfatal("allocmemimage: %r");
+	bpp = (i0->depth+7)/8;
+
+	for(p.y = 0; p.y < i0->r.max.y; p.y++)
+		for(p.x = 0; p.x < i0->r.max.x; p.x++){
+			s0 = byteaddr(i0, addpt(i0->r.min, p));
+			s1 = byteaddr(i1, addpt(i1->r.min, p));
+			d = byteaddr(ri, addpt(ri->r.min, p));
+			switch(bpp){
+			case 4:
+				d[3] = flerp(s0[3], s1[3], blendf);
+			case 3:
+				d[2] = flerp(s0[2], s1[2], blendf);
+			case 2:
+				d[1] = flerp(s0[1], s1[1], blendf);
+			case 1:
+				d[0] = flerp(s0[0], s1[0], blendf);
+			}
+		}
+	return ri;
+}
+
+void
+usage(void)
+{
+	fprint(2, "usage: %s [-f factor] image0 image1\n", argv0);
+	exits("usage");
+}
+
+void
+main(int argc, char *argv[])
+{
+	Memimage *m[2], *r;
+	char *s;
+	int fd;
+	double f;
+
+	f = 0.5;
+	ARGBEGIN{
+	case 'f':
+		f = strtod(EARGF(usage()), &s);
+		if(*s != 0)
+			sysfatal("wrong blending factor");
+		break;
+	default: usage();
+	}ARGEND;
+	if(argc != 2)
+		usage();
+
+	if(memimageinit() != 0)
+		sysfatal("memimageinit: %r");
+	fd = open(argv[0], OREAD);
+	if(fd < 0)
+		sysfatal("open: %r");
+	if((m[0] = readmemimage(fd)) == nil)
+		sysfatal("readmemimage: %r");
+	close(fd);
+	fd = open(argv[1], OREAD);
+	if(fd < 0)
+		sysfatal("open: %r");
+	if((m[1] = readmemimage(fd)) == nil)
+		sysfatal("readmemimage: %r");
+	close(fd);
+	r = lerpimages(m[0], m[1], fclamp(f, 0, 1));
+	if(writememimage(1, r) < 0)
+		sysfatal("writememimage: %r");
+	exits(nil);
+}
+
diff --git a/mkfile b/mkfile
index 8c07918..2848dce 100644
--- a/mkfile
+++ b/mkfile
@@ -9,6 +9,7 @@ TARG=\
 	isometric\
 	ptinline\
 	chain\
+	imagelerp\
 
 HFILES=\
 	libgeometry/geometry.h\
-- 
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