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authorP. J. McDermott <pjm@nac.net>2013-03-04 02:03:44 (EST)
committer P. J. McDermott <pjm@nac.net>2013-03-04 02:03:44 (EST)
commitf9e339b9345b90621e6c2a585033ce20b3837570 (patch)
tree559efbd0fab717b32c87b47e11c385e7ee4b6b95
parentd41706737aa268903955dad9006326b26c106833 (diff)
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src/main.c: Tweak cosine palette cycling macro.
-rw-r--r--src/main.c23
1 files changed, 19 insertions, 4 deletions
diff --git a/src/main.c b/src/main.c
index 7bfcdc2..c0b26a4 100644
--- a/src/main.c
+++ b/src/main.c
@@ -25,21 +25,36 @@
} while (0)
#define CYCLE_COS(t_max, r1, g1, b1, r2, g2, b2) \
do { \
- x = t * 3.14159 / t_max; \
+ /* \
+ * t = t \
+ * t_max = t_max \
+ * x = (t / t_max) * π \
+ * for y in {r, g, b}: \
+ * m = y_end - y_start \
+ * x = x \
+ * b = y_start \
+ * y = m * ((cos(x) / 2) + 0.5) + b \
+ */ \
+ /* \
+ * cos(x) => [-1 .. 1] \
+ * (cos(x)/2)+0.5 => [0 .. 1] \
+ * y => [y_start .. y_end] \
+ */ \
+ x = (double) t / (double) t_max * 3.14159; \
y_end = (i % 8) * 36; \
y_start = y_end * r2; \
y_end = y_end * r1; \
- colors[i].r = ((cos(x) + 1) / 2) * \
+ colors[i].r = ((cos(x) / 2) + 0.5) * \
(y_end - y_start) + y_start; \
y_end = (i % 64 / 8) * 36; \
y_start = y_end * g2; \
y_end = y_end * g1; \
- colors[i].g = ((cos(x) + 1) / 2) * \
+ colors[i].g = ((cos(x) / 2) + 0.5) * \
(y_end - y_start) + y_start; \
y_end = (i / 64) * 85; \
y_start = y_end * b2; \
y_end = y_end * b1; \
- colors[i].b = ((cos(x) + 1) / 2) * \
+ colors[i].b = ((cos(x) / 2) + 0.5) * \
(y_end - y_start) + y_start; \
} while (0)