ray: add rudimentary gamma correction

color banding has been quite visible, and somewhat expected with a
direct conversion from the linear float color space to the 8-bit
integral rgb color components.

A simple lookup table is used here to non-linearly map the values, table
generation is taken from Greg Ward's REAL PIXELS gem in Graphics Gems II.

1 files changed, 15 insertions, 0 deletions

diff --git a/src/libs/ray/ray_gamma.c b/src/libs/ray/ray_gamma.c
new file mode 100644
index 0000000..21a9afc
--- /dev/null
+++ b/src/libs/ray/ray_gamma.c
@@ -0,0 +1,15 @@
+#include <math.h>
+
+#include "ray_gamma.h"
+
+void ray_gamma_prepare(float gamma, ray_gamma_t *res_gamma)
+{
+	if (res_gamma->gamma == gamma)
+		return;
+
+	/* This is from graphics gems 2 "REAL PIXELS" */
+	for (unsigned i = 0; i < 1024; i++)
+		res_gamma->table[i] = 256.0f * powf((((float)i + .5f) / 1024.0f), 1.0f/gamma);
+
+	res_gamma->gamma = gamma;
+}