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, 37 insertions, 0 deletions

diff --git a/src/libs/ray/ray_gamma.h b/src/libs/ray/ray_gamma.h
new file mode 100644
index 0000000..c46d631
--- /dev/null
+++ b/src/libs/ray/ray_gamma.h
@@ -0,0 +1,37 @@
+#ifndef _RAY_GAMMA_H
+#define _RAY_GAMMA_H
+
+#include <stdint.h>
+
+#include "ray_color.h"
+
+typedef struct ray_gamma_t {
+	float	gamma;
+	uint8_t	table[1024];
+} ray_gamma_t;
+
+void ray_gamma_prepare(float gamma, ray_gamma_t *res_gamma);
+
+/* convert a color into a gamma-corrected, packed, 32-bit rgb pixel value */
+static inline uint32_t ray_gamma_color_to_uint32_rgb(ray_gamma_t *gamma, ray_color_t color) {
+	uint32_t	pixel;
+
+	if (color.x > 1.0f)
+		color.x = 1.0f;
+
+	if (color.y > 1.0f)
+		color.y = 1.0f;
+
+	if (color.z > 1.0f)
+		color.z = 1.0f;
+
+	pixel = (uint32_t)gamma->table[(unsigned)floorf(1023.0f * color.x)];
+	pixel <<= 8;
+	pixel |= (uint32_t)gamma->table[(unsigned)floorf(1023.0f * color.y)];
+	pixel <<= 8;
+	pixel |= (uint32_t)gamma->table[(unsigned)floorf(1023.0f * color.z)];
+
+	return pixel;
+}
+
+#endif