Add display_gamma option for client

src/light.cpp

@@ -18,31 +18,93 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 */
 
 #include "light.h"
+#include <math.h>
+#include "util/numeric.h"
+
+#ifndef SERVER
 
-#if 1
-// Middle-raised variation of a_n+1 = a_n * 0.786
 // Length of LIGHT_MAX+1 means LIGHT_MAX is the last value.
 // LIGHT_SUN is read as LIGHT_MAX from here.
-u8 light_decode_table[LIGHT_MAX+1] = 
+
+u8 light_LUT[LIGHT_MAX+1] =
 {
-8,
-11+2,
-14+7,
-18+10,
-22+15,
-29+20,
-37+20,
-47+15,
-60+10,
-76+7,
-97+5,
-123+2,
-157,
-200,
-255,
+	/* Middle-raised variation of a_n+1 = a_n * 0.786
+	 * Length of LIGHT_MAX+1 means LIGHT_MAX is the last value.
+	 * LIGHT_SUN is read as LIGHT_MAX from here.
+	 */
+	8,
+	11+2,
+	14+7,
+	18+10,
+	22+15,
+	29+20,
+	37+20,
+	47+15,
+	60+10,
+	76+7,
+	97+5,
+	123+2,
+	157,
+	200,
+	255,
 };
+
+const u8 *light_decode_table = light_LUT;
+
+/** Initialize or update the light value tables using the specified \p gamma.
+ *  If \p gamma == 1.0 then the light table is linear.  Typically values for
+ *  gamma range between 1.8 and 2.2.
+ *
+ *  @note The value for gamma will be restricted to the range 1.1 <= gamma <= 3.0.
+ *
+ *  @note This function is not, currently, a simple linear to gamma encoding
+ *        because adjustments are made so that a gamma of 1.8 gives the same
+ *        results as those hardcoded for use by the server.
+ */
+void set_light_table(float gamma)
+{
+	static const float brightness_step = 255.0f / (LIGHT_MAX + 1);
+
+	/* These are adjustment values that are added to the calculated light value
+	 * after gamma is applied.  Currently they are used so that given a gamma
+	 * of 1.8 the light values set by this function are the same as those
+	 * hardcoded in the initalizer list for the declaration of light_LUT.
+	 */
+	static const int adjustments[LIGHT_MAX + 1] = {
+		 7,
+		 7,
+		 7,
+		 5,
+		 2,
+		 0,
+		-7,
+		-20,
+		-31,
+		-39,
+		-43,
+		-45,
+		-40,
+		-25,
+		0
+	};
+
+	gamma = rangelim(gamma, 1.1, 3.0);
+
+	float brightness = brightness_step;
+
+	for (size_t i = 0; i < LIGHT_MAX; i++) {
+		light_LUT[i] = (u8)(255 * powf(brightness / 255.0f,  gamma));
+		light_LUT[i] = rangelim(light_LUT[i] + adjustments[i], 0, 255);
+		if (i > 1 && light_LUT[i] < light_LUT[i-1])
+			light_LUT[i] = light_LUT[i-1] + 1;
+		brightness += brightness_step;
+	}
+	light_LUT[LIGHT_MAX] = 255;
+}
 #endif
 
+
+
 #if 0
 /*
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