Add random_int(min,max) utility function

Author: hollasch

books/RayTracingTheNextWeek.html

@@ -767,7 +767,7 @@
 
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
     bvh_node::bvh_node(hittable **l, int n, double time0, double time1) {
-        int axis = int(random_double(0,3));
+        int axis = random_int(0,2);
 
         if (axis == 0)
            qsort(l, n, sizeof(hittable *), box_x_compare);
@@ -1045,7 +1045,7 @@
 
     void permute(int *p, int n) {
         for (int i = n-1; i > 0; i--) {
-            int target = int(random_double(0, i+1));
+            int target = random_int(0, i);
             int tmp = p[i];
             p[i] = p[target];
             p[target] = tmp;

books/RayTracingTheRestOfYourLife.html

@@ -2105,7 +2105,7 @@
     }
 
     vec3 hittable_list::random(const vec3& o) const {
-        int index = int(random_double() * list_size);
+        int index = random_int(0, list_size-1);
         return list[ index ]->random(o);
     }
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

src/TheNextWeek/bvh.h

@@ -88,7 +88,7 @@ int box_z_compare (const void * a, const void * b)
 }
 
 bvh_node::bvh_node(hittable **l, int n, double time0, double time1) {
-    int axis = int(random_double(0,3));
+    int axis = random_int(0,2);
 
     if (axis == 0)
         qsort(l, n, sizeof(hittable *), box_x_compare);

src/TheRestOfYourLife/hittable_list.h

@@ -37,8 +37,8 @@ double hittable_list::pdf_value(const vec3& o, const vec3& v) const {
 }
 
 vec3 hittable_list::random(const vec3& o) const {
-        int index = int(random_double() * list_size);
-        return list[ index ]->random(o);
+    int index = random_int(0, list_size-1);
+    return list[ index ]->random(o);
 }
 
 

src/common/perlin.h

@@ -78,7 +78,7 @@ static vec3* perlin_generate() {
 
 void permute(int *p, int n) {
     for (int i = n-1; i > 0; i--) {
-        int target = int(random_double()*(i+1));
+        int target = random_int(0,i);
         int tmp = p[i];
         p[i] = p[target];
         p[target] = tmp;

src/common/rtweekend.h

@@ -43,6 +43,11 @@ inline double random_double(double min, double max) {
     return min + (max-min)*random_double();
 }
 
+inline int random_int(int min, int max) {
+    // Returns a random integer in [min,max].
+    return static_cast<int>(random_double(min, max+1));
+}
+
 // Common Headers
 
 #include "common/ray.h"