Merge pull request #24964 from oscargus/pathspeedup

tacaswell · web-flow · commit e86ad1eb6198 · 2023-02-02T13:00:15.000-05:00
Minor cleanup and optimization of Sketch
diff --git a/src/path_converters.h b/src/path_converters.h
@@ -1018,6 +1018,9 @@ class Sketch
           m_rand(0)
     {
         rewind(0);
+        const double d_M_PI = 3.14159265358979323846;
+        m_p_scale = (2.0 * d_M_PI) / (m_length * m_randomness);
+        m_log_randomness = 2.0 * log(m_randomness);
     }
 
     unsigned vertex(double *x, double *y)
@@ -1037,18 +1040,31 @@ class Sketch
             // We want the "cursor" along the sine wave to move at a
             // random rate.
             double d_rand = m_rand.get_double();
-            double d_M_PI = 3.14159265358979323846;
-            m_p += pow(m_randomness, d_rand * 2.0 - 1.0);
-            double r = sin(m_p / (m_length / (d_M_PI * 2.0))) * m_scale;
+            // Original computation
+            // p += pow(k, 2*rand - 1)
+            // r = sin(p * c)
+            // x86 computes pow(a, b) as exp(b*log(a))
+            // First, move -1 out, so
+            // p' += pow(k, 2*rand)
+            // r = sin(p * c') where c' = c / k
+            // Next, use x86 logic (will not be worse on other platforms as
+            // the log is only computed once and pow and exp are, at worst,
+            // the same)
+            // So p+= exp(2*rand*log(k))
+            // lk = 2*log(k)
+            // p += exp(rand*lk)
+            m_p += exp(d_rand * m_log_randomness);
             double den = m_last_x - *x;
             double num = m_last_y - *y;
             double len = num * num + den * den;
             m_last_x = *x;
             m_last_y = *y;
             if (len != 0) {
                 len = sqrt(len);
-                *x += r * num / len;
-                *y += r * -den / len;
+                double r = sin(m_p * m_p_scale) * m_scale;
+                double roverlen = r / len;
+                *x += roverlen * num;
+                *y -= roverlen * den;
             }
         } else {
             m_last_x = *x;
@@ -1083,6 +1099,8 @@ class Sketch
     bool m_has_last;
     double m_p;
     RandomNumberGenerator m_rand;
+    double m_p_scale;
+    double m_log_randomness;
 };
 
 #endif // MPL_PATH_CONVERTERS_H
