rename jitter spread to scatter, dual brush scatter mode single and both axis, fix scatter to follow the direction

src/brush.h

@@ -43,7 +43,8 @@ public:
     bool  m_tip_size_pressure = false;
     float m_jitter_scale = 0;
     float m_jitter_angle = 0;
-    float m_jitter_spread = 0;
+    float m_jitter_scatter = 0;
+    bool m_jitter_scatter_bothaxis = false;
     float m_jitter_flow = 0;
     float m_jitter_opacity = 0;
     float m_jitter_hue = 0;
@@ -61,7 +62,7 @@ public:
     float m_dual_size = .75;
     float m_dual_spacing = .25;
     float m_dual_scatter = 0;
-    bool m_dual_scatter_axis = false;
+    bool m_dual_scatter_bothaxis = false;
     bool m_dual_invert = false;
     bool m_dual_flipx = false;
     bool m_dual_flipy = false;
@@ -107,8 +108,15 @@ struct StrokeSample
         return !(
             glm::isnan(angle) ||
             glm::isinf(angle) ||
+            glm::isnan(flow) ||
+            glm::isinf(flow) ||
+            glm::isnan(opacity) ||
+            glm::isinf(opacity) ||
+            glm::isnan(size) ||
+            glm::isinf(size) ||
             glm::any(glm::isnan(col)) ||
             glm::any(glm::isnan(pos)) ||
+            glm::any(glm::isnan(scale)) ||
             glm::any(glm::isnan(origin))
         );
     }