non linear slider for brush tip control

engine/node_stroke_preview.cpp

@@ -65,8 +65,10 @@ void NodeStrokePreview::draw_stroke()
         glEnable(GL_BLEND);
         glm::mat4 proj = glm::ortho<float>(0, (float)m_rtt.getWidth(), 0, (float)m_rtt.getHeight(), -1, 1);
 
+        auto b = m_brush;
+        b.m_tip_size *= .7f; // reduce the size in the preview
         m_stroke.reset();
-        m_stroke.start(m_brush);
+        m_stroke.start(b);
         auto samples = m_stroke.compute_samples();
         auto& tex = TextureManager::get(m_brush.m_tex_id);
         tex.bind();