implement stencil from file

src/node_panel_stroke.cpp

@@ -2,6 +2,8 @@
 #include "log.h"
 #include "node_panel_stroke.h"
 #include "canvas.h"
+#include "node_button.h"
+#include "app.h"
 
 Node* NodePanelStroke::clone_instantiate() const
 {
@@ -85,6 +87,17 @@ void NodePanelStroke::init_controls()
 
     m_preview->m_brush = Canvas::I->m_current_brush;
     m_preview->draw_stroke();
+
+    auto load_stencil = find<NodeButton>("tip-stencil-load");
+    load_stencil->on_click = [this](Node*) {
+        App::I.pick_image([this](std::string path) {
+            if (TextureManager::load(path.c_str()))
+            {
+                if (on_stencil_changed)
+                    on_stencil_changed(this, const_hash(path.c_str()));
+            }
+        });
+    };
 }
 
 void NodePanelStroke::init_slider(NodeSliderH*& target, const char* id, float Brush::* prop)