linear interpolation on layers draw

engine/node_canvas.cpp

@@ -15,6 +15,7 @@ void NodeCanvas::init()
     m_canvas = std::make_unique<ui::Canvas>();
     m_canvas->create(RES, RES);
     m_sampler.create(GL_NEAREST);
+    m_sampler_linear.create(GL_LINEAR);
     m_sampler_stencil.create(GL_LINEAR, GL_REPEAT);
     m_face_plane.create<1>(2, 2);
     m_line.create();
@@ -174,7 +175,7 @@ void NodeCanvas::draw()
             }
             else
             {
-                m_sampler_stencil.bind(0);
+                m_sampler_linear.bind(0);
                 ui::ShaderManager::use(kShader::TextureAlpha);
                 ui::ShaderManager::u_int(kShaderUniform::Tex, 0);
                 ui::ShaderManager::u_float(kShaderUniform::Alpha, m_canvas->m_layers[layer_index].m_opacity);

engine/node_canvas.h

@@ -9,6 +9,7 @@ public:
     std::unique_ptr<ui::Canvas> m_canvas;
     ui::Brush m_brush;
     Sampler m_sampler;
+    Sampler m_sampler_linear;
     Sampler m_sampler_stencil;
     ui::Plane m_face_plane;
     ui::LineSegment m_line;