diff --git a/engine/app_shaders.cpp b/engine/app_shaders.cpp
index e2e0e41..4535baf 100644
--- a/engine/app_shaders.cpp
+++ b/engine/app_shaders.cpp
@@ -101,18 +101,27 @@ void App::initShaders()
         "   sum += textureOffset(t, uv, ivec2( 1,  1));\n"
         "   return sum / vec4(9.0);\n"
         "}\n"
-        "mediump vec3 blend_normal(mediump vec4 base, mediump vec4 stroke, mediump float alpha_tot) { return mix(base.rgb, stroke.rgb, stroke.a/alpha_tot); }\n"
-        "mediump vec3 blend_multiply(mediump vec4 base, mediump vec4 stroke, mediump float alpha_tot) { return mix(stroke.rgb, mix(base.rgb, base.rgb*stroke.rgb, stroke.a/alpha_tot), base.a/alpha_tot); }\n"
-        "mediump vec3 blend_screen(mediump vec4 base, mediump vec4 stroke, mediump float alpha_tot) { return mix(stroke.rgb, mix(base.rgb, 1.0-(1.0-base.rgb)*(1.0-stroke.rgb), stroke.a/alpha_tot), base.a/alpha_tot); }\n"
-        "mediump vec3 blend_colorDodge(mediump vec4 base, mediump vec4 stroke, mediump float alpha_tot) { return mix(stroke.rgb, mix(base.rgb, base.rgb/(1.0-stroke.rgb), stroke.a/alpha_tot), base.a/alpha_tot); }\n"
-        "mediump vec3 blend_overlay(mediump vec4 base, mediump vec4 stroke, mediump float alpha_tot) { return mix(stroke.rgb, mix(base.rgb, mix(2.0*base.rgb*stroke.rgb, 1.0-2.0*(1.0-base.rgb)*(1.0-stroke.rgb), floor(base.rgb*2.0)), stroke.a/alpha_tot), base.a/alpha_tot); }\n"
-        "mediump vec3 blend(mediump vec4 base, mediump vec4 stroke, mediump float alpha_tot, int mode) { switch(mode){\n"
-        "   case 0: return blend_normal(base, stroke, alpha_tot);"
-        "   case 1: return blend_multiply(base, stroke, alpha_tot);"
-        "   case 2: return blend_screen(base, stroke, alpha_tot);"
-        "   case 3: return blend_colorDodge(base, stroke, alpha_tot);"
-        "   case 4: return blend_overlay(base, stroke, alpha_tot);"
-        "}}\n"
+    
+        "mediump vec3 blend_normal(mediump vec4 base, mediump vec4 stroke, mediump float alpha_tot)"
+        "{ return mix(base.rgb, stroke.rgb, stroke.a/alpha_tot); }\n"
+        "mediump vec3 blend_multiply(mediump vec4 base, mediump vec4 stroke, mediump float alpha_tot)"
+        "{ return mix(stroke.rgb, mix(base.rgb, base.rgb*stroke.rgb, stroke.a/alpha_tot), base.a/alpha_tot); }\n"
+        "mediump vec3 blend_screen(mediump vec4 base, mediump vec4 stroke, mediump float alpha_tot)"
+        "{ return mix(stroke.rgb, mix(base.rgb, 1.0-(1.0-base.rgb)*(1.0-stroke.rgb), stroke.a/alpha_tot), base.a/alpha_tot); }\n"
+        "mediump vec3 blend_colorDodge(mediump vec4 base, mediump vec4 stroke, mediump float alpha_tot)"
+        "{ return mix(stroke.rgb, mix(base.rgb, base.rgb/(1.0-stroke.rgb), stroke.a/alpha_tot), base.a/alpha_tot); }\n"
+        "mediump vec3 blend_overlay(mediump vec4 base, mediump vec4 stroke, mediump float alpha_tot)"
+        "{ return mix(stroke.rgb, mix(base.rgb, mix(2.0*base.rgb*stroke.rgb, 1.0-2.0*(1.0-base.rgb)*(1.0-stroke.rgb), floor(base.rgb*2.0)), stroke.a/alpha_tot), base.a/alpha_tot); }\n"
+    
+        "mediump vec3 blend(mediump vec4 base, mediump vec4 stroke, mediump float alpha_tot, int mode) {\n"
+        "   if (mode == 0) return blend_normal(base, stroke, alpha_tot);\n"
+        "   else if (mode == 1) return blend_multiply(base, stroke, alpha_tot);\n"
+        "   else if (mode == 2) return blend_screen(base, stroke, alpha_tot);\n"
+        "   else if (mode == 3) return blend_colorDodge(base, stroke, alpha_tot);\n"
+        "   else if (mode == 4) return blend_overlay(base, stroke, alpha_tot);\n"
+        "   else return blend_multiply(base, stroke, alpha_tot);\n"
+        "}\n"
+    
         "void main(){\n"
         "   mediump vec4 base = texture(tex, uv.xy);\n"
         "   mediump vec4 stroke = texture(tex_stroke, uv.xy);\n"
diff --git a/engine/canvas.cpp b/engine/canvas.cpp
index 02b5a55..280b581 100644
--- a/engine/canvas.cpp
+++ b/engine/canvas.cpp
@@ -240,7 +240,9 @@ void ui::Canvas::stroke_draw()
             glDisable(GL_BLEND);
             ShaderManager::use(ui::kShader::Stroke);
             ShaderManager::u_int(kShaderUniform::Tex, 0); // brush
+            #ifndef __IOS__
             ShaderManager::u_int(kShaderUniform::TexBG, 1); // bg
+            #endif
             //ShaderManager::u_int(kShaderUniform::TexStencil, 3); // stencil
             ShaderManager::u_vec4(kShaderUniform::Col, m_brush.m_tip_color);
             ShaderManager::u_vec2(kShaderUniform::Resolution, { m_width, m_height });
diff --git a/engine/node_canvas.cpp b/engine/node_canvas.cpp
index 1895e49..dbdbb79 100644
--- a/engine/node_canvas.cpp
+++ b/engine/node_canvas.cpp
@@ -143,7 +143,7 @@ void NodeCanvas::draw()
             }
             else if(m_canvas->m_show_tmp && m_canvas->m_current_layer_idx == layer_index)
             {
-                m_sampler_linear.bind(0);
+                m_sampler.bind(0);
                 auto& paper = TextureManager::get(const_hash("data/paper.jpg"));
                 ui::ShaderManager::use(kShader::CompDraw);
                 ui::ShaderManager::u_int(kShaderUniform::Tex, 0);
diff --git a/engine/shader.cpp b/engine/shader.cpp
index b76e02b..fae1554 100644
--- a/engine/shader.cpp
+++ b/engine/shader.cpp
@@ -112,30 +112,32 @@ void Shader::use()
 }
 void Shader::u_vec4(kShaderUniform id, const glm::vec4& v)
 {
-    if (m_umap.count(id) == 0) LOG("UNIFORM %d NOT FOUND in shader %d", (int)id, (int)name);
-    glUniform4fv(m_umap[id], 1, glm::value_ptr(v));
+    if (m_umap.count(id) == 0) LOG("UNIFORM vec4 %d NOT FOUND in shader %d", (int)id, (int)name)
+    else glUniform4fv(m_umap[id], 1, glm::value_ptr(v));
 }
 
 void Shader::u_vec2(kShaderUniform id, const glm::vec2& v)
 {
-    if (m_umap.count(id) == 0) LOG("UNIFORM %d NOT FOUND in shader %d", (int)id, (int)name);
-    glUniform2fv(m_umap[id], 1, glm::value_ptr(v));
+    if (m_umap.count(id) == 0) LOG("UNIFORM vec2 %d NOT FOUND in shader %d", (int)id, (int)name)
+    else glUniform2fv(m_umap[id], 1, glm::value_ptr(v));
 }
 
 void Shader::u_mat4(kShaderUniform id, const glm::mat4& m)
 {
-    if (m_umap.count(id) == 0) LOG("UNIFORM %d NOT FOUND in shader %d", (int)id, (int)name);
-    glUniformMatrix4fv(m_umap[id], 1, GL_FALSE, glm::value_ptr(m));
+    if (m_umap.count(id) == 0) LOG("UNIFORM mat4 %d NOT FOUND in shader %d", (int)id, (int)name)
+    else glUniformMatrix4fv(m_umap[id], 1, GL_FALSE, glm::value_ptr(m));
 }
 void Shader::u_int(kShaderUniform id, int i)
 {
-    if (m_umap.count(id) == 0) LOG("UNIFORM %d NOT FOUND in shader %d", (int)id, (int)name);
-    glUniform1i(m_umap[id], i);
+    if (m_umap.count(id) == 0)
+        LOG("UNIFORM int %d NOT FOUND in shader %d", (int)id, (int)name)
+    else
+        glUniform1i(m_umap[id], i);
 }
 void Shader::u_float(kShaderUniform id, float f)
 {
-    if (m_umap.count(id) == 0) LOG("UNIFORM %d NOT FOUND in shader %d", (int)id, (int)name);
-    glUniform1f(m_umap[id], f);
+    if (m_umap.count(id) == 0) LOG("UNIFORM float %d NOT FOUND in shader %d", (int)id, (int)name)
+    else glUniform1f(m_umap[id], f);
 }
 GLint ui::Shader::GetAttribLocation(const char* name)
 {