shader fix

src/app_shaders.cpp

@@ -155,7 +155,6 @@ void App::initShaders()
     static const char* shader_stroke_preview_f =
         SHADER_VERSION
         "uniform sampler2D tex;\n"
-        "uniform mediump float alpha;\n"
         "uniform mediump vec4 col;\n"
         "in mediump vec2 uv;\n"
         "out mediump vec4 frag;\n"

src/canvas_modes.cpp

@@ -207,7 +207,6 @@ void CanvasModePen::on_Draw(const glm::mat4& ortho, const glm::mat4& proj, const
             pos.x = pos.x - canvas->m_current_brush.m_tip_size * 500.f;
         ShaderManager::use(kShader::StrokePreview);
         ShaderManager::u_int(kShaderUniform::Tex, 0);
-        ShaderManager::u_float(kShaderUniform::Alpha, canvas->m_current_brush.m_tip_flow);
         float tip_scale_fix = 1.f / glm::tan(glm::radians(Canvas::I->m_cam_fov * 0.5f));
         float tip_scale = canvas->m_current_brush.m_tip_size * 800.f * tip_scale_fix;
         float tip_angle = canvas->m_current_brush.m_tip_angle * (float)(M_PI * 2.0);