Shaders: allow Phong with zero lights.

Which makes it equivalent to Flat3D. Useful to reduce complexity in apps
that render models with pre-baked lighting.

doc/changelog.dox

@@ -346,6 +346,9 @@ See also:
 
 -   @ref Shaders::Phong now clamps the specular factor to minimize artifacts
     when shininess is near zero
+-   @ref Shaders::Phong can now handle zero lights, in which case its output is
+    equivalent to @ref Shaders::Flat3D. See @ref Shaders-Phong-zero-lights for
+    more information.
 
 @subsubsection changelog-latest-changes-texturetools TextureTools library
 

src/Magnum/Shaders/Flat.h

@@ -65,10 +65,13 @@ and then at render time don't forget to bind also the texture via
 @ref bindTexture(). The texture is multipled by the color, which is by default
 set to @cpp 0xffffffff_rgbaf @ce.
 
-For coloring the texture based on intensity you can use the @ref Vector shader.
-
 @image html shaders-flat.png width=256px
 
+For coloring the texture based on intensity you can use the @ref Vector shader.
+The 3D version of this shader is equivalent to @ref Phong with zero lights,
+however this implementation is much simpler and thus likely also faster. See
+@ref Shaders-Phong-zero-lights "its documentation" for more information.
+
 @section Shaders-Flat-usage Example usage
 
 @subsection Shaders-Flat-usage-colored Colored mesh

src/Magnum/Shaders/Phong.cpp

@@ -69,23 +69,25 @@ Phong::Phong(const Flags flags, const UnsignedInt lightCount): _flags{flags}, _l
     GL::Shader frag = Implementation::createCompatibilityShader(rs, version, GL::Shader::Type::Fragment);
 
     #ifndef MAGNUM_TARGET_GLES
-    /* Initializer for the light color array -- we need a list of vec4(1.0)
-       joined by commas. For GLES we'll simply upload the values directly. */
-    constexpr const char lightInitializerPreamble[] = "#define LIGHT_COLOR_INITIALIZER ";
-    constexpr std::size_t lightInitializerPreambleSize =
-        Containers::arraySize(lightInitializerPreamble) - 1;
-    constexpr const char lightInitializerItem[] = "vec4(1.0), ";
-    constexpr std::size_t lightInitializerItemSize =
-        Containers::arraySize(lightInitializerItem) - 1;
     std::string lightInitializer;
-    lightInitializer.reserve(Containers::arraySize(lightInitializerPreamble) - 1 + lightCount*lightInitializerItemSize);
-    lightInitializer.append(lightInitializerPreamble, lightInitializerPreambleSize);
-    for(std::size_t i = 0; i != lightCount; ++i)
-        lightInitializer.append(lightInitializerItem, lightInitializerItemSize);
-
-    /* Drop the last comma and add a newline at the end */
-    lightInitializer[lightInitializer.size() - 2] = '\n';
-    lightInitializer.resize(lightInitializer.size() - 1);
+    if(lightCount) {
+        /* Initializer for the light color array -- we need a list of vec4(1.0)
+           joined by commas. For GLES we'll simply upload the values directly. */
+        constexpr const char lightInitializerPreamble[] = "#define LIGHT_COLOR_INITIALIZER ";
+        constexpr std::size_t lightInitializerPreambleSize =
+            Containers::arraySize(lightInitializerPreamble) - 1;
+        constexpr const char lightInitializerItem[] = "vec4(1.0), ";
+        constexpr std::size_t lightInitializerItemSize =
+            Containers::arraySize(lightInitializerItem) - 1;
+        lightInitializer.reserve(Containers::arraySize(lightInitializerPreamble) - 1 + lightCount*lightInitializerItemSize);
+        lightInitializer.append(lightInitializerPreamble, lightInitializerPreambleSize);
+        for(std::size_t i = 0; i != lightCount; ++i)
+            lightInitializer.append(lightInitializerItem, lightInitializerItemSize);
+
+        /* Drop the last comma and add a newline at the end */
+        lightInitializer[lightInitializer.size() - 2] = '\n';
+        lightInitializer.resize(lightInitializer.size() - 1);
+    }
     #endif
 
     vert.addSource(flags & (Flag::AmbientTexture|Flag::DiffuseTexture|Flag::SpecularTexture|Flag::NormalTexture) ? "#define TEXTURED\n" : "")
@@ -103,11 +105,11 @@ Phong::Phong(const Flags flags, const UnsignedInt lightCount): _flags{flags}, _l
         #endif
         .addSource(Utility::formatString(
             "#define LIGHT_COUNT {}\n"
-            "#define LIGHT_COLORS_LOCATION {}\n", lightCount, _lightPositionsUniform + lightCount))
-        #ifndef MAGNUM_TARGET_GLES
-        .addSource(std::move(lightInitializer))
-        #endif
-        .addSource(rs.get("generic.glsl"))
+            "#define LIGHT_COLORS_LOCATION {}\n", lightCount, _lightPositionsUniform + lightCount));
+    #ifndef MAGNUM_TARGET_GLES
+    if(lightCount) frag.addSource(std::move(lightInitializer));
+    #endif
+    frag.addSource(rs.get("generic.glsl"))
         .addSource(rs.get("Phong.frag"));
 
     CORRADE_INTERNAL_ASSERT_OUTPUT(GL::Shader::compile({vert, frag}));
@@ -122,8 +124,9 @@ Phong::Phong(const Flags flags, const UnsignedInt lightCount): _flags{flags}, _l
     #endif
     {
         bindAttributeLocation(Position::Location, "position");
-        bindAttributeLocation(Normal::Location, "normal");
-        if(flags & Flag::NormalTexture)
+        if(lightCount)
+            bindAttributeLocation(Normal::Location, "normal");
+        if((flags & Flag::NormalTexture) && lightCount)
             bindAttributeLocation(Tangent::Location, "tangent");
         if(flags & (Flag::AmbientTexture|Flag::DiffuseTexture|Flag::SpecularTexture))
             bindAttributeLocation(TextureCoordinates::Location, "textureCoordinates");
@@ -144,17 +147,19 @@ Phong::Phong(const Flags flags, const UnsignedInt lightCount): _flags{flags}, _l
     {
         _transformationMatrixUniform = uniformLocation("transformationMatrix");
         _projectionMatrixUniform = uniformLocation("projectionMatrix");
-        _normalMatrixUniform = uniformLocation("normalMatrix");
         _ambientColorUniform = uniformLocation("ambientColor");
-        _diffuseColorUniform = uniformLocation("diffuseColor");
-        _specularColorUniform = uniformLocation("specularColor");
-        _shininessUniform = uniformLocation("shininess");
+        if(lightCount) {
+            _normalMatrixUniform = uniformLocation("normalMatrix");
+            _diffuseColorUniform = uniformLocation("diffuseColor");
+            _specularColorUniform = uniformLocation("specularColor");
+            _shininessUniform = uniformLocation("shininess");
+            _lightPositionsUniform = uniformLocation("lightPositions");
+            _lightColorsUniform = uniformLocation("lightColors");
+        }
         if(flags & Flag::AlphaMask) _alphaMaskUniform = uniformLocation("alphaMask");
         #ifndef MAGNUM_TARGET_GLES2
         if(flags & Flag::ObjectId) _objectIdUniform = uniformLocation("objectId");
         #endif
-        _lightPositionsUniform = uniformLocation("lightPositions");
-        _lightColorsUniform = uniformLocation("lightColors");
     }
 
     #ifndef MAGNUM_TARGET_GLES
@@ -162,9 +167,11 @@ Phong::Phong(const Flags flags, const UnsignedInt lightCount): _flags{flags}, _l
     #endif
     {
         if(flags & Flag::AmbientTexture) setUniform(uniformLocation("ambientTexture"), AmbientTextureLayer);
-        if(flags & Flag::DiffuseTexture) setUniform(uniformLocation("diffuseTexture"), DiffuseTextureLayer);
-        if(flags & Flag::SpecularTexture) setUniform(uniformLocation("specularTexture"), SpecularTextureLayer);
-        if(flags & Flag::NormalTexture) setUniform(uniformLocation("normalTexture"), NormalTextureLayer);
+        if(lightCount) {
+            if(flags & Flag::DiffuseTexture) setUniform(uniformLocation("diffuseTexture"), DiffuseTextureLayer);
+            if(flags & Flag::SpecularTexture) setUniform(uniformLocation("specularTexture"), SpecularTextureLayer);
+            if(flags & Flag::NormalTexture) setUniform(uniformLocation("normalTexture"), NormalTextureLayer);
+        }
     }
 
     /* Set defaults in OpenGL ES (for desktop they are set in shader code itself) */
@@ -172,17 +179,18 @@ Phong::Phong(const Flags flags, const UnsignedInt lightCount): _flags{flags}, _l
     /* Default to fully opaque white so we can see the textures */
     if(flags & Flag::AmbientTexture) setAmbientColor(Color4{1.0f});
     else setAmbientColor(Color4{0.0f});
-    setDiffuseColor(Color4{1.0f});
-    setSpecularColor(Color4{1.0f});
-    setShininess(80.0f);
-    if(flags & Flag::AlphaMask) setAlphaMask(0.5f);
-    /* Object ID is zero by default */
-    setLightColors(Containers::Array<Color4>{Containers::DirectInit, lightCount, Color4{1.0f}});
-    /* Light position is zero by default */
-
     setTransformationMatrix({});
     setProjectionMatrix({});
-    setNormalMatrix({});
+    if(lightCount) {
+        setDiffuseColor(Color4{1.0f});
+        setSpecularColor(Color4{1.0f});
+        setShininess(80.0f);
+        if(flags & Flag::AlphaMask) setAlphaMask(0.5f);
+        /* Object ID is zero by default */
+        setLightColors(Containers::Array<Color4>{Containers::DirectInit, lightCount, Color4{1.0f}});
+        /* Light position is zero by default */
+        setNormalMatrix({});
+    }
     #endif
 }
 
@@ -196,21 +204,21 @@ Phong& Phong::bindAmbientTexture(GL::Texture2D& texture) {
 Phong& Phong::bindDiffuseTexture(GL::Texture2D& texture) {
     CORRADE_ASSERT(_flags & Flag::DiffuseTexture,
         "Shaders::Phong::bindDiffuseTexture(): the shader was not created with diffuse texture enabled", *this);
-    texture.bind(DiffuseTextureLayer);
+    if(_lightCount) texture.bind(DiffuseTextureLayer);
     return *this;
 }
 
 Phong& Phong::bindSpecularTexture(GL::Texture2D& texture) {
     CORRADE_ASSERT(_flags & Flag::SpecularTexture,
         "Shaders::Phong::bindSpecularTexture(): the shader was not created with specular texture enabled", *this);
-    texture.bind(SpecularTextureLayer);
+    if(_lightCount) texture.bind(SpecularTextureLayer);
     return *this;
 }
 
 Phong& Phong::bindNormalTexture(GL::Texture2D& texture) {
     CORRADE_ASSERT(_flags & Flag::NormalTexture,
         "Shaders::Phong::bindNormalTexture(): the shader was not created with normal texture enabled", *this);
-    texture.bind(NormalTextureLayer);
+    if(_lightCount) texture.bind(NormalTextureLayer);
     return *this;
 }
 
@@ -240,7 +248,7 @@ Phong& Phong::setObjectId(UnsignedInt id) {
 Phong& Phong::setLightPositions(const Containers::ArrayView<const Vector3> positions) {
     CORRADE_ASSERT(_lightCount == positions.size(),
         "Shaders::Phong::setLightPositions(): expected" << _lightCount << "items but got" << positions.size(), *this);
-    setUniform(_lightPositionsUniform, positions);
+    if(_lightCount) setUniform(_lightPositionsUniform, positions);
     return *this;
 }
 
@@ -254,7 +262,7 @@ Phong& Phong::setLightPosition(UnsignedInt id, const Vector3& position) {
 Phong& Phong::setLightColors(const Containers::ArrayView<const Color4> colors) {
     CORRADE_ASSERT(_lightCount == colors.size(),
         "Shaders::Phong::setLightColors(): expected" << _lightCount << "items but got" << colors.size(), *this);
-    setUniform(_lightColorsUniform, colors);
+    if(_lightCount) setUniform(_lightColorsUniform, colors);
     return *this;
 }
 

src/Magnum/Shaders/Phong.frag

@@ -53,6 +53,7 @@ uniform lowp vec4 ambientColor
     #endif
     ;
 
+#if LIGHT_COUNT
 #ifdef DIFFUSE_TEXTURE
 #ifdef EXPLICIT_TEXTURE_LAYER
 layout(binding = 1)
@@ -100,6 +101,7 @@ uniform mediump float shininess
     = 80.0
     #endif
     ;
+#endif
 
 #ifdef ALPHA_MASK
 #ifdef EXPLICIT_UNIFORM_LOCATION
@@ -120,6 +122,7 @@ layout(location = 9)
 uniform highp uint objectId; /* defaults to zero */
 #endif
 
+#if LIGHT_COUNT
 /* Needs to be last because it uses locations 10 + LIGHT_COUNT to
    10 + 2*LIGHT_COUNT - 1. Location 10 is lightPositions. Also it can't be
    specified as 10 + LIGHT_COUNT because that requires ARB_enhanced_layouts. */
@@ -131,13 +134,16 @@ uniform lowp vec4 lightColors[LIGHT_COUNT]
     = vec4[](LIGHT_COLOR_INITIALIZER)
     #endif
     ;
+#endif
 
+#if LIGHT_COUNT
 in mediump vec3 transformedNormal;
 #ifdef NORMAL_TEXTURE
 in mediump vec3 transformedTangent;
 #endif
 in highp vec3 lightDirections[LIGHT_COUNT];
 in highp vec3 cameraDirection;
+#endif
 
 #if defined(AMBIENT_TEXTURE) || defined(DIFFUSE_TEXTURE) || defined(SPECULAR_TEXTURE) || defined(NORMAL_TEXTURE)
 in mediump vec2 interpolatedTextureCoords;
@@ -163,6 +169,7 @@ void main() {
         texture(ambientTexture, interpolatedTextureCoords)*
         #endif
         ambientColor;
+    #if LIGHT_COUNT
     lowp const vec4 finalDiffuseColor =
         #ifdef DIFFUSE_TEXTURE
         texture(diffuseTexture, interpolatedTextureCoords)*
@@ -173,10 +180,12 @@ void main() {
         texture(specularTexture, interpolatedTextureCoords)*
         #endif
         specularColor;
+    #endif
 
     /* Ambient color */
     fragmentColor = finalAmbientColor;
 
+    #if LIGHT_COUNT
     /* Normal */
     mediump vec3 normalizedTransformedNormal = normalize(transformedNormal);
     #ifdef NORMAL_TEXTURE
@@ -203,6 +212,7 @@ void main() {
             fragmentColor += vec4(finalSpecularColor.rgb*specularity, finalSpecularColor.a);
         }
     }
+    #endif
 
     #ifdef ALPHA_MASK
     /* Using <= because if mask is set to 1.0, it should discard all, similarly

src/Magnum/Shaders/Phong.h

@@ -107,6 +107,14 @@ example.
 @requires_gles30 Object ID output requires integer buffer attachments, which
     are not available in OpenGL ES 2.0 or WebGL 1.0.
 
+@section Shaders-Phong-zero-lights Zero lights
+
+Creating this shader with zero lights makes its output equivalent to the
+@ref Flat3D shader --- only @ref setAmbientColor() and @ref bindAmbientTexture()
+(if @ref Flag::AmbientTexture is enabled) are taken into account, which
+correspond to @ref Flat::setColor() and @ref Flat::bindTexture(). This is
+useful to reduce complexity in apps that render models with pre-baked lights.
+
 @see @ref shaders
 */
 class MAGNUM_SHADERS_EXPORT Phong: public GL::AbstractShaderProgram {
@@ -305,11 +313,13 @@ class MAGNUM_SHADERS_EXPORT Phong: public GL::AbstractShaderProgram {
          * @brief Set diffuse color
          * @return Reference to self (for method chaining)
          *
-         * Initial value is @cpp 0xffffffff_rgbaf @ce.
+         * Initial value is @cpp 0xffffffff_rgbaf @ce. If @ref lightCount() is
+         * zero, this function is a no-op, as diffuse color doesn't contribute
+         * to the output in that case.
          * @see @ref bindDiffuseTexture()
          */
         Phong& setDiffuseColor(const Color4& color) {
-            setUniform(_diffuseColorUniform, color);
+            if(_lightCount) setUniform(_diffuseColorUniform, color);
             return *this;
         }
 
@@ -318,7 +328,8 @@ class MAGNUM_SHADERS_EXPORT Phong: public GL::AbstractShaderProgram {
          * @return Reference to self (for method chaining)
          *
          * Expects that the shader was created with @ref Flag::DiffuseTexture
-         * enabled.
+         * enabled. If @ref lightCount() is zero, this function is a no-op, as
+         * diffuse color doesn't contribute to the output in that case.
          * @see @ref bindTextures(), @ref setDiffuseColor()
          */
         Phong& bindDiffuseTexture(GL::Texture2D& texture);
@@ -337,7 +348,9 @@ class MAGNUM_SHADERS_EXPORT Phong: public GL::AbstractShaderProgram {
          * @return Reference to self (for method chaining)
          *
          * Expects that the shader was created with @ref Flag::NormalTexture
-         * enabled and the @ref Tangent attribute was supplied.
+         * enabled and the @ref Tangent attribute was supplied. If
+         * @ref lightCount() is zero, this function is a no-op, as normals
+         * dosn't contribute to the output in that case.
          * @see @ref bindTextures()
          */
         Phong& bindNormalTexture(GL::Texture2D& texture);
@@ -349,11 +362,13 @@ class MAGNUM_SHADERS_EXPORT Phong: public GL::AbstractShaderProgram {
          * Initial value is @cpp 0xffffffff_rgbaf @ce. Color will be multiplied
          * with specular texture if @ref Flag::SpecularTexture is set. If you
          * want to have a fully diffuse material, set specular color to
-         * @cpp 0x000000ff_rgbaf @ce.
+         * @cpp 0x000000ff_rgbaf @ce. If @ref lightCount() is zero, this
+         * function is a no-op, as specular color doesn't contribute to the
+         * output in that case.
          * @see @ref bindSpecularTexture()
          */
         Phong& setSpecularColor(const Color4& color) {
-            setUniform(_specularColorUniform, color);
+            if(_lightCount) setUniform(_specularColorUniform, color);
             return *this;
         }
 
@@ -362,7 +377,8 @@ class MAGNUM_SHADERS_EXPORT Phong: public GL::AbstractShaderProgram {
          * @return Reference to self (for method chaining)
          *
          * Expects that the shader was created with @ref Flag::SpecularTexture
-         * enabled.
+         * enabled. If @ref lightCount() is zero, this function is a no-op, as
+         * specular color doesn't contribute to the output in that case.
          * @see @ref bindTextures(), @ref setSpecularColor()
          */
         Phong& bindSpecularTexture(GL::Texture2D& texture);
@@ -409,10 +425,12 @@ class MAGNUM_SHADERS_EXPORT Phong: public GL::AbstractShaderProgram {
          * @return Reference to self (for method chaining)
          *
          * The larger value, the harder surface (smaller specular highlight).
-         * Initial value is @cpp 80.0f @ce.
+         * Initial value is @cpp 80.0f @ce. If @ref lightCount() is zero, this
+         * function is a no-op, as specular color doesn't contribute to the
+         * output in that case.
          */
         Phong& setShininess(Float shininess) {
-            setUniform(_shininessUniform, shininess);
+            if(_lightCount) setUniform(_shininessUniform, shininess);
             return *this;
         }
 
@@ -462,10 +480,12 @@ class MAGNUM_SHADERS_EXPORT Phong: public GL::AbstractShaderProgram {
          * The matrix doesn't need to be normalized, as the renormalization
          * must be done in the shader anyway. You need to set also
          * @ref setTransformationMatrix() with a corresponding value. Initial
-         * value is an identity matrix.
+         * value is an identity matrix. If @ref lightCount() is zero, this
+         * function is a no-op, as normals don't contribute to the output in
+         * that case.
          */
         Phong& setNormalMatrix(const Matrix3x3& matrix) {
-            setUniform(_normalMatrixUniform, matrix);
+            if(_lightCount) setUniform(_normalMatrixUniform, matrix);
             return *this;
         }
 

src/Magnum/Shaders/Phong.vert

@@ -46,6 +46,7 @@ uniform highp mat4 projectionMatrix
     #endif
     ;
 
+#if LIGHT_COUNT
 #ifdef EXPLICIT_UNIFORM_LOCATION
 layout(location = 2)
 #endif
@@ -54,18 +55,22 @@ uniform mediump mat3 normalMatrix
     = mat3(1.0)
     #endif
     ;
+#endif
 
+#if LIGHT_COUNT
 /* Needs to be last because it uses locations 10 to 10 + LIGHT_COUNT - 1 */
 #ifdef EXPLICIT_UNIFORM_LOCATION
 layout(location = 10)
 #endif
 uniform highp vec3 lightPositions[LIGHT_COUNT]; /* defaults to zero */
+#endif
 
 #ifdef EXPLICIT_ATTRIB_LOCATION
 layout(location = POSITION_ATTRIBUTE_LOCATION)
 #endif
 in highp vec4 position;
 
+#if LIGHT_COUNT
 #ifdef EXPLICIT_ATTRIB_LOCATION
 layout(location = NORMAL_ATTRIBUTE_LOCATION)
 #endif
@@ -77,6 +82,7 @@ layout(location = TANGENT_ATTRIBUTE_LOCATION)
 #endif
 in mediump vec3 tangent;
 #endif
+#endif
 
 #ifdef TEXTURED
 #ifdef EXPLICIT_ATTRIB_LOCATION
@@ -87,18 +93,21 @@ in mediump vec2 textureCoords;
 out mediump vec2 interpolatedTextureCoords;
 #endif
 
+#if LIGHT_COUNT
 out mediump vec3 transformedNormal;
 #ifdef NORMAL_TEXTURE
 out mediump vec3 transformedTangent;
 #endif
 out highp vec3 lightDirections[LIGHT_COUNT];
 out highp vec3 cameraDirection;
+#endif
 
 void main() {
     /* Transformed vertex position */
     highp vec4 transformedPosition4 = transformationMatrix*position;
     highp vec3 transformedPosition = transformedPosition4.xyz/transformedPosition4.w;
 
+    #if LIGHT_COUNT
     /* Transformed normal and tangent vector */
     transformedNormal = normalMatrix*normal;
     #ifdef NORMAL_TEXTURE
@@ -111,6 +120,7 @@ void main() {
 
     /* Direction to the camera */
     cameraDirection = -transformedPosition;
+    #endif
 
     /* Transform the position */
     gl_Position = projectionMatrix*transformedPosition4;

src/Magnum/Shaders/Test/CMakeLists.txt

@@ -139,7 +139,10 @@ if(BUILD_GL_TESTS)
             PhongTestFiles/textured-diffuse.tga
             PhongTestFiles/textured-normal.tga
             PhongTestFiles/textured-specular.tga
-            PhongTestFiles/textured.tga)
+            PhongTestFiles/textured.tga
+
+            # For zero lights test (equivalency to Flat3D)
+            FlatTestFiles/textured3D-alpha-mask0.5.tga)
     if(NOT BUILD_PLUGINS_STATIC)
         target_include_directories(ShadersPhongGLTest PRIVATE $<TARGET_FILE_DIR:ShadersPhongGLTest>)
     else()

src/Magnum/Shaders/Test/PhongGLTest.cpp

@@ -95,6 +95,8 @@ struct PhongGLTest: GL::OpenGLTester {
     void renderObjectId();
     #endif
 
+    void renderZeroLights();
+
     private:
         PluginManager::Manager<Trade::AbstractImporter> _manager{"nonexistent"};
 
@@ -139,7 +141,8 @@ constexpr struct {
     {"object ID", Phong::Flag::ObjectId, 1},
     {"object ID + alpha mask + specular texture", Phong::Flag::ObjectId|Phong::Flag::AlphaMask|Phong::Flag::SpecularTexture, 1},
     #endif
-    {"five lights", {}, 5}
+    {"five lights", {}, 5},
+    {"zero lights", {}, 0}
 };
 
 using namespace Math::Literals;
@@ -299,6 +302,16 @@ PhongGLTest::PhongGLTest() {
         &PhongGLTest::renderObjectIdTeardown);
     #endif
 
+    addTests({&PhongGLTest::renderZeroLights},
+        #ifndef MAGNUM_TARGET_GLES2
+        &PhongGLTest::renderObjectIdSetup,
+        &PhongGLTest::renderObjectIdTeardown
+        #else
+        &PhongGLTest::renderSetup,
+        &PhongGLTest::renderTeardown
+        #endif
+    );
+
     /* Load the plugins directly from the build tree. Otherwise they're either
        static and already loaded or not present in the build tree */
     #ifdef ANYIMAGEIMPORTER_PLUGIN_FILENAME
@@ -1065,6 +1078,99 @@ void PhongGLTest::renderObjectId() {
 }
 #endif
 
+void PhongGLTest::renderZeroLights() {
+    CORRADE_COMPARE(_framebuffer.checkStatus(GL::FramebufferTarget::Draw), GL::Framebuffer::Status::Complete);
+
+    if(!(_manager.loadState("AnyImageImporter") & PluginManager::LoadState::Loaded) ||
+       !(_manager.loadState("TgaImporter") & PluginManager::LoadState::Loaded))
+        CORRADE_SKIP("AnyImageImporter / TgaImageImporter plugins not found.");
+
+    GL::Mesh sphere = MeshTools::compile(Primitives::uvSphereSolid(16, 32,
+        Primitives::UVSphereTextureCoords::Generate));
+
+    Phong shader{
+        Phong::Flag::AmbientTexture|Phong::Flag::AlphaMask
+        #ifndef MAGNUM_TARGET_GLES2
+        |Phong::Flag::ObjectId
+        #endif
+    , 0};
+
+    Containers::Pointer<Trade::AbstractImporter> importer = _manager.loadAndInstantiate("AnyImageImporter");
+    CORRADE_VERIFY(importer);
+
+    GL::Texture2D ambient;
+    Containers::Optional<Trade::ImageData2D> ambientImage;
+    CORRADE_VERIFY(importer->openFile(Utility::Directory::join(SHADERS_TEST_DIR, "TestFiles/diffuse-alpha-texture.tga")) && (ambientImage = importer->image2D(0)));
+    ambient.setMinificationFilter(GL::SamplerFilter::Linear)
+        .setMagnificationFilter(GL::SamplerFilter::Linear)
+        .setWrapping(GL::SamplerWrapping::ClampToEdge)
+        .setStorage(1, TextureFormatRGBA, ambientImage->size())
+        .setSubImage(0, {}, *ambientImage);
+
+    GL::Texture2D bogus;
+
+    shader
+        .bindAmbientTexture(ambient)
+        .setAmbientColor(0x9999ff_rgbf)
+        .setTransformationMatrix(
+            Matrix4::translation(Vector3::zAxis(-2.15f))*
+            Matrix4::rotationY(-15.0_degf)*
+            Matrix4::rotationX(15.0_degf))
+        .setProjectionMatrix(Matrix4::perspectiveProjection(60.0_degf, 1.0f, 0.1f, 10.0f))
+        .setAlphaMask(0.5f)
+        #ifndef MAGNUM_TARGET_GLES2
+        .setObjectId(65534)
+        #endif
+        /* Passing a zero-sized light position / color array, shouldn't assert */
+        .setLightPositions({})
+        .setLightColors({})
+        /* Using a bogus normal matrix -- it's not used so it should be okay.
+           Same for all other unused values, they should get ignored. */
+        .setNormalMatrix(Matrix3x3{Math::ZeroInit})
+        .setDiffuseColor(0xfa9922_rgbf)
+        .setSpecularColor(0xfa9922_rgbf)
+        .setShininess(0.2f);
+
+    /* For proper Z order draw back faces first and then front faces */
+    GL::Renderer::setFaceCullingMode(GL::Renderer::PolygonFacing::Front);
+    sphere.draw(shader);
+    GL::Renderer::setFaceCullingMode(GL::Renderer::PolygonFacing::Back);
+    sphere.draw(shader);
+
+    MAGNUM_VERIFY_NO_GL_ERROR();
+
+    #if !(defined(MAGNUM_TARGET_GLES2) && defined(MAGNUM_TARGET_WEBGL))
+    /* Compared to FlatGLTest::renderAlpha3D(0.5), there's a bit more different
+       pixels on the edges, caused by matrix multiplication being done in the
+       shader and not on the CPU side. */
+    const Float maxThreshold = 139.0f, meanThreshold = 0.122f;
+    #else
+    /* WebGL 1 doesn't have 8bit renderbuffer storage, so it's way worse */
+    const Float maxThreshold = 139.0f, meanThreshold = 2.896f;
+    #endif
+    CORRADE_COMPARE_WITH(
+        /* Dropping the alpha channel, as it's always 1.0 */
+        Containers::arrayCast<Color3ub>(_framebuffer.read(_framebuffer.viewport(), {PixelFormat::RGBA8Unorm}).pixels<Color4ub>()),
+        /* Should be equivalent to masked Flat3D */
+        Utility::Directory::join(SHADERS_TEST_DIR, "FlatTestFiles/textured3D-alpha-mask0.5.tga"),
+        (DebugTools::CompareImageToFile{_manager, maxThreshold, meanThreshold}));
+
+    #ifndef MAGNUM_TARGET_GLES2
+    /* Object ID -- no need to verify the whole image, just check that pixels
+       on known places have expected values. SwiftShader insists that the read
+       format has to be 32bit, so the renderbuffer format is that too to make
+       it the same (ES3 Mesa complains if these don't match). */
+    _framebuffer.mapForRead(GL::Framebuffer::ColorAttachment{1});
+    CORRADE_COMPARE(_framebuffer.checkStatus(GL::FramebufferTarget::Read), GL::Framebuffer::Status::Complete);
+    Image2D image = _framebuffer.read(_framebuffer.viewport(), {PixelFormat::R32UI});
+    MAGNUM_VERIFY_NO_GL_ERROR();
+    /* Outside of the object, cleared to 27 */
+    CORRADE_COMPARE(image.pixels<UnsignedInt>()[10][10], 27);
+    /* Inside of the object. Verify that it can hold 16 bits at least. */
+    CORRADE_COMPARE(image.pixels<UnsignedInt>()[40][46], 65534);
+    #endif
+}
+
 }}}}
 
 CORRADE_TEST_MAIN(Magnum::Shaders::Test::PhongGLTest)