Shaders: add a generic texture layer attribute and UBO definition.

The attribute will be used for instanced texture layers in
texture-array-enabled shaders.

src/Magnum/Shaders/Generic.h

@@ -374,10 +374,9 @@ Used only if @ref DistanceFieldVectorGL::Flag::TextureTransformation,
 */
 struct TextureTransformationUniform {
     /** @brief Construct with default parameters */
-    constexpr explicit TextureTransformationUniform(DefaultInitT = DefaultInit) noexcept: rotationScaling{Math::IdentityInit}
+    constexpr explicit TextureTransformationUniform(DefaultInitT = DefaultInit) noexcept: rotationScaling{Math::IdentityInit}, offset{0.0f, 0.0f}, layer{0}
         #if (defined(CORRADE_TARGET_CLANG) && __clang_major__ < 4) || (defined(CORRADE_TARGET_APPLE_CLANG) && __clang_major__ < 8)
-        /* Otherwise it refuses to constexpr, on 3.8 at least */
-        , _pad0{}, _pad1{}
+        , _pad0{} /* Otherwise it refuses to constexpr, on 3.8 at least */
         #endif
         {}
     /** @brief Construct without initializing the contents */
@@ -407,6 +406,15 @@ struct TextureTransformationUniform {
         return *this;
     }
 
+    /**
+     * @brief Set the @ref layer field
+     * @return Reference to self (for method chaining)
+     */
+    TextureTransformationUniform& setLayer(UnsignedInt layer) {
+        this->layer = layer;
+        return *this;
+    }
+
     /**
      * @}
      */
@@ -449,6 +457,14 @@ struct TextureTransformationUniform {
      */
     Vector2 offset;
 
+    /**
+     * @brief Texture layer
+     *
+     * Descibes which layer of a texture array to use. Default value is
+     * @cpp 0.5f @ce.
+     */
+    UnsignedInt layer;
+
     /* warning: Member __pad0__ is not documented. FFS DOXYGEN WHY DO YOU THINK
        I MADE THOSE UNNAMED, YOU DUMB FOOL */
     #ifndef DOXYGEN_GENERATING_OUTPUT
@@ -456,11 +472,6 @@ struct TextureTransformationUniform {
         #if (defined(CORRADE_TARGET_CLANG) && __clang_major__ < 4) || (defined(CORRADE_TARGET_APPLE_CLANG) && __clang_major__ < 8)
         _pad0 /* Otherwise it refuses to constexpr, on 3.8 at least */
         #endif
-        :32; /* reserved for layer */
-    Int
-        #if (defined(CORRADE_TARGET_CLANG) && __clang_major__ < 4) || (defined(CORRADE_TARGET_APPLE_CLANG) && __clang_major__ < 8)
-        _pad1 /* Otherwise it refuses to constexpr, on 3.8 at least */
-        #endif
         :32; /* reserved for coordinateSet */
     #endif
 };

src/Magnum/Shaders/GenericGL.h

@@ -186,9 +186,7 @@ rotation and scale
 <tr>
 <td>15</td>
 <td>
-@ref TextureOffset (instanced)
-
-* *Reserved* --- third component for a layer
+@ref TextureOffset / @ref TextureOffsetLayer (instanced)
 </td>
 <td>
 * *Reserved* --- a single component \n
@@ -420,8 +418,9 @@ template<UnsignedInt dimensions> struct GenericGL {
      * @brief (Instanced) texture offset
      * @m_since{2020,06}
      *
-     * @ref Magnum::Vector2 "Vector2". Currently doesn't have a corresponding
-     * @ref Trade::MeshAttribute.
+     * @ref Magnum::Vector2 "Vector2". Use either this or the
+     * @ref TextureOffsetLayer attribute. Currently doesn't have a
+     * corresponding @ref Trade::MeshAttribute.
      * @requires_gl33 Extension @gl_extension{ARB,instanced_arrays}
      * @requires_gles30 Extension @gl_extension{ANGLE,instanced_arrays},
      *      @gl_extension{EXT,instanced_arrays} or
@@ -430,6 +429,22 @@ template<UnsignedInt dimensions> struct GenericGL {
      *      in WebGL 1.0.
      */
     typedef GL::Attribute<15, Vector2> TextureOffset;
+
+    #ifndef MAGNUM_TARGET_GLES2
+    /**
+     * @brief (Instanced) texture offset and layer
+     * @m_since_latest
+     *
+     * @ref Magnum::Vector3 "Vector3", with the last component interpreted as
+     * an integer. Use either this or the @ref TextureOffset attribute.
+     * Currently doesn't have a corresponding @ref Trade::MeshAttribute.
+     * @requires_gl33 Extension @gl_extension{EXT,texture_array} and
+     *      @gl_extension{ARB,instanced_arrays}
+     * @requires_gles30 Texture arrays are not available in OpenGL ES 2.0.
+     * @requires_webgl20 Texture arrays are not available in WebGL 1.0.
+     */
+    typedef GL::Attribute<15, Vector3> TextureOffsetLayer;
+    #endif
 };
 #endif
 
@@ -462,6 +477,9 @@ struct BaseGenericGL {
     #endif
 
     typedef GL::Attribute<15, Vector2> TextureOffset;
+    #ifndef MAGNUM_TARGET_GLES2
+    typedef GL::Attribute<15, Vector3> TextureOffsetLayer;
+    #endif
 };
 
 template<> struct GenericGL<2>: BaseGenericGL {

src/Magnum/Shaders/Test/GenericTest.cpp

@@ -378,6 +378,8 @@ void GenericTest::textureTransformationUniformConstructDefault() {
     }));
     CORRADE_COMPARE(a.offset, (Vector2{0.0f, 0.0f}));
     CORRADE_COMPARE(b.offset, (Vector2{0.0f, 0.0f}));
+    CORRADE_COMPARE(a.layer, 0);
+    CORRADE_COMPARE(b.layer, 0);
 
     constexpr TextureTransformationUniform ca;
     constexpr TextureTransformationUniform cb{DefaultInit};
@@ -391,6 +393,8 @@ void GenericTest::textureTransformationUniformConstructDefault() {
     }));
     CORRADE_COMPARE(ca.offset, (Vector2{0.0f, 0.0f}));
     CORRADE_COMPARE(cb.offset, (Vector2{0.0f, 0.0f}));
+    CORRADE_COMPARE(ca.layer, 0);
+    CORRADE_COMPARE(cb.layer, 0);
 
     CORRADE_VERIFY(std::is_nothrow_default_constructible<TextureTransformationUniform>::value);
     CORRADE_VERIFY(std::is_nothrow_constructible<TextureTransformationUniform, DefaultInitT>::value);
@@ -403,6 +407,7 @@ void GenericTest::textureTransformationUniformConstructNoInit() {
     TextureTransformationUniform a;
     a.rotationScaling[1] = {2.5f, -3.0f};
     a.offset = {2.7f, 0.3f};
+    a.layer = 37;
 
     new(&a) TextureTransformationUniform{NoInit};
     {
@@ -411,6 +416,7 @@ void GenericTest::textureTransformationUniformConstructNoInit() {
         #endif
         CORRADE_COMPARE(a.rotationScaling[1], (Vector2{2.5f, -3.0f}));
         CORRADE_COMPARE(a.offset, (Vector2{2.7f, 0.3f}));
+        CORRADE_COMPARE(a.layer, 37);
     }
 
     CORRADE_VERIFY(std::is_nothrow_constructible<TextureTransformationUniform, NoInitT>::value);
@@ -422,12 +428,14 @@ void GenericTest::textureTransformationUniformConstructNoInit() {
 void GenericTest::textureTransformationUniformSetters() {
     TextureTransformationUniform a;
     a.setTextureMatrix(Matrix3::translation({2.6f, 0.3f})*
-                       Matrix3::rotation(90.0_degf));
+                       Matrix3::rotation(90.0_degf))
+     .setLayer(37);
     CORRADE_COMPARE(a.rotationScaling, (Matrix2x2{
         Vector2{ 0.0f, 1.0f},
         Vector2{-1.0f, 0.0f}
     }));
     CORRADE_COMPARE(a.offset, (Vector2{2.6f, 0.3f}));
+    CORRADE_COMPARE(a.layer, 37);
 }
 
 }}}}