Trade: improve compat of deprecated PhongMaterialData::textureMatrix().

The new materials now commonly import separate per-texture matrices
instead of a single one even if they're all the same because that makes
the plugin implementation *much* simpler. However, existing code that
assumes there's just one matrix would get broken because textureMatrix()
would not return something else. By changing that to return a common
matrix if present and falling back to the global one we can preserve the
original behavior.

src/Magnum/Trade/PhongMaterialData.cpp

@@ -331,6 +331,7 @@ Matrix3 PhongMaterialData::commonTextureMatrix() const {
 
 #ifdef MAGNUM_BUILD_DEPRECATED
 Matrix3 PhongMaterialData::textureMatrix() const {
+    if(hasCommonTextureTransformation()) return commonTextureMatrix();
     return attributeOr(MaterialAttribute::TextureMatrix, Matrix3{});
 }
 #endif

src/Magnum/Trade/Test/MaterialDataTest.cpp

@@ -4211,6 +4211,14 @@ void MaterialDataTest::phongAccessCommonTransformationCoordinatesNoTextures() {
     CORRADE_COMPARE(a.commonTextureMatrix(), Matrix3{});
     CORRADE_COMPARE(a.commonTextureCoordinates(), 0);
 
+    #ifdef MAGNUM_BUILD_DEPRECATED
+    /* textureMatrix() should return the common matrix, if possible, and
+       fall back to the global one if not */
+    CORRADE_IGNORE_DEPRECATED_PUSH
+    CORRADE_COMPARE(a.textureMatrix(), Matrix3{});
+    CORRADE_IGNORE_DEPRECATED_POP
+    #endif
+
     PhongMaterialData b{{}, {
         {MaterialAttribute::TextureMatrix, Matrix3::scaling({0.5f, 0.5f})},
         {MaterialAttribute::TextureCoordinates, 7u}
@@ -4219,6 +4227,14 @@ void MaterialDataTest::phongAccessCommonTransformationCoordinatesNoTextures() {
     CORRADE_VERIFY(b.hasCommonTextureCoordinates());
     CORRADE_COMPARE(b.commonTextureMatrix(), Matrix3::scaling({0.5f, 0.5f}));
     CORRADE_COMPARE(b.commonTextureCoordinates(), 7);
+
+    #ifdef MAGNUM_BUILD_DEPRECATED
+    /* textureMatrix() should return the common matrix, if possible, and
+       fall back to the global one if not */
+    CORRADE_IGNORE_DEPRECATED_PUSH
+    CORRADE_COMPARE(b.textureMatrix(), Matrix3::scaling({0.5f, 0.5f}));
+    CORRADE_IGNORE_DEPRECATED_POP
+    #endif
 }
 
 void MaterialDataTest::phongAccessCommonTransformationCoordinatesOneTexture() {
@@ -4239,6 +4255,14 @@ void MaterialDataTest::phongAccessCommonTransformationCoordinatesOneTexture() {
     CORRADE_COMPARE(data.commonTextureMatrix(), Matrix3::scaling({0.5f, 1.0f}));
     CORRADE_VERIFY(data.hasCommonTextureCoordinates());
     CORRADE_COMPARE(data.commonTextureCoordinates(), 17u);
+
+    #ifdef MAGNUM_BUILD_DEPRECATED
+    /* textureMatrix() should return the common matrix, if possible, and
+       fall back to the global one if not */
+    CORRADE_IGNORE_DEPRECATED_PUSH
+    CORRADE_COMPARE(data.textureMatrix(), Matrix3::scaling({0.5f, 1.0f}));
+    CORRADE_IGNORE_DEPRECATED_POP
+    #endif
 }
 
 void MaterialDataTest::phongAccessCommonTransformationCoordinatesOneDifferentTexture() {
@@ -4261,6 +4285,14 @@ void MaterialDataTest::phongAccessCommonTransformationCoordinatesOneDifferentTex
 
     CORRADE_VERIFY(!data.hasCommonTextureTransformation());
     CORRADE_VERIFY(!data.hasCommonTextureCoordinates());
+
+    #ifdef MAGNUM_BUILD_DEPRECATED
+    /* textureMatrix() should return the common matrix, if possible, and
+       fall back to the global one if not */
+    CORRADE_IGNORE_DEPRECATED_PUSH
+    CORRADE_COMPARE(data.textureMatrix(), Matrix3::translation({0.5f, 0.0f}));
+    CORRADE_IGNORE_DEPRECATED_POP
+    #endif
 }
 
 void MaterialDataTest::phongAccessNoCommonTransformationCoordinates() {