Shaders: fix default alpha mask in a zero-light Phong on GLES.

A corner case of a corner case, of a corner case. Adapted the test to
check the defaults as well.

doc/changelog.dox

@@ -391,6 +391,8 @@ See also:
 -   @ref Resource was unnecessarily querying the @ref ResourceManager for
     updated data even in cases where no resource update was done since last
     check
+-   For a @ref Shaders::Phong with zero lights, alpha mask default value was
+    incorrectly @cpp 0.0f @ce instead of @cpp 0.5f @ce on OpenGL ES
 
 @subsection changelog-latest-deprecated Deprecated APIs
 

src/Magnum/Shaders/Phong.cpp

@@ -191,12 +191,12 @@ Phong::Phong(const Flags flags, const UnsignedInt lightCount): _flags{flags}, _l
         setDiffuseColor(Magnum::Color4{1.0f});
         setSpecularColor(Magnum::Color4{1.0f});
         setShininess(80.0f);
-        if(flags & Flag::AlphaMask) setAlphaMask(0.5f);
-        /* Object ID is zero by default */
         setLightColors(Containers::Array<Magnum::Color4>{Containers::DirectInit, lightCount, Magnum::Color4{1.0f}});
         /* Light position is zero by default */
         setNormalMatrix({});
     }
+    if(flags & Flag::AlphaMask) setAlphaMask(0.5f);
+    /* Object ID is zero by default */
     #endif
 }
 

src/Magnum/Shaders/Test/PhongGLTest.cpp

@@ -1063,7 +1063,9 @@ void PhongGLTest::renderAlpha() {
         .setSpecularColor(0xffffff00_rgbaf)
         .bindTextures(&ambient, &diffuse, nullptr, nullptr);
 
-    if(data.flags & Phong::Flag::AlphaMask)
+    /* Test that the default is correct by not setting the threshold if it's
+       equal to the default */
+    if(data.flags & Phong::Flag::AlphaMask && data.threshold != 0.5f)
         shader.setAlphaMask(data.threshold);
 
     /* For proper Z order draw back faces first and then front faces */
@@ -1213,7 +1215,7 @@ void PhongGLTest::renderZeroLights() {
             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)
+        /* Keep alpha mask at the default 0.5 to test the default */
         #ifndef MAGNUM_TARGET_GLES2
         .setObjectId(65534)
         #endif