GL: new "intel-windows-half-baked-dsa-texture-bind" workaround.

This is broken as well, in a novel and interesting way. Haha.

doc/changelog.dox

@@ -81,6 +81,9 @@ See also:
         @ref GL::Mesh::setIndexBuffer()
     -   @cpp "intel-windows-broken-dsa-for-cubemaps" @ce fixing everything
         about @ref GL::CubeMapTexture (see [mosra/magnum-examples#55](https://github.com/mosra/magnum-examples/issues/55))
+    -   @cpp "intel-windows-half-baked-dsa-texture-bind" @ce fixing texture
+        binding inconsistencies (affected [mosra/magnum-examples#55](https://github.com/mosra/magnum-examples/issues/55)
+        as well)
 -   New `--magnum-gpu-validation` @ref GL-Context-command-line "command-line option"
     and a corresponding environment variable to conveniently enable
     @gl_extension{KHR,debug} debug output

src/Magnum/GL/AbstractTexture.cpp

@@ -361,6 +361,14 @@ void AbstractTexture::bindImplementationMulti(GLint textureUnit) {
 void AbstractTexture::bindImplementationDSA(const GLint textureUnit) {
     glBindTextureUnit(textureUnit, _id);
 }
+
+#ifdef CORRADE_TARGET_WINDOWS
+void AbstractTexture::bindImplementationDSAIntelWindows(const GLint textureUnit) {
+    /* See the "intel-windows-half-baked-dsa-texture-bind" workaround */
+    if(_target == GL_TEXTURE_CUBE_MAP) bindImplementationDefault(textureUnit);
+    else bindImplementationDSA(textureUnit);
+}
+#endif
 #endif
 
 #ifndef MAGNUM_TARGET_GLES2

src/Magnum/GL/AbstractTexture.h

@@ -531,6 +531,9 @@ class MAGNUM_GL_EXPORT AbstractTexture: public AbstractObject {
         #ifndef MAGNUM_TARGET_GLES
         void MAGNUM_GL_LOCAL bindImplementationMulti(GLint textureUnit);
         void MAGNUM_GL_LOCAL bindImplementationDSA(GLint textureUnit);
+        #ifdef CORRADE_TARGET_WINDOWS
+        void MAGNUM_GL_LOCAL bindImplementationDSAIntelWindows(GLint textureUnit);
+        #endif
         #endif
 
         void MAGNUM_GL_LOCAL parameterImplementationDefault(GLenum parameter, GLint value);

src/Magnum/GL/Implementation/TextureState.cpp

@@ -79,8 +79,19 @@ TextureState::TextureState(Context& context, std::vector<std::string>& extension
     if(context.isExtensionSupported<Extensions::ARB::direct_state_access>()) {
         /* Extension name added below */
 
-        unbindImplementation = &AbstractTexture::unbindImplementationDSA;
-        bindImplementation = &AbstractTexture::bindImplementationDSA;
+        #ifdef CORRADE_TARGET_WINDOWS
+        if((context.detectedDriver() & Context::DetectedDriver::IntelWindows) &&
+            !context.isDriverWorkaroundDisabled("intel-windows-half-baked-dsa-texture-bind"))
+        {
+            unbindImplementation = &AbstractTexture::unbindImplementationDefault;
+            bindImplementation = &AbstractTexture::bindImplementationDSAIntelWindows;
+        } else
+        #endif
+        {
+            unbindImplementation = &AbstractTexture::unbindImplementationDSA;
+            bindImplementation = &AbstractTexture::bindImplementationDSA;
+        }
+
     } else if(context.isExtensionSupported<Extensions::ARB::multi_bind>()) {
         /* Extension name added below */
 

src/Magnum/GL/Implementation/driverSpecific.cpp

@@ -218,6 +218,12 @@ namespace {
            for <target> 34067" (GL_TEXTURE_CUBE_MAP is 34067). Using the
             non-DSA code path as a workaround. */
         "intel-windows-broken-dsa-for-cubemaps",
+
+        /* DSA glBindTextureUnit() on Intel Windows drivers simply doesn't work
+           when passing 0 to it. Non-zero IDs work correctly except for cube
+           maps. Using the non-DSA code path for unbinding and cube maps as a
+           workaround. */
+        "intel-windows-half-baked-dsa-texture-bind",
         #endif
 
         #ifndef MAGNUM_TARGET_GLES