New explicit-uniform-location-is-less-explicit-than-you-hoped workaround.

Intel drivers on Windows. Surprisingly unsurprising.

doc/changelog.dox

@@ -449,6 +449,10 @@ See also:
 -   @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.
+-   @ref Shaders::MeshVisualizer is fixed to work properly on Intel Windows
+    drivers, adding a new
+    @cpp "intel-windows-explicit-uniform-location-is-less-explicit-than-you-hoped" @ce
+    workaround
 
 @subsubsection changelog-latest-changes-texturetools TextureTools library
 

src/Magnum/GL/Implementation/driverSpecific.cpp

@@ -253,6 +253,18 @@ namespace {
    glVertexAttribIFormat() works or not. A test that triggers this issue is in
    MeshGLTest::addVertexBufferIntWithShort(). */
 "intel-windows-broken-dsa-integer-vertex-attributes",
+
+/* When using more than just a vertex and fragment shader (geometry shader,
+   e.g.), ARB_explicit_uniform_location on Intel silently uses wrong
+   locations, blowing up with either a non-descript
+    Error has been generated. GL error GL_INVALID_OPERATION in ProgramUniformMatrix4fv: (ID: 2052228270) Generic error
+   or, if you are lucky, a highly-cryptic-but-still-better-than-nothing
+    Error has been generated. GL error GL_INVALID_OPERATION in ProgramUniform4fv: (ID: 1725519030) GL error GL_INVALID_OPERATION: mismatched type setting uniform of location "3" in program 1, "" using shaders, 2, "", 3, "", 8, ""
+   *unless* you have vertex uniform locations first, fragment locations second
+   and geometry locations last. Not sure about the other stages. Note that this
+   workaround doesn't actually do anything, it's just printed as a heads-up
+   for the sleepless nights debugging issues that happen only on Intel. */
+"intel-windows-explicit-uniform-location-is-less-explicit-than-you-hoped",
 #endif
 
 #ifndef MAGNUM_TARGET_GLES
@@ -396,16 +408,22 @@ void Context::setupDriverWorkarounds() {
             _extensionRequiredVersion[Extensions::extension::Index] = Version::version
 
     #ifndef MAGNUM_TARGET_GLES
-    #ifdef CORRADE_TARGET_WINDOWS
-    if((detectedDriver() & DetectedDriver::IntelWindows) && !isExtensionSupported<Extensions::ARB::shading_language_420pack>() && !isDriverWorkaroundDisabled("intel-windows-glsl-exposes-unsupported-shading-language-420pack"))
-        _setRequiredVersion(ARB::shading_language_420pack, None);
-    #endif
-
     if(!isDriverWorkaroundDisabled("no-layout-qualifiers-on-old-glsl")) {
         _setRequiredVersion(ARB::explicit_attrib_location, GL320);
         _setRequiredVersion(ARB::explicit_uniform_location, GL320);
         _setRequiredVersion(ARB::shading_language_420pack, GL320);
     }
+
+    #ifdef CORRADE_TARGET_WINDOWS
+    if((detectedDriver() & DetectedDriver::IntelWindows) && !isExtensionSupported<Extensions::ARB::shading_language_420pack>() && !isDriverWorkaroundDisabled("intel-windows-glsl-exposes-unsupported-shading-language-420pack"))
+        _setRequiredVersion(ARB::shading_language_420pack, None);
+
+    if((detectedDriver() & DetectedDriver::IntelWindows) && isExtensionSupported<Extensions::ARB::explicit_uniform_location>() && !isDriverWorkaroundDisabled("intel-windows-explicit-uniform-location-is-less-explicit-than-you-hoped")) {
+        /* Just to have it printed in the log. Ideal would be to have this
+           covered with a minimal repro case but I have better things to do
+           in my life. */
+    }
+    #endif
     #endif
 
     #ifndef MAGNUM_TARGET_GLES

src/Magnum/Shaders/MeshVisualizer.frag

@@ -45,7 +45,7 @@
 #endif
 
 #ifdef EXPLICIT_UNIFORM_LOCATION
-layout(location = 2)
+layout(location = 1)
 #endif
 uniform lowp vec4 color
     #ifndef GL_ES
@@ -55,7 +55,7 @@ uniform lowp vec4 color
 
 #ifdef WIREFRAME_RENDERING
 #ifdef EXPLICIT_UNIFORM_LOCATION
-layout(location = 3)
+layout(location = 2)
 #endif
 uniform lowp vec4 wireframeColor
     #ifndef GL_ES
@@ -64,7 +64,7 @@ uniform lowp vec4 wireframeColor
     ;
 
 #ifdef EXPLICIT_UNIFORM_LOCATION
-layout(location = 4)
+layout(location = 3)
 #endif
 uniform lowp float wireframeWidth
     #ifndef GL_ES
@@ -73,7 +73,7 @@ uniform lowp float wireframeWidth
     ;
 
 #ifdef EXPLICIT_UNIFORM_LOCATION
-layout(location = 5)
+layout(location = 4)
 #endif
 uniform lowp float smoothness
     #ifndef GL_ES

src/Magnum/Shaders/MeshVisualizer.geom

@@ -35,7 +35,7 @@
 #endif
 
 #ifdef EXPLICIT_UNIFORM_LOCATION
-layout(location = 1)
+layout(location = 5)
 #endif
 uniform lowp vec2 viewportSize; /* defaults to zero */
 

src/Magnum/Shaders/MeshVisualizer.h

@@ -252,11 +252,11 @@ class MAGNUM_SHADERS_EXPORT MeshVisualizer: public GL::AbstractShaderProgram {
     private:
         Flags _flags;
         Int _transformationProjectionMatrixUniform{0},
-            _viewportSizeUniform{1},
+            _colorUniform{1},
-            _colorUniform{2},
+            _wireframeColorUniform{2},
-            _wireframeColorUniform{3},
+            _wireframeWidthUniform{3},
-            _wireframeWidthUniform{4},
+            _smoothnessUniform{4},
-            _smoothnessUniform{5};
+            _viewportSizeUniform{5};
 };
 
 /** @debugoperatorclassenum{MeshVisualizer,MeshVisualizer::Flag} */