GL: new pseudo-extension MAGNUM_shader_vertex_id.

Will be used to distinguish if the driver supports gl_VertexID. This is
not the case on SwiftShader ES3 contexts (and could be elsewhere,
probably).

doc/changelog.dox

@@ -64,6 +64,13 @@ See also:
     that's fixing misbehaving buffers when using
     @ref GL::Buffer::TargetHint::TransformFeedback. See @ref opengl-workarounds
     for more information.
+-   New pseudo-extension `GL_MAGNUM_shader_vertex_id` denoting support of the
+    @glsl gl_VertexID @ce shader builtin. Present on all GL 3.0+, GLES 3.0+ and
+    WebGL 2 contexts, but disabled for SwiftShader as its support is broken
+    (see the @cpp "swiftshader-broken-shader-vertex-id" @ce workaround in
+    @ref opengl-workarounds for more information). This pseudo-extension can be
+    also explicitly disabled using the usual `--magnum-disable-extensions`
+    @ref GL-Context-command-line "command-line option" for testing purposes.
 -   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

doc/opengl-support.dox

@@ -81,6 +81,7 @@ GLSL 1.30                                   | done
 @gl_extension{EXT,draw_buffers2}            | |
 @gl_extension{EXT,texture_integer}          | done (GL 3.0 subset)
 @gl_extension{EXT,transform_feedback}       | done
+`MAGNUM_shader_vertex_id` \n @m_span{m-text m-dim} Pseudo-extension denoting support for the @glsl gl_VertexID @ce GLSL builtin. @m_endspan | done
 @gl_extension{NV,depth_buffer_float}        | |
 @gl_extension{NV,conditional_render}        | done
 
@@ -399,6 +400,7 @@ Extension                                   | Status
 @gl_extension{EXT,draw_buffers}             | done
 @gl_extension{EXT,instanced_arrays}         | done
 @gl_extension{EXT,draw_instanced}           | done
+`MAGNUM_shader_vertex_id` \n @m_span{m-text m-dim} Pseudo-extension denoting support for the @glsl gl_VertexID @ce \n GLSL builtin. Exposed on ES3 builds as well. @m_endspan | done
 @gl_extension{NV,draw_buffers}              | done
 @gl_extension{NV,fbo_color_attachments}     | done
 @gl_extension{NV,read_buffer}               | done
@@ -495,6 +497,7 @@ Extension                                   | Status
 @webgl_extension{EXT,color_buffer_half_float} | |
 @webgl_extension{EXT,blend_minmax}          | done
 @webgl_extension{EXT,shader_texture_lod}    | done (shading language only)
+`MAGNUM_shader_vertex_id` \n @m_span{m-text m-dim} Pseudo-extension denoting support for the @glsl gl_VertexID @ce \n GLSL builtin. Exposed on WebGL 2 builds as well. @m_endspan | done
 @webgl_extension{OES,texture_float}         | done
 @webgl_extension{OES,texture_half_float}    | done
 @webgl_extension{OES,standard_derivatives}  | done

src/Magnum/GL/Context.cpp

@@ -118,6 +118,7 @@ const std::vector<Extension>& Extension::extensions(Version version) {
         _extension(EXT,draw_buffers2),
         _extension(EXT,texture_integer),
         _extension(EXT,transform_feedback),
+        _extension(MAGNUM,shader_vertex_id),
         _extension(NV,depth_buffer_float),
         _extension(NV,conditional_render)};
     static const std::vector<Extension> extensions310{
@@ -247,13 +248,16 @@ const std::vector<Extension>& Extension::extensions(Version version) {
         _extension(EXT,color_buffer_float),
         _extension(OES,texture_float_linear),
         _extension(WEBGL,compressed_texture_s3tc)};
-    #ifdef MAGNUM_TARGET_GLES2
     static const std::vector<Extension> extensionsES300{
+        #ifdef MAGNUM_TARGET_GLES2
         _extension(ANGLE,instanced_arrays),
         _extension(EXT,color_buffer_half_float),
         _extension(EXT,sRGB),
         _extension(EXT,blend_minmax),
         _extension(EXT,shader_texture_lod),
+        #endif
+        _extension(MAGNUM,shader_vertex_id),
+        #ifdef MAGNUM_TARGET_GLES2
         _extension(OES,texture_float),
         _extension(OES,texture_half_float),
         _extension(OES,standard_derivatives),
@@ -263,8 +267,9 @@ const std::vector<Extension>& Extension::extensions(Version version) {
         _extension(OES,fbo_render_mipmap),
         _extension(WEBGL,depth_texture),
         _extension(WEBGL,color_buffer_float),
-        _extension(WEBGL,draw_buffers)};
+        _extension(WEBGL,draw_buffers)
         #endif
+    };
     #else
     static const std::vector<Extension> extensions{
         #ifndef MAGNUM_TARGET_GLES2
@@ -309,8 +314,8 @@ const std::vector<Extension>& Extension::extensions(Version version) {
         _extension(OES,stencil1),
         _extension(OES,stencil4),
         _extension(OES,texture_float_linear)};
-    #ifdef MAGNUM_TARGET_GLES2
     static const std::vector<Extension> extensionsES300{
+        #ifdef MAGNUM_TARGET_GLES2
         _extension(ANGLE,framebuffer_blit),
         _extension(ANGLE,framebuffer_multisample),
         _extension(ANGLE,instanced_arrays),
@@ -332,6 +337,9 @@ const std::vector<Extension>& Extension::extensions(Version version) {
         _extension(EXT,draw_buffers),
         _extension(EXT,instanced_arrays),
         _extension(EXT,draw_instanced),
+        #endif
+        _extension(MAGNUM,shader_vertex_id),
+        #ifdef MAGNUM_TARGET_GLES2
         _extension(NV,draw_buffers),
         _extension(NV,fbo_color_attachments),
         _extension(NV,read_buffer),
@@ -357,8 +365,9 @@ const std::vector<Extension>& Extension::extensions(Version version) {
         _extension(OES,standard_derivatives),
         _extension(OES,vertex_array_object),
         _extension(OES,required_internalformat),
-        _extension(OES,surfaceless_context)};
+        _extension(OES,surfaceless_context)
         #endif
+        };
     static const std::vector<Extension> extensionsES320{
         _extension(EXT,color_buffer_half_float),
         #ifndef MAGNUM_TARGET_GLES2
@@ -418,12 +427,7 @@ const std::vector<Extension>& Extension::extensions(Version version) {
         case Version::GLES320: return empty;
         #else
         case Version::GLES200: return empty;
-        case Version::GLES300:
-            #ifdef MAGNUM_TARGET_GLES2
-            return extensionsES300;
-            #else
-            return empty;
-            #endif
+        case Version::GLES300: return extensionsES300;
         #ifndef MAGNUM_TARGET_WEBGL
         case Version::GLES310: return empty;
         case Version::GLES320: return extensionsES320;

src/Magnum/GL/Context.h

@@ -58,9 +58,9 @@ namespace Implementation {
             #ifndef MAGNUM_TARGET_GLES
             192
             #elif !defined(MAGNUM_TARGET_WEBGL)
-            128
+            144
             #else
-            24
+            32
             #endif
     };
 }

src/Magnum/GL/Extensions.h

@@ -255,6 +255,8 @@ namespace AMD {
     _extension(170,NV,depth_buffer_float,               GL210, GL300) // #334
     _extension(171,NV,conditional_render,               GL210, GL300) // #346
     /* NV_draw_texture not supported */                               // #430
+} namespace MAGNUM {
+    _extension(180,MAGNUM,shader_vertex_id,             GL300, GL300)
 }
 #elif defined(MAGNUM_TARGET_WEBGL)
 namespace ANGLE {
@@ -295,6 +297,8 @@ namespace ANGLE {
     _extension(19,WEBGL,color_buffer_float,         GLES200,    None) // #14
     _extension(20,WEBGL,draw_buffers,               GLES200, GLES300) // #18
     #endif
+} namespace MAGNUM {
+    _extension(30,MAGNUM,shader_vertex_id,          GLES300, GLES300)
 }
 #else
 namespace ANDROID {
@@ -465,6 +469,8 @@ namespace ANDROID {
     #ifndef MAGNUM_TARGET_GLES2
     _extension(126,OES,texture_storage_multisample_2d_array, GLES310, GLES320) // #174
     #endif
+} namespace MAGNUM {
+    _extension(130,MAGNUM,shader_vertex_id,         GLES300, GLES300)
 }
 #endif
 #undef _extension

src/Magnum/GL/Implementation/BufferState.cpp

@@ -182,7 +182,7 @@ BufferState::BufferState(Context& context, std::vector<std::string>& extensions)
     }
     #endif
 
-    #ifdef MAGNUM_TARGET_GLES
+    #if defined(MAGNUM_TARGET_GLES) && !defined(MAGNUM_TARGET_GLES2) && !defined(MAGNUM_TARGET_WEBGL)
     if((context.detectedDriver() & Context::DetectedDriver::SwiftShader) &&
       !context.isDriverWorkaroundDisabled("swiftshader-broken-xfb-buffer-binding-target"))
     {

src/Magnum/GL/Implementation/driverSpecific.cpp

@@ -168,6 +168,13 @@ namespace {
            workaround, setting Buffer::TargetHint::TransformFeedback will make
            it use Buffer::TargetHint::Array instead, as that works okay. */
         "swiftshader-broken-xfb-buffer-binding-target",
+
+        /* SwiftShader 4.1.0 does implement gl_VertexID for ES3 contexts, but
+           in practice it doesn't work, returning a constant value. In order to
+           make this easier to check, there's a dummy MAGNUM_shader_vertex_id
+           extension that's defined on all GL 3.0+ and GLES 3.0+ / WebGL 2+
+           contexts *except* for SwiftShader. */
+        "swiftshader-broken-shader-vertex-id",
         #endif
 
         #ifndef MAGNUM_TARGET_GLES
@@ -356,6 +363,12 @@ void Context::setupDriverWorkarounds() {
     }
     #endif
 
+    #if defined(MAGNUM_TARGET_GLES) && !defined(MAGNUM_TARGET_GLES2) && !defined(MAGNUM_TARGET_WEBGL)
+    if((detectedDriver() & Context::DetectedDriver::SwiftShader) &&
+       !isDriverWorkaroundDisabled("swiftshader-broken-shader-vertex-id"))
+        _setRequiredVersion(MAGNUM::shader_vertex_id, None);
+    #endif
+
     #undef _setRequiredVersion
 }