DebugTools, MeshTools, TextureTools: handle broken gl_VertexID.

DebugTools::textureSubImage(), MeshTools::fullScreenTriangle() and
TextureTools::distanceField() all plagued by this on SwiftShader.

doc/changelog.dox

@@ -101,6 +101,18 @@ See also:
     other variants are now usable directly through @ref CORRADE_COMPARE_AS(),
     no need to pass an explicit instance to @ref CORRADE_COMPARE_WITH() when
     just the default parameters are needed
+-   @ref DebugTools::textureSubImage() for float textures was updated to work
+    with SwiftShader (which has broken @glsl gl_VertexID @ce)
+
+@subsubsection changelog-latest-changes-meshtools MeshTools library
+
+-   @ref MeshTools::fullScreenTriangle() was updated to work on ES3 SwiftShader
+    contexts (which have broken @glsl gl_VertexID @ce)
+
+@subsubsection changelog-latest-changes-texturetools TextureTools library
+
+-   @ref TextureTools::distanceField() was updated to work on ES3 SwiftShader
+    contexts (which have broken @glsl gl_VertexID @ce)
 
 @subsubsection changelog-latest-changes-platform Platform libraries
 

src/Magnum/DebugTools/TextureImage.cpp

@@ -81,13 +81,19 @@ FloatReinterpretShader::FloatReinterpretShader() {
 
     GL::Shader vert{GL::Version::GLES300, GL::Shader::Type::Vertex};
     GL::Shader frag{GL::Version::GLES300, GL::Shader::Type::Fragment};
+    if(!GL::Context::current().isExtensionSupported<GL::Extensions::MAGNUM::shader_vertex_id>())
+        vert.addSource("#define DISABLE_GL_MAGNUM_shader_vertex_id\n");
     vert.addSource(rs.get("TextureImage.vert"));
     frag.addSource(rs.get("TextureImage.frag"));
 
-    CORRADE_INTERNAL_ASSERT(GL::Shader::compile({vert, frag}));
+    CORRADE_INTERNAL_ASSERT_OUTPUT(GL::Shader::compile({vert, frag}));
     attachShaders({vert, frag});
 
-    CORRADE_INTERNAL_ASSERT(link());
+    if(!GL::Context::current().isExtensionSupported<GL::Extensions::MAGNUM::shader_vertex_id>()) {
+        bindAttributeLocation(0, "position");
+    }
+
+    CORRADE_INTERNAL_ASSERT_OUTPUT(link());
 
     levelUniform = uniformLocation("level");
     setUniform(uniformLocation("textureData"), 0);
@@ -145,8 +151,20 @@ void textureSubImage(GL::Texture2D& texture, const Int level, const Range2Di& ra
         shader.setTexture(texture, level);
 
         GL::Mesh mesh;
-        mesh.setCount(3)
-            .draw(shader);
+        mesh.setCount(3);
+
+        if(!GL::Context::current().isExtensionSupported<GL::Extensions::MAGNUM::shader_vertex_id>()) {
+            constexpr Vector2 triangle[]{
+                {-1.0f,  1.0f},
+                {-1.0f, -3.0f},
+                { 3.0f,  1.0f}
+            };
+            GL::Buffer buffer{GL::Buffer::TargetHint::Array};
+            buffer.setData(triangle, GL::BufferUsage::StaticDraw);
+            mesh.addVertexBuffer(std::move(buffer), 0, GL::Attribute<0, Vector2>{});
+        }
+
+        mesh.draw(shader);
 
         /* release() needs to be called after querying the size to avoid zeroing it out */
         const Vector2i imageSize = image.size();

src/Magnum/DebugTools/TextureImage.vert

@@ -23,7 +23,15 @@
     DEALINGS IN THE SOFTWARE.
 */
 
+#ifdef DISABLE_GL_MAGNUM_shader_vertex_id
+in lowp vec4 position;
+#endif
+
 void main() {
+    #ifndef DISABLE_GL_MAGNUM_shader_vertex_id
     gl_Position = vec4((gl_VertexID == 2) ?  3.0 : -1.0,
                        (gl_VertexID == 1) ? -3.0 :  1.0, 0.0, 1.0);
+    #else
+    gl_Position = position;
+    #endif
 }

src/Magnum/MeshTools/FullScreenTriangle.cpp

@@ -28,6 +28,7 @@
 #include "Magnum/GL/Attribute.h"
 #include "Magnum/GL/Buffer.h"
 #include "Magnum/GL/Context.h"
+#include "Magnum/GL/Extensions.h"
 #include "Magnum/GL/Mesh.h"
 #include "Magnum/GL/Version.h"
 #include "Magnum/Math/Vector2.h"
@@ -39,12 +40,7 @@ GL::Mesh fullScreenTriangle(const GL::Version version) {
     mesh.setPrimitive(GL::MeshPrimitive::Triangles)
         .setCount(3);
 
-    #ifndef MAGNUM_TARGET_GLES
-    if(version < GL::Version::GL300)
-    #else
-    if(version < GL::Version::GLES300)
-    #endif
-    {
+    if(!GL::Context::current().isExtensionSupported<GL::Extensions::MAGNUM::shader_vertex_id>(version)) {
         constexpr Vector2 triangle[]{
             {-1.0f,  1.0f},
             {-1.0f, -3.0f},

src/Magnum/Shaders/FullScreenTriangle.glsl

@@ -23,12 +23,15 @@
     DEALINGS IN THE SOFTWARE.
 */
 
+#if !defined(NEW_GLSL) || defined(DISABLE_GL_MAGNUM_shader_vertex_id)
 #ifndef NEW_GLSL
-attribute lowp vec4 position;
+#define in attribute
+#endif
+in lowp vec4 position;
 #endif
 
 void fullScreenTriangle() {
-    #ifdef NEW_GLSL
+    #if defined(NEW_GLSL) && !defined(DISABLE_GL_MAGNUM_shader_vertex_id)
     gl_Position = vec4((gl_VertexID == 2) ?  3.0 : -1.0,
                        (gl_VertexID == 1) ? -3.0 :  1.0, 0.0, 1.0);
     #else

src/Magnum/Shaders/Implementation/CreateCompatibilityShader.h

@@ -53,6 +53,11 @@ inline GL::Shader createCompatibilityShader(const Utility::Resource& rs, GL::Ver
         shader.addSource("#define DISABLE_GL_ARB_explicit_uniform_location\n");
     #endif
 
+    #ifndef MAGNUM_TARGET_GLES2
+    if(type == GL::Shader::Type::Vertex && GL::Context::current().isExtensionDisabled<GL::Extensions::MAGNUM::shader_vertex_id>(version))
+        shader.addSource("#define DISABLE_GL_MAGNUM_shader_vertex_id\n");
+    #endif
+
     /* My Android emulator (running on NVidia) doesn't define GL_ES
        preprocessor macro, thus *all* the stock shaders fail to compile */
     /** @todo remove this when Android emulator is sane */

src/Magnum/TextureTools/DistanceField.cpp

@@ -106,13 +106,7 @@ DistanceFieldShader::DistanceFieldShader(const UnsignedInt radius) {
 
     attachShaders({vert, frag});
 
-    /* Older GLSL doesn't have gl_VertexID, vertices must be supplied explicitly */
-    #ifndef MAGNUM_TARGET_GLES
-    if(!GL::Context::current().isVersionSupported(GL::Version::GL300))
-    #else
-    if(!GL::Context::current().isVersionSupported(GL::Version::GLES300))
-    #endif
-    {
+    if(!GL::Context::current().isExtensionSupported<GL::Extensions::MAGNUM::shader_vertex_id>()) {
         bindAttributeLocation(Position::Location, "position");
     }
 
@@ -160,12 +154,7 @@ DistanceField::DistanceField(const UnsignedInt radius): _state{new State{radius}
     _state->mesh.setPrimitive(GL::MeshPrimitive::Triangles)
         .setCount(3);
 
-    /* Older GLSL doesn't have gl_VertexID, vertices must be supplied explicitly */
-    #ifndef MAGNUM_TARGET_GLES
-    if(!GL::Context::current().isVersionSupported(GL::Version::GL300))
-    #else
-    if(!GL::Context::current().isVersionSupported(GL::Version::GLES300))
-    #endif
+    if(!GL::Context::current().isExtensionSupported<GL::Extensions::MAGNUM::shader_vertex_id>())
     {
         constexpr Vector2 triangle[] = {
             Vector2(-1.0,  1.0),