GL: fix various Mesh test failures specific to WebGL 1.

Annoying, nothing else.

src/Magnum/GL/Test/MeshGLTest.cpp

@@ -784,7 +784,12 @@ void MeshGLTest::construct() {
 }
 
 struct FloatShader: AbstractShaderProgram {
-    explicit FloatShader(Containers::StringView type, Containers::StringView conversion);
+    explicit FloatShader(Containers::StringView type, Containers::StringView conversion
+        /* See the definition for details */
+        #if defined(MAGNUM_TARGET_WEBGL) && defined(MAGNUM_TARGET_GLES2)
+        , bool dummy = false
+        #endif
+    );
 };
 
 void MeshGLTest::constructMove() {
@@ -994,7 +999,15 @@ struct Checker {
 };
 
 #ifndef DOXYGEN_GENERATING_OUTPUT
-FloatShader::FloatShader(Containers::StringView type, Containers::StringView conversion) {
+FloatShader::FloatShader(Containers::StringView type, Containers::StringView conversion
+    /* WebGL 1 requires that at least one attribute is not instanced. The
+       addVertexBufferInstancedFloat() and drawInstancedAttributeSingleInstance()
+       tests set this to true to add a dummy input (that isn't even present in
+       the mesh) to fix that. */
+    #if defined(MAGNUM_TARGET_WEBGL) && defined(MAGNUM_TARGET_GLES2)
+    , bool dummy
+    #endif
+) {
     /* We need special version for ES3, because GLSL in ES2 doesn't support
        rectangle matrices */
     #ifndef MAGNUM_TARGET_GLES
@@ -1021,20 +1034,39 @@ FloatShader::FloatShader(Containers::StringView type, Containers::StringView con
     #endif
 
     vert.addSource(Utility::format(
-        "#if !defined(GL_ES) && __VERSION__ == 120\n"
+        #if defined(MAGNUM_TARGET_WEBGL) && defined(MAGNUM_TARGET_GLES2)
-        "#define mediump\n"
+        dummy ?
-        "#endif\n"
+            "#if !defined(GL_ES) && __VERSION__ == 120\n"
-        "#if (defined(GL_ES) && __VERSION__ < 300) || __VERSION__ == 120\n"
+            "#define mediump\n"
-        "#define in attribute\n"
+            "#endif\n"
-        "#define out varying\n"
+            "#if (defined(GL_ES) && __VERSION__ < 300) || __VERSION__ == 120\n"
-        "#endif\n"
+            "#define in attribute\n"
-        "in mediump {0} value;\n"
+            "#define out varying\n"
-        "out mediump {0} valueInterpolated;\n"
+            "#endif\n"
-        "void main() {{\n"
+            "in mediump {0} value;\n"
-        "    valueInterpolated = value;\n"
+            "in mediump float dummy;\n"
-        "    gl_PointSize = 1.0;\n"
+            "out mediump {0} valueInterpolated;\n"
-        "    gl_Position = vec4(0.0, 0.0, 0.0, 1.0);\n"
+            "void main() {{\n"
-        "}}\n", type));
+            "    valueInterpolated = value;\n"
+            "    gl_PointSize = 1.0;\n"
+            "    gl_Position = vec4(0.0, 0.0, dummy, 1.0);\n"
+            "}}\n" :
+        #endif
+            "#if !defined(GL_ES) && __VERSION__ == 120\n"
+            "#define mediump\n"
+            "#endif\n"
+            "#if (defined(GL_ES) && __VERSION__ < 300) || __VERSION__ == 120\n"
+            "#define in attribute\n"
+            "#define out varying\n"
+            "#endif\n"
+            "in mediump {0} value;\n"
+            "out mediump {0} valueInterpolated;\n"
+            "void main() {{\n"
+            "    valueInterpolated = value;\n"
+            "    gl_PointSize = 1.0;\n"
+            "    gl_Position = vec4(0.0, 0.0, 0.0, 1.0);\n"
+            "}}\n",
+        type));
     frag.addSource(Utility::format(
         "#if !defined(GL_ES) && __VERSION__ == 120\n"
         "#define mediump\n"
@@ -3550,7 +3582,13 @@ void MeshGLTest::addVertexBufferInstancedFloat() {
 
     MAGNUM_VERIFY_NO_GL_ERROR();
 
-    const auto value = Checker(FloatShader("float", "vec4(valueInterpolated, 0.0, 0.0, 0.0)"),
+    const auto value = Checker(FloatShader("float", "vec4(valueInterpolated, 0.0, 0.0, 0.0)"
+        /* WebGL 1 requires that at least one attribute is not instanced. Add
+           a dummy input (that isn't even present in the mesh) to fix that. */
+        #if defined(MAGNUM_TARGET_WEBGL) && defined(MAGNUM_TARGET_GLES2)
+        , /* dummy */ true
+        #endif
+    ),
         #ifndef MAGNUM_TARGET_GLES2
         RenderbufferFormat::RGBA8,
         #else
@@ -3768,7 +3806,13 @@ void MeshGLTest::drawInstancedAttributeSingleInstance() {
     framebuffer.attachRenderbuffer(Framebuffer::ColorAttachment{0}, renderbuffer)
                .bind();
 
-    FloatShader shader{"float", "vec4(valueInterpolated, 0.0, 0.0, 0.0)"};
+    FloatShader shader{"float", "vec4(valueInterpolated, 0.0, 0.0, 0.0)"
+        /* WebGL 1 requires that at least one attribute is not instanced. Add
+           a dummy input (that isn't even present in the mesh) to fix that. */
+        #if defined(MAGNUM_TARGET_WEBGL) && defined(MAGNUM_TARGET_GLES2)
+        , /* dummy */ true
+        #endif
+    };
 
     MAGNUM_VERIFY_NO_GL_ERROR();
 
@@ -3838,7 +3882,17 @@ MultiDrawShader::MultiDrawShader(bool vertexId, bool drawId) {
         "in mediump vec4 value;\n"
         "out mediump float valueInterpolated;\n"
         "void main() {\n"
+        /* WebGL 1 doesn't allow dynamic indexing into a vec4. Similar thing is
+           in MultiDrawInstancedShader below or in the SUBSCRIPTING_WORKAROUND
+           in Shaders/MeshVisualizer.vert. */
+        #if defined(MAGNUM_TARGET_WEBGL) && defined(MAGNUM_TARGET_GLES2)
+        "         if(vertexOrDrawId == 0) valueInterpolated = value.x;\n"
+        "    else if(vertexOrDrawId == 1) valueInterpolated = value.y;\n"
+        "    else if(vertexOrDrawId == 2) valueInterpolated = value.z;\n"
+        "    else                         valueInterpolated = value.w;\n"
+        #else
         "    valueInterpolated = value[vertexOrDrawId];\n"
+        #endif
         "    gl_PointSize = 1.0;\n"
         "    gl_Position = vec4(position, 0.0, 1.0);\n"
         "}\n");
@@ -4644,6 +4698,13 @@ MultiDrawInstancedShader::MultiDrawInstancedShader(bool vertexId, bool drawId
         "void main() {\n"
         #ifndef MAGNUM_TARGET_GLES2
         "    valueInterpolated = value[vertexOrDrawIdOrInstanceOffset + gl_InstanceID];\n"
+        /* WebGL 1 doesn't allow dynamic indexing into a vec3. Similar thing is
+           in MultiDrawShader above or in the SUBSCRIPTING_WORKAROUND in
+           Shaders/MeshVisualizer.vert. */
+        #elif defined(MAGNUM_TARGET_WEBGL)
+        "         if(vertexOrDrawIdOrInstanceOffset + int(instanceId) == 0) valueInterpolated = value.x;\n"
+        "    else if(vertexOrDrawIdOrInstanceOffset + int(instanceId) == 1) valueInterpolated = value.y;\n"
+        "    else                                                           valueInterpolated = value.z;\n"
         #else
         "    valueInterpolated = value[vertexOrDrawIdOrInstanceOffset + int(instanceId)];\n"
         #endif