GL: implement ANGLE_multi_draw and WEBGL_multi_draw support.

doc/changelog.dox

@@ -62,12 +62,14 @@ See also:
     @webgl_extension{WEBGL,debug_renderer_info} and
     @webgl_extension{WEBGL,debug_shaders} extensions, no implementation done
     yet
--   Recognizing ANGLE GLES and WebGL multi-draw extensions:
+-   Recognizing ANGLE GLES and WebGL multi-draw extensions and using them in
+    @ref GL::AbstractShaderProgram::draw(Containers::ArrayView<const Containers::Reference<MeshView>>):
     -   @m_class{m-doc-external} [ANGLE_multi_draw](https://chromium.googlesource.com/angle/angle/+/master/extensions/ANGLE_multi_draw.txt)
+    -   @webgl_extension{WEBGL,multi_draw}
+-   The following extensions are recognized but not used yet:
     -   @m_class{m-doc-external} [ANGLE_base_vertex_base_instance](https://chromium.googlesource.com/angle/angle/+/master/extensions/ANGLE_base_vertex_base_instance.txt)
     -   @gl_extension{EXT,draw_elements_base_vertex}
     -   @gl_extension{OES,draw_elements_base_vertex}
-    -   @webgl_extension{WEBGL,multi_draw}
     -   @webgl_extension{WEBGL,draw_instanced_base_vertex_base_instance}
     -   @webgl_extension{WEBGL,multi_draw_instanced_base_vertex_base_instance}
 -   Added a @ref GL::AbstractTexture::target() getter to simplify interaction

doc/opengl-support.dox

@@ -449,7 +449,7 @@ Extension                                   | Status
 @gl_extension2{ANGLE,texture_compression_dxt1,ANGLE_texture_compression_dxt} | done
 @gl_extension2{ANGLE,texture_compression_dxt3,ANGLE_texture_compression_dxt} | done
 @gl_extension2{ANGLE,texture_compression_dxt5,ANGLE_texture_compression_dxt} | done
-@m_class{m-doc-external} [ANGLE_multi_draw](https://chromium.googlesource.com/angle/angle/+/master/extensions/ANGLE_multi_draw.txt) (unlisted) | |
+@m_class{m-doc-external} [ANGLE_multi_draw](https://chromium.googlesource.com/angle/angle/+/master/extensions/ANGLE_multi_draw.txt) (unlisted) | done
 @m_class{m-doc-external} [ANGLE_base_vertex_base_instance](https://chromium.googlesource.com/angle/angle/+/master/extensions/ANGLE_base_vertex_base_instance.txt) (unlisted) | |
 @gl_extension{APPLE,texture_format_BGRA8888} | done
 @gl_extension{APPLE,clip_distance}          | done
@@ -571,10 +571,10 @@ Extension                                   | Status
 @webgl_extension{WEBGL,compressed_texture_pvrtc} | done
 @webgl_extension{WEBGL,compressed_texture_astc} | done
 @webgl_extension{WEBGL,compressed_texture_s3tc_srgb} | done
-@webgl_extension{WEBGL,multi_draw}          | missing support in Emscripten
+@webgl_extension{WEBGL,multi_draw}          | done
 @webgl_extension{WEBGL,blend_equation_advanced_coherent} | done
-@webgl_extension{WEBGL,draw_instanced_base_vertex_base_instance} | missing support in Emscripten
-@webgl_extension{WEBGL,multi_draw_instanced_base_vertex_base_instance} | missing support in Emscripten
+@webgl_extension{WEBGL,draw_instanced_base_vertex_base_instance} | |
+@webgl_extension{WEBGL,multi_draw_instanced_base_vertex_base_instance} | |
 
 @section opengl-unsupported Unsupported OpenGL features
 

src/Magnum/GL/AbstractShaderProgram.h

@@ -840,8 +840,10 @@ class MAGNUM_GL_EXPORT AbstractShaderProgram: public AbstractObject {
          * @brief Draw multiple meshes at once
          * @m_since{2020,06}
          *
-         * In OpenGL ES, if @gl_extension{EXT,multi_draw_arrays} is not
-         * present, the functionality is emulated using a sequence of
+         * On OpenGL ES, if neither @gl_extension{EXT,multi_draw_arrays} nor
+         * @m_class{m-doc-external} [ANGLE_multi_draw](https://chromium.googlesource.com/angle/angle/+/master/extensions/ANGLE_multi_draw.txt)
+         * is present, and on WebGL if @webgl_extension{WEBGL,multi_draw} is
+         * not present, the functionality is emulated using a sequence of
          * @ref draw(MeshView&) calls.
          *
          * If @gl_extension{ARB,vertex_array_object} (part of OpenGL 3.0),

src/Magnum/GL/Implementation/MeshState.cpp

@@ -108,16 +108,43 @@ MeshState::MeshState(Context& context, ContextState& contextState, std::vector<s
     #endif
 
     #ifdef MAGNUM_TARGET_GLES
+    /* Multi draw implementation on ES. Because there's a lot of dispatch logic
+       involved, the multiDrawImplementationDefault then has internal
+       extension-specific codepaths based on whether EXT, OES, ANGLE or
+       whichever entrypoints are supported. */
     #ifndef MAGNUM_TARGET_WEBGL
-    /* Multi draw implementation on ES */
-    if(context.isExtensionSupported<Extensions::EXT::multi_draw_arrays>()) {
-        extensions.push_back(Extensions::EXT::multi_draw_arrays::string());
+    if(context.isExtensionSupported<Extensions::EXT::multi_draw_arrays>() ||
+       context.isExtensionSupported<Extensions::ANGLE::multi_draw>())
+    #else
+    if(context.isExtensionSupported<Extensions::WEBGL::multi_draw>())
+    #endif
+    {
+        #ifndef MAGNUM_TARGET_WEBGL
+        if(context.isExtensionSupported<Extensions::EXT::multi_draw_arrays>()) {
+            extensions.push_back(Extensions::EXT::multi_draw_arrays::string());
+
+            multiDrawArraysImplementation = glMultiDrawArraysEXT;
+            multiDrawElementsImplementation = glMultiDrawElementsEXT;
+        } else if(context.isExtensionSupported<Extensions::ANGLE::multi_draw>()) {
+            extensions.push_back(Extensions::ANGLE::multi_draw::string());
+
+            multiDrawArraysImplementation = glMultiDrawArraysANGLE;
+            multiDrawElementsImplementation = glMultiDrawElementsANGLE;
+        } else CORRADE_INTERNAL_ASSERT_UNREACHABLE();
+        #else
+        {
+            extensions.push_back(Extensions::WEBGL::multi_draw::string());
+
+            /* The WEBGL extension uses the same entrypoints as the ANGLE
+               extension it was based on */
+            multiDrawArraysImplementation = glMultiDrawArraysANGLE;
+            multiDrawElementsImplementation = glMultiDrawElementsANGLE;
+        }
+        #endif
 
         multiDrawImplementation = &MeshView::multiDrawImplementationDefault;
+
     } else multiDrawImplementation = &MeshView::multiDrawImplementationFallback;
-    #else
-    multiDrawImplementation = &MeshView::multiDrawImplementationFallback;
-    #endif
     #endif
 
     #ifdef MAGNUM_TARGET_GLES2

src/Magnum/GL/Implementation/MeshState.h

@@ -60,6 +60,8 @@ struct MeshState {
 
     #ifdef MAGNUM_TARGET_GLES
     void(*multiDrawImplementation)(Containers::ArrayView<const Containers::Reference<MeshView>>);
+    void(APIENTRY *multiDrawArraysImplementation)(GLenum, const GLint*, const GLsizei*, GLsizei);
+    void(APIENTRY *multiDrawElementsImplementation)(GLenum, const GLsizei*, GLenum, const void* const*, GLsizei);
     #endif
 
     void(*bindVAOImplementation)(GLuint);

src/Magnum/GL/MeshView.cpp

@@ -84,7 +84,6 @@ MeshView& MeshView::draw(AbstractShaderProgram&& shader, TransformFeedback& xfb,
 #endif
 #endif
 
-#ifndef MAGNUM_TARGET_WEBGL
 void MeshView::multiDrawImplementationDefault(Containers::ArrayView<const Containers::Reference<MeshView>> meshes) {
     CORRADE_INTERNAL_ASSERT(meshes.size());
 
@@ -123,10 +122,11 @@ void MeshView::multiDrawImplementationDefault(Containers::ArrayView<const Contai
     /* Non-indexed meshes */
     if(!original._indexBuffer.id()) {
         #ifndef MAGNUM_TARGET_GLES
-        glMultiDrawArrays(GLenum(original._primitive), baseVertex, count, meshes.size());
+        glMultiDrawArrays
         #else
-        glMultiDrawArraysEXT(GLenum(original._primitive), baseVertex, count, meshes.size());
+        state.multiDrawArraysImplementation
         #endif
+            (GLenum(original._primitive), baseVertex, count, meshes.size());
 
     /* Indexed meshes */
     } else {
@@ -140,16 +140,16 @@ void MeshView::multiDrawImplementationDefault(Containers::ArrayView<const Contai
         #endif
         {
             #ifndef MAGNUM_TARGET_GLES
-            glMultiDrawElements(GLenum(original._primitive), count, GLenum(original._indexType), indices, meshes.size());
+            glMultiDrawElements
             #else
-            glMultiDrawElementsEXT(GLenum(original._primitive), count, GLenum(original._indexType), indices, meshes.size());
+            state.multiDrawElementsImplementation
             #endif
+                (GLenum(original._primitive), count, GLenum(original._indexType), indices, meshes.size());
         }
     }
 
     (original.*state.unbindImplementation)();
 }
-#endif
 
 #ifdef MAGNUM_TARGET_GLES
 void MeshView::multiDrawImplementationFallback(Containers::ArrayView<const Containers::Reference<MeshView>> meshes) {

src/Magnum/GL/MeshView.h

@@ -257,9 +257,7 @@ class MAGNUM_GL_EXPORT MeshView {
         friend AbstractShaderProgram;
         friend Implementation::MeshState;
 
-        #ifndef MAGNUM_TARGET_WEBGL
         static MAGNUM_GL_LOCAL void multiDrawImplementationDefault(Containers::ArrayView<const Containers::Reference<MeshView>> meshes);
-        #endif
         #ifdef MAGNUM_TARGET_GLES
         static MAGNUM_GL_LOCAL void multiDrawImplementationFallback(Containers::ArrayView<const Containers::Reference<MeshView>> meshes);
         #endif

src/Magnum/GL/Test/MeshGLTest.cpp

@@ -3005,9 +3005,15 @@ template<class T> T MultiChecker::get(PixelFormat format, PixelType type) {
 #endif
 
 void MeshGLTest::multiDraw() {
-    #if defined(MAGNUM_TARGET_GLES) && !defined(MAGNUM_TARGET_WEBGL)
-    if(!Context::current().isExtensionSupported<Extensions::EXT::multi_draw_arrays>())
-        Debug() << Extensions::EXT::multi_draw_arrays::string() << "not supported, using fallback implementation";
+    #ifdef MAGNUM_TARGET_GLES
+    #ifndef MAGNUM_TARGET_WEBGL
+    if(!Context::current().isExtensionSupported<Extensions::EXT::multi_draw_arrays>() &&
+       !Context::current().isExtensionSupported<Extensions::ANGLE::multi_draw>())
+        Debug{} << "Neither" << Extensions::EXT::multi_draw_arrays::string() << "nor" << Extensions::ANGLE::multi_draw::string() << "is supported, using fallback implementation";
+    #else
+    if(!Context::current().isExtensionSupported<Extensions::WEBGL::multi_draw>())
+        Debug{} << Extensions::WEBGL::multi_draw::string() << "is not supported, using fallback implementation";
+    #endif
     #endif
 
     typedef Attribute<0, Float> Attribute;
@@ -3042,9 +3048,15 @@ void MeshGLTest::multiDraw() {
 }
 
 void MeshGLTest::multiDrawIndexed() {
-    #if defined(MAGNUM_TARGET_GLES) && !defined(MAGNUM_TARGET_WEBGL)
-    if(!Context::current().isExtensionSupported<Extensions::EXT::multi_draw_arrays>())
-        Debug() << Extensions::EXT::multi_draw_arrays::string() << "not supported, using fallback implementation";
+    #ifdef MAGNUM_TARGET_GLES
+    #ifndef MAGNUM_TARGET_WEBGL
+    if(!Context::current().isExtensionSupported<Extensions::EXT::multi_draw_arrays>() &&
+       !Context::current().isExtensionSupported<Extensions::ANGLE::multi_draw>())
+        Debug{} << "Neither" << Extensions::EXT::multi_draw_arrays::string() << "nor" << Extensions::ANGLE::multi_draw::string() << "is supported, using fallback implementation";
+    #else
+    if(!Context::current().isExtensionSupported<Extensions::WEBGL::multi_draw>())
+        Debug{} << Extensions::WEBGL::multi_draw::string() << "is not supported, using fallback implementation";
+    #endif
     #endif
 
     Buffer vertices;