LibWeb/WebGL: Implement WEBGL_draw_buffers extension

Author: https://github.com/Lubrsi
Commit: https://github.com/LadybirdBrowser/ladybird/commit/55f7cb4f10a
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3239
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/kalenikaliaksandr

Libraries/LibWeb/CMakeLists.txt

@@ -825,6 +825,7 @@ set(SOURCES
     WebDriver/TimeoutsConfiguration.cpp
     WebGL/Extensions/ANGLEInstancedArrays.cpp
     WebGL/Extensions/OESVertexArrayObject.cpp
+    WebGL/Extensions/WebGLDrawBuffers.cpp
     WebGL/Extensions/WebGLVertexArrayObjectOES.cpp
     WebGL/EventNames.cpp
     WebGL/OpenGLContext.cpp

Libraries/LibWeb/Forward.h

@@ -863,6 +863,7 @@ class WebGLVertexArrayObject;
 namespace Web::WebGL::Extensions {
 class ANGLEInstancedArrays;
 class OESVertexArrayObject;
+class WebGLDrawBuffers;
 class WebGLVertexArrayObjectOES;
 }
 

Libraries/LibWeb/WebGL/Extensions/WebGLDrawBuffers.cpp

@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2025, Luke Wilde <luke@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Runtime/Realm.h>
+#include <LibWeb/Bindings/Intrinsics.h>
+#include <LibWeb/Bindings/WebGLDrawBuffersPrototype.h>
+#include <LibWeb/WebGL/Extensions/WebGLDrawBuffers.h>
+#include <LibWeb/WebGL/OpenGLContext.h>
+#include <LibWeb/WebGL/WebGLRenderingContext.h>
+
+#define GL_GLEXT_PROTOTYPES 1
+#include <GLES2/gl2.h>
+#include <GLES2/gl2ext.h>
+
+namespace Web::WebGL::Extensions {
+
+GC_DEFINE_ALLOCATOR(WebGLDrawBuffers);
+
+JS::ThrowCompletionOr<GC::Ptr<WebGLDrawBuffers>> WebGLDrawBuffers::create(JS::Realm& realm, GC::Ref<WebGLRenderingContext> context)
+{
+    return realm.create<WebGLDrawBuffers>(realm, context);
+}
+
+WebGLDrawBuffers::WebGLDrawBuffers(JS::Realm& realm, GC::Ref<WebGLRenderingContext> context)
+    : PlatformObject(realm)
+    , m_context(context)
+{
+    m_context->context().request_extension("GL_EXT_draw_buffers");
+}
+
+void WebGLDrawBuffers::draw_buffers_webgl(Vector<GLenum> buffers)
+{
+    m_context->context().make_current();
+    glDrawBuffersEXT(buffers.size(), buffers.data());
+}
+
+void WebGLDrawBuffers::initialize(JS::Realm& realm)
+{
+    Base::initialize(realm);
+    WEB_SET_PROTOTYPE_FOR_INTERFACE(WebGLDrawBuffers);
+}
+
+void WebGLDrawBuffers::visit_edges(Visitor& visitor)
+{
+    Base::visit_edges(visitor);
+    visitor.visit(m_context);
+}
+
+}

Libraries/LibWeb/WebGL/Extensions/WebGLDrawBuffers.h

@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) 2025, Luke Wilde <luke@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/Bindings/PlatformObject.h>
+#include <LibWeb/Forward.h>
+#include <LibWeb/WebGL/Types.h>
+
+namespace Web::WebGL::Extensions {
+
+class WebGLDrawBuffers : public Bindings::PlatformObject {
+    WEB_PLATFORM_OBJECT(WebGLDrawBuffers, Bindings::PlatformObject);
+    GC_DECLARE_ALLOCATOR(WebGLDrawBuffers);
+
+public:
+    static JS::ThrowCompletionOr<GC::Ptr<WebGLDrawBuffers>> create(JS::Realm&, GC::Ref<WebGLRenderingContext>);
+
+    void draw_buffers_webgl(Vector<GLenum> buffers);
+
+protected:
+    void initialize(JS::Realm&) override;
+    void visit_edges(Visitor&) override;
+
+private:
+    WebGLDrawBuffers(JS::Realm&, GC::Ref<WebGLRenderingContext>);
+
+    GC::Ref<WebGLRenderingContext> m_context;
+};
+
+}

Libraries/LibWeb/WebGL/Extensions/WebGLDrawBuffers.idl

@@ -0,0 +1,49 @@
+#import <WebGL/Types.idl>
+
+// https://registry.khronos.org/webgl/extensions/WEBGL_draw_buffers/
+// NOTE: Original WEBGL_draw_buffers name is changed to title case,
+//       so it matches corresponding C++ class name, and does not require
+//       IDL generator to handle snake_case to TitleCase conversion.
+//       Having a different name is totally fine, because LegacyNoInterfaceObject
+//       prevents the name from being exposed to JavaScript.
+[Exposed=(Window,Worker), LegacyNoInterfaceObject]
+interface WebGLDrawBuffers {
+    const GLenum COLOR_ATTACHMENT0_WEBGL     = 0x8CE0;
+    const GLenum COLOR_ATTACHMENT1_WEBGL     = 0x8CE1;
+    const GLenum COLOR_ATTACHMENT2_WEBGL     = 0x8CE2;
+    const GLenum COLOR_ATTACHMENT3_WEBGL     = 0x8CE3;
+    const GLenum COLOR_ATTACHMENT4_WEBGL     = 0x8CE4;
+    const GLenum COLOR_ATTACHMENT5_WEBGL     = 0x8CE5;
+    const GLenum COLOR_ATTACHMENT6_WEBGL     = 0x8CE6;
+    const GLenum COLOR_ATTACHMENT7_WEBGL     = 0x8CE7;
+    const GLenum COLOR_ATTACHMENT8_WEBGL     = 0x8CE8;
+    const GLenum COLOR_ATTACHMENT9_WEBGL     = 0x8CE9;
+    const GLenum COLOR_ATTACHMENT10_WEBGL    = 0x8CEA;
+    const GLenum COLOR_ATTACHMENT11_WEBGL    = 0x8CEB;
+    const GLenum COLOR_ATTACHMENT12_WEBGL    = 0x8CEC;
+    const GLenum COLOR_ATTACHMENT13_WEBGL    = 0x8CED;
+    const GLenum COLOR_ATTACHMENT14_WEBGL    = 0x8CEE;
+    const GLenum COLOR_ATTACHMENT15_WEBGL    = 0x8CEF;
+
+    const GLenum DRAW_BUFFER0_WEBGL          = 0x8825;
+    const GLenum DRAW_BUFFER1_WEBGL          = 0x8826;
+    const GLenum DRAW_BUFFER2_WEBGL          = 0x8827;
+    const GLenum DRAW_BUFFER3_WEBGL          = 0x8828;
+    const GLenum DRAW_BUFFER4_WEBGL          = 0x8829;
+    const GLenum DRAW_BUFFER5_WEBGL          = 0x882A;
+    const GLenum DRAW_BUFFER6_WEBGL          = 0x882B;
+    const GLenum DRAW_BUFFER7_WEBGL          = 0x882C;
+    const GLenum DRAW_BUFFER8_WEBGL          = 0x882D;
+    const GLenum DRAW_BUFFER9_WEBGL          = 0x882E;
+    const GLenum DRAW_BUFFER10_WEBGL         = 0x882F;
+    const GLenum DRAW_BUFFER11_WEBGL         = 0x8830;
+    const GLenum DRAW_BUFFER12_WEBGL         = 0x8831;
+    const GLenum DRAW_BUFFER13_WEBGL         = 0x8832;
+    const GLenum DRAW_BUFFER14_WEBGL         = 0x8833;
+    const GLenum DRAW_BUFFER15_WEBGL         = 0x8834;
+
+    const GLenum MAX_COLOR_ATTACHMENTS_WEBGL = 0x8CDF;
+    const GLenum MAX_DRAW_BUFFERS_WEBGL      = 0x8824;
+
+    undefined drawBuffersWEBGL(sequence<GLenum> buffers);
+};

Libraries/LibWeb/WebGL/WebGLRenderingContext.cpp

@@ -16,6 +16,7 @@
 #include <LibWeb/WebGL/EventNames.h>
 #include <LibWeb/WebGL/Extensions/ANGLEInstancedArrays.h>
 #include <LibWeb/WebGL/Extensions/OESVertexArrayObject.h>
+#include <LibWeb/WebGL/Extensions/WebGLDrawBuffers.h>
 #include <LibWeb/WebGL/OpenGLContext.h>
 #include <LibWeb/WebGL/WebGLContextEvent.h>
 #include <LibWeb/WebGL/WebGLRenderingContext.h>
@@ -92,6 +93,7 @@ void WebGLRenderingContext::visit_edges(Cell::Visitor& visitor)
     visitor.visit(m_canvas_element);
     visitor.visit(m_angle_instanced_arrays_extension);
     visitor.visit(m_oes_vertex_array_object_extension);
+    visitor.visit(m_webgl_draw_buffers_extension);
 }
 
 void WebGLRenderingContext::present()
@@ -207,6 +209,15 @@ JS::Object* WebGLRenderingContext::get_extension(String const& name)
         return m_oes_vertex_array_object_extension;
     }
 
+    if (Infra::is_ascii_case_insensitive_match(name, "WEBGL_draw_buffers"sv)) {
+        if (!m_webgl_draw_buffers_extension) {
+            m_webgl_draw_buffers_extension = MUST(Extensions::WebGLDrawBuffers::create(realm(), *this));
+        }
+
+        VERIFY(m_webgl_draw_buffers_extension);
+        return m_webgl_draw_buffers_extension;
+    }
+
     return nullptr;
 }
 

Libraries/LibWeb/WebGL/WebGLRenderingContext.h

@@ -83,6 +83,7 @@ private:
     // "Multiple calls to getExtension with the same extension string, taking into account case-insensitive comparison, must return the same object as long as the extension is enabled."
     GC::Ptr<Extensions::ANGLEInstancedArrays> m_angle_instanced_arrays_extension;
     GC::Ptr<Extensions::OESVertexArrayObject> m_oes_vertex_array_object_extension;
+    GC::Ptr<Extensions::WebGLDrawBuffers> m_webgl_draw_buffers_extension;
 
     virtual void set_error(GLenum error) override;
 };

Libraries/LibWeb/idl_files.cmake

@@ -382,6 +382,7 @@ libweb_js_bindings(WebAudio/PeriodicWave)
 libweb_js_bindings(WebAudio/StereoPannerNode)
 libweb_js_bindings(WebGL/Extensions/ANGLEInstancedArrays)
 libweb_js_bindings(WebGL/Extensions/OESVertexArrayObject)
+libweb_js_bindings(WebGL/Extensions/WebGLDrawBuffers)
 libweb_js_bindings(WebGL/Extensions/WebGLVertexArrayObjectOES)
 libweb_js_bindings(WebGL/WebGL2RenderingContext)
 libweb_js_bindings(WebGL/WebGLActiveInfo)