From a6617e1096ba5fffbb1884f122a8c03155167b62 Mon Sep 17 00:00:00 2001
From: Luke Wilde <lukew@serenityos.org>
Date: Mon, 13 Jun 2022 16:54:27 +0100
Subject: [PATCH] LibWeb/WebGL: Implement error handling and getError()

---
 .../WebGL/WebGLRenderingContextBase.cpp       | 32 +++++++++++++++++++
 .../LibWeb/WebGL/WebGLRenderingContextBase.h  |  5 +++
 .../WebGL/WebGLRenderingContextBase.idl       |  2 ++
 3 files changed, 39 insertions(+)

diff --git a/Userland/Libraries/LibWeb/WebGL/WebGLRenderingContextBase.cpp b/Userland/Libraries/LibWeb/WebGL/WebGLRenderingContextBase.cpp
index 35144898f1..d05435182a 100644
--- a/Userland/Libraries/LibWeb/WebGL/WebGLRenderingContextBase.cpp
+++ b/Userland/Libraries/LibWeb/WebGL/WebGLRenderingContextBase.cpp
@@ -21,6 +21,13 @@ WebGLRenderingContextBase::WebGLRenderingContextBase(HTML::HTMLCanvasElement& ca
 
 WebGLRenderingContextBase::~WebGLRenderingContextBase() = default;
 
+#define RETURN_WITH_WEBGL_ERROR_IF(condition, error)                         \
+    if (condition) {                                                         \
+        dbgln_if(WEBGL_CONTEXT_DEBUG, "{}(): error {:#x}", __func__, error); \
+        set_error(error);                                                    \
+        return;                                                              \
+    }
+
 void WebGLRenderingContextBase::present()
 {
     if (!m_should_present)
@@ -71,6 +78,15 @@ void WebGLRenderingContextBase::needs_to_present()
     m_canvas_element->layout_node()->set_needs_display();
 }
 
+void WebGLRenderingContextBase::set_error(GLenum error)
+{
+    auto context_error = m_context->gl_get_error();
+    if (context_error != GL_NO_ERROR)
+        m_error = context_error;
+    else
+        m_error = error;
+}
+
 bool WebGLRenderingContextBase::is_context_lost() const
 {
     dbgln_if(WEBGL_CONTEXT_DEBUG, "WebGLRenderingContextBase::is_context_lost()");
@@ -210,6 +226,22 @@ void WebGLRenderingContextBase::front_face(GLenum mode)
     m_context->gl_front_face(mode);
 }
 
+GLenum WebGLRenderingContextBase::get_error()
+{
+    dbgln_if(WEBGL_CONTEXT_DEBUG, "WebGLRenderingContextBase::get_error()");
+
+    // "If the context's webgl context lost flag is set, returns CONTEXT_LOST_WEBGL the first time this method is called. Afterward, returns NO_ERROR until the context has been restored."
+    // FIXME: The plan here is to make the context lost handler unconditionally set m_error to CONTEXT_LOST_WEBGL, which we currently do not have.
+    //        The idea for the unconditional set is that any potentially error generating functions will not execute when the context is lost.
+    if (m_error != GL_NO_ERROR || m_context_lost) {
+        auto last_error = m_error;
+        m_error = GL_NO_ERROR;
+        return last_error;
+    }
+
+    return m_context->gl_get_error();
+}
+
 void WebGLRenderingContextBase::polygon_offset(GLfloat factor, GLfloat units)
 {
     if (m_context_lost)
diff --git a/Userland/Libraries/LibWeb/WebGL/WebGLRenderingContextBase.h b/Userland/Libraries/LibWeb/WebGL/WebGLRenderingContextBase.h
index ed3adfa01e..d5fe6313a8 100644
--- a/Userland/Libraries/LibWeb/WebGL/WebGLRenderingContextBase.h
+++ b/Userland/Libraries/LibWeb/WebGL/WebGLRenderingContextBase.h
@@ -46,6 +46,8 @@ public:
 
     void front_face(GLenum mode);
 
+    GLenum get_error();
+
     void polygon_offset(GLfloat factor, GLfloat units);
 
     void scissor(GLint x, GLint y, GLsizei width, GLsizei height);
@@ -81,7 +83,10 @@ private:
     // - clear, drawArrays, or drawElements has been called while the drawing buffer is the currently bound framebuffer
     bool m_should_present { true };
 
+    GLenum m_error { GL_NO_ERROR };
+
     void needs_to_present();
+    void set_error(GLenum error);
 };
 
 }
diff --git a/Userland/Libraries/LibWeb/WebGL/WebGLRenderingContextBase.idl b/Userland/Libraries/LibWeb/WebGL/WebGLRenderingContextBase.idl
index a850aa4af6..1e536e8817 100644
--- a/Userland/Libraries/LibWeb/WebGL/WebGLRenderingContextBase.idl
+++ b/Userland/Libraries/LibWeb/WebGL/WebGLRenderingContextBase.idl
@@ -41,6 +41,8 @@ interface mixin WebGLRenderingContextBase {
 
     undefined frontFace(GLenum mode);
 
+    GLenum getError();
+
     undefined polygonOffset(GLfloat factor, GLfloat units);
 
     undefined scissor(GLint x, GLint y, GLsizei width, GLsizei height);