update according to reviews

libopenage/renderer/opengl/geometry.cpp

@@ -54,7 +54,7 @@ void GlGeometry::update_verts_offset(std::vector<uint8_t> const &verts, size_t o
 void GlGeometry::draw() const {
 	switch (this->get_type()) {
 	case geometry_t::bufferless_quad:
-		// a VAO must be bound before this call. This is handled by GlRenderer.
+		// any VAO must be bound before this call
 		glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 		break;
 

libopenage/renderer/opengl/geometry.h

@@ -1,4 +1,4 @@
-// Copyright 2015-2025 the openage authors. See copying.md for legal info.
+// Copyright 2015-2023 the openage authors. See copying.md for legal info.
 
 #pragma once
 

libopenage/renderer/opengl/renderer.cpp

@@ -28,7 +28,7 @@ GlRenderer::GlRenderer(const std::shared_ptr<GlContext> &ctx,
 	display{std::make_shared<GlRenderTarget>(ctx,
                                              viewport_size[0],
                                              viewport_size[1])},
-	shared_quad_vao(std::make_shared<GlVertexArray>(ctx)) {
+	shared_quad_vao{std::make_unique<GlVertexArray>(ctx)} {
 	// color used to clear the color buffers
 	glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
 
@@ -171,7 +171,9 @@ void GlRenderer::render(const std::shared_ptr<RenderPass> &pass) {
 	auto gl_target = std::dynamic_pointer_cast<GlRenderTarget>(pass->get_target());
 	gl_target->bind_write();
 
-	// bind the shared quad vao for all bufferless quad geometries
+	// ensure that an (empty) VAO is bound before rendering geometry
+	// a bound VAO is required to render bufferless quad geometries by OpenGL
+	// see https://www.khronos.org/opengl/wiki/Vertex_Rendering#Causes_of_rendering_failure
 	shared_quad_vao->bind();
 
 	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

libopenage/renderer/opengl/renderer.h

@@ -69,7 +69,13 @@ class GlRenderer final : public Renderer {
 	/// The main screen surface as a render target.
 	std::shared_ptr<GlRenderTarget> display;
 
-	std::shared_ptr<GlVertexArray> shared_quad_vao;
+	/// An empty vertex array object (VAO).
+	///
+	/// This VAO has to be bound at the start of a render pass to ensure
+	/// that bufferless quad geometry can be drawn without errors. Drawing a
+	/// bufferless quad requires any VAO to be bound
+	/// see https://www.khronos.org/opengl/wiki/Vertex_Rendering#Causes_of_rendering_failure
+	std::unique_ptr<GlVertexArray> shared_quad_vao;
 };
 
 } // namespace opengl