Merge pull request #1734 from ZzzhHe/opengl-bufferless-quad-vao

Bind empty VAO for bufferless quad rendering

Author: heinezen

libopenage/renderer/opengl/geometry.cpp

@@ -1,4 +1,4 @@
-// Copyright 2015-2024 the openage authors. See copying.md for legal info.
+// Copyright 2015-2025 the openage authors. See copying.md for legal info.
 
 #include "geometry.h"
 
@@ -54,6 +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:
+		// any VAO must be bound before this call
 		glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 		break;
 

libopenage/renderer/opengl/renderer.cpp

@@ -1,4 +1,4 @@
-// Copyright 2017-2024 the openage authors. See copying.md for legal info.
+// Copyright 2017-2025 the openage authors. See copying.md for legal info.
 
 #include "renderer.h"
 
@@ -15,6 +15,7 @@
 #include "renderer/opengl/texture.h"
 #include "renderer/opengl/uniform_buffer.h"
 #include "renderer/opengl/uniform_input.h"
+#include "renderer/opengl/vertex_array.h"
 #include "renderer/opengl/window.h"
 #include "renderer/resources/buffer_info.h"
 
@@ -26,7 +27,8 @@ GlRenderer::GlRenderer(const std::shared_ptr<GlContext> &ctx,
 	gl_context{ctx},
 	display{std::make_shared<GlRenderTarget>(ctx,
                                              viewport_size[0],
-                                             viewport_size[1])} {
+                                             viewport_size[1])},
+	shared_quad_vao{std::make_shared<GlVertexArray>(ctx)} {
 	// color used to clear the color buffers
 	glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
 
@@ -100,7 +102,7 @@ std::shared_ptr<UniformBuffer> GlRenderer::add_uniform_buffer(resources::Uniform
 		                     resources::UniformBufferInfo::get_size(input, info.get_layout()),
 		                     resources::UniformBufferInfo::get_stride_size(input.type, info.get_layout()),
 		                     input.count,
-							 input.name});
+		                     input.name});
 
 		offset += size;
 	}
@@ -169,6 +171,11 @@ void GlRenderer::render(const std::shared_ptr<RenderPass> &pass) {
 	auto gl_target = std::dynamic_pointer_cast<GlRenderTarget>(pass->get_target());
 	gl_target->bind_write();
 
+	// 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);
 
 	// TODO: Option for face culling

libopenage/renderer/opengl/renderer.h

@@ -1,4 +1,4 @@
-// Copyright 2017-2024 the openage authors. See copying.md for legal info.
+// Copyright 2017-2025 the openage authors. See copying.md for legal info.
 
 #pragma once
 
@@ -17,6 +17,7 @@ namespace opengl {
 class GlContext;
 class GlRenderPass;
 class GlRenderTarget;
+class GlVertexArray;
 class GlWindow;
 
 /// The OpenGL specialization of the rendering interface.
@@ -67,6 +68,14 @@ class GlRenderer final : public Renderer {
 
 	/// The main screen surface as a render target.
 	std::shared_ptr<GlRenderTarget> display;
+
+	/// 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::shared_ptr<GlVertexArray> shared_quad_vao;
 };
 
 } // namespace opengl