Method Init

src/video/opengl.cpp:530–736

* Check for the needed OpenGL functionality and allocate all resources. * @param screen_res Current display resolution. * @return Error string or std::nullopt if successful. */

 * @return Error string or std::nullopt if successful.
 */
std::optional<std::string_view> OpenGLBackend::Init(const Dimension &screen_res)
{
	if (!BindBasicInfoProcs()) return "OpenGL not supported";

	/* Always query the supported OpenGL version as the current context might have changed. */
	auto ver = GlGetString(GL_VERSION);
	auto vend = GlGetString(GL_VENDOR);
	auto renderer = GlGetString(GL_RENDERER);

	if (!ver.has_value() || !vend.has_value() || !renderer.has_value()) return "OpenGL not supported";

	Debug(driver, 1, "OpenGL driver: {} - {} ({})", *vend, *renderer, *ver);

#ifndef GL_ALLOW_SOFTWARE_RENDERER
	/* Don't use MESA software rendering backends as they are slower than
	 * just using a non-OpenGL video driver. */
	if (renderer->starts_with("llvmpipe") || renderer->starts_with("softpipe")) return "Software renderer detected, not using OpenGL";
#endif

	std::tie(_gl_major_ver, _gl_minor_ver) = DecodeVersion(*ver);

#ifdef _WIN32
	/* Old drivers on Windows (especially if made by Intel) seem to be
	 * unstable, so cull the oldest stuff here.  */
	if (!IsOpenGLVersionAtLeast(3, 2)) return "Need at least OpenGL version 3.2 on Windows";
#endif

	if (!BindBasicOpenGLProcs()) return "Failed to bind basic OpenGL functions.";

	SetupDebugOutput();

	/* OpenGL 1.3 is the absolute minimum. */
	if (!IsOpenGLVersionAtLeast(1, 3)) return "OpenGL version >= 1.3 required";
	/* Check for non-power-of-two texture support. */
	if (!IsOpenGLVersionAtLeast(2, 0) && !IsOpenGLExtensionSupported("GL_ARB_texture_non_power_of_two")) return "Non-power-of-two textures not supported";
	/* Check for single element texture formats. */
	if (!IsOpenGLVersionAtLeast(3, 0) && !IsOpenGLExtensionSupported("GL_ARB_texture_rg")) return "Single element texture formats not supported";
	if (!BindTextureExtensions()) return "Failed to bind texture extension functions";
	/* Check for vertex buffer objects. */
	if (!IsOpenGLVersionAtLeast(1, 5) && !IsOpenGLExtensionSupported("ARB_vertex_buffer_object")) return "Vertex buffer objects not supported";
	if (!BindVBOExtension()) return "Failed to bind VBO extension functions";
	/* Check for pixel buffer objects. */
	if (!IsOpenGLVersionAtLeast(2, 1) && !IsOpenGLExtensionSupported("GL_ARB_pixel_buffer_object")) return "Pixel buffer objects not supported";
	/* Check for vertex array objects. */
	if (!IsOpenGLVersionAtLeast(3, 0) && (!IsOpenGLExtensionSupported("GL_ARB_vertex_array_object") || !IsOpenGLExtensionSupported("GL_APPLE_vertex_array_object"))) return "Vertex array objects not supported";
	if (!BindVBAExtension()) return "Failed to bind VBA extension functions";
	/* Check for shader objects. */
	if (!IsOpenGLVersionAtLeast(2, 0) && (!IsOpenGLExtensionSupported("GL_ARB_shader_objects") || !IsOpenGLExtensionSupported("GL_ARB_fragment_shader") || !IsOpenGLExtensionSupported("GL_ARB_vertex_shader"))) return "No shader support";
	if (!BindShaderExtensions()) return "Failed to bind shader extension functions";
	if (IsOpenGLVersionAtLeast(3, 2) && _glBindFragDataLocation == nullptr) return "OpenGL claims to support version 3.2 but doesn't have glBindFragDataLocation";

	this->persistent_mapping_supported = IsOpenGLVersionAtLeast(3, 0) && (IsOpenGLVersionAtLeast(4, 4) || IsOpenGLExtensionSupported("GL_ARB_buffer_storage"));
#ifndef NO_GL_BUFFER_SYNC
	this->persistent_mapping_supported = this->persistent_mapping_supported && (IsOpenGLVersionAtLeast(3, 2) || IsOpenGLExtensionSupported("GL_ARB_sync"));
#endif

	if (this->persistent_mapping_supported && !BindPersistentBufferExtensions()) {
		Debug(driver, 1, "OpenGL claims to support persistent buffer mapping but doesn't export all functions, not using persistent mapping.");