From 31e11bc4e83d4d0c407c27cc0abd26b017441c49 Mon Sep 17 00:00:00 2001
From: "Lubomir I. Ivanov" <neolit123@gmail.com>
Date: Wed, 1 Nov 2017 14:31:04 +0200
Subject: [PATCH] desktop-main.cpp: further improve the GL version detection

First, attempt to use glGetString(GL_VERSION), which works
on legacy profiles but has to be parsed (unsafe and vendor specific?).
If the above fails attempt to use the newer version API from
glGetIntegerv().

If both fail, fall back to a software renderer or exit.

If GLES is detected from glGetString() (for some odd reason -
e.g. emulated driver) show a warning and return early as we don't
handle it's versioning.

Signed-off-by: Lubomir I. Ivanov <neolit123@gmail.com>
---
 subsurface-desktop-main.cpp | 34 ++++++++++++++++++++++++++++++----
 1 file changed, 30 insertions(+), 4 deletions(-)

diff --git a/subsurface-desktop-main.cpp b/subsurface-desktop-main.cpp
index e8f57ecff..a37fd3cb5 100644
--- a/subsurface-desktop-main.cpp
+++ b/subsurface-desktop-main.cpp
@@ -152,11 +152,13 @@ void validateGL()
 		}
 		return;
 	}
-	GLint verMajor, verMinor;
+	GLint verMajor = -1, verMinor;
 	const char *glError = NULL;
 	QOpenGLContext ctx;
 	QOffscreenSurface surface;
 	QOpenGLFunctions *func;
+	const char *verChar;
+	float verFloat;
 
 	surface.setFormat(ctx.format());
 	surface.create();
@@ -174,8 +176,32 @@ void validateGL()
 	}
 	if (verbose)
 		qDebug() << QStringLiteral(VALIDATE_GL_PREFIX "obtained QOpenGLFunctions.").toUtf8().data();
-	func->glGetIntegerv(GL_MAJOR_VERSION, &verMajor);
-	func->glGetIntegerv(GL_MINOR_VERSION, &verMinor);
+	// detect version for legacy profiles
+	verChar = (const char *)func->glGetString(GL_VERSION);
+	if (verChar) {
+		// detect GLES, show a warning and return early as we don't handle it's versioning
+		if (strstr(verChar, " ES ") != NULL) {
+			 qWarning() << QStringLiteral(VALIDATE_GL_PREFIX "WARNING: Detected OpenGL ES!\n"
+			 "Attempting to run with the available profile!\n"
+			 "If this fails try manually setting the environment variable\n"
+			 "'QT_QUICK_BACKEND' with the value of 'software'\n"
+			 "before running Subsurface!\n").toUtf8().data();
+			 return;
+		}
+		if (sscanf(verChar, "%f", &verFloat) == 1) {
+			verMajor = (GLint)verFloat;
+			verMinor = (GLint)((verFloat - verMajor) * 10.f);
+		}
+	}
+	// attempt to detect version using the newer API
+	if (verMajor == -1) {
+		func->glGetIntegerv(GL_MAJOR_VERSION, &verMajor);
+		func->glGetIntegerv(GL_MINOR_VERSION, &verMinor);
+	}
+	if (verMajor == -1) {
+		glError = "Cannot detect OpenGL version";
+		goto exit;
+	}
 	if (verbose)
 		qDebug() << QStringLiteral(VALIDATE_GL_PREFIX "detected OpenGL version %1.%2.").arg(verMajor).arg(verMinor).toUtf8().data();
 	if (verMajor * 10 + verMinor < 21) { // set 2.1 as the minimal version
@@ -191,7 +217,7 @@ exit:
 		qWarning() << QStringLiteral(VALIDATE_GL_PREFIX "ERROR: %1.\n"
 			"Cannot automatically fallback to a software renderer!\n"
 			"Set the environment variable 'QT_QUICK_BACKEND' with the value of 'software'\n"
-			"before running Subsurface!").arg(glError).toUtf8().data();
+			"before running Subsurface!\n").arg(glError).toUtf8().data();
 		exit(0);
 #else
 		qWarning() << QStringLiteral(VALIDATE_GL_PREFIX "WARNING: %1. Using a software renderer!").arg(glError).toUtf8().data();