better workaround for Intel GPU crash for glDrawBuffer on Linux

fix a linux build issue

Demos3/bullet2/RagdollDemo/RagdollDemo.h

@@ -2,7 +2,7 @@
 #define RAGDOLL_DEMO_H
 
 
-#include "../../Demos/CommonRigidBodySetup.h"
+#include "../../../Demos/CommonRigidBodySetup.h"
 #include "../BasicDemo/BasicDemo.h"
 
 struct BulletDemoInterface;

btgui/OpenGLWindow/GLRenderToTexture.cpp

@@ -1,6 +1,8 @@
 
 ///See http://www.opengl-tutorial.org/intermediate-tutorials/tutorial-14-render-to-texture/
 
+bool gIntelLinuxglDrawBufferWorkaround=false;
+
 #include "GLRenderToTexture.h"
 #include "Bullet3Common/b3Scalar.h" // for b3Assert
 GLRenderToTexture::GLRenderToTexture()
@@ -66,9 +68,16 @@ bool GLRenderToTexture::enable()
 		}
 		case RENDERTEXTURE_DEPTH:
 		{
-			GLenum drawBuffers[2] = { GL_COLOR_ATTACHMENT0, 0 };// GL_DEPTH_ATTACHMENT, 0};
-            glDrawBuffers(1, drawBuffers);
-//			glDrawBuffer(GL_NONE);
+			//Intel OpenGL driver crashes when using GL_NONE for glDrawBuffer on Linux, so use a workaround
+			if (gIntelLinuxglDrawBufferWorkaround)
+			{
+				GLenum drawBuffers[2] = { GL_DEPTH_ATTACHMENT,0};
+                        	glDrawBuffers(1, drawBuffers);
+				
+			} else
+			{	
+				glDrawBuffer(GL_NONE);
+			}
 			break;
 		}
 		default:

btgui/OpenGLWindow/X11OpenGLWindow.cpp

@@ -15,6 +15,7 @@
 #include <unistd.h>
 
 #include <pthread.h>
+extern bool gIntelLinuxglDrawBufferWorkaround;
 
 GLint                   att[] = { GLX_RGBA, GLX_DEPTH_SIZE, 24, GLX_DOUBLEBUFFER, None };
 static bool forceOpenGL3 = true;
@@ -233,6 +234,12 @@ void X11OpenGLWindow::enableOpenGL()
     }
     const GLubyte* ven = glGetString(GL_VENDOR);
     printf("GL_VENDOR=%s\n", ven);
+
+    if (strncmp((const char*)ven,"Intel",5)==0)
+	{
+		printf("Workaround for some crash in the Intel OpenGL driver on Linux/Ubuntu\n");
+		gIntelLinuxglDrawBufferWorkaround=true;
+	}
     const GLubyte* ren = glGetString(GL_RENDERER);
     printf("GL_RENDERER=%s\n",ren);
     const GLubyte* ver = glGetString(GL_VERSION);