Add the GPU rigid body pipeline from https://github.com/erwincoumans/experiments as a Bullet 3.x preview for Bullet 2.80

Extras/RigidBodyGpuPipeline/opencl/gpu_rigidbody_pipeline2/GlutRenderer.cpp

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+/*
+Copyright (c) 2012 Advanced Micro Devices, Inc.  
+
+This software is provided 'as-is', without any express or implied warranty.
+In no event will the authors be held liable for any damages arising from the use of this software.
+Permission is granted to anyone to use this software for any purpose, 
+including commercial applications, and to alter it and redistribute it freely, 
+subject to the following restrictions:
+
+1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
+2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
+3. This notice may not be removed or altered from any source distribution.
+*/
+//Originally written by Erwin Coumans
+
+
+#include <GL/glew.h>
+#include "GlutRenderer.h"
+#include <stdio.h>
+
+
+GlutRenderer* GlutRenderer::gDemoApplication;
+
+
+
+void GlutRenderer::runMainLoop()
+{
+	glutMainLoop();
+
+}
+
+
+static	void glutKeyboardCallback(unsigned char key, int x, int y) {	GlutRenderer::gDemoApplication->keyboardCallback(key,x,y); }
+static	void glutKeyboardUpCallback(unsigned char key, int x, int y){  GlutRenderer::gDemoApplication->keyboardUpCallback(key,x,y);}
+static void glutSpecialKeyboardCallback(int key, int x, int y){	GlutRenderer::gDemoApplication->specialKeyboard(key,x,y);}
+static void glutSpecialKeyboardUpCallback(int key, int x, int y){	GlutRenderer::gDemoApplication->specialKeyboardUp(key,x,y);}
+static void glutReshapeCallback(int w, int h){	GlutRenderer::gDemoApplication->resize(w,h);}
+static void glutIdleCallback(){ glutPostRedisplay (); }
+static void glutMouseFuncCallback(int button, int state, int x, int y){	GlutRenderer::gDemoApplication->mouseFunc(button,state,x,y);}
+static void	glutMotionFuncCallback(int x,int y){	GlutRenderer::gDemoApplication->mouseMotionFunc(x,y);}
+static void glutDisplayCallback(void){	GlutRenderer::gDemoApplication->displayCallback();}
+
+
+void GlutRenderer::resize(int width, int height)
+{
+	m_glutScreenWidth = width;
+	m_glutScreenHeight = height;
+}
+
+void GlutRenderer::mouseFunc(int button, int state, int x, int y)
+{
+}
+void	GlutRenderer::mouseMotionFunc(int x,int y)
+{
+}
+
+void GlutRenderer::renderScene()
+{
+	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+	glutSwapBuffers();
+	glutPostRedisplay();
+
+	GLint err = glGetError();
+	assert(err==GL_NO_ERROR);
+}
+
+void GlutRenderer::displayCallback()
+{
+	updateScene();
+	
+	renderScene();
+}
+
+GlutRenderer::GlutRenderer(int argc, char* argv[])
+{
+	glutInit(&argc, argv);
+	gDemoApplication = this;
+}
+
+void GlutRenderer::initGraphics(int width, int height)
+{
+	m_glutScreenWidth = width;
+	m_glutScreenHeight = height;
+		
+	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA);
+
+	glutInitWindowSize(m_glutScreenWidth, m_glutScreenHeight);
+	glutCreateWindow("GPU rigid body pipeline2");
+	glutKeyboardFunc(glutKeyboardCallback);
+	glutKeyboardUpFunc(glutKeyboardUpCallback);
+	glutSpecialFunc(glutSpecialKeyboardCallback);
+	glutSpecialUpFunc(glutSpecialKeyboardUpCallback);
+	glutReshapeFunc(glutReshapeCallback);
+	glutIdleFunc(glutIdleCallback);
+	glutMouseFunc(glutMouseFuncCallback);
+	glutPassiveMotionFunc(glutMotionFuncCallback);
+	glutMotionFunc(glutMotionFuncCallback);
+	glutDisplayFunc( glutDisplayCallback );
+
+	GLenum err = glewInit();
+	if (GLEW_OK != err)
+	{
+		printf("Error: %s\n", glewGetErrorString(err));
+	}
+
+	glClearColor(0.6f,0.6f,1.f,1.f);
+}