struct StoneBlock {
	unsigned int vbuf, ebuf, lbuf;
	unsigned int vertex_shader;
	unsigned int fragment_shader;
	unsigned int program;
	unsigned int vertex_attrib; 
	unsigned int mvp_uniform;
	unsigned int tex_uniform;
	unsigned int element_count;
	unsigned int tex;
	vector<vec4> locations;
	// initialization:  Texture and vertices into memory
	bool init(){
		GLfloat cube_vertices[] = {
			// front
			-0.5, -0.5,  0.5,
			0.5, -0.5,  0.5,
			0.5,  0.5,  0.5,
			-0.5,  0.5,  0.5,
			// back
			-0.5, -0.5, -0.5,
			0.5, -0.5, -0.5,
			0.5,  0.5, -0.5,
			-0.5,  0.5, -0.5,
		};

		glGenBuffers(1, &vbuf);
		glBindBuffer(GL_SHADER_STORAGE_BUFFER, vbuf);
		glBufferData(GL_SHADER_STORAGE_BUFFER, sizeof(cube_vertices), cube_vertices, GL_STATIC_DRAW);

		GLushort cube_elements[] = {
			// front
			0, 1, 2,
			2, 3, 0,
			// top
			1, 5, 6,
			6, 2, 1,
			// back
			7, 6, 5,
			5, 4, 7,
			// bottom
			4, 0, 3,
			3, 7, 4,
			// left
			4, 5, 1,
			1, 0, 4,
			// right
			3, 2, 6,
			6, 7, 3,
		};
		element_count = sizeof(cube_elements) / sizeof(GLushort);
		glGenBuffers(1, &ebuf);
		glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebuf);
		glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(cube_elements), cube_elements, GL_STATIC_DRAW);

		glGenBuffers(1, &lbuf);
		glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, lbuf);
		float test_position[] = {0, 1, 3, 0};
		glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(vec4) * locations.size(), locations.data(), GL_STATIC_DRAW);

		int texwidth, texheight;
		unsigned char *image_data = SOIL_load_image("brick.jpg", &texwidth, &texheight, 0, SOIL_LOAD_RGB);
		printf("Loaded texture %d by %d\n", texwidth, texheight);
		if(!image_data)
			return false;
		glGenTextures(1, &tex);
		glBindTexture(GL_TEXTURE_2D, tex);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
		glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, texwidth, texheight, 0, GL_RGB, GL_UNSIGNED_BYTE, image_data);
		free(image_data);

		vertex_shader = make_shader("cube_vertex.glsl", GL_VERTEX_SHADER);
		fragment_shader = make_shader("cube_fragment.glsl", GL_FRAGMENT_SHADER);
		if(!(vertex_shader && fragment_shader))
			return 0;

		program = glCreateProgram();
		glAttachShader(program, vertex_shader);
		glAttachShader(program, fragment_shader);
		glLinkProgram(program);
		GLint link_ok;
		glGetProgramiv(program, GL_LINK_STATUS, &link_ok);
		if(!link_ok){
			glGetProgramInfoLog(program, GBLEN, NULL, general_buffer);
			puts(general_buffer);
			printf(RED("Link Failed\n").c_str());
			return false;
		}
		vertex_attrib = glGetAttribLocation(program, "in_vertex");
		mvp_uniform = glGetUniformLocation(program, "mvp");
		tex_uniform = glGetUniformLocation(program, "tex");
		return true;
	}

	// drawing:  set up and call glDrawElementsInstanced
	void draw(const mat4 &vp){
		glUseProgram(program);
		glActiveTexture(GL_TEXTURE0);
		glBindTexture(GL_TEXTURE_2D, tex);
		glUniform1i(tex_uniform, 0);
		glUniformMatrix4fv(mvp_uniform, 1, 0, glm::value_ptr(vp));
		glEnableVertexAttribArray(vertex_attrib);
		glBindBuffer(GL_ARRAY_BUFFER, vbuf);
		glVertexAttribPointer(vertex_attrib, 3, GL_FLOAT, GL_FALSE, 0, 0);
		glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebuf);
		glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, lbuf);
		printf("Element count = %d, locations.size = %d\n", element_count, locations.size());
		glDrawElementsInstanced(GL_TRIANGLES, element_count, GL_UNSIGNED_SHORT, 0, locations.size());
	}

	// movement:  for falling calculations
	// Returns the effective floor level
	float movement(){
		return 0.0;
	}

};