#define GL_GLEXT_PROTOTYPES
#include <GL/glut.h>

#if 1

static const GLchar *source[] = {
	"void main() {\n",
	"  gl_Position = ftransform();\n",
	"  if (gl_Vertex.xy == vec2(-1, -1)) {\n",
	"    gl_FrontColor.rgb = vec3(0, 0, 1);\n",
	"  } else {\n",
	"    gl_FrontColor.rg = (gl_Vertex.xy + vec2(1, 1)) * 0.5;\n",
	"  }\n",
	"}\n",
};

#else

static const GLchar *source[] = {
	"void main() {\n",
	"  gl_Position = ftransform();\n",
	"  if (gl_Vertex.xy == vec2(-1, -1)) {\n",
	"    gl_FrontColor.rgb = vec3(0, 0, 1);\n",
	"    return;\n",
	"  }\n",
	"  gl_FrontColor.rg = (gl_Vertex.xy + vec2(1, 1)) * 0.5;\n",
	"}\n",
};

#endif

static void display(void){
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	glLoadIdentity();
	glBegin(GL_QUADS);
	glVertex2f(-1, -1);
	glVertex2f(-1, 1);
	glVertex2f(1, 1);
	glVertex2f(1, -1);
	glEnd();
	glFinish();
}

static void reshape(int width, int height){
	glViewport(0, 0, width, height);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glMatrixMode(GL_MODELVIEW);
}

int main(int argc, char **argv){
	GLuint shader, program;

	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_RGB);

	glutCreateWindow(argv[0]);
	glutDisplayFunc(display);
	glutReshapeFunc(reshape);

	shader = glCreateShader(GL_VERTEX_SHADER);
	glShaderSource(shader, sizeof(source) / sizeof(source[0]),
		       source, NULL);
	glCompileShader(shader);

	program = glCreateProgram();
	glAttachShader(program, shader);
	glLinkProgram(program);
	glUseProgram(program);

	glutMainLoop();
	return 0;
}