#include <stdio.h>
#include <unistd.h>
#include "SDL.h"
#define GL_GLEXT_PROTOTYPES
#include <GL/gl.h>
#include <GL/glext.h>


static PFNGLGETOBJECTPARAMETERIVARBPROC		eglGetObjectParameterivARB      =NULL;
static PFNGLGETINFOLOGARBPROC			eglGetInfoLogARB		=NULL;
static PFNGLCREATESHADEROBJECTARBPROC		eglCreateShaderObjectARB	=NULL;
static PFNGLSHADERSOURCEARBPROC			eglShaderSourceARB		=NULL;
static PFNGLCOMPILESHADERARBPROC		eglCompileShaderARB		=NULL;
static PFNGLCREATEPROGRAMOBJECTARBPROC		eglCreateProgramObjectARB	=NULL;
static PFNGLATTACHOBJECTARBPROC			eglAttachObjectARB		=NULL;
static PFNGLLINKPROGRAMARBPROC			eglLinkProgramARB		=NULL;
static PFNGLUNIFORM1IARBPROC			eglUniform1iARB			=NULL;
static PFNGLGETUNIFORMLOCATIONARBPROC		eglGetUniformLocationARB	=NULL;
static PFNGLUSEPROGRAMOBJECTARBPROC		eglUseProgramObjectARB		=NULL;

static void vr_glext_glsl_init_exts()
{
	static bool init=false;
	if (init)
		return;
	eglGetObjectParameterivARB=(PFNGLGETOBJECTPARAMETERIVARBPROC)SDL_GL_GetProcAddress("glGetObjectParameterivARB");
	eglGetInfoLogARB=(PFNGLGETINFOLOGARBPROC)SDL_GL_GetProcAddress("glGetInfoLogARB");
	eglCreateShaderObjectARB=(PFNGLCREATESHADEROBJECTARBPROC)SDL_GL_GetProcAddress("glCreateShaderObjectARB");
	eglShaderSourceARB=(PFNGLSHADERSOURCEARBPROC)SDL_GL_GetProcAddress("glShaderSourceARB");
	eglCompileShaderARB=(PFNGLCOMPILESHADERARBPROC)SDL_GL_GetProcAddress("glCompileShaderARB");
	eglCreateProgramObjectARB=(PFNGLCREATEPROGRAMOBJECTARBPROC)SDL_GL_GetProcAddress("glCreateProgramObjectARB");
	eglAttachObjectARB=(PFNGLATTACHOBJECTARBPROC)SDL_GL_GetProcAddress("glAttachObjectARB");
	eglLinkProgramARB=(PFNGLLINKPROGRAMARBPROC)SDL_GL_GetProcAddress("glLinkProgramARB");
	eglUniform1iARB=(PFNGLUNIFORM1IARBPROC)SDL_GL_GetProcAddress("glUniform1iARB");
	eglGetUniformLocationARB=(PFNGLGETUNIFORMLOCATIONARBPROC)SDL_GL_GetProcAddress("glGetUniformLocationARB");
	eglUseProgramObjectARB=(PFNGLUSEPROGRAMOBJECTARBPROC)SDL_GL_GetProcAddress("glUseProgramObjectARB");
}


static void vr_glext_glsl_dump_log(GLhandleARB p,const GLcharARB* shader)
{
	vr_glext_glsl_init_exts();
	GLint log_size;
	eglGetObjectParameterivARB(p, GL_OBJECT_INFO_LOG_LENGTH_ARB, &log_size);
	if (log_size>1)
	{
		GLcharARB* s=(GLcharARB*)malloc((log_size+1)*sizeof(GLcharARB));
		eglGetInfoLogARB(p,log_size,NULL,s);
		printf("============================================================\n");
		printf("Faulty ARB program. Log (%d bytes) : \n%s\n",log_size,s);
		free(s);
		printf("Faulty ARB program : \n");
		int lc=0;
		printf("\n%4d: ",++lc);
		for(int i=0;i<(int)strlen(shader);i++)
		{
			if (shader[i]=='\n')
				printf("\n%4d: ",++lc);
			else
				printf("%c",shader[i]);
		}
		printf("\n");
		printf("============================================================\n");
	}
}

bool vr_glext_glsl_create_program(const GLcharARB* vshader,const GLcharARB* fshader,GLhandleARB* res)
{
	vr_glext_glsl_init_exts();
	GLint ok;

	GLhandleARB vs=eglCreateShaderObjectARB(GL_VERTEX_SHADER_ARB);
	GLhandleARB fs=eglCreateShaderObjectARB(GL_FRAGMENT_SHADER_ARB);
	eglShaderSourceARB(vs, 1, &vshader,NULL);
	eglShaderSourceARB(fs, 1, &fshader,NULL);
	eglCompileShaderARB(vs);
	vr_glext_glsl_dump_log(vs,vshader);
	eglGetObjectParameterivARB(vs,GL_OBJECT_COMPILE_STATUS_ARB,&ok);
	if (!ok)
	{
		printf("compiling vertex shader\n");
		return false;
	}
	eglCompileShaderARB(fs);
	vr_glext_glsl_dump_log(fs,fshader);
	eglGetObjectParameterivARB(fs,GL_OBJECT_COMPILE_STATUS_ARB,&ok);
	if (!ok)
	{
		printf("compiling fragment shader\n");
		return false;
	}
	GLhandleARB p = eglCreateProgramObjectARB();
	eglAttachObjectARB(p,vs);
	eglAttachObjectARB(p,fs);
	eglLinkProgramARB(p);
	vr_glext_glsl_dump_log(p,"(Linking Stage)");
	eglGetObjectParameterivARB(p,GL_OBJECT_LINK_STATUS_ARB,&ok);
	if (!ok)
	{
		printf("linking program\n");
		return false;
	}
	*res=p;
	return true;
}

char vshader[] = 
"void main()"
"{"
"	gl_TexCoord[0] = gl_Vertex;"
"	gl_Position = ftransform();"
"}";

char fshader_pass1[] =
"uniform vec2 center;									\n"
"void main ()										\n"
"{											\n"
"	float dist = 400.0 / ( (gl_TexCoord[0].x - center.x)*(gl_TexCoord[0].x - center.x) + (gl_TexCoord[0].y - center.y)*(gl_TexCoord[0].y - center.y));	\n"
"	gl_FragColor = vec4(dist,dist,dist,1.0);						\n"
"}											\n"
;

char fshader_pass2[] =
"uniform sampler2D pass1_tex;								\n"
"void main ()										\n"
"{											\n"
"	const vec2 light=vec2(-0.707, -0.707);						\n"
"	vec4 v=texture2D(pass1_tex, gl_TexCoord[0].xy/vec2(1024.0));			\n"
"	float vv = v.r;									\n"
"	float dx = dFdx(vv);								\n"
"	float dy = dFdy(vv);								\n"
"	vec2 gradient = (vec2(dx,dy))*vec2(2000.0);					\n"
"	float shading = 0.1 + 0.05 * min(max(dot(gradient,light),0.0),200.0);		\n"
"	if (vv>0.1)									\n"
"	{										\n"
"		gl_FragColor = vec4(0.1,0.2,0.6,200.0) * vec4(shading);			\n"
"		return;									\n"
"	}										\n"
"	gl_FragColor = vec4(0.1,0.1,0.2,0.0);						\n"
"}											\n"
;

GLuint render_tex;


#define NUM_BALLS 10
float ball[NUM_BALLS*2];
float balldir[NUM_BALLS*2];

int main(int argc, char* argv[])
{
	int i;

	SDL_Init( SDL_INIT_EVERYTHING );
	SDL_GL_SetAttribute( SDL_GL_RED_SIZE, 5 );
	SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 5 );
	SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 5 );
	SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, 0 );
	SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );
	SDL_SetVideoMode( 1024, 1024, 0, SDL_OPENGL );

	GLhandleARB prog_pass1,prog_pass2;

	if ( !vr_glext_glsl_create_program(vshader,fshader_pass1,&prog_pass1) )
		return 0;

	if ( !vr_glext_glsl_create_program(vshader,fshader_pass2,&prog_pass2) )
		return 0;

	glDisable(GL_CULL_FACE);
	glDisable(GL_BLEND);
	glDisable(GL_DEPTH_TEST);

	glMatrixMode(GL_PROJECTION);
	glLoadIdentity ();
	glOrtho(0.,1024., 0.,1024.,-1.0,1.0);
	glMatrixMode (GL_MODELVIEW);
	glLoadIdentity ();
	glColor4f(1.0, 1.0, 1.0, 1.0);

	glGenTextures(1,&render_tex);

	glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 1);
	glBindTexture(GL_TEXTURE_2D, render_tex);
	glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE32F_ARB, 1024,1024, 0, GL_LUMINANCE, GL_FLOAT, NULL);

	// Attach texture to FBO
	glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, render_tex, 0);

	i=0;

	srand(42);
	int before = SDL_GetTicks();
	for(int i=0;i<NUM_BALLS*2;i++)
	{
		ball[i] = (float)(rand()%1024);
		balldir[i] = (float)((rand()%10)-5);
	}

	while(i<1000)
	{
		glMatrixMode(GL_PROJECTION);
		glLoadIdentity ();
		glOrtho(0.,1024., 0.,1024.,-1.0,1.0);
		glMatrixMode (GL_MODELVIEW);
		glLoadIdentity ();

		glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 1);
		glDrawBuffer(GL_COLOR_ATTACHMENT0_EXT);
		glViewport(0,0,1024,1024);
		glClearColor(0.0,0.0,0.0,0.0);
		glClear(GL_COLOR_BUFFER_BIT);

		glDisable(GL_TEXTURE_2D);
		glEnable(GL_BLEND);
		glBlendFunc(GL_ONE,GL_ONE);

		glUseProgramObjectARB(prog_pass1);
		for(unsigned b=0;b<NUM_BALLS;b++)
		{
			float x= ball[b*2];
			float y= ball[b*2+1];
			glUniform2fARB(eglGetUniformLocationARB(prog_pass1, "center"),x,y);
			float r = 800.0;
			float minx = x - r;
			float maxx = x + r;
			float miny = y - r;
			float maxy = y + r;

			glBegin(GL_QUADS);
			glVertex2f(minx,miny);
			glVertex2f(maxx,miny);
			glVertex2f(maxx,maxy);
			glVertex2f(minx,maxy);
			glEnd();

			ball[b*2] += balldir[b*2];
			ball[b*2+1] += balldir[b*2+1];

			if ( (ball[b*2]<0) || (ball[b*2]>1024))
				balldir[b*2] = -balldir[b*2];
			if ( (ball[b*2+1]<0) || (ball[b*2+1]>1024))
				balldir[b*2+1] = -balldir[b*2+1];

		}

		glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);

		glDisable(GL_BLEND);

		glUseProgramObjectARB(prog_pass2);

		glActiveTextureARB( GL_TEXTURE0_ARB );
		glEnable(GL_TEXTURE_2D);
		glBindTexture(GL_TEXTURE_2D, render_tex);
		eglUniform1iARB(eglGetUniformLocationARB(prog_pass2, "pass1_tex"),0);

		glBegin(GL_QUADS);
		glTexCoord2f(0.0, 0.0); glVertex2f(0.0,0.0);
		glTexCoord2f(1.0, 0.0); glVertex2f(1024.0, 0.0);
		glTexCoord2f(1.0, 1.0); glVertex2f(1024.0, 1024.0);
		glTexCoord2f(0.0, 1.0); glVertex2f(0.0, 1024.0);
		glEnd();

		SDL_GL_SwapBuffers();

		i++;
	}
	int after = SDL_GetTicks();
	float time = (after-before)/1000.0;
	printf("%.2f seconds total (avg %.2f fps)\n",time,i/time);

	SDL_Quit();
}