#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#include <GL/gl.h>
#include <GL/glu.h>

#include <SDL/SDL.h>
#include <SDL/SDL_ttf.h>

/* adjust these accordingly */
char fontpath[] = "/path/to/a/font/file.ttf";
int screenwidth = 640;
int screenheight = 480;

int round(double x)
{
	return (int)(x + 0.5);
}

int nextpoweroftwo(int x)
{
	double logbase2 = log(x) / log(2);
	return round(pow(2,ceil(logbase2)));
}

char *init_sdl(SDL_Surface** screen)
{
	if(SDL_Init(SDL_INIT_VIDEO))
		return SDL_GetError();
	atexit(SDL_Quit);
	
	*screen = SDL_SetVideoMode(screenwidth, screenheight, 0, SDL_OPENGL);
	
	SDL_WM_SetCaption("C-Junkie's SDLGL text example", 0);
	
	if(TTF_Init())
		return TTF_GetError();
	atexit(TTF_Quit);
	
	return 0;
}

void SDL_GL_RenderText(char *text, 
                      TTF_Font *font,
                      SDL_Color color,
                      SDL_Rect *location)
{
	SDL_Surface *initial;
	SDL_Surface *intermediary;
	SDL_Rect rect;
	int w,h;
	int texture;
	
	/* Use SDL_TTF to render our text */
	initial = TTF_RenderText_Blended(font, text, color);
	
	/* Convert the rendered text to a known format */
	w = nextpoweroftwo(initial->w);
	h = nextpoweroftwo(initial->h);
	
	intermediary = SDL_CreateRGBSurface(0, w, h, 32, 
			0x00ff0000, 0x0000ff00, 0x000000ff, 0xff000000);

	SDL_BlitSurface(initial, 0, intermediary, 0);
	
	/* Tell GL about our new texture */
	glGenTextures(1, &texture);
	glBindTexture(GL_TEXTURE_2D, texture);
	glTexImage2D(GL_TEXTURE_2D, 0, 4, w, h, 0, GL_BGRA, 
			GL_UNSIGNED_BYTE, intermediary->pixels );
	
	/* GL_NEAREST looks horrible, if scaled... */
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);	

	/* prepare to render our texture */
	glEnable(GL_TEXTURE_2D);
	glBindTexture(GL_TEXTURE_2D, texture);
	glColor3f(1.0f, 1.0f, 1.0f);
	
	/* Draw a quad at location */
	glBegin(GL_QUADS);
		/* Recall that the origin is in the lower-left corner
		   That is why the TexCoords specify different corners
		   than the Vertex coors seem to. */
		glTexCoord2f(0.0f, 1.0f); 
			glVertex2f(location->x    , location->y);
		glTexCoord2f(1.0f, 1.0f); 
			glVertex2f(location->x + w, location->y);
		glTexCoord2f(1.0f, 0.0f); 
			glVertex2f(location->x + w, location->y + h);
		glTexCoord2f(0.0f, 0.0f); 
			glVertex2f(location->x    , location->y + h);
	glEnd();
	
	/* Bad things happen if we delete the texture before it finishes */
	glFinish();
	
	/* return the deltas in the unused w,h part of the rect */
	location->w = initial->w;
	location->h = initial->h;
	
	/* Clean up */
	SDL_FreeSurface(initial);
	SDL_FreeSurface(intermediary);
	glDeleteTextures(1, &texture);
}

void glEnable2D()
{
	int vPort[4];
  
	glGetIntegerv(GL_VIEWPORT, vPort);
  
	glMatrixMode(GL_PROJECTION);
	glPushMatrix();
	glLoadIdentity();
  
	glOrtho(0, vPort[2], 0, vPort[3], -1, 1);
	glMatrixMode(GL_MODELVIEW);
	glPushMatrix();
	glLoadIdentity();
}

void glDisable2D()
{
	glMatrixMode(GL_PROJECTION);
	glPopMatrix();   
	glMatrixMode(GL_MODELVIEW);
	glPopMatrix();	
}

void init_gl()
{
	/* Irrelevant stuff for this demo */
	glShadeModel(GL_SMOOTH);
	glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
	glClearDepth(1.0f);
	glDepthFunc(GL_LEQUAL);
	glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
	
	/* Required if you want alpha-blended textures (for our fonts) */
	glBlendFunc(GL_ONE, GL_ONE);
	glEnable(GL_BLEND);
	
	/* Required setup stuff */
	glViewport(0, 0, 800, 600);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	gluPerspective(45.0f, screenwidth / (float)screenheight, 0.1f, 50.0f);
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();	
}

int main()
{
	SDL_Surface *screen;
	TTF_Font* font;
	char *err;
	SDL_Color color;
	SDL_Rect position;
	SDL_Event event;
	int done;
	
	/* Do boring initialization */
	if((err = init_sdl(&screen))) {
		printf("Error while initializing: %s", err);
		return 1;
	}
	
	if(!(font = TTF_OpenFont(fontpath, 20))) {
		printf("Error loading font: %s", TTF_GetError());
		return 1;
	}
	
	init_gl();

	done = 0;
	while(!done) {
		/* render a fun litte quad */
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
		glLoadIdentity();
		glTranslatef(0.0f, 0.0f, -5.0f);
		glDisable(GL_TEXTURE_2D);
		
		glBegin(GL_QUADS);
			glNormal3f(0.0f, 0.0f, 1.0f);
			glColor3f(0.5f, 0.0f, 0.0f); glVertex3f(-1.5f, -1.0f,  1.0f);
			glColor3f(0.0f, 0.5f, 0.0f); glVertex3f( 1.0f, -2.0f,  1.0f);
			glColor3f(0.0f, 0.0f, 0.5f); glVertex3f( 1.5f,  1.0f,  1.0f);
			glColor3f(0.5f, 0.0f, 0.0f); glVertex3f(-2.0f,  1.0f, -1.0f);
		glEnd();
		
		/* Go in HUD-drawing mode */
		glEnable2D();
		glDisable(GL_DEPTH_TEST);
		
		/* Draw some text */
		color.r = 255;
		color.g = 255;
		color.b = 255;
		/** A quick note about position.
		 * Enable2D puts the origin in the lower-left corner of the
		 * screen, which is different from the normal coordinate
		 * space of most 2D api's. position, therefore,
		 * gives the X,Y coordinates of the lower-left corner of the
		 * rectangle **/
		position.x = screenwidth / 3;
		position.y = screenheight / 2;
		SDL_GL_RenderText("Hello, World!", font, color, &position);
		position.y -= position.h;
		SDL_GL_RenderText("A line right underneath", font, color, &position);
		position.y -= position.h;
		SDL_GL_RenderText("Yay text rendering.", font, color, &position);

		/* Come out of HUD mode */
		glEnable(GL_DEPTH_TEST);
		glDisable2D();
		
		/* Show the screen */
		SDL_GL_SwapBuffers( );
		
		/* Wait until you click the X */
	
		SDL_WaitEvent(&event);
		switch(event.type) {
		case SDL_QUIT:
			done = 1;
			break;
		}
	}
	
	/* Clean up (the atexit's take care of the rest) */
	TTF_CloseFont(font);
	
	return 0;
}