for reference: Using SDL_ttf with OpenGL

C-Junkie · 2011-02-28T13:22:19

Here is some example code that I've been meaning to cook up for awhile, that shows a short example of how to use SDL_ttf to render text for use with OpenGL. NeHe's freetype code seems to involve rendering of each letter into a texture, which is slight overkill for what many people would like to do. (it IS more efficient, however, since it doesn't involve the creation and deletion of textures for dynamic data) Anyway, for reference, a simple method to render text in opengl using SDL_ttf. #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; } Here's a screenshot of what the output should look like Hosted on imageshack I don't remember who I borrowed the Enable/Disable2D functions from.

cyberpuk

122

December 20, 2005 11:08 AM

Thank you very much. The two things run very well!.

kaolin fire

122

June 21, 2006 04:58 AM

I've been tinkering with Bob Pendleton's SDL_ttf font class and made it support newlines... I also took out a few things that I wasn't using, do forgive... it should be pretty obvious how to mix/match :) [[and I split it into the .h and .cpp, and took out the 'background color', instead using alpha blending, and... not sure what else, TBH, sorry]]

### font.h ###

/** BTW, it is covered by the LGPL  ** Bob Pendleton **//** http://www.devolution.com/pipermail/sdl/2004-December/066119.html **/

/**

+--------------------------------------+
+ Bob Pendleton: writer and programmer +
+ email: Bob@xxxxxxxxxxxxx +
+ blog: www.Stonewolf.net +
+ web: www.GameProgrammer.com +
+--------------------------------------+

http://www.oreillynet.com/pub/au/1205

Edits by Kaolin Fire ( kfire@xxxxxxxx; web: erif.org )
now takes into account glyph minx so glyphs can overlap as intended
now takes into account newline character

**/

class Font
{
private:
static const int minGlyph = ' ';
static const int maxGlyph = 126;

static int initCounter;

typedef struct
{
int minx, maxx;
int miny, maxy;
int advance;
SDL_Surface *pic;
GLuint tex;
GLfloat texMinX, texMinY;
GLfloat texMaxX, texMaxY;
} glyph;

int height;
int ascent;
int descent;
int lineSkip;
glyph glyphs[maxGlyph + 1];

const char *fontName;
int pointSize;
float fgRed, fgGreen, fgBlue;

TTF_Font *ttfFont;

SDL_Color foreground;

void loadChar(char c);

public:

Font(const char *fontName,
int pointSize,
float fgRed, float fgGreen, float fgBlue);

~Font();

void initFont();

int getLineSkip();

int getHeight();

void textSize(char *text, SDL_Rect *r);

void drawText(char *text, int x, int y);

};

###font.cpp###

#include "font.h"  void Font::loadChar(char c)  {    GLfloat texcoord[4];    char letter[2] = {0, 0};    if ((minGlyph <= c) &&         (c <= maxGlyph) &&        (NULL == glyphs[((int)c)].pic))    {      SDL_Surface *g0 = NULL;      SDL_Surface *g1 = NULL;      letter[0] = c;      TTF_GlyphMetrics(ttfFont,                        (Uint16)c,                        &glyphs[((int)c)].minx,                        &glyphs[((int)c)].maxx,                        &glyphs[((int)c)].miny,                        &glyphs[((int)c)].maxy,                        &glyphs[((int)c)].advance);      g0 = TTF_RenderText_Blended(ttfFont,                                  letter,                                  foreground);      if (NULL != g0)      {        g1 = SDL_DisplayFormatAlpha(g0);        SDL_FreeSurface(g0);      }      if (NULL != g1)      {        glyphs[((int)c)].pic = g1;        glyphs[((int)c)].tex = SDL_GL_LoadTexture(g1, texcoord);        glyphs[((int)c)].texMinX = texcoord[0];        glyphs[((int)c)].texMinY = texcoord[1];        glyphs[((int)c)].texMaxX = texcoord[2];        glyphs[((int)c)].texMaxY = texcoord[3];      }    }  }  Font::Font(const char *fontName,       int pointSize,       float fgRed, float fgGreen, float fgBlue):    fontName(fontName),    pointSize(pointSize),    fgRed(fgRed), fgGreen(fgGreen), fgBlue(fgBlue),    ttfFont(NULL)  {    if (0 == initCounter)    {      if (TTF_Init() < 0)      {        //TODO :: errorExit("Can't init SDL_ttf");printf("Can't init sdl_ttf !?\n");      }    }    initCounter++;    initFont();  }  Font::~Font()  {    initCounter--;    if (0 == initCounter)    {      TTF_Quit();    }  }  void Font::initFont()  {    int i;    ttfFont = TTF_OpenFont(fontName, pointSize);    if (NULL == ttfFont)    {printf("Can't open font file\n");      //TODO :: errorExit("Can't open font file");    }    foreground.r = (Uint8)(255 * fgRed);    foreground.g  = (Uint8)(255 * fgGreen);    foreground.b = (Uint8)(255 * fgBlue);    height = TTF_FontHeight(ttfFont);    ascent = TTF_FontAscent(ttfFont);    descent = TTF_FontDescent(ttfFont);    lineSkip = TTF_FontLineSkip(ttfFont);    for (i = minGlyph; i <= maxGlyph; i++)    {      glyphs.pic = NULL;      glyphs.tex = 0;    }  }  int Font::getLineSkip()  {    return lineSkip;  }  int Font::getHeight()  {    return height;  }  void Font::textSize(char *text,                 SDL_Rect *r)  {    int maxx = 0;    int advance = 0;    int minx = 0;		int w_largest = 0;		char lastchar = 0;    r->x = 0;    r->y = 0;    r->w = 0;    r->h = height;    while (0 != *text)    {      if ((minGlyph <= *text) && (*text <= maxGlyph))      {				lastchar = *text;				if (*text == '\n') {					r->h += lineSkip;    			r->w = r->w - advance + maxx;					if (r->w > w_largest) w_largest = r->w;					r->w = 0;				} else {        	loadChar(*text);        	maxx = glyphs[((int)*text)].maxx;        	advance = glyphs[((int)*text)].advance;        	r->w += advance;				}      }      text++;    }		if (lastchar != '\n') {    	r->w = r->w - advance + maxx;			if (r->w > w_largest) w_largest = r->w;		} else {			r->h -= lineSkip;		}		if (w_largest > r->w) r->w = w_largest;  }  void Font::drawText(char *text, int x, int y)  {    GLfloat left, right;    GLfloat top, bottom;    GLfloat texMinX, texMinY;    GLfloat texMaxX, texMaxY;    GLfloat minx;    GLfloat baseleft = x;    glPushAttrib(GL_ALL_ATTRIB_BITS);    glEnable(GL_BLEND);    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);    glEnable(GL_TEXTURE_2D);    glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);    while (0 != *text) {			if (*text == '\n') {				x = baseleft;				y += lineSkip;			} else if ((minGlyph <= *text) && (*text <= maxGlyph)) {        loadChar(*text);        texMinX = glyphs[((int)*text)].texMinX;        texMinY = glyphs[((int)*text)].texMinY;        texMaxX = glyphs[((int)*text)].texMaxX;        texMaxY = glyphs[((int)*text)].texMaxY;        minx = glyphs[((int)*text)].minx;        left   = x + minx;        right  = x + glyphs[((int)*text)].pic->w + minx;        top    = y;        bottom = y + glyphs[((int)*text)].pic->h;        glBindTexture(GL_TEXTURE_2D, glyphs[((int)*text)].tex);        glBegin(GL_TRIANGLE_STRIP);        glTexCoord2f(texMinX, texMinY); glVertex2f( left,    top);        glTexCoord2f(texMaxX, texMinY); glVertex2f(right,    top);        glTexCoord2f(texMinX, texMaxY); glVertex2f( left, bottom);        glTexCoord2f(texMaxX, texMaxY); glVertex2f(right, bottom);        glEnd();        x += glyphs[((int)*text)].advance;      }      text++;    }    glPopAttrib();  }	int Font::initCounter = 0;

mattn

122

July 03, 2006 12:53 PM

i wonder whether this works with uft-8, too?

UFO:AI UFO:AI@Sourceforge

Anonymous

January 17, 2007 01:12 PM

Hi,
Sorry for the UP but I want to know how to use this code with Latin specials chars like "é" "ê" "à" ?

Garkader

122

August 05, 2008 04:50 AM

@kaolin fire
function Font::textSize is not handling newlines properly.
The first condition in the while loop should be corrected to something like:

if (((minGlyph <= *text) && (*text <= maxGlyph)) || *text == '\n')

instead of

if ((minGlyph <= *text) && (*text <= maxGlyph))

Otherwise '\n' won't be processed.

AlasdairDeacon

100

February 28, 2011 01:22 PM

Thank you, that works instantly! I just called RenderText_Blended and (when I passed it into my gl texture creation function) it just returned a texture all of the colour passed into the TTF function.

Also Koshmaar thanks for the management system, saved me a lot of time

for reference: Using SDL_ttf with OpenGL

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