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mpledge52

OpenGL Text in openGL

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At the minute I'm using bitmap fonts and print_bitmap_string() to display text on screen. The problem I have is that it only allows me to use 7 different fonts. These fonts are all too 'skinny' which is quite hard to see on screen, I need bold text really. The trouble is that this print_bitmap_string() function is absolutely perfect for what I need -apart from the limited fonts- it is easy to place on screen, it stays the same size and always rotates to face the camera etc. However I think I need to use another method to display my text. Is there any other method which is similar but has a wider range of fonts? Ideally what I need to do is draw the character in white and have a black outline round each letter. However, if that is quite hard then I should be able to cope with a simple "chunky" font. Any ideas? Thanks.

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Well I've just looked for the function and I cant find it anywhere, I must of got it from some sample code or a tutorial somewhere. But anyhow, with the print_bitmap_string() function I can only use the following fonts:

GLUT_BITMAP_9_BY_15
GLUT_BITMAP_8_BY_13
GLUT_BITMAP_HELVETICA_18
GLUT_BITMAP_HELVETICA_12
GLUT_BITMAP_HELVETICA_10
GLUT_BITMAP_TIMES_ROMAN_24
GLUT_BITMAP_TIMES_ROMAN_10


The code I've got to print something is:

char string[0][256];
string[0][0] = 'H'; string[0][1] = 'e'; string[0][2] = 'l'; string[0][3] = 'p';

glRasterPos3f(42000, 75000, -3000);
print_bitmap_string( GLUT_BITMAP_9_BY_15 , string[0]);



That's all I do, I've not included any fancy libraries or anything.
I'll have to look through some tutorials, maybe I'm using the wrong type of function to use bitmap fonts.

***edit*** Sorry, just realised that the print_bitmap_string function actually makes a call to glutBitmapCharacter() function. No wonder I couldn't find it anywhere... :-S

[Edited by - mpledge52 on February 22, 2008 2:18:56 PM]

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Yeah, the GLUT has only few fonts hardcoded as (small) bitmaps. You can use font libraries like freetype or SDL_TTF to load and render any truetype font you want to image(s), then use it as texture. There is also a Nehe tutorial on bitmap fonts although it uses some os-specific functions.

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Thanks snoutmate, do you know if the bitmap fonts used in the Nehe tutorial (or any other fonts for that matter) behave in the same way as the bitmap fonts I have used so far? i.e. the stay the same size no matter where the camera is positioned, and (more importantly) the text rotates to face the camera at all times.

Thanks again.

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That is different thing alltogether - if you want something drawn this way (text, HUD in games, etc.), you simply draw your scene, then set orthogonal projection matrix (glOrtho) and render the text (you'd also want to disable things like depth buffer and lighting usually for this pass).

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You could always use freetype. Here's my simple wrapper I use for loading and drawing text.


#ifndef _FT_WRAPPER_H
#define _FT_WRAPPER_H

#include <string>
#include <vector>
#include <ft2build.h>
#include FT_FREETYPE_H
#include FT_GLYPH_H

namespace freetype
{
// Glyph entry structure
// stores data for a single ascii character
struct GlyphEntry
{
unsigned char ascii, width, height;
unsigned short x, y;
};

// Font data structure
// stores all infomration pertaining to a loaded font
struct FontData
{
std::string fontFile;
float fontSize;
int pixelSize;
bool antiAlias;
unsigned char* imagePixels;
size_t imageWidth;
size_t imageHeight;

std::vector<GlyphEntry> glyphEntries;
unsigned char glyphBase;
};

// Frees any memory associated with FontData object
void FreeFont(FontData* font)
{
delete[] font->imagePixels;
font->glyphEntries.clear();
delete font;
}

// Creates a truetype font from specified fontfile
FontData* LoadFont(const std::string& fontfile, float font_size, bool antialias)
{
// Create new FontData object
FontData* fontData = new FontData;
fontData->fontFile = fontfile;
fontData->fontSize = font_size;
fontData->antiAlias = antialias;

// Compute pixel size
size_t y_resolution = 96;
size_t pixel_size = font_size * y_resolution / 72;

// Margins around characters to prevent them from 'bleeding' into each other
const size_t margin = 3;
size_t image_height = 0;
size_t image_width = 256;

// Initialize FreeType
FT_Library library;
if (FT_Init_FreeType(&library) != 0)
throw "Could not initialize FreeType2 library.";

// Load the font
FT_Face face;
if (FT_New_Face(library, fontfile.c_str(), 0, &face) != 0)
throw "Could not load font file.";

// Abort if this is not a 'true type', scalable font
if (!(face->face_flags & FT_FACE_FLAG_SCALABLE) || !(face->face_flags && FT_FACE_FLAG_HORIZONTAL))
throw "Error setting font size.";

// Set the font size
FT_Set_Pixel_Sizes(face, pixel_size, 0);

// First we go over all the characters to find the max descent
// and ascent (space required above and below the base of a
// line of text) and needed image size. There are simpler methods
// to obtain these with FreeType but they are unreliable.
int max_descent = 0, max_ascent = 0;
size_t space_on_line = image_width - margin, lines = 1;

unsigned int startChar = 32;
unsigned int endChar = 126;
for (unsigned int i = startChar; i <= endChar; i++) {

// Look up the character in the font file
size_t char_index = FT_Get_Char_Index(face, i);

// Render the current glyph
FT_Load_Glyph(face, char_index, FT_LOAD_DEFAULT);
FT_Render_Glyph(face->glyph, FT_RENDER_MODE_NORMAL);

size_t advance = (face->glyph->metrics.horiAdvance >> 6) + margin;

// If the line is full, go to the next line
if (advance > space_on_line) {
space_on_line = image_width - margin;
lines++;
}

space_on_line -= advance;

max_ascent = max(face->glyph->bitmap_top, max_ascent);
max_descent = max(face->glyph->bitmap.rows - face->glyph->bitmap_top, max_descent);
}

// Compute how high the texture has to be
size_t needed_image_height = (max_ascent + max_descent + margin) * lines + margin;

// Get the first power of two in which it fits
image_height = 16;
while (image_height < needed_image_height)
image_height *= 2;

// Allocate memory for the texture
unsigned char* image = new unsigned char[image_width * image_height];
for (unsigned int i = 0; i < image_width * image_height; i++)
image[i] = 0;

// Allocate space for the glyph entries
fontData->glyphEntries.resize(endChar - startChar + 1);
fontData->glyphBase = startChar;

// These are the positions at which to draw the next glyph
unsigned int x = margin, y = margin + max_ascent;

// Drawing loop
for (unsigned int i = startChar; i <= endChar; i++) {

unsigned int char_index = FT_Get_Char_Index(face, i);

// Handle antialias text
if (antialias == true) {

// Render the glyph
FT_Load_Glyph(face, char_index, FT_LOAD_DEFAULT);
FT_Render_Glyph(face->glyph, FT_RENDER_MODE_NORMAL);

// See whether the character fits on the current line
unsigned int advance = (face->glyph->metrics.horiAdvance >> 6) + margin;
if (advance > image_width - x) {
x = margin;
y += (max_ascent + max_descent + margin);
}

// Fill in the glyph entries
fontData->glyphEntries[i - startChar].ascii = (unsigned char)i;
fontData->glyphEntries[i - startChar].width = advance - margin;
fontData->glyphEntries[i - startChar].height = pixel_size;
fontData->glyphEntries[i - startChar].x = x;
fontData->glyphEntries[i - startChar].y = y - max_ascent;

// Copy the image gotten from FreeType onto the texture at the correct position
for (unsigned int row = 0; row < face->glyph->bitmap.rows; row++) {
for (unsigned int pixel = 0; pixel < face->glyph->bitmap.width; pixel++) {

image[(x + face->glyph->bitmap_left + pixel) + (y - face->glyph->bitmap_top + row) * image_width] =
face->glyph->bitmap.buffer[pixel + row * face->glyph->bitmap.pitch];
}
}

x += advance;
}
// Handle monochrome text
else {

// Render the glyph
FT_Bitmap* ft_bmp;
FT_Glyph glyph;
FT_BitmapGlyph bmp_glyph;

FT_Load_Glyph(face, char_index, FT_LOAD_DEFAULT);
FT_Render_Glyph(face->glyph, FT_RENDER_MODE_MONO);
FT_Get_Glyph(face->glyph, &glyph);

FT_Glyph_To_Bitmap(&glyph, FT_RENDER_MODE_MONO, 0, 1);

bmp_glyph = (FT_BitmapGlyph)glyph;
ft_bmp = &bmp_glyph->bitmap;

// See whether the character fits on the current line
unsigned int advance = (face->glyph->metrics.horiAdvance >> 6) + margin;
if (advance > image_width - x) {
x = margin;
y += (max_ascent + max_descent + margin);
}

// Fill in the glyph entries
fontData->glyphEntries[i - startChar].ascii = (unsigned char)i;
fontData->glyphEntries[i - startChar].width = advance - margin;
fontData->glyphEntries[i - startChar].height = pixel_size;
fontData->glyphEntries[i - startChar].x = x;
fontData->glyphEntries[i - startChar].y = y - max_ascent;

// Copy the image onto the texture at the correct position
unsigned char* monochromeData = ft_bmp->buffer;
int bit;

for (size_t row = 0; row < ft_bmp->rows; row++) {

unsigned char* nextPtr = monochromeData + ft_bmp->pitch;
bit = 7;

for (size_t pixel = 0; pixel < ft_bmp->width; pixel++) {

unsigned char value = (*monochromeData & (1 << bit)) >> bit;

image[(x + bmp_glyph->left + pixel) + (y - bmp_glyph->top + row) * image_width] = value;

bit--;
if (bit == -1) {
bit = 7;
monochromeData++;
}
}

bit = 7;
monochromeData = nextPtr;
}

x += advance;

}
}

// Return FT_FontData object
fontData->pixelSize = pixel_size;
fontData->imagePixels = image;
fontData->imageWidth = image_width;
fontData->imageHeight = image_height;
return fontData;
}
}

#endif





freetype::FontData* font;
GLuint texID;

void init()
{
font = freetype::LoadFont("c:\\windows\\fonts\\arial.ttf", 9.0f, false);
CreateTextureFromFont(&fontTexID, *font);
}

void CreateTextureFromFont(GLuint* texID, const freetype::FontData& font)
{
glGenTextures(1, texID);
glBindTexture(GL_TEXTURE_2D, *texID);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, font.imageWidth, font.imageHeight, 0, GL_ALPHA, GL_UNSIGNED_BYTE, font.imagePixels);
}

void drawString(freetype::FontData* f, GLuint texID, std::string str)
{
if (f->antiAlias) {
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
}
else {
glEnable(GL_ALPHA_TEST);
glAlphaFunc(GL_GREATER, 0);
}

glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, texID);

glBegin(GL_QUADS);
glColor4f(0, 0, 1, 1);

float x = 0, y = 0;

for (int i = 0; i < str.size(); i++) {

freetype::GlyphEntry g = f->glyphEntries[str[i] - f->glyphBase];

float tx1 = g.x / (float)f->imageWidth;
float ty1 = g.y / (float)f->imageHeight;
float tx2 = (g.x + g.width) / (float)f->imageWidth;
float ty2 = (g.y + g.height) / (float)f->imageHeight;

glTexCoord2f(tx1, ty1); glVertex2i(x, y);
glTexCoord2f(tx2, ty1); glVertex2i(x + g.width, y);
glTexCoord2f(tx2, ty2); glVertex2i(x + g.width, y + g.height);
glTexCoord2f(tx1, ty2); glVertex2i(x, y + g.height);

x += g.width;
}

glEnd();

if (f->antiAlias) {
glDisable(GL_BLEND);
}
else {
glDisable(GL_ALPHA_TEST);
}
}


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