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* \file SDLGLFont.cpp
* \brief Bitmap font class.
* Defines a bitmap font class. A bitmap font is represented with 95
* characters that represent ASCII characters 32 to 126 (0x20 to 0x7E).
* Characters that fall out of this range should be represented with 0x20, or
* space.
#include "SDLGLFont.hpp"
#include "SDLGLTexture.hpp"
#include <assert.h>
#include <vector>
/* Prerequisites:
To support alpha-blended textures, you need to call the following GL functions
somewhere earlier in your program:
* \brief Creates an SDLGLFont object from the PNG of the given filename.
* \param fileName The file name of the PNG with the bitmap font.
SDLGLFont::SDLGLFont( std::string fileName ) {
fontLoaded = LoadFontFromFile(fileName);
* \brief Destructor for fonts.
SDLGLFont::~SDLGLFont( ) {
if ( fontLoaded == true )
SDLGL_FreeTexture( fontTexture );
* \brief Finds the next power of two for an integer.
* \param v The integer to find the next power of two for.
* \return The next power of two of v.
* This code is directly copy/pasted from:
static unsigned int NextPowerOfTwo( unsigned int v ) {
v |= v >> 1;
v |= v >> 2;
v |= v >> 4;
v |= v >> 8;
v |= v >> 16;
return v;
* \brief Loads a font from a file.
* \param fileName File name of the PNG containing the bitmap font.
* \return True if the font loaded.
bool SDLGLFont::LoadFontFromFile( std::string fileName ) {
// Linear filtering will make the SDLGLFont look crappy.
fontTexture = SDLGL_LoadTextureFromFileBestFit( fileName,
fontY );
// If the font doesn't load, we've got a problem.
if ( fontTexture )
fontLoaded = true;
// charX and charY are the width and height of a single character.
charX = fontX / 95; // 95 = number of characters in the SDLGLFont
charY = fontY; // character height is the same.
// texX and texY are the width and height of the font in the OpenGL texture
// buffer, the dimensions of which must be a power of two. As a result, we
// waste a little memory and use the next power of two from the actual
// texture size.
texX = NextPowerOfTwo( fontX );
texY = NextPowerOfTwo( fontY );
return fontLoaded;
* \brief Draws the string. Use this if you are already in a glOrtho state.
* \param x The x coordinate on the screen to draw from (upper-left corner).
* \param y The y coordinate on the screen to draw from (upper-left corner).
* \param theString The string to draw on the screen.
void SDLGLFont::DrawString( float x, float y, std::string theString ) {
float charPieceX = ((float)fontX/(float)texX)/95.0f;
// These are the coordinate arrays we're going to send to the GPU.
GLfloat vertices[theString.length()*2*4];
GLfloat texcoords[theString.length()*2*4];
// Set the current GL texture to the font we want to use.
glBindTexture( GL_TEXTURE_2D, fontTexture );
// Populate the vertices & texcoords arrays.
for ( int count = 0; count < theString.length(); count++ ) {
// These must be defined in a counter-clockwise order.
// Upper-left
vertices[count*2*4+0] = x + charX*count;
vertices[count*2*4+1] = y;
texcoords[count*2*4+0] = charPieceX*(theString[count]-32);
texcoords[count*2*4+1] = 0.0f;
// Lower-left
vertices[count*2*4+2] = x + charX*count;
vertices[count*2*4+3] = y + charY;
texcoords[count*2*4+2] = charPieceX*(theString[count]-32);
texcoords[count*2*4+3] = (float)fontY/(float)texY;
// Lower-right
vertices[count*2*4+4] = x + charX*(count+1);
vertices[count*2*4+5] = y + charY;
texcoords[count*2*4+4] = charPieceX*(theString[count]-32+1);
texcoords[count*2*4+5] = (float)fontY/(float)texY;
// Upper-right
vertices[count*2*4+6] = x + charX*(count+1);
vertices[count*2*4+7] = y;
texcoords[count*2*4+6] = charPieceX*(theString[count]-32+1);
texcoords[count*2*4+7] = 0.0f;
// Set up the GL state so vertex and texcoord arrays can be uploaded.
// Send the arrays to the GPU.
glVertexPointer(2, GL_FLOAT, 0, vertices);
glTexCoordPointer(2, GL_FLOAT, 0, texcoords);
// draw the letters
glDrawArrays(GL_QUADS, 0, theString.length()*4);
// deactivate vertex arrays after drawing
* \brief Draws the string. Use if you need a glOrtho overlay made for you.
* \param x The x coordinate on the screen to draw from (upper-left corner).
* \param y The y coordinate on the screen to draw from (upper-left corner).
* \param theString The string to draw on the screen.
* \param xResolution The total resolution of the glOrtho overlay to make.
* \param yResolution The total resolution of the glOrtho overlay to make.
void SDLGLFont::DrawString( float x, float y, std::string theString, int xResolution, int yResolution ) {
// Saves the old ModelView and Projection matrices, then puts you
// into a GLOrtho environment. Activates textures.
GLfloat modelview[16];
GLfloat projection[16];
// Get the current Modelview and Projection matrices so we can put them
// back when we're done here.
// Blank out the projection matrix.
// Set the projection matrix to orthoganal to make a "HUD-style" overlay.
glOrtho(0, xResolution, yResolution, 0, -1, 1);
// Blank out the Modelview matrix.
// Depth test is inconvenient, texturing is necessary.
glDisable( GL_DEPTH_TEST );
glEnable( GL_TEXTURE_2D );
// Now that everything's in order, actually draw the string.
DrawString( x, y, theString );
// Reloads the old Modelview and Projection matrices. Deactivates textures.
glDisable( GL_TEXTURE_2D);
glEnable( GL_DEPTH_TEST );
// Put the Projection and Modelview matrices back.