load Texture into OpenGL

OpenGL(GL/GLU/GLUT)自体は、殆んどの画像フォーマットをサポートしていないので、 Textureの読込みは骨が折れます。そこで、 OpenGLとSDLの連携を参考にして、SDLで様々な画像をTextureとして読み込む例を挙げてみます。

TextureImage.h

#ifndef TEXTUREIMAGE_H
#define TEXTUREIMAGE_H

#include <iostream>
#include <GL/glut.h>
#include <SDL/SDL_image.h>
#include <vector>
#include <map>
#include <string>

typedef struct{
  std::string filename;
  GLuint textureID;
  int width;
  int height;
} TextureInfo;

class TextureImage
{
  private:
  std::map<std::string, TextureInfo> Textures;
  public:
  int loadImage(char * filename);
  TextureInfo * getTexture(char * filename);
};

#endif

TextureImage.cpp

#include "TextureImage.h"
#include <string.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>

int TextureImage::loadImage(char *filename)
{
  SDL_Surface *Image = NULL;
  SDL_Surface *tmpImage;
  GLuint texID = 0;
  TextureInfo texture;

  if(Image = IMG_Load(filename))
  {
    tmpImage = SDL_CreateRGBSurface(SDL_SWSURFACE, 0, 0, 32, 
        0x000000ff, 
        0x0000ff00, 
        0x00ff0000, 
        0xff000000);
    Image = SDL_ConvertSurface(Image, tmpImage->format, SDL_SWSURFACE);
    SDL_FreeSurface(tmpImage);

    glGenTextures(1, &texID);
    glBindTexture(GL_TEXTURE_2D, texID);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

    // これだと規定のサイズの画像しか読み込めない
    /* glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, Image->w, Image->h, 0,
        GL_RGBA, GL_UNSIGNED_BYTE, Image->pixels); */

    gluBuild2DMipmaps(GL_TEXTURE_2D, GL_RGBA, Image->w, Image->h,
        GL_RGBA, GL_UNSIGNED_BYTE, Image->pixels);

    SDL_FreeSurface(Image);

    texture.filename = filename;
    texture.textureID = texID;
    texture.width = Image->w;
    texture.height = Image->h;
    Textures.insert(std::pair<std::string, TextureInfo>(filename, texture));
    return 0;
  }
  return -1;
}

TextureInfo * TextureImage::getTexture(char *filename)
{
  std::map<std::string, TextureInfo>::iterator i = Textures.find(filename);
  if(i != Textures.end())
    {
      return &(i->second);
    }
  if(loadImage(filename) == 0)
    {
      return getTexture(filename);
    }
  return NULL;
}

glTexImage2Dの代わりにgluBuild2DMipmapsを使えば、画像Pixelサイズに左右されずに詠みこめる筈です。もっとも、最近のOpenGLでは、その問題は解消されたようですが。あとは、以下のようにすれば一応Textureは使える筈です。

#include "TextureImage.h"
...
TextureImage *texture;
...
texture = new TextureImage();
...
void display(void)
{
  TextureInfo * tex;

  glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
  glRotated(1.1, 0.0, 1.0, 0.0);

  glEnable(GL_LINE_SMOOTH);  
  glEnable(GL_DEPTH_TEST);

  glEnable(GL_TEXTURE_2D);
  if((tex = texture->getTexture("sample.gif")) == NULL)
    exit(-1);
  glBindTexture(GL_TEXTURE_2D, tex->textureID);
  glBegin(GL_POLYGON);
  glTexCoord2f(0, 1);
  glVertex2f(0, 0);
  glTexCoord2f(0, 0);
  glVertex2f(0, tex->height/100);
  glTexCoord2f(1, 0);
  glVertex2f(tex->width/100, tex->height/100);
  glTexCoord2f(1, 1);
  glVertex2f(tex->width/100, 0);
  glEnd();
  glDisable(GL_TEXTURE_2D);

  glEnable(GL_TEXTURE_2D);
  // エラーチェックなし
  glBindTexture(GL_TEXTURE_2D, texture->getTexture("tiles.png")->textureID);
  glBegin(GL_POLYGON);
  glTexCoord2f(0 , 0); glVertex3f(-4.9 ,1,3);
  glTexCoord2f(0 , 1); glVertex3f(-4.9 ,1,-3);
  glTexCoord2f(1 , 1); glVertex3f(3.9 , 1,-3);
  glTexCoord2f(1 , 0); glVertex3f(3.9 , 1,3);
  glEnd();
  glDisable(GL_TEXTURE_2D);
  ...
  glutSwapBuffers();
}
...

Let's look at a small example. The Unix programming culture holds in high
esteem programs which can be called from the command line, which take
arguments that control every aspect of their behavior, and the output of which
can be captured as regularly-formatted, machine readable plain text. Such
programs are valued because they can easily be incorporated into other
programs or larger software systems by programmers. To take one miniscule
example, there is a core value in the Unix culture, which Raymond calls
"Silence is Golden," that a program that has done exactly what you told it to
do successfully should provide no output whatsoever. It doesn't matter if
you've just typed a 300 character command line to create a file system, or
built and installed a complicated piece of software, or sent a manned rocket
to the moon. If it succeeds, the accepted thing to do is simply output
nothing. The user will infer from the next command prompt that everything must
be OK.

    -- Joel Spolsky
    -- "Biculturalism" ( http://www.joelonsoftware.com/articles/Biculturalism.html )

Rule of Open-Source Programming #8:

Open-Source is not a panacea.

    -- Shlomi Fish
    -- "Rules of Open Source Programming"

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SDL_imageをOpenGLのTextureで利用する

TextureImage.h

TextureImage.cpp