OpenGL第八节:非二次幂的纹理渲染处理

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纹理渲染的图片的宽度和高度需要是二次幂的,如果不是二次幂的,需要通过填充的方式(就是添加边距),填充到二次幂。

LTexture.h

bool loadTextureFromPixels32( GLuint* pixels, GLuint imgWidth, GLuint imgHeight, GLuint texWidth, GLuint texHeight );//imgWidth图片宽,imgHeight图片高,texWidth纹理宽,texHeight纹理高

private:
  GLuint powerOfTwo( GLuint num );//计算对应的幂,比例num为60时返回64 。

  GLuint mTextureID;

  GLuint mTextureWidth;//纹理宽高
  GLuint mTextureHeight;

  GLuint mImageWidth;//图片的宽高
  GLuint mImageHeight;

 

LTexture.cpp

LTexture::LTexture()
{
  mTextureID = 0;

  mImageWidth = 0;
  mImageHeight = 0;

  mTextureWidth = 0;
  mTextureHeight = 0;
}

bool LTexture::loadTextureFromFile( std::string path )
{
  bool textureLoaded = false;

  ILuint imgID = 0;
  ilGenImages( 1, &imgID );//生成ID
  ilBindImage( imgID );//绑定

  ILboolean success = ilLoadImage( path.c_str() );//加载

  if( success == IL_TRUE )
  {
    success = ilConvertImage( IL_RGBA, IL_UNSIGNED_BYTE );//换为rgba
    if( success == IL_TRUE )
    {
      GLuint imgWidth = (GLuint)ilGetInteger( IL_IMAGE_WIDTH );
      GLuint imgHeight = (GLuint)ilGetInteger( IL_IMAGE_HEIGHT );

      GLuint texWidth = powerOfTwo( imgWidth );
      GLuint texHeight = powerOfTwo( imgHeight );

      if( imgWidth != texWidth || imgHeight != texHeight )//图片宽高和纹理的宽高不一样
      {
        iluImageParameter( ILU_PLACEMENT, ILU_UPPER_LEFT );//设置参数,让它图片位置左上角

        iluEnlargeCanvas( (int)texWidth, (int)texHeight, 1 );//拉伸画布到和纹理的宽高一样,这样图片在左上角,右下角就会被ilClearColor的颜色填充
      }

      textureLoaded = loadTextureFromPixels32( (GLuint*)ilGetData(), imgWidth, imgHeight, texWidth, texHeight );//根据图片像素创建纹理
    }

    ilDeleteImages( 1, &imgID );//从内存删除图片
  }

  if( !textureLoaded )
  {
    printf( "Unable to load %s\n", path.c_str() );
  }

  return textureLoaded;
}

bool LTexture::loadTextureFromPixels32( GLuint* pixels, GLuint imgWidth, GLuint imgHeight, GLuint texWidth, GLuint texHeight )
{
  freeTexture();

  mImageWidth = imgWidth;
  mImageHeight = imgHeight;
  mTextureWidth = texWidth;
  mTextureHeight = texHeight;

  glGenTextures( 1, &mTextureID );//生成纹理ID

  glBindTexture( GL_TEXTURE_2D, mTextureID );//绑定

  glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA, mTextureWidth, mTextureHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, pixels );//创建

  glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
  glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );

  glBindTexture( GL_TEXTURE_2D, NULL );//解除

  GLenum error = glGetError();
  if( error != GL_NO_ERROR )
  {
    printf( "Error loading texture from %p pixels! %s\n", pixels, gluErrorString( error ) );
    return false;
  }

  return true;
}

void LTexture::freeTexture()
{
  if( mTextureID != 0 )
  {
    glDeleteTextures( 1, &mTextureID );
    mTextureID = 0;
  }

  mImageWidth = 0;
  mImageHeight = 0;
  mTextureWidth = 0;
  mTextureHeight = 0;
}

void LTexture::render( GLfloat x, GLfloat y, LFRect* clip )
{
  if( mTextureID != 0 )
  {  //下面是纹理坐标处理
    glLoadIdentity();//重置,移除之前的变换

    GLfloat texTop = 0.f;
    GLfloat texBottom = (GLfloat)mImageHeight / (GLfloat)mTextureHeight;
    GLfloat texLeft = 0.f;
    GLfloat texRight = (GLfloat)mImageWidth / (GLfloat)mTextureWidth;

    GLfloat quadWidth = mImageWidth;
    GLfloat quadHeight = mImageHeight;

    if( clip != NULL )
    {
      texLeft = clip->x / mTextureWidth;
      texRight = ( clip->x + clip->w ) / mTextureWidth;
      texTop = clip->y / mTextureHeight;
      texBottom = ( clip->y + clip->h ) / mTextureHeight;

      quadWidth = clip->w;
      quadHeight = clip->h;
    }

    glTranslatef( x, y, 0.f );

    glBindTexture( GL_TEXTURE_2D, mTextureID );//绑定

    glBegin( GL_QUADS );//渲染
      glTexCoord2f( texLeft, texTop ); glVertex2f( 0.f, 0.f );
      glTexCoord2f( texRight, texTop ); glVertex2f( quadWidth, 0.f );
      glTexCoord2f( texRight, texBottom ); glVertex2f( quadWidth, quadHeight );
      glTexCoord2f( texLeft, texBottom ); glVertex2f( 0.f, quadHeight );
    glEnd();
  }
}

GLuint LTexture::powerOfTwo( GLuint num )
{
  if( num != 0 )
  {
    num--;
    num |= (num >> 1); //Or first 2 bits
    num |= (num >> 2); //Or next 2 bits
    num |= (num >> 4); //Or next 4 bits
    num |= (num >> 8); //Or next 8 bits
    num |= (num >> 16); //Or next 16 bits
    num++;
  }

  return num;
}

 

LUtil.cpp

LTexture gNon2NTexture;

bool initGL()
{

  ...

  ilInit();//初始化DevIL
  iluInit();//初始化DevILU工具类
  ilClearColour( 255, 255, 255, 000 );

  ILenum ilError = ilGetError();
  if( ilError != IL_NO_ERROR )
  {
    printf( "Error initializing DevIL! %s\n", iluErrorString( ilError ) );
    return false;
  }

  return true;
}

bool loadMedia()
{
  if( !gNon2NTexture.loadTextureFromFile( "opengl.png" ) )
  {
    printf( "Unable to load non-power-of-two texture!\n" );
    return false;
  }

  return true;
}

void render()
{
  glClear( GL_COLOR_BUFFER_BIT );

  gNon2NTexture.render( ( SCREEN_WIDTH - gNon2NTexture.imageWidth() ) / 2.f, ( SCREEN_HEIGHT - gNon2NTexture.imageHeight() ) / 2.f );

  glutSwapBuffers();
}

 

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