How to load a bmp on GLUT to use it as a texture?

问题:

I've been searching all around for a simple solution to add sprites to my OpenGl GLUT simple moon lander game in c++ and it appears I must use bmp's since they're easiest to load and use them as textures on a rectangle.

How exactly can I load the bmp's as textures though?

回答1:

Look my simple c implementation function to load texture.

GLuint LoadTexture( const char * filename )
{

  GLuint texture;

  int width, height;

  unsigned char * data;

  FILE * file;

  file = fopen( filename, "rb" );

  if ( file == NULL ) return 0;
  width = 1024;
  height = 512;
  data = (unsigned char *)malloc( width * height * 3 );
  //int size = fseek(file,);
  fread( data, width * height * 3, 1, file );
  fclose( file );

 for(int i = 0; i < width * height ; ++i)
{
   int index = i*3;
   unsigned char B,R;
   B = data[index];
   R = data[index+2];

   data[index] = R;
   data[index+2] = B;

}


glGenTextures( 1, &texture );
glBindTexture( GL_TEXTURE_2D, texture );
glTexEnvf( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE,GL_MODULATE );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,GL_LINEAR_MIPMAP_NEAREST );


glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,GL_LINEAR );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S,GL_REPEAT );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T,GL_REPEAT );
gluBuild2DMipmaps( GL_TEXTURE_2D, 3, width, height,GL_RGB, GL_UNSIGNED_BYTE, data );
free( data );

return texture;
}

Above function returns the texture data. Store the texture data in variable

 GLuint texture
 texture= LoadTexture( "your_image_name.bmp" );

Now you can bind the texure using glBindTexture

glBindTexture (GL_TEXTURE_2D, texture);

回答2:

Checkout my the TextureLoader (TextureLoader.h + TextureLoader.cpp) from OpenGL_3_2_Utils:

https://github.com/mortennobel/OpenGL_3_2_Utils

The two files does not depend on any other files and should also work seamless on any version of OpenGL (and any platform). Example usage can be found in the file comment.

回答3:

You can use library GLAUX and SOIL(Simple OpenGL Image Library) . There are also other image libriries for OpenGL.

回答4:

How to load a bmp on GLUT to use it as a texture?

Another very simple solution would be to use STB library, which can be found at GitHub - nothings/stb.

All what is needed is one source file, the header file "stb_image.h".

Include the header file and enable image reading by the setting the preprocessor define STB_IMAGE IMPLEMENTATION:

#define STB_IMAGE_IMPLEMENTATION
#include <stb_image.h>

The image file can be read by the function stbi_load:

const char *filename = .....; // path and filename
int         req_channels = 3; // 3 color channels of BMP-file   

int width = 0, height = 0, channels = 0;
stbi_uc *image = stbi_load( filename, &width, &height, &channels, 3 ); 

When the image is loaded to a texture object, then GL_UNPACK_ALIGNMENT has to be set to 1, because the length of one line of an BMP-file is aligned to 4.
After loading the image, the memory on the can be freed by stbi_image_free:

GLuint texture_obj = 0;
if ( image != nullptr )
{
    glGenTextures(1, &texture_obj);
    glBindTexture(GL_TEXTURE_2D, texture_obj);

    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, image);
    glPixelStorei(GL_UNPACK_ALIGNMENT, 4); // default

    stbi_image_free( image );
}