Old-school OpenGL to draw a grey-level image texture between four 3D points.

texture.c

/*
  Draws a grey-level image between four 3D points.

  @pixels points to an array of @cols*@rows grey values.

  @tl[x,y,z] 3D coordinate for top-left image pixel
  @tr[x,y,z] 3D coordinate top-right  
  @bl[x,y,z] 3D coordinate bottom-left 
  @tr[x,y,z] 3D coordinate bottom-right 

  You probably need to have these calls in your OpenGL initialization:

  glEnable(GL_BLEND); 
  glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

*/

void DrawTexture( const uint8_t* pixels,
		  const unsigned int cols,
		  const unsigned int rows,
		  const float tl[3], 
		  const float tr[3], 
		  const float bl[3], 
		  const float br[3] ) 
{
  glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
  
  glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
  glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
  glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
  glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

  glEnable(GL_TEXTURE_2D);
     
  glTexImage2D(GL_TEXTURE_2D, 0, 4, cols, rows, 0, 
	       GL_BGR,	GL_UNSIGNED_BYTE, pixels );
  
  glColor3f(1,1,1); // white

  glBegin(GL_QUADS);
  
  glTexCoord2f(0.0, 0.0);
  glVertex3fv( tl );
  
  glTexCoord2f(0.0, 1.0);
  glVertex3fv( bl );
  
  glTexCoord2f(1.0, 1.0);
  glVertex3fv( br );

  glTexCoord2f(1.0, 0.0);
  glVertex3fv( tr );

  glEnd();

  glDisable(GL_TEXTURE_2D);
}