Как сделать фон моей текстуры прозрачным? (Мое изображение уже без фона)

У меня без фона изображение пистолета. Я пытаюсь создать шутер от первого лица с помощью этого двумерного изображения оружия. Я загрузил текстуру в свою программу, но не могу сделать фон пистолета прозрачным. Более того, зачем мне это делать, когда мое изображение уже без фона. Я использовал clippingmagic.com, чтобы удалить фон моего изображения. Код является:

#include <iostream>
#include <stdlib.h> //Needed for "exit" function
#include<SOIL/SOIL.h>

//Include OpenGL header files, so that we can use OpenGL
#ifdef __APPLE__
#include <OpenGL/OpenGL.h>
#include <GLUT/glut.h>
#else
#include <GL/glut.h>
#endif

using namespace std;
const float A = 1366.0; //width of the computer screen
const float B = 768.0;  //height of the computer screen

//Called when a key is pressed
void handleKeypress(unsigned char key, //The key that was pressed
int x, int y) {    //The current mouse coordinates
switch (key) {
case 27: //Escape key
exit(0); //Exit the program
}
}

//Initializes 3D rendering
void initRendering() {
//Makes 3D drawing work when something is in front of something else
glEnable(GL_DEPTH_TEST);
}

//Called when the window is resized
void handleResize(int w, int h) {
//Tell OpenGL how to convert from coordinates to pixel values
glViewport(0, 0, w, h);

glMatrixMode(GL_PROJECTION); //Switch to setting the camera perspective

//Set the camera perspective
glLoadIdentity(); //Reset the camera
gluPerspective(45.0,                  //The camera angle
(double)w / (double)h, //The width-to-height ratio
1.0,                   //The near z clipping coordinate
200.0);                //The far z clipping coordinate
}

//Draws the 3D scene
void drawScene() {
//Clear information from last draw
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glMatrixMode(GL_MODELVIEW); //Switch to the drawing perspective
glLoadIdentity(); //Reset the drawing perspective
glTranslatef(0.0,0.0,-10.0);
//DRAW WALL OF ROOM
glBegin(GL_QUADS);
glColor3f(0.0, 1.0, 1.0);
glVertex3f(-100.0, -100.0, -100.0);
glVertex3f(-100.0,  100.0, -100.0);
glVertex3f( 100.0,  100.0, -100.0);
glVertex3f( 100.0, -100.0, -100.0);
glEnd();

//DRAW GUN
glEnable(GL_TEXTURE_2D);
glEnable(GL_BLEND);
glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
GLuint gun_tex_id = SOIL_load_OGL_texture
(
"GUN.png",
SOIL_LOAD_RGB,  //I even tried SOIL_LOAD_AUTO and SOIL_LOAD_RGBA but it didn't help
SOIL_CREATE_NEW_ID,
SOIL_FLAG_MIPMAPS | SOIL_FLAG_INVERT_Y  | SOIL_FLAG_COMPRESS_TO_DXT | SOIL_FLAG_MULTIPLY_ALPHA
);
glBindTexture(GL_TEXTURE_2D, gun_tex_id);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTranslatef(2.0,0.0,0.0);
glColor3f(1.0,1.0,1.0);
glBegin(GL_QUADS);
glTexCoord2f(0.0f, 0.0f);
glVertex3f(-4.1,-4.15, 0.0);
glTexCoord2f(1.0f, 0.0f);
glVertex3f( 3.0,-4.15, 0.0);
glTexCoord2f(1.0f, 1.0f);
glVertex3f( 3.0, 1.2, 0.0);
glTexCoord2f(0.0f, 1.0f);
glVertex3f(-4.1, 1.2, 0.0);
glEnd();
glDisable(GL_BLEND);
glutSwapBuffers(); //Send the 3D scene to the screen
}

void myinit(void)
{
glClearColor(1.0, 1.0, 1.0, 0.0); /* gray background */

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho( -A/2, A/2, -B/2, B/2, -200, 200);
/* In World coordinates:position the "clipping rectangle" at -A/2, its right edge at +A/2, its bottom edge at -B/2 and its top edge at +B/2 */
glMatrixMode(GL_MODELVIEW);
}

int main(int argc, char** argv) {
//Initialize GLUT
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
glutInitWindowSize(A, B); //Set the window size

//Create the window
glutCreateWindow("My shooting game");
initRendering(); //Initialize rendering

//Set handler functions for drawing, keypresses, and window resizes
glutDisplayFunc(drawScene);
glutKeyboardFunc(handleKeypress);
glutReshapeFunc(handleResize);

myinit();
glutMainLoop(); //Start the main loop.  glutMainLoop doesn't return.
return 0; //This line is never reached
}