opengl texture coordinates for full-screen effect

Question

how can i create the full-screen effect with a texture image ? till now i do this :

static void Draw(void)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 
    glLoadIdentity();
    glTranslatef(0.0f,0.0f,-5.0f);
    texture[0] = SOIL_load_OGL_texture // load an image file directly as a new OpenGL texture
    (
        "my_img.jpg",
        SOIL_LOAD_AUTO,
        SOIL_CREATE_NEW_ID,
         SOIL_FLAG_INVERT_Y | SOIL_FLAG_NTSC_SAFE_RGB | SOIL_FLAG_COMPRESS_TO_DXT
    );

    glBindTexture(GL_TEXTURE_2D, texture[0]);
    glBegin(GL_POLYGON);

    glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, -1.0f,  1.0f);
    glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, -1.0f,  1.0f);
    glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f,  1.0f,  1.0f);
    glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f,  1.0f,  1.0f);

    glEnd();
    glutSwapBuffers();
}

this code places my image in the top-left position of the screen, but i would like the full-screen texture effect. So, How can i accomplish that ?

Remove the `glTranslate` transform, and set the vertex z-coords to 0.0? Make sure your projection & modelview matrices are identity. — Brett Hale, Jun 26 '14 at 17:29

score 2 · Accepted Answer · answered Jun 27 '14 at 05:30

As @BrettHale already suggested in the comment, just set all the matrices to the identity transformation:

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

Then get rid of any other transformations you have in place, like the glTranslatef() call you currently have in the code. Use 0.0f instead of 1.0f for the last coordinate of your vertices, and you should be good to go.

score 0 · Answer 2 · answered Jun 26 '14 at 22:25

ok , I did it , and now it works. for a full-screen image i added this function

void resize(int height, int width) {
    const float ar = (float) widthX / (float) heightY;
    glViewport(0, 20, widthX, heightY);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glFrustum(-ar+1, ar-1, -1.0, 1.0, 2.0, 90.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity() ;
}

make sure to add this :

glutReshapeFunc(resize); // calling the "resize function"

opengl texture coordinates for full-screen effect

2 Answers2