glFog causing transparent png to lose transparency

Question

Without glFog, my transparent png displays fine, but with it you can see the rectanglular background and strips of other colours (notice the other dirt material is working as intended, but not using a png or transparency).

Here's my code for the fog:

GLfloat colour[4]={0.8f,0.8f,1.0f, 1.0f};
glFogi(GL_FOG_MODE, GL_EXP);
glFogfv(GL_FOG_COLOR, colour);
glFogf(GL_FOG_DENSITY, 0.1);
glHint(GL_FOG_HINT, GL_NICEST);
glFogf(GL_FOG_START, 1.0);
glFogf(GL_FOG_END, 5.0);
glEnable(GL_FOG);   
glClearColor(0.8f,0.8f,1.0f,1.0f);

And my code for the png:

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

    GLfloat myAmbient[] = {0.7,0.7,0.7,1.0};
    glMaterialfv(GL_FRONT, GL_AMBIENT, myAmbient);
    glEnable(GL_TEXTURE_2D);
    glBindTexture(GL_TEXTURE_2D, plantTexture);
    glColor3f(0.5,0.5,0.2);

    glPushMatrix();
        glTranslated(-1,-14,10);
        glScaled(10,10,10);
        glBegin(GL_QUADS);
            glNormal3f(0,0,1);
            glTexCoord2f(0,1); glVertex2i(1,0);
            glNormal3f(0,0,1);
            glTexCoord2f(0,0); glVertex2i(1,1);
            glNormal3f(0,0,1);
            glTexCoord2f(1,0); glVertex2i(0,1);
            glNormal3f(0,0,1);
            glTexCoord2f(1,1); glVertex2i(0,0);
        glEnd();
    glPopMatrix();
    glDisable(GL_TEXTURE_2D);
    glDisable(GL_BLEND);

I'm completely lost on this one. Any ideas?

Answer 1

Since your quad is translucent, you should disable writes to the depth buffer with glDepthMask(false) prior to draw it (assuming GL_DEPTH_TEST is enabled).