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FIXED by setting near clipping plane to 1, rather than 0 (not sure why it was like that to start with). See the question for skeleton code, and Adrian's answer for how and why this works. I have a few different camera positions, and my scene consists of a single quad. The quad is such that it projects exactly onto the viewport/window in the first frame. I want to project a texture from this camera position onto the quad. The texture also covers the viewport exactly. The first thing I did was // GL_QUADS... glTexCoord2f( /*one corner of s,t space*/); glVertex3f(/* appropriate vertex */);; and ended up with something like (picture not mine) And then I realised yes, of course, it needs to be a projective transformation. According to these notes : A modelview transform to orient the projection in the scene. A projective transform (perspective or orthogonal). A scale and bias to map the near clipping plane to texture coordinates. Now that it works, here's a rough implementation of the code: // in init code glEnable(GL_TEXTURE_2D); glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL); double ratio = width/height; // set up FROM modelview matrix glMatrixMode(GL_MODELVIEW); glLoadIdentity(); gluPerspective(pcam._fov/ratio, ratio, 1, far_z); gluLookAt(/* FROM camera's parameters */); glTexGeni(GL_Q, GL_TEXTURE_GEN_MODE, GL_EYE_LINEAR); //S, T, R and Q GLfloat Splane[] = {1.f, 0.f, 0.f, 0.f}; //S, T, R and Q, diagonal glTexGenfv(GL_S,GL_EYE_PLANE,Splane); //S, T, R and Q // -- load and bind texture -- glEnable(GL_TEXTURE_GEN_S); //S, T, R and Q // scale and bias glMatrixMode(GL_TEXTURE); glPushMatrix(); glLoadIdentity(); glTranslatef(0.5,

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