I am trying to draw to a texture using a framebuffer using OpenGL ES 1.1 on Android, Java. Afterwords I want to overlay this texture full-screen over my game. In theory, this works like a charm, but somehow the coordinates are off. For testing I drew something at (0,0) with width and height 200, and it partly is off-screen.

This is how I create the framebuffer:

fb = new int[1];
depthRb = new int[1];
renderTex = new int[1];

gl11ep.glGenFramebuffersOES(1, fb, 0);
gl11ep.glGenRenderbuffersOES(1, depthRb, 0); // the depth buffer

gl.glGenTextures(1, renderTex, 0);// generate texture
gl.glBindTexture(GL10.GL_TEXTURE_2D, renderTex[0]);

gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MIN_FILTER, GL10.GL_LINEAR);
gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MAG_FILTER, GL10.GL_LINEAR);
gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_S, GL10.GL_REPEAT);
gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_T, GL10.GL_REPEAT);

texBuffer = ByteBuffer.allocateDirect(buf.length*4).order(ByteOrder.nativeOrder()).asIntBuffer();

gl.glTexImage2D(GL10.GL_TEXTURE_2D, 0, GL10.GL_LUMINANCE, texW, texH, 0, GL10.GL_LUMINANCE, GL10.GL_UNSIGNED_BYTE, texBuffer);


gl11ep.glBindRenderbufferOES(GL11ExtensionPack.GL_RENDERBUFFER_OES, depthRb[0]);
gl11ep.glRenderbufferStorageOES(GL11ExtensionPack.GL_RENDERBUFFER_OES, GL11ExtensionPack.GL_DEPTH_COMPONENT16, texW, texH);

Before I draw, I do this:

gl11ep.glBindFramebufferOES(GL11ExtensionPack.GL_FRAMEBUFFER_OES, fb[0]);
gl.glClearColor(0f, 0f, 0f, 0f);
// specify texture as color attachment
gl11ep.glFramebufferTexture2DOES(GL11ExtensionPack.GL_FRAMEBUFFER_OES, GL11ExtensionPack.GL_COLOR_ATTACHMENT0_OES, GL10.GL_TEXTURE_2D, renderTex[0], 0);
// attach render buffer as depth buffer
gl11ep.glFramebufferRenderbufferOES(GL11ExtensionPack.GL_FRAMEBUFFER_OES, GL11ExtensionPack.GL_DEPTH_ATTACHMENT_OES, GL11ExtensionPack.GL_RENDERBUFFER_OES, depthRb[0]);

I set texW = 1024 and texH = 512. When rendering this texture fullscreen, with a lightmask (size 200x200) placed at (0, 0) and (texW/2, texH/2). You can see that it seems like the coordinate system doesnt start at (0,0) as that light overlaps the screen and the images are not drawn as squares (my lightcone-texture is a circle, not an ellipse).

So, how is the coordinate system of this offscreen-drawn texture defined? Thanks