Sphere Texture Mapping

OpenGL OpenGL: Basic Coding
1

Anyone has a link to a nice tutorial or some code for sphere texture mapping? Only part of the sky texture is being mapped onto the sphere when am trying to make a sky.

2

Easiest is to create the sphere in a modeler like 3ds Max, and apply the texturing you want in there.

Second easiest is to map the X/Z coordinates to the U/V texture coordinates (a planar mapping), assuming Y is up. This will give some stretching at the horizon, though.

Third easiest is to apply a spherical mapping. You have to create the sphere geometry youself to do this. Here’s some code that does just that (in Java, you can translate):

    static final VertexBuffer makeVertexBuffer(GLWrap gl, float radius, int slices, int wedges) throws Exception {
        byte[] data = new byte[(slices + 1) * (wedges + 1) * 32];
        ByteBuffer bb = ByteBuffer.wrap(data);
        bb.order(ByteOrder.nativeOrder());
        bb.rewind();
        for (int slice = 0; slice <= slices; ++slice) {
            float v = slice / (float) slices;
            float y = (float) Math.sin(Math.PI * (v - 0.5f));
            float r = 1.0f - y * y;
            if (r < 0) r = 0;
            r = (float) Math.sqrt(r);
            for (int wedge = 0; wedge <= wedges; ++wedge) {
                float u = wedge / (float) wedges;
                float phi = (float) Math.PI * (u * 2 - 1);
                float x = (float) Math.sin(phi) * r;
                float z = (float) Math.cos(phi) * r;
                assert Math.abs(x * x + y * y + z * z - 1) < 1e-5;
                bb.putFloat(x * radius);
                bb.putFloat(y * radius);
                bb.putFloat(z * radius);
                bb.putFloat(x);
                bb.putFloat(y);
                bb.putFloat(z);
                bb.putFloat(u);
                bb.putFloat(v);
            }
        }
        bb.flip();
        return new VertexBuffer(Scene.Usage.Static, data, VertexChannel.PositionNormalTexCoord);
    }

    static final VertexBuffer makeIndexBuffer(GLWrap gl, int slices, int wedges) throws Exception {
        byte[] data = new byte[slices * wedges * 6 * 2];
        int max = (slices + 1) * (wedges + 1);
        ByteBuffer bb = ByteBuffer.wrap(data);
        bb.order(ByteOrder.nativeOrder());
        bb.rewind();
        for (int slice = 0; slice < slices; ++slice) {
            int base = slice * (wedges + 1);
            int secondBase = (slice + 1) * (wedges + 1);
            assert secondBase + 1 < max;
            for (int wedge = 0; wedge < wedges; ++wedge) {
                bb.putShort((short) base);
                bb.putShort((short) (base + 1));
                bb.putShort((short) (secondBase + 1));
                bb.putShort((short) (secondBase + 1));
                bb.putShort((short) (secondBase));
                bb.putShort((short) base);
                ++base;
                ++secondBase;
            }
        }
        bb.flip();
        return new VertexBuffer(Scene.Usage.Static, data, VertexChannel.Index);
    }
3

Thanks!