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 Applying a texture to a sphere, using QUAD_STRIPS  (Read 2103 times) 0 Members and 1 Guest are viewing this topic.
ajmas

Junior Devvie

Miles away from here!

 « Posted 2007-10-27 21:57:19 »

I have a method for drawing a sphere:

 1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40 `    static public void drawSphere(GL gl, double radius, int lats, int longs) {        /*         * This algorithm moves along the z-axis, for PI radians and then at         * each point rotates around the z-axis drawing a QUAD_STRIP.         *          * If you you start i at a non-zero value then you will see an open         * end along the z-axis. If you start j at a none zero-axis then you         * will see segements taken out.         */        gl.glEnable(GL.GL_TEXTURE_GEN_S);                          // Enable Texture Coord Generation For S (NEW)        gl.glEnable(GL.GL_TEXTURE_GEN_T);                          // Enable Texture Coord Generation For T (NEW)        for ( int i = 0; i <= lats; i++) {            double lat0 = Math.PI * (-0.5 + (double) (i - 1) / lats);            double z0 = Math.sin(lat0) * radius;            double zr0 = Math.cos(lat0) * radius;            double lat1 = Math.PI * (-0.5 + (double) i / lats);            double z1 = Math.sin(lat1) * radius;            double zr1 = Math.cos(lat1) * radius;            gl.glBegin(GL.GL_QUAD_STRIP);            for ( int j = 0; j <= longs; j++) {                double lng = 2 * Math.PI * (double) (j - 1) / longs;                double x = Math.cos(lng) *radius;                double y = Math.sin(lng) *radius;                                gl.glNormal3d(x * zr0, y * zr0, z0);                gl.glVertex3d(x * zr0, y * zr0, z0);                                gl.glNormal3d(x * zr1, y * zr1, z1);                gl.glVertex3d(x * zr1, y * zr1, z1);            }            gl.glEnd();        }        gl.glDisable(GL.GL_TEXTURE_GEN_S);                              gl. glDisable(GL.GL_TEXTURE_GEN_T);           }`

I now want to modify this to allow for applying a texture around the globe. If I had split the sphere into QUADs, then I would probably have applied the texture as a percentage of the rotation, but I am not sure how I would do this with a quad strip?

I would like the texture to wrap around the object, like a map around a globe, rather than repeat.
turquoise3232

Junior Devvie

Java (games) rock!

 « Reply #1 - Posted 2007-10-28 12:11:49 »

Hi, to map a rectangle texture of earth onto a quad you have to disable the automatic texture coordinates generation and provide yourself the texture coordinates of you vertex defining your quads mesh. It's quite easy using latitude and longitude...

I think that i have the code somewhere on my hard drive but it's quite a good exercise to do it yourself.

Hope it helps.
cylab

JGO Kernel

Medals: 180

 « Reply #2 - Posted 2007-10-28 12:59:46 »

First google hit for "spherical mapping": http://local.wasp.uwa.edu.au/~pbourke/texture_colour/spheremap/. Haven't read it, but from the pictures it appears to be what you want

Mathias - I Know What [you] Did Last Summer!
ajmas

Junior Devvie

Miles away from here!

 « Reply #3 - Posted 2007-10-28 15:30:55 »

Thanks, looks like what I was looking for

BTW Google is great, but you just need to know the right search terms.
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