Texturing a Sphere
Let's assume you want to create something that looks like the planet earth. You want to apply a map of the earth to a sphere.
There are 2 ways to texture a sphere. Either by applying a cubemap or either by applying a 2D texture. For best result, use a cubemap. The problem with applying a 2D texture is that when you wrap a 2D texture onto a sphere, the top and bottom area of the sphere, the texture looks squeezed.
Cubemapping a Sphere
Load a cubemap as shown in Creating a Cubemap Texture
Let's assume that we'll be using shaders. If you haven't learned shaders yet, now is the time.
This code is in GLSL 1.10. The vertex shader :
//[VERTEX SHADER]
#version 110
uniform mat4 ProjectionModelviewMatrix;
varying vec3 TexCoord0;
void main()
{
gl_Position = ProjectionModelviewMatrix * gl_Vertex;
TexCoord0 = gl_Normal;
}
The fragment shader. Notice that the normal has been copied to TexCoord0 and this will be used to sample the cubemap.
//[FRAGMENT SHADER]
#version 110
uniform samplerCube Texture0;
varying vec3 TexCoord0;
void main()
{
vec4 texel = textureCube(Texture0, TexCoord0);
gl_FragColor = texel;
}
2D Texture Mapping a Sphere
Either you need to write your own code to create a sphere and you compute the texcoords yourself or you use another library like GLU or glhlib.
GLU
C
GLUquadricObj *sphere=NULL; sphere = gluNewQuadric(); gluQuadricDrawStyle(sphere, GLU_FILL); gluQuadricTexture(sphere, TRUE); gluQuadricNormals(sphere, GLU_SMOOTH); //Making a display list mysphereID = glGenLists(1); glNewList(mysphereID, GL_COMPILE); gluSphere(sphere, 1.0, 20, 20); glEndList(); gluDeleteQuadric(sphere); //----------------- //and whenever you want to render, call glCallList(mysphereID) //to kill the display list, glDeleteLists(mysphereID, 1);
Java
Texture earth; try { earth = TextureIO.newTexture(new File(dataPath("EarthMap_2500x1250.jpg")), true); } catch (IOException e) { javax.swing.JOptionPane.showMessageDialog(null, e); } GLUQuadric sphere = new GLUQuadric(); gluQuadricDrawStyle(sphere, GLU_FILL); gluQuadricTexture(sphere, true); gluQuadricNormals(sphere, GLU_SMOOTH); //Making a display list mysphereID = glGenLists(1); glNewList(mysphereID, GL_COMPILE); earth.enable(); earth.bind(); gluSphere(sphere, 1000.0, 20, 20); earth.disable(); glEndList(); gluDeleteQuadric(sphere); //----------------- //and whenever you want to render, call glCallList(mysphereID) //to kill the display list, glDeleteLists(mysphereID, 1);
GLHLIB
If you want to use glhlib http://sourceforge.net/projects/glhlib/
The header file glhlib.h explains how to use :
glhSphereObject2 Sphere; memset(&Sphere, 0, sizeof(glhSphereObject2)); Sphere.RadiusA=1.0; Sphere.RadiusB=1.0; Sphere.RadiusC=1.0; Sphere.Stacks=10; Sphere.Slices=10; Sphere.IndexFormat=GLH_INDEXFORMAT_16BIT; Sphere.VertexFormat=GLHVERTEXFORMAT_VNT; Sphere.TexCoordStyle[0]=1; Sphere.ScaleFactorS[0]=Sphere.ScaleFactorT[0]=1.0; //----------------- glhCreateSpheref2(&Sphere); //----------------- //HOW TO RENDER (You might want to use VBO, I'm just using VA here): glBindTexture(GL_TEXTURE_2D, TextureID); //----------------- glVertexPointer(3, GL_FLOAT, sizeof(GLHVertex_VNT), Sphere.pVertex); uint mypointer=(uint)Sphere.pVertex; mypointer+=12; glNormalPointer(GL_FLOAT, sizeof(GLHVertex_VNT), (uint *)mypointer); mypointer+=12; glTexCoordPointer(2, GL_FLOAT, sizeof(GLHVertex_VNT), (uint *)mypointer); glDrawRangeElements(GL_TRIANGLES, Sphere.Start_DrawRangeElements, Sphere.End_DrawRangeElements, Sphere.TotalIndex, GL_UNSIGNED_SHORT, Sphere.pIndex16Bit); //.........and delete it when your program closes glhDeleteSpheref2(Sphere);