问题
I found this code to generate a sphere in Opengl es. I am unable to understand the logic, could someone please give me some insights on this.
private void generateData() {
slicesBuffers = new FloatBuffer[slices];
normalsBuffers = new FloatBuffer[slices];
texCoordsBuffers = new FloatBuffer[slices];
for (int i = 0; i < slices; i++) {
float[] vertexCoords = new float[7 * (stacks + 1)];
float[] normalCoords = new float[4* (stacks + 1)];
float[] textureCoords = new float[10 * (stacks + 1)];
double alpha0 = i * (2 * Math.PI) / slices;
double alpha1 = (i + 1) * (2 * Math.PI) / slices;
float cosAlpha0 = (float) Math.cos(alpha0);
float sinAlpha0 = (float) Math.sin(alpha0);
float cosAlpha1 = (float) Math.cos(alpha1);
float sinAlpha1 = (float) Math.sin(alpha1);
for (int j = 0; j <= stacks; j++) {
double beta = j * Math.PI / stacks - Math.PI / 2;
float cosBeta = (float) Math.cos(beta);
float sinBeta = (float) Math.sin(beta);
Utils.setXYZ(vertexCoords, 6 * j,
radius * cosBeta * cosAlpha1,
radius * sinBeta,
radius * cosBeta * sinAlpha1);
Utils.setXYZ(vertexCoords, 6 * j + 3,
radius * cosBeta * cosAlpha0,
radius * sinBeta,
radius * cosBeta * sinAlpha0);
Utils.setXYZ(normalCoords, 6 * j,
cosBeta * cosAlpha1,
sinBeta,
cosBeta * sinAlpha1);
Utils.setXYZ(normalCoords, 6 * j + 3,
cosBeta * cosAlpha0,
sinBeta,
cosBeta * sinAlpha0);
Utils.setXY(textureCoords, 4 * j,
((float) (i + 1)) / slices,
((float) j) / stacks);
Utils.setXY(textureCoords, 4 * j + 2,
((float) i) / slices,
((float) j) / stacks);
}
slicesBuffers[i] = FloatBuffer.wrap(vertexCoords);
normalsBuffers[i] = FloatBuffer.wrap(normalCoords);
texCoordsBuffers[i] = FloatBuffer.wrap(textureCoords);
}
}
Thankyou
回答1:
For the theory of sphere generation see:
en.wikipedia.org/wiki/Sphere (Vertex)
en.wikipedia.org/wiki/UV_mapping (Texture coordinate) http://groups.google.com/group/android-developers/browse_thread/thread/0030261b82ed71e5/338fc1dcbfe6945f?lnk=raot(Normal surface)
Your code is right, it have a little bit issues, I have make some corrections:
public Sphere(int slices,int stacks, float radius, float H,float K,float Z, Bitmap image,Bitmap first,Bitmap second){
FloatBuffer[] slicesBuffers = new FloatBuffer[slices];
FloatBuffer[] normalsBuffers = new FloatBuffer[slices];
FloatBuffer[] texCoordsBuffers = new FloatBuffer[slices];
float[] total_vertexBuff;
float[] total_normalsBuff;
float[] total_textCoordsBuff;
int vertex_counter = 0;
int normals_counter = 0;
int texCoords_counter = 0;
int position_dst;
float tmp[];
for (int i = 0; i < slices; i++) {
float[] vertexCoords = new float[ 2 * 3 * (stacks + 1)];
float[] normalCoords = new float[ 2 * 3 *(stacks + 1)];
float[] textureCoords = new float[ 4 * (stacks + 1) ];
double alpha0 = i * (2 * Math.PI) / slices;
double alpha1 = (i + 1) * (2 * Math.PI) / slices;
float cosAlpha0 = (float) Math.cos(alpha0);
float sinAlpha0 = (float) Math.sin(alpha0);
float cosAlpha1 = (float) Math.cos(alpha1);
float sinAlpha1 = (float) Math.sin(alpha1);
for (int j = 0; j <= stacks; j++) {
double beta = j * Math.PI / stacks - Math.PI / 2;
float cosBeta = (float) Math.cos(beta);
float sinBeta = (float) Math.sin(beta);
setXYZ(vertexCoords, 6 * j, radius * cosBeta * cosAlpha1, radius * sinBeta, radius * cosBeta * sinAlpha1 );
setXYZ(vertexCoords, 6 * j + 3,radius * cosBeta * cosAlpha0,radius * sinBeta,radius * cosBeta * sinAlpha0);
vertex_counter += 2;
Log.d(TAG, "j:"+j);
setXYZ(normalCoords, 6 * j,cosBeta * cosAlpha1,sinBeta,cosBeta * sinAlpha1);
setXYZ(normalCoords, 6 * j + 3,cosBeta * cosAlpha0,sinBeta,cosBeta * sinAlpha0);
normals_counter += 2;
setXY(textureCoords, 4 * j,((float) (i + 1)) / slices,((float) j) / stacks);
setXY(textureCoords, 4 * j + 2,((float) i) / slices,((float) j) / stacks);
texCoords_counter += 2;
}
slicesBuffers[i] = FloatBuffer.wrap(vertexCoords);
normalsBuffers[i] = FloatBuffer.wrap(normalCoords);
texCoordsBuffers[i] = FloatBuffer.wrap(textureCoords);
}
total_vertexBuff = new float[vertex_counter * 3];
total_normalsBuff = new float[normals_counter * 3];
total_textCoordsBuff = new float[texCoords_counter * 2];
position_dst = 0;
// ricopio vertici
for (int i = 0; i < slicesBuffers.length; i++) {
for(int j = 0; j < slicesBuffers[i].capacity();j++,position_dst++)
total_vertexBuff[position_dst] = slicesBuffers[i].get(j);
}
position_dst = 0;
// ricopio normali
for (int i = 0; i < normalsBuffers.length; i++) {
for(int j = 0; j < normalsBuffers[i].capacity();j++,position_dst++)
total_normalsBuff[position_dst] = normalsBuffers[i].get(j);
}
position_dst = 0;
// ricopio coordinate texture
for (int i = 0; i < texCoordsBuffers.length; i++) {
for(int j = 0; j < texCoordsBuffers[i].capacity();j++,position_dst++)
total_textCoordsBuff[position_dst] = texCoordsBuffers[i].get(j);
}
this.image = image;
this.half_first = first;
this.half_second = second;
this.vertexBuffer = FloatBuffer.wrap(total_vertexBuff);
this.normalsBuffer = FloatBuffer.wrap(total_normalsBuff);
this.texCoordsBuffer = FloatBuffer.wrap(total_textCoordsBuff);
Log.d(TAG, "vertex_counter:"+vertex_counter);
Log.d(TAG, "texCoords_counter:"+texCoords_counter);
Log.d(TAG, "vertexBuffer:"+this.vertexBuffer.capacity());
Log.d(TAG, "texCoordsBuffer:"+this.texCoordsBuffer.capacity());
this.textures_ids = IntBuffer.allocate(2);
this.totalVertexCount = vertex_counter;
this.setPlaneBuffer();
return;
}
I really hope I help you.
Bye
pedr0
来源：https://stackoverflow.com/questions/3811082/spinning-globe-in-opengl-es