把手头的opengl driver代码打开，看来看去，还是mesa的好些，整理一下贴出来，顺便测试一下如何贴代码, 颜色显示的还不正常，需要上传一个css文件，不知道blogspot如何才能上传文件。
namespace sglib{
namespace gfx{
class bezier{
public:
/*
* Horner scheme for Bezier curves
*
* Bezier curves can be computed via a Horner scheme.
* Horner is numerically less stable than the de Casteljau
* algorithm, but it is faster. For curves of degree n
* the complexity of Horner is O(n) and de Casteljau is O(n^2).
* Since stability is not important for displaying curve
* points I decided to use the Horner scheme.
*
* A cubic Bezier curve with control points b0, b1, b2, b3 can be
* written as
*
* (([3] [3] ) [3] ) [3]
* c(t) = (([0]*s*b0 + [1]*t*b1)*s + [2]*t^2*b2)*s + [3]*t^2*b3
*
* [n]
* where s=1-t and the binomial coefficients [i]. These can
* be computed iteratively using the identity:
*
* [n] [n ] [n]
* [i] = (n-i+1)/i * [i-1] and [0] = 1
*/
static void curve(
const float * cp
, float * out
, float t
, int dim
, int order ) {
#define MAX_EVAL_ORDER 30
static float inv_tab[MAX_EVAL_ORDER];
static bool inited = false;
if(!inited){
// KW: precompute 1/x for useful x.
for (int i = 1; i < MAX_EVAL_ORDER; i++)
inv_tab[i] = 1.0F / i;
inited = true;
}
float s, powert, bincoeff;
unsigned int i, k;
if(t == 0){
for (k = 0; k < dim; k++)
out[k] = cp[k];
}
else if( t == 1.0){
for (k = 0; k<dim; k++)
out[k] = cp[dim*(order-1)+k];
}
else {
if (order >= 2) {
bincoeff = (float) (order - 1);
s = 1.0F - t;
for (k = 0; k < dim; k++)
out[k] = s * cp[k] + bincoeff * t * cp[dim + k];
for (i = 2, cp += 2 * dim, powert = t * t; i < order; i++, powert *= t, cp += dim) {
bincoeff *= (float) (order - i);
bincoeff *= inv_tab[i];
for (k = 0; k < dim; k++)
out[k] = s * out[k] + bincoeff * powert * cp[k];
}
}
else { /* order=1 -> constant curve */
for (k = 0; k < dim; k++)
out[k] = cp[k];
}
}
}
private:
void cleanup(){
if(_ver)
delete []_ver;
_ver = 0;
}
bool gen_vertex(int usize, int vsize){
cleanup();
int total = _dim * usize * vsize;
float * vcp = new float [_dim*_vorder];
_ver = new float[total];
if(!_cp || !_ver || !vcp)
return false;
float ustep = 1.0f/(usize-1);
float vstep = 1.0f/(vsize-1);
float fu, fv;
int u, v;
for(u=0, fu=0 ; u<usize; u++, fu += ustep){
//1. calc control point first
for(v=0; v<_vorder; v++){
curve (&_cp[_dim*v*_uorder], &vcp[v*_dim], fu, _dim, _uorder);
}
float * ver = _ver + _dim*u;
//2. calc vertex along v dir
for(v=0, fv=0; v<vsize; v++, fv += vstep){
curve (vcp, ver, fv, _dim, _vorder);
ver += usize*_dim;
}
}
delete []vcp;
return true;
}
public:
bezier(): _cp(0) , _ver(0) {
}
~bezier(){
cleanup();
}
void init(const float * cp, int dim, int uorder, int vorder){
_cp = cp, _dim = dim, _uorder = uorder, _vorder = vorder;
}
bool gen(int usize, int vsize){
bool b = true;
b &= gen_vertex(usize, vsize);
return b;
}
float * get_vertex() {
return _ver;
}
protected:
const float * _cp; // control points
int _uorder;
int _vorder;
int _dim;
float * _ver;
};
}} //gfx, sglib
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