Document sws_getConstVec().

Originally committed as revision 28524 to svn://svn.mplayerhq.hu/mplayer/trunk/libswscale

libswscale/swscale.h

@@ -130,6 +130,11 @@ int sws_scale_ordered(struct SwsContext *context, uint8_t* src[], int srcStride[
 int sws_setColorspaceDetails(struct SwsContext *c, const int inv_table[4], int srcRange, const int table[4], int dstRange, int brightness, int contrast, int saturation);
 int sws_getColorspaceDetails(struct SwsContext *c, int **inv_table, int *srcRange, int **table, int *dstRange, int *brightness, int *contrast, int *saturation);
 SwsVector *sws_getGaussianVec(double variance, double quality);
+
+/**
+ * Allocates and returns a vector with \p lenght coefficients, all
+ * with the same value \p c.
+ */
 SwsVector *sws_getConstVec(double c, int length);
 SwsVector *sws_getIdentityVec(void);
 void sws_scaleVec(SwsVector *a, double scalar);