5.14.4 Swizzle Operators for Vectors

The programming model implementation supports the following "swizzle" operators. These operators are used as suffixes to a variable name. They can be used on either side (left or right) of an assignment operator. When used on the left hand side of an assignment, each component must be uniquely identifiable.

.x, .y, .z, or .w

Access an element of a vector whose length is <= 4.

char4 my_c4 = (char4)(1, 2, 3, 4);
char  tmp   = my_c4.y * my_c4.w; /* ".y" accesses 2nd element
                                  * ".w" accesses 4th element
                                  * tmp = 2 * 4 = 8;   */

.s0, .s1, ..., .s9, .sa, ..., .sf

Access one of up to 16 elements in a vector.

uchar16 ucvec16 = (uchar16)(1, 2, 3, 4, 5, 6, 7, 8, 
                            9, 10, 11, 12, 13, 14, 15, 16 );
uchar8  ucvec8  = (uchar8)(2, 4, 6, 8, 10, 12, 14, 16);

int tmp = ucvec16.sa * ucvec8.s7; /* ".sa" is 11th element of ucvec16
                                   * ".s7" is  8th element of ucvec8
                                   *  tmp = 11 * 16 = 176;   */

.s[0], .s[1], ..., .s[63]

Access one of up to 64 elements in a vector.

uchar16 ucvec16 = (uchar16)(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 );
uchar8 ucvec8 = (uchar8)(2, 4, 6, 8, 10, 12, 14, 16);

int tmp = ucvec16.s[10] * ucvec8.s[7];
/* ".s[10]" is 11th element of ucvec16; ".s[7]" is 8th element of ucvec8
 * tmp = 11 * 16 = 176; */

.even, .odd

Access the even or odd elements of a vector, where the zeroth element is even.

ushort4 usvec4 = (ushort4)(1, 2, 3, 4);
ushort2 usvecodd  = usvec4.odd;  /* usvecodd  = (ushort2)(2, 4); */
ushort2 usveceven = usvec4.even; /* usveceven = (ushort2)(1, 3); */

.hi, .lo

Access the elements in the upper half of a vector with .hi or the elements in the lower half of a vector with .lo.

ushort8 usvec8 = (ushort8)(1, 2, 3, 4, 5, 6, 7, 8); 
ushort4 usvechi = usvec8.hi; /* usvechi = (ushort4)(5, 6, 7, 8);	*/ 
ushort4 usveclo = usvec8.lo; /* usveclo = (ushort4)(1, 2, 3, 4); */

Access the real parts of each of the elements in a complex type vector.

cfloat2 cfa = (cfloat2)(1.0, -2.0, 3.0, -4.0); 
float2 rfa = cfa.r;    /* rfa = (float2)(1.0, 3.0); */

Access the imaginary parts of each of the elements in a complex type vector.

cfloat2 cfa = (cfloat2)(1.0, -2.0, 3.0, -4.0); 
float2 ifa = cfa.i;    /* ifa = (float2)(-2.0, -4.0); */

Swizzle operators can be combined to access a subset of the subset of elements. The result of the combination must be well-defined. For example, after the following code runs, usvec4 contains (1, 2, 5, 4).

ushort4 usvec4 = (ushort4)(1, 2, 3, 4); 
 
usvec4.hi.even = 5;