+
+/**
+ * Compute quad X,Y,Z,W for the four fragments in a quad.
+ *
+ * This should really be part of the compiled shader.
+ */
+static void
+setup_pos_vector(const struct tgsi_interp_coef *coef,
+ float x, float y,
+ struct tgsi_exec_vector *quadpos)
+{
+ uint chan;
+ /* do X */
+ quadpos->xyzw[0].f[0] = x;
+ quadpos->xyzw[0].f[1] = x + 1;
+ quadpos->xyzw[0].f[2] = x;
+ quadpos->xyzw[0].f[3] = x + 1;
+
+ /* do Y */
+ quadpos->xyzw[1].f[0] = y;
+ quadpos->xyzw[1].f[1] = y;
+ quadpos->xyzw[1].f[2] = y + 1;
+ quadpos->xyzw[1].f[3] = y + 1;
+
+ /* do Z and W for all fragments in the quad */
+ for (chan = 2; chan < 4; chan++) {
+ const float dadx = coef->dadx[chan];
+ const float dady = coef->dady[chan];
+ const float a0 = coef->a0[chan] + dadx * x + dady * y;
+ quadpos->xyzw[chan].f[0] = a0;
+ quadpos->xyzw[chan].f[1] = a0 + dadx;
+ quadpos->xyzw[chan].f[2] = a0 + dady;
+ quadpos->xyzw[chan].f[3] = a0 + dadx + dady;
+ }
+}
+
+