openGL之API学习（一二六）fwidth

只能用在片段着色器。

w = fwidth(uv); 
w.x = abs(dFdx(uv).x);
w.y = abs(dFdy(uv).y);

 

genType fwidth(     genType p);
 
genType fwidthCoarse(     genType p);
 
genType fwidthFine(     genType p);

 

p

    Specifies the expression of which to take the partial derivative.

 

Available only in the fragment shader, these functions return the sum of the absolute derivatives in x and y using local differencing for the input argument p. fwidth is equivalent to abs(dFdx(p)) + abs(dFdy(p)) . fwidthCoarse is equivalent to abs(dFdxCoarse(p)) + abs(dFdyCoarse(p)) . fwidthFine is equivalent to abs(dFdxFine(p)) + abs(dFdyFine(p)) .