opengl es 2.0 - iOS Simulator GL_OES_standard_derivatives -

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on ios4 gl_oes_standard_derivatives supported on device (from see when output extensions), there way able to:

  1. detect in fragment shader if extension supported or not

  2. if not supported, have code dfdx , dfdy? can't seems find on google.

tia!

i had same issue antialiasing sdm fonts. can calculate similar dfdx/dfdx translating 2 2d vectors using current transform matrix : 

vec2 p1(0,0); vec2 p2(1,1);  p1=transformusingcurrentmatrix(p1); p2=transformusingcurrentmatrix(p2);  float magic=35; // you'll need play - it's linked screen size think :p  float dfdx=(p2.x-p1.x)/magic; float dfdy=(p2.y-p1.y)/magic;

then send dfdx/dfdy shader uniforms - , multiply parameter same functionality i.e.

dfdx(myval) becomes 

dfdx*myval; dfdy(myval)   dfdy*myval; fwidth(myval) abs(dfdx*myval)+abs(dfdy*myval);

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