EyeonTips:Manual/Fusion 6/Custom Tool

From VFXPedia

• Since Fusion 6.1.697, expressions in the Custom tool and Expression modifier can now get number/point inputs at different times, using n1_at(time), etc. and p1x_at(time)/p1y_at(time), etc.

• Be careful when using the == operator to compare against fixed color values. Due to rounding (especially in int8 images) and the limited precision of even float16, a comparison like if(r1 == 0.1,...) might not work as expected.

The solution is, be aware of this issue, and instead compare against a small range of values, e.g: (r1 > 0.09999 && r1 < 0.1001). The range you compare against may have to be widened when using less accurate values, so for int8 images you would need (r1 > 0.098 && r1 < 0.101). Programmers (who deal with this issue every day) often compare the absolute difference instead, e.g. abs(r1 - 0.1) < 0.0001.
-- Daniel Koch on the Laffey list

• Fusion 6.2 adds support for the world position pass: px1, py1, pz1 are used to get the values of the X, Y and Z positions of the first image. The appropriate getter-functions are also available: getpx1b() etc...