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varying vs computation performance in fragment shader

Shawn Chang

I want to know the cost of varying or the cost of calculation, which is greater？

Take the following example as an example:
A*(1-factor), the factor is calculated in the vertex shader, and the factor will be passed to the fragment shader as varying. In order to achieve the same effect, there are the following two solutions:
1. A is the uniform of the vertex shader, A* (1-factor) is calculated in the vertex shader, and the result is passed to the fragment shader as a varying, and fragment shader uses the result directly - in this case, the main overhead should be varying interpolation.
2. A is the uniform of the fragment shader, A* (1-factor) is calculated in the fragment shader, and then fragment shader directly uses the result of the calculation - in this case, the main cost should be the calculation cost in fragment shader.

For the above two solutions, which performance is better? Also, where can I find the varying interpolation efficiency data of arm's GPU? For example: How many floats can by interpolated in a cycle?

// solution 1:
uniform float A;
varying float result;
varying float factor;
void vs()
{
factor = ...;
result = A * (1-factor);
}

void fs()
{
 // directly uses result to other computations
}

// solution 2:
varying float factor;
void vs()
{
factor = ...;

}

uniform float A;
void fs()
{
// ...
result = A * (1-factor);
// ...
}