In usf shader, how to know if the uv's v start from top or bottom?

Development Rendering
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1

hi, Friends, I got a usf shader written like this, in Vertex Shader, I need to transform a world position to screen space.

Output.Position = mul(float4(InPosition, 1.0f), Matrix_MVP);
float2 puv = Output.Position.xy / Output.Position.w;
puv = puv * 0.5 + float2(0.5, 0.5);

however, if the uv’s v start from top, I will have to
puv.y = 1.0 - puv.y
so how to know if the uv.y start from top or bottom?

2

UVs always start at top left corner.