Question by Mene · Nov 08, 2013 at 01:44 AM · transform surface surface shader calculations surfaceshader

uv-space to screenSpace in surface shader

Hello, I'm trying to get the screenSpace-Coordinates from a Point in uv-space (for an not-tiling texture).

I found screenPos which seems to give me the position for the current pixel, but I need also the ability to calculate it for other pixels, which correspond to certain points like the center (0.5, 0.5) and so on.

I tried this:

 float4 p = mul (UNITY_MATRIX_MVP, float4(IN.uv_MainTex.x, IN.uv_MainTex.y, 0, 1));
 p.xy /= p.w;

and expect it to be equivalent to

 float2 screenUV = IN.screenPos.xy / IN.screenPos.w;

Which is not the case.

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GrahamReeves ♦♦ · Apr 10, 2014 at 03:17 PM 0

the matrix UNITY_MATRIX_MVP is the ModelViewProjection matrix for converting from model-space to projection/clip space (basically, vertex to screen). So multiplying it with "uv-space" will produce the wrong results.

When you say "uv-space" do you mean, a coordinate on the triangle? or a point in the view (which goes from [-1,-1] to [1,1]) into pixel coordinates?

GrahamReeves ♦♦ · Apr 10, 2014 at 03:33 PM 0

What you might want is

float2 viewCenter = float2( 0, 0 );

float4 screenCenterPx4 = mul( UNITY_MATRIX_P, float4( viewCenter.x, viewCenter.y, 0, 1 ) );

float2 screenCenterPx = (screenCenterPx4.xyz / screenCenterPx4.w).xy;

to convert view space to screen coordinates.