Writing only red color component to AGAL pixel shader output

Question

I want a pixel shader om AGAL that instead of simply copying the color passed to it from the vertex shader to the output, only copies the red component from the passed color and sets the green and blue components to zero. In pseudo code:

temp = 0
temp.red = in.red
temp.alpha = in.alpha
out = temp

I can't figure out how to write this in AGAL. The following doesn't do it:

mov ft0.ra, v0.ra
mov oc, ft0

How can I get the result I want?

The same result as if I would have copied all components of v0 to oc. I tried mov ft0.rgba, v0.rrra. No difference. — user2010596, Mar 06 '13 at 08:12

score 1 · Answer 1 · answered Apr 10 '13 at 19:14

You must remember that

using ".something" on the right of the destination register means you are using masks
using ".something" on the right of a source register means you are using swizzles.

Supposing that

fc0 contains a zero in the first component
v0 contains the color from which you want to extract the red component

So here is your fragment shader:

// shader.
mov ft0, fc0.xxxx     // fill ft0 with zeros
mov ft0.xw, v0.xxxw   // fill ft0.x with v0.x and ft0.w with v0.w
mov oc, ft0

Source: I wrote Minko's ActionScript 3 to AGAL compiler.

Writing only red color component to AGAL pixel shader output

1 Answers1