Is it possible to create a transparent (empty) Texture2D that hides other textures under it?

I have a health gauge that has a sharp 45 degree angle. Basically I need someway to have an area on the screen under which other textures become invisible, but the alpha texture is still see-through.

I already tried rotating groups, etc. It works fine on normal GUI.matrix, but I have changed it so all of my other textures would scale nicely under every resolution.

How do I make the transparent hider texture? Or maybe there is some other approach?

This should work - assuming that your red “pointy-ended” object is drawn with a transparent shader (and therefore in the transparent queue), then create a new material using this shader and put it on the transparent object that you want to use to mask it.

Shader "Mask" {
    SubShader {
        Tags {
        	"Queue" = "Transparent-1" // Needs to be in a queue *before* the thing that you want to mask
        	"IgnoreProjector" = "True"
        }
        Pass {
	    	Cull Back
			Blend Zero One
            Lighting Off 
            CGPROGRAM
            #include "UnityCG.cginc"
    		#pragma vertex vert
    		#pragma fragment frag
            v2f_img vert (appdata_base v)
            {
               	v2f_img o;
               	o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
               	return o;
            }
            fixed4 frag (v2f_img IN) : COLOR
    		{
        		return fixed4(0,0,0,0);
    		}
            ENDCG
        }
    }
}